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415v Supply to Domestic Homes in the UK
|
|
| bbrundell@gmail.com 2005-07-15, 6:25 pm |
| Hi
I have a normal domestic supply to a house in the UK. I have seen a
printing press that needs 415v. I assume my house is fed with 240v,
and not transformed within the house down from something else.
Question: if I need to supply 415v to this press, how would I do it?
Would I need a massive transformer (any guess at cost?); or would new
lines have to be laid by my electicity distributor? Has anyone any
experience of getting 415v at home?
Thanks
Ben
| |
| Andrew Gabriel 2005-07-15, 6:25 pm |
| In article <1121454928.292557.85440@z14g2000cwz.googlegroups.com>,
bbrundell@gmail.com writes:
quote:
> Hi
>
> I have a normal domestic supply to a house in the UK. I have seen a
> printing press that needs 415v. I assume my house is fed with 240v,
> and not transformed within the house down from something else.
>
> Question: if I need to supply 415v to this press, how would I do it?
> Would I need a massive transformer (any guess at cost?); or would new
> lines have to be laid by my electicity distributor? Has anyone any
> experience of getting 415v at home?
If it needs 415V, it probably needs 3-phase too.
What power rating is it?
It would be useful to know everything on the rating plate.
You could ask for a 3-phase supply. If 3-phase runs down the
street (very likely unless you are in a sparse rural area),
this should be possible, but I've no idea what the costs
might be now the supply industry is all split into separate
companies. If you will need a supply > 24kW when adding the
press to your household load, you will be required to have
a 3-phase supply anyway (100A is max allowed for a 1-phase
supply).
Other options would be a motor-generator to generate 3-phase,
or to change the motor in the press to a single phase one.
Depends what power consumption we're talking about, and what
rating supply feed you currently have.
--
Andrew Gabriel
| |
| Beachcomber 2005-07-16, 4:25 am |
|
quote:
>
>If it needs 415V, it probably needs 3-phase too.
>What power rating is it?
>It would be useful to know everything on the rating plate.
>
>You could ask for a 3-phase supply. If 3-phase runs down the
>street (very likely unless you are in a sparse rural area),
>this should be possible, but I've no idea what the costs
>might be now the supply industry is all split into separate
>companies. If you will need a supply > 24kW when adding the
>press to your household load, you will be required to have
>a 3-phase supply anyway (100A is max allowed for a 1-phase
>supply).
>
Question from a Yank about service in the UK.
If 100A is max allowed, what happens if you have a super large home
(or castle) with all electric appliances? Do you need to install
extra panels? 3-phase service? Are there restrictions on this?
Also, are the British unique among the EU community for having ring
wiring in house distribution services?
Beachcomber
| |
| Andrew Gabriel 2005-07-16, 12:25 pm |
| In article <42d8a813.3216703@newsgroups.comcast.net>,
not_real@xxx.yyy (Beachcomber) writes:
quote:
> Question from a Yank about service in the UK.
>
> If 100A is max allowed, what happens if you have a super large home
> (or castle) with all electric appliances? Do you need to install
> extra panels? 3-phase service? Are there restrictions on this?
You can have as much power as you want (and can afford), but
the maximum single phase supply provided is 100A which probably
covers 99% of homes. Above that, a 3-phase supply is provided.
There's no 100A limit on a 3-phase supply.
Sometimes you'll also see 2 phases from a 3-phase supply provided,
but I don't think that's been an install option for some years now.
I think this is pretty similar across all the EU, except the single
phase supply limit varies by country. In some countries, it's as
low as 20A, so almost everyone has a 3-phase supply.
For a 3-phase supply, you can use multiple single phase Consumer
Units (panels) and/or a 3-phase Consumer Unit. If you have any
internal 3-phase circuits/appliances, you will have to have a 3-phase
Consumer Unit.
quote:
> Also, are the British unique among the EU community for having ring
> wiring in house distribution services?
No, I think Malta does too.
We use ring circuits in the house only for supplying socket outlets,
where you might want high power loads almost anywhere in the house
on a portable basis, but not everywhere at once. It's not actually
a requirement that a house be wired with ring circuits, but it is
always done.
Some countries outside the EU also use them (such as current/former
British Commonwealth countries and colonies), due to having adopted
the british wiring regulations for their own use at some time in
the past, or having used the british wiring regs as the basis for
their own (as was the case with Malta too). Whilst lots of countries
use the british 13A socket outlet, but I doubt that they all also
use ring circuits, although a number do.
--
Andrew Gabriel
| |
| bbrundell@gmail.com 2005-07-16, 6:25 pm |
| Thanks Gabriel
You said you've no idea of the costs now, but are we talking about it
being a set fee, or would they pass costs directly on to me for digging
up roads etc.
At a guess is it hundreds of pounds or thousands if it doesn't run up
the street?
Cheers
Ben
| |
| Palindr☻me 2005-07-17, 12:25 pm |
| bbrundell@gmail.com wrote:
quote:
> Thanks Gabriel
>
> You said you've no idea of the costs now, but are we talking about it
> being a set fee, or would they pass costs directly on to me for digging
> up roads etc.
>
> At a guess is it hundreds of pounds or thousands if it doesn't run up
> the street?
>
You need to discuss this with your local distribution
company. The local manager has considerable discretion as to
the cost passed on to you - which can be anything from
nothing to the full cost, which /could/ be thousands of
pounds. Crossing a road, particularly a trunk road, costs
lots and lots.
Offering to do part of the job yourself can help. I got mine
fitted for free, in return for digging the trench to the
property line, putting in the new hockey stick and plastic
cableway tubing (both of which they supplied) and making
good after they had pulled the new cable through and
connected up. They joined it to the lv cable, about 1m from
my property line.
--
Sue
| |
|
| Andrew Gabriel wrote:
quote:
> In article <42d8a813.3216703@newsgroups.comcast.net>,
> not_real@xxx.yyy (Beachcomber) writes:
>
>
>
> You can have as much power as you want (and can afford), but
> the maximum single phase supply provided is 100A which probably
> covers 99% of homes. Above that, a 3-phase supply is provided.
> There's no 100A limit on a 3-phase supply.
> Sometimes you'll also see 2 phases from a 3-phase supply provided,
> but I don't think that's been an install option for some years now.
>
> I think this is pretty similar across all the EU, except the single
> phase supply limit varies by country. In some countries, it's as
> low as 20A, so almost everyone has a 3-phase supply.
>
> For a 3-phase supply, you can use multiple single phase Consumer
> Units (panels) and/or a 3-phase Consumer Unit. If you have any
> internal 3-phase circuits/appliances, you will have to have a 3-phase
> Consumer Unit.
>
Know of any internet info on British/European voltages, frequencies,
common supply currents? Would also be interesting why different areas
have different voltage/frequency.
quote:
>
>
> No, I think Malta does too.
> We use ring circuits in the house only for supplying socket outlets,
> where you might want high power loads almost anywhere in the house
> on a portable basis, but not everywhere at once. It's not actually
> a requirement that a house be wired with ring circuits, but it is
> always done.
>
Know of any internet info on ring circuits? Like:
What are typical "high power loads"?
Are there just 1 or 2 rings in a large house?
Are they just used because of lower copper costs? Other advantages?
How much is the ring conductor reduced in size?
In a large house (ring to far end) are rings still an advantage?
Are there problems with long rings with an outlet near one end (long
side too long to keep short side at acceptable current?
Permitted only in dwelling?
Bud--
| |
| Andrew Gabriel 2005-07-18, 6:25 pm |
| In article <e99c0$42dbcaf8$4304c9d9$10139@dialupusa.net>,
Bud <remove.BudNews@isp.com> writes:
quote:
>
>Know of any internet info on British/European voltages, frequencies,
>common supply currents? Would also be interesting why different areas
>have different voltage/frequency.
One resource is:
http://users.pandora.be/worldstandards/electricity.htm
Voltages of EU countries are all now 230V nominal. In practice,
you'll find 220-240V. Actually, this initiative is wider than
just the EU -- it applies to all CENELEC countries.
quote:
>Know of any internet info on ring circuits? Like:
>What are typical "high power loads"?
13A/3kW is the max single item load on a ring circuit, and
32A/7.5kW is the max total load on a ring circuit.
quote:
>Are there just 1 or 2 rings in a large house?
Normally more than one, but it depends. You should size a ring
circuit so the total load is unlikely to be exceeded. There is
a recommendation that a ring circuit should not supply power for
more than 100m² of floor area, but if it is known some area is
going to have a non-typical loading, the designer should adjust
the area covered by the ring circuits and the number of them
appropriately. For example, it's not uncommon for a kitchen to
have a dedicated ring circuit. In practice, most ring circuits
are hardly ever run anywhere near their full capacity. The main
building heating (if electric) and main water heating (if electric)
require dedicated circuits to themselves, and would not be on a
ring circuit.
quote:
>Are they just used because of lower copper costs? Other advantages?
They were the result of a post WWII redesign of building wiring,
and usage of copper was one factor, but not the only one. The
pre-WWII wiring consisted of 15A socket outlets each on a dedicated
wire back to the fuseboard. This wasn't a problem when each room
typically had only one socket, but increasing use of electrical
appliances was already showing one socket per room was inadiquate,
and leading to heavy use of multi-way adaptors. The existing scheme
didn't scale -- multiple 15A outlets would have required vastly
more copper, but actually the copper was all under used -- the 15A
sockets were rarely supplying anything like 15A. There were also
2A and 5A sockets connected to lighting circuits, but having more
than one socket type had become a major inconvenience.
The new design therefore sought to provide multiple socket outlets
for choice and convenience, but didn't need to provide any more
total power. 13A was chosen to enable a max appliance power of 3kW.
This was probably the same design power which led to the earlier
choice of 15A, as the mains voltage had risen in most areas since
then. (In contrast, some European countries had designed for 3.5kW
socket outlets between WWI and WWII.) The ring circuit enabled
any number of socket outlets with less copper required.
The ring circuit wire was the same as had been used for the 15A
socket outlets, which avoided the need to generate any new cable
size. It also meant it was quite easy to convert a 15A radial
installation to a 30A ring circuit, but in practice I don't think
much such conversion was done.
quote:
>How much is the ring conductor reduced in size?
By 1/3rd. A reevaluation of the current carrying capacity of the
2.5mm² cable used a few years ago revealed it actually had a
higher current rating than previously thought, so in most cases,
the size reduction is effectively less than 1/3rd, and in some
cases, almost no reduction at all.
quote:
>In a large house (ring to far end) are rings still an advantage?
They are always used. The other options require thicker wire which
is harder to handle, or a circuit which covers much less floor area,
so many more circuits would be required. Other factors such as the
requirement for multiple earthing paths where use of IT equipment
with expected earth leakage is likely is also harder to meet when
not using a ring circuit.
quote:
>Are there problems with long rings with an outlet near one end (long
>side too long to keep short side at acceptable current?
In theory, yes. It is recommended that a ring should not be designed
with a large proportion of its load within 10% of the ring ends.
In practice, this never seems to be a problem -- it is a recent
recommendation based on theoretical analysis, not on any problems
observed in reality AFAIK.
quote:
>Permitted only in dwelling?
No, it is used in most commercial premises too.
It's also been used for the street distribution of electricity in
the form of Ring Mains for many years before Ring Circuits for
socket outlets became common. (Ring Circuits are very often
incorrectly called Ring Mains.)
Use of ring circuits has never been mandatory in the UK. It is a
permitted option which most people find the most convenient, hence
its use.
--
Andrew Gabriel
| |
|
| Andrew Gabriel wrote:
> In article <e99c0$42dbcaf8$4304c9d9$10139@dialupusa.net>,
> Bud <remove.BudNews@isp.com> writes:
>
> Voltages of EU countries are all now 230V nominal. In practice,
> you'll find 220-240V. Actually, this initiative is wider than
> just the EU -- it applies to all CENELEC countries.
>
Standardization - what a radical idea. Almost shocking.
>
>
>
> 13A/3kW is the max single item load on a ring circuit, and
> 32A/7.5kW is the max total load on a ring circuit.
>
Seems like 13A connectors and line cords on a 32A circuit could invite
problems. Although, if I remember other posts, UK circuit breakers dont
have a time delay (US small breakers would be hard to find without a
thermal delay element).
>
>
> Normally more than one, but it depends. You should size a ring
> circuit so the total load is unlikely to be exceeded. There is
> a recommendation that a ring circuit should not supply power for
> more than 100m² of floor area, but if it is known some area is
> going to have a non-typical loading, the designer should adjust
> the area covered by the ring circuits and the number of them
> appropriately. For example, it's not uncommon for a kitchen to
> have a dedicated ring circuit. In practice, most ring circuits
> are hardly ever run anywhere near their full capacity. The main
> building heating (if electric) and main water heating (if electric)
> require dedicated circuits to themselves, and would not be on a
> ring circuit.
My understanding from your post is that ring circuits are for all
general purpose loads - like US 15 & 20A branch circuits (although they
usually also usually contain lighting) and 20A kitchen and laundry circuits.
>
>
>
> They were the result of a post WWII redesign ....
Great description.
Thanks for the info. It would be nice if there were Wiring Practice FAQs
for the UK, US, ....
Bud--
| |
|
| Bud wrote:
> Andrew Gabriel wrote:
>
>
> Seems like 13A connectors and line cords on a 32A circuit could invite
> problems. Although, if I remember other posts, UK circuit breakers dont
> have a time delay (US small breakers would be hard to find without a
> thermal delay element).
>
I read your suggested web reference on world power and discovered fused
plugs - kind of like RTFM.
Bud--
| |
| Andrew Gabriel 2005-07-24, 9:03 pm |
| In article <98e88$42de9338$4304c20f$27278@dialupusa.net>,
Bud <remove.BudNews@isp.com> writes:
> Andrew Gabriel wrote:
>
> Seems like 13A connectors and line cords on a 32A circuit could invite
The 13A plugs all have fuses in them, anything from 2A to 13A
depending on the appliance and flex size/length.
> problems. Although, if I remember other posts, UK circuit breakers dont
> have a time delay (US small breakers would be hard to find without a
> thermal delay element).
Need to introduce some terminology here before continuing...
An overload current happens when an otherwise non-faulty circuit is
simply carrying more than its maximum design current, e.g. too much load.
A fault current happens when a circuit is carrying a current limited
only by the supply and circuit impedance, e.g. some type of short circuit.
In the UK (and now all the EU too) breakers have two tripping components
in them -- overload protection (thermal) and fault protection (magnetic).
The current rating marked on the breaker is the max continuous non-trip
rating of the overload protection component. Typically, a breaker would
allow twice the marked current rating for a minute without tripping,
just as any cable is going to handle twice its current rating for a
minute without coming to any harm. At progressively higher currents,
the overload trip will operate faster.
The fault current component's trip rating is a multiple of the overload
trip rating. The multiple is specified by a letter: B is 3-5 times,
C is 5-10 times, and D is 10-50 times. The magnetic trip is pretty
instant, disconnecting the supply within a mains cycle (20ms), although
most makes of breaker actually manage to do it within less than half
this time.
A ring circuit would normally be protected by a B32 breaker in the
home (C32 is possible too, but more likely in commercial premises).
This means the circuit will run continuously at 32A. At 64A, it would
probably trip after a minute, and at 100A probably within 20 seconds.
This behaviour allows things like startup surges through, without
compromising the circuit cable.
At much over 100A, the fault current protection would kick in and
disconnect within 20ms. This is intended to very quickly disconnect
in the event of a short circuit. The circuit designer is required to
check that the supply impedance and earth fault loop impedance are
low enough that in the event of a fault current, enough current will
flow to trip the fault current protection and give an instant
disconnect. (This is a gross simplification, but you get the idea.)
> My understanding from your post is that ring circuits are for all
> general purpose loads - like US 15 & 20A branch circuits (although they
> usually also usually contain lighting) and 20A kitchen and laundry circuits.
Yes, that's right. Lighting can go on a ring circuit -- it's never
done when a building is initially wired up, but it is sometimes done
when modifying an installation if it's easier to pickup from the ring
circuit in a given situation. Such lighting will require an additional
fuse in the circuit (5A normally used). Other fixed low power or
fixed occasional use high power loads (3kW max) can be fed from the
ring circuit through a permanent connection with a switch and fuse
(same fuse type as used in 13A plugs).
--
Andrew Gabriel
| |
| Ted Rubberford 2005-07-24, 9:03 pm |
|
"Andrew Gabriel" <andrew@cucumber.demon.co.uk> wrote in message
news:42deaf9b$0$38046$5a6aecb4@news.aaisp.net.uk...
> In article <98e88$42de9338$4304c20f$27278@dialupusa.net>,
> Bud <remove.BudNews@isp.com> writes:
>
> The 13A plugs all have fuses in them, anything from 2A to 13A
> depending on the appliance and flex size/length.
>
>
> Need to introduce some terminology here before continuing...
> An overload current happens when an otherwise non-faulty circuit is
> simply carrying more than its maximum design current, e.g. too much load.
> A fault current happens when a circuit is carrying a current limited
> only by the supply and circuit impedance, e.g. some type of short circuit.
>
> In the UK (and now all the EU too) breakers have two tripping components
> in them -- overload protection (thermal) and fault protection (magnetic).
>
> The current rating marked on the breaker is the max continuous non-trip
> rating of the overload protection component. Typically, a breaker would
> allow twice the marked current rating for a minute without tripping,
> just as any cable is going to handle twice its current rating for a
> minute without coming to any harm. At progressively higher currents,
> the overload trip will operate faster.
>
> The fault current component's trip rating is a multiple of the overload
> trip rating. The multiple is specified by a letter: B is 3-5 times,
> C is 5-10 times, and D is 10-50 times. The magnetic trip is pretty
> instant, disconnecting the supply within a mains cycle (20ms), although
> most makes of breaker actually manage to do it within less than half
> this time.
>
> A ring circuit would normally be protected by a B32 breaker in the
> home (C32 is possible too, but more likely in commercial premises).
> This means the circuit will run continuously at 32A. At 64A, it would
> probably trip after a minute, and at 100A probably within 20 seconds.
> This behaviour allows things like startup surges through, without
> compromising the circuit cable.
> At much over 100A, the fault current protection would kick in and
> disconnect within 20ms. This is intended to very quickly disconnect
> in the event of a short circuit. The circuit designer is required to
> check that the supply impedance and earth fault loop impedance are
> low enough that in the event of a fault current, enough current will
> flow to trip the fault current protection and give an instant
> disconnect. (This is a gross simplification, but you get the idea.)
>
>
> Yes, that's right. Lighting can go on a ring circuit -- it's never
> done when a building is initially wired up, but it is sometimes done
> when modifying an installation if it's easier to pickup from the ring
> circuit in a given situation. Such lighting will require an additional
> fuse in the circuit (5A normally used). Other fixed low power or
> fixed occasional use high power loads (3kW max) can be fed from the
> ring circuit through a permanent connection with a switch and fuse
> (same fuse type as used in 13A plugs).
>
> --
> Andrew Gabriel
A pleasure to see an acurate post from a fellow uk engineer.
| |
| phil-news-nospam@ipal.net 2005-07-24, 9:03 pm |
| On 20 Jul 2005 20:10:03 GMT Andrew Gabriel <andrew@cucumber.demon.co.uk> wrote:
| In article <98e88$42de9338$4304c20f$27278@dialupusa.net>,
| Bud <remove.BudNews@isp.com> writes:
|> Andrew Gabriel wrote:
|>>
|>> 13A/3kW is the max single item load on a ring circuit, and
|>> 32A/7.5kW is the max total load on a ring circuit.
|>
|> Seems like 13A connectors and line cords on a 32A circuit could invite
|
| The 13A plugs all have fuses in them, anything from 2A to 13A
| depending on the appliance and flex size/length.
Can a 32A receptacle also be put on the circuit? Or are such circuits
limited to receptacles of 13A?
What size of wire is required for that circuit?
| In the UK (and now all the EU too) breakers have two tripping components
| in them -- overload protection (thermal) and fault protection (magnetic).
They do in the US, too. You can get them for special applications
just one way or the other. But most homes would never have any use
for such.
| A ring circuit would normally be protected by a B32 breaker in the
| home (C32 is possible too, but more likely in commercial premises).
| This means the circuit will run continuously at 32A. At 64A, it would
| probably trip after a minute, and at 100A probably within 20 seconds.
| This behaviour allows things like startup surges through, without
| compromising the circuit cable.
| At much over 100A, the fault current protection would kick in and
| disconnect within 20ms. This is intended to very quickly disconnect
| in the event of a short circuit. The circuit designer is required to
| check that the supply impedance and earth fault loop impedance are
| low enough that in the event of a fault current, enough current will
| flow to trip the fault current protection and give an instant
| disconnect. (This is a gross simplification, but you get the idea.)
If the fault drew fewer amps because of significant impedance, then
shouldn't there be less risk? If it drew 100 amps, the wire should
be OK for 20 seconds and then the breaker trips.
Of course, there is an answer to this. Faults have harms above and
beyond the current drawn. They are typically arcing faults. The
arc of 100 amps can start a fire in a second, long before the thermal
trip kicks in. Since most faults will (if the impedance is low)
draw well over 100 amps, we get to use the magnetic trip to protect
in most of these cases. Now we have arc-fault detection to cover
the rest of them. Are such being used in UK?
|> My understanding from your post is that ring circuits are for all
|> general purpose loads - like US 15 & 20A branch circuits (although they
|> usually also usually contain lighting) and 20A kitchen and laundry circuits.
|
| Yes, that's right. Lighting can go on a ring circuit -- it's never
| done when a building is initially wired up, but it is sometimes done
| when modifying an installation if it's easier to pickup from the ring
| circuit in a given situation. Such lighting will require an additional
| fuse in the circuit (5A normally used). Other fixed low power or
| fixed occasional use high power loads (3kW max) can be fed from the
| ring circuit through a permanent connection with a switch and fuse
| (same fuse type as used in 13A plugs).
When I was in my teens, I thought up the idea of a ring circuit as a
way to cut wire size and/or increase circuit capacity. At the time,
my family was building a new house and I got to talk with the electrician
doing the work on the house. I told him of the idea. He didn't tell me
about it being used anywhere, but he reacted like he understood just
what I was talking about. He told me it would be unsafe because one
span could break and not carry any current, forcing the other span to
carry all of it. Then I suggested that each span be connected to it's
own 15A breaker, instead of both connected to the same 30A breaker.
He said that might work, but they'd never change the way things are
done now. I never thought about it again until I heard about ring
circuits in the UK. I didn't call it a "ring", nor did the electrician
I talked to. I didn't have any name for it.
--
-----------------------------------------------------------------------------
| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
| (first name) at ipal.net | http://phil.ipal.org/ http://ka9wgn.ham.org/ |
-----------------------------------------------------------------------------
| |
| Andrew Gabriel 2005-07-24, 9:03 pm |
| In article <dbot9o1279o@news2.newsguy.com>,
phil-news-nospam@ipal.net writes:
>
> Can a 32A receptacle also be put on the circuit? Or are such circuits
> limited to receptacles of 13A?
No, 13A is the max single load allowed either by socket or by some
appliance being permanently connected.
> What size of wire is required for that circuit?
The regs require that the wire be rated for 2/3rds of the circuit
capacity. The size of wire for this rating depends on the type of
wire, where it's fitted (e.g. on a cable tray, inside thermal
insulation, etc), and how many other wires are in close proximity
(we call this Grouping Factor). Most commonly, 2.5mm² cross-section
area conductors are used, which when embedded in a wall as is most
commonly done in the home, is rated at 27A. The thinnest allowed
is 1.5mm² MICC cable (Mineral Insulated Copper Covered -- not sure
if that exists in the US or what you would call it). Also, remember
that voltage drop isn't an issue for us to anything like the same
extent it is for you.
>| A ring circuit would normally be protected by a B32 breaker in the
>| home (C32 is possible too, but more likely in commercial premises).
>| This means the circuit will run continuously at 32A. At 64A, it would
>| probably trip after a minute, and at 100A probably within 20 seconds.
>| This behaviour allows things like startup surges through, without
>| compromising the circuit cable.
>| At much over 100A, the fault current protection would kick in and
>| disconnect within 20ms. This is intended to very quickly disconnect
>| in the event of a short circuit. The circuit designer is required to
>| check that the supply impedance and earth fault loop impedance are
>| low enough that in the event of a fault current, enough current will
>| flow to trip the fault current protection and give an instant
>| disconnect. (This is a gross simplification, but you get the idea.)
>
> If the fault drew fewer amps because of significant impedance, then
> shouldn't there be less risk? If it drew 100 amps, the wire should
> be OK for 20 seconds and then the breaker trips.
We have other requirements in our regs though. A circuit breaker must
trip within 5 seconds in the case of a short to earth, and for
circuits supplying sockets, this is reduced to just 0.4 seconds.
> Of course, there is an answer to this. Faults have harms above and
> beyond the current drawn. They are typically arcing faults. The
> arc of 100 amps can start a fire in a second, long before the thermal
> trip kicks in. Since most faults will (if the impedance is low)
> draw well over 100 amps, we get to use the magnetic trip to protect
> in most of these cases. Now we have arc-fault detection to cover
> the rest of them. Are such being used in UK?
No. That particular type of fault seems to be much more of a
problem in the US than elsewhere. Our approach over the last
50 or so years was to engineer out the situations which give
rise to arcing in the first place.
> When I was in my teens, I thought up the idea of a ring circuit as a
> way to cut wire size and/or increase circuit capacity. At the time,
> my family was building a new house and I got to talk with the electrician
> doing the work on the house. I told him of the idea. He didn't tell me
> about it being used anywhere, but he reacted like he understood just
> what I was talking about. He told me it would be unsafe because one
> span could break and not carry any current, forcing the other span to
This is the often quoted concern, but it just isn't a problem
in practice. OTOH, if you get a bad connection in a ring, then
it's much less likely to overheat as there's another path.
> carry all of it. Then I suggested that each span be connected to it's
> own 15A breaker, instead of both connected to the same 30A breaker.
Problem there is that the current isn't balanced in a ring, so
you could legitimately and safely have more than 15A in one leg.
Maybe you could argue for a 21A or 27A breaker in each leg, ganged,
feeding from a common 32A breaker, but that's a lot of extra
complexity to solve a problem that just doesn't exist in practice.
> He said that might work, but they'd never change the way things are
> done now. I never thought about it again until I heard about ring
> circuits in the UK. I didn't call it a "ring", nor did the electrician
> I talked to. I didn't have any name for it.
--
Andrew Gabriel
| |
| Bill Shymanski 2005-07-24, 9:03 pm |
|
"Andrew Gabriel" <andrew@cucumber.demon.co.uk> wrote in message
news:42e04041$0$38040$5a6aecb4@news.aaisp.net.uk...
Most commonly, 2.5mm² cross-section
> area conductors are used, which when embedded in a wall as is most
> commonly done in the home, is rated at 27A.
A #14 AWG with a cross section of 2.1 square millimetres is rated 20
amperes in free air and 15 in cable (CSA and NEC, 60 C insulation). A
#12 with an area of 3.3 square millimetres is rated 25 amperes in free
air ( at 60 C insulation in a 30 C ambient) and 20 A in cable. We don't
embed single wires in walls, it's always cable.
>The thinnest allowed
> is 1.5mm² MICC cable (Mineral Insulated Copper Covered -- not sure
> if that exists in the US or what you would call it).
A No. 16 AWG has a cross section of 1.48 square millimetres and is not
permitted as a size for fixed building wiring (though it's common in
flexible cords).
It's called Mineral Insulated Cable here, too - it's faboulously
expensive to install, though, and never used for residential or
commercial work in my admittedly limited experience. I did see a great
deal of it at an irrigation dam, though.
>Also, remember
> that voltage drop isn't an issue for us to anything like the same
> extent it is for you.
>
Oh, yeah, we're constantly fumbling around in the dim light due to the
massive voltage drops running a 100 watt bulb at 120 V instead of 240.
It's a wonder that the State of Califonia alone manages to use more
residential electric energy than the entire UK, given this drawback.
Really, it's less of an issue than you think. Don't forget that with
the split 120-240 system we have all the advantages of 240 and light
bulbs that last longer, too.
Bill
| |
| Andrew Gabriel 2005-07-24, 9:03 pm |
| In article <9Q_De.8547$mN.99173@news1.mts.net>,
"Bill Shymanski" <wtshyman@mb.sympatico.ca> writes:
>
> "Andrew Gabriel" <andrew@cucumber.demon.co.uk> wrote in message
> news:42e04041$0$38040$5a6aecb4@news.aaisp.net.uk...
> Most commonly, 2.5mm² cross-section
> A #14 AWG with a cross section of 2.1 square millimetres is rated 20
> amperes in free air and 15 in cable (CSA and NEC, 60 C insulation). A
> #12 with an area of 3.3 square millimetres is rated 25 amperes in free
> air ( at 60 C insulation in a 30 C ambient) and 20 A in cable.
Actually, I was referring to cable in all cases too. Wasn't
sure what term to use which would make sense in the US so I
just stuck with that of the poster's.
Our Twin and Earth cable comes in 70C and 90C types. The figures
I gave were for 70C type, which is what's normally used in a house.
> We don't embed single wires in walls, it's always cable.
Same here.
>
> A No. 16 AWG has a cross section of 1.48 square millimetres and is not
> permitted as a size for fixed building wiring (though it's common in
> flexible cords).
We use 1mm² and 1.5mm² for lighting, normally protected at
6A (10A commercially). The cable rating is significantly higher
than this -- the 6A and 10A protection is imposed by the use of
certain types of lampholders. As a side effect, it also means the
cable can be safely embedded in attic insulation material without
having to be concerned.
2.5mm² is used for ring circuits at 32A and for radial circuits
protected at 20A. For higher currents, 4mm², 6mm² and 10mm² are
used. A 100A supply is usually on 25mm² for the parts owned by
the householder (different rules apply to the supply company's wiring).
> It's called Mineral Insulated Cable here, too - it's faboulously
> expensive to install, though, and never used for residential or
> commercial work in my admittedly limited experience. I did see a great
> deal of it at an irrigation dam, though.
It was common in UK in commercial premises perhaps 40 years ago.
Not common now -- too expensive in both parts and labor -- unless
you really need cable that continues working in a fire or cable
that is impact-proof. I've also seen it used when rewiring old
buildings of historic architecturual value, where the thin cable
can be better hidden.
> Oh, yeah, we're constantly fumbling around in the dim light due to the
> massive voltage drops running a 100 watt bulb at 120 V instead of 240.
> It's a wonder that the State of Califonia alone manages to use more
> residential electric energy than the entire UK, given this drawback.
> Really, it's less of an issue than you think. Don't forget that with
> the split 120-240 system we have all the advantages of 240 and light
> bulbs that last longer, too.
Well, life of filaments lamps is a question of what efficiency
tradeoff is made. I thought your A-line lamps were normally rated
750 hours, whereas our GLS lamps are normally rated 1000 hours
(longer life ones are also available with a lower efficiency).
For the same life, a 120V filament lamp is more efficient than
a 240V filament lamp. I'm not sure this matters any more though;
there have been almost no 240V filament lamps in my house for
the last 10 years.
One thing most UK people notice when visiting the US is the way
your lights get brighter and dimmer when other loads in the house
switch on and off. That's very rare here in UK and when it does
happen, it will normally trigger a search for a fault, which is
probably why it initially alarms visitors to the US.
--
Andrew Gabriel
| |
| Beachcomber 2005-07-24, 9:03 pm |
|
>
>One thing most UK people notice when visiting the US is the way
>your lights get brighter and dimmer when other loads in the house
>switch on and off. That's very rare here in UK and when it does
>happen, it will normally trigger a search for a fault, which is
>probably why it initially alarms visitors to the US.
>
>--
You may not have the dimming lights phenomenon in the UK, but it is
not something that is confined to US. In fact, it rarely, if ever
occurs in modern wiring or new construction if the codes are followed
and the installation was done properly. Sometimes if you are unlucky
enough to live at the end of the line in the most distant house of a
rural area, you may be subject to fluctuating voltage levels. It also
depends on what other loads (the aluminum factory?) are connected to
your system on the primary side.
I recall seeing dimming lights when I lived in France. In some
cases, an entire small village would be served by one 240 volt
transformer and there were thick cables (apparently not thick enough
though) that would string all of the houses together. The
incandescent lights would be subject to all sorts of flickering
variations as neighbors switched loads in and out of the system.
Beachcomber
| |
| phil-news-nospam@ipal.net 2005-07-24, 9:03 pm |
| On 22 Jul 2005 00:39:29 GMT Andrew Gabriel <andrew@cucumber.demon.co.uk> wrote:
| No. That particular type of fault seems to be much more of a
| problem in the US than elsewhere. Our approach over the last
| 50 or so years was to engineer out the situations which give
| rise to arcing in the first place.
How has this been done?
A series arc is one example. Twice the voltage and half the current
does change the character of the arc. But over twice the distance
it can still dissipate the same energy with half the current. That
would be an arc that would drop out at a lower voltage.
Are the cords leading to appliances mechanically protected to avoid
stepping on them causing damage? That would be something I'd like to
see here.
|> When I was in my teens, I thought up the idea of a ring circuit as a
|> way to cut wire size and/or increase circuit capacity. At the time,
|> my family was building a new house and I got to talk with the electrician
|> doing the work on the house. I told him of the idea. He didn't tell me
|> about it being used anywhere, but he reacted like he understood just
|> what I was talking about. He told me it would be unsafe because one
|> span could break and not carry any current, forcing the other span to
|
| This is the often quoted concern, but it just isn't a problem
| in practice. OTOH, if you get a bad connection in a ring, then
| it's much less likely to overheat as there's another path.
OTOH, you wouldn't know something is going wrong. The lights won't
be blinking.
|> carry all of it. Then I suggested that each span be connected to it's
|> own 15A breaker, instead of both connected to the same 30A breaker.
|
| Problem there is that the current isn't balanced in a ring, so
| you could legitimately and safely have more than 15A in one leg.
| Maybe you could argue for a 21A or 27A breaker in each leg, ganged,
| feeding from a common 32A breaker, but that's a lot of extra
| complexity to solve a problem that just doesn't exist in practice.
I've given up on the ring circuit idea for over here, anyway. Perhaps
the biggest problem bringing it in here would be educating people about
how it works. But I'll just stick with radial and bus.
--
-----------------------------------------------------------------------------
| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
| (first name) at ipal.net | http://phil.ipal.org/ http://ka9wgn.ham.org/ |
-----------------------------------------------------------------------------
| |
| phil-news-nospam@ipal.net 2005-07-24, 9:03 pm |
| On 22 Jul 2005 09:03:34 GMT Andrew Gabriel <andrew@cucumber.demon.co.uk> wrote:
|> Oh, yeah, we're constantly fumbling around in the dim light due to the
|> massive voltage drops running a 100 watt bulb at 120 V instead of 240.
|> It's a wonder that the State of Califonia alone manages to use more
|> residential electric energy than the entire UK, given this drawback.
|> Really, it's less of an issue than you think. Don't forget that with
|> the split 120-240 system we have all the advantages of 240 and light
|> bulbs that last longer, too.
|
| Well, life of filaments lamps is a question of what efficiency
| tradeoff is made. I thought your A-line lamps were normally rated
| 750 hours, whereas our GLS lamps are normally rated 1000 hours
| (longer life ones are also available with a lower efficiency).
| For the same life, a 120V filament lamp is more efficient than
| a 240V filament lamp. I'm not sure this matters any more though;
| there have been almost no 240V filament lamps in my house for
| the last 10 years.
|
| One thing most UK people notice when visiting the US is the way
| your lights get brighter and dimmer when other loads in the house
| switch on and off. That's very rare here in UK and when it does
| happen, it will normally trigger a search for a fault, which is
| probably why it initially alarms visitors to the US.
We can both have low voltage (e.g. 12V) lighting and have all the same
bulb advantages. Maybe if I run my 12V transformers from 240V instead
of from 120V, I would avoid much of the dimming effect as well. If I
could get 480V, I'd use that (not to the bulb, of course).
I don't notice any such dimming at all except when the garbage disposal
is turned on. I suspect that thing is pulling over 100 amps to start up.
It lasts about 1-2 cycles.
--
-----------------------------------------------------------------------------
| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
| (first name) at ipal.net | http://phil.ipal.org/ http://ka9wgn.ham.org/ |
-----------------------------------------------------------------------------
| |
| Andrew Gabriel 2005-07-24, 9:03 pm |
| In article <dbr0hp42oes@news1.newsguy.com>,
phil-news-nospam@ipal.net writes:
> On 22 Jul 2005 00:39:29 GMT Andrew Gabriel <andrew@cucumber.demon.co.uk> wrote:
>
>| No. That particular type of fault seems to be much more of a
>| problem in the US than elsewhere. Our approach over the last
>| 50 or so years was to engineer out the situations which give
>| rise to arcing in the first place.
>
> How has this been done?
I don't claim to know all the areas, but some of the better known
areas where problems of this sort had been observed...
Wirenuts ceased to be used (actually, that's over 60 years ago, but
their use was never very widespread for mains wiring even before then).
Wrap-around screw terminals have been gradually phased out.
Plugs and sockets have much larger contact areas, higher contact pressure,
and firmer grip -- no wobbling around (this is also well over 60 years
ago, as it was started with the design of our previous round pin plugs).
We didn't use Alumin{i}um wiring in houses.
> A series arc is one example. Twice the voltage and half the current
> does change the character of the arc. But over twice the distance
> it can still dissipate the same energy with half the current. That
> would be an arc that would drop out at a lower voltage.
Arcs are sustained by current. The higher the current they pass,
the lower voltage they need to sustain them. They aren't ohmic.
> Are the cords leading to appliances mechanically protected to avoid
> stepping on them causing damage? That would be something I'd like to
> see here.
Yes. All appliance cords are sheathed, since 1960's I think.
All except low current ones were sheathed long before that.
They probably get stepped on quite often, but I don't ever
recall any damage due to stepping on one.
Unsheathed cords are limited to 50V max, so they can be used
for LV side of LV lighting.
--
Andrew Gabriel
| |
|
| Andrew Gabriel wrote:
>
> One thing most UK people notice when visiting the US is the way
> your lights get brighter and dimmer when other loads in the house
> switch on and off. That's very rare here in UK and when it does
> happen, it will normally trigger a search for a fault, which is
> probably why it initially alarms visitors to the US.
>
I suspect the major cause of dimming is mixing lighting and other loads
on the same circuit.
Bud--
| |
|
| Andrew Gabriel wrote:
> In article <dbr0hp42oes@news1.newsguy.com>,
> phil-news-nospam@ipal.net writes:
>
>
> I don't claim to know all the areas, but some of the better known
> areas where problems of this sort had been observed...
> Wirenuts ceased to be used (actually, that's over 60 years ago, but
> their use was never very widespread for mains wiring even before then).
> Wrap-around screw terminals have been gradually phased out.
> Plugs and sockets have much larger contact areas, higher contact pressure,
> and firmer grip -- no wobbling around (this is also well over 60 years
> ago, as it was started with the design of our previous round pin plugs).
>
When I was doing service work I don't remember a failure caused by a
wirenut. What do you use to join wires. At devices do you use screw
tightened pressure contacts instead of wrap around? Anything else?
> We didn't use Alumin{i}um wiring in houses.
>
[Nice spelling] Alunin(i)um branch circuit wiring has definitely been a
headache - a lot of it caused by failed terminations at devices. There
have been devices and wirenuts that are UL listed for alumin(i)um since
about the 1970s I think. I havn't heard what their in-service
reliability is. Services have for a long time been mostly alumin(i)um
and far as I know are very reliable - with listed terminations and
anti-oxide pastes.
>
>
>
> Yes. All appliance cords are sheathed, since 1960's I think.
> All except low current ones were sheathed long before that.
> They probably get stepped on quite often, but I don't ever
> recall any damage due to stepping on one.
> Unsheathed cords are limited to 50V max, so they can be used
> for LV side of LV lighting.
>
'Heavy duty' US cords have a rubber or plastic jacket over the insulated
wires - probably the same as sheathed. Would be interesting to see
actuarial insurance info on electrical causes of fire in the US and UK.
| |
| Andrew Gabriel 2005-07-24, 9:03 pm |
| In article <dc214$42e15814$4304c718$8018@dialupusa.net>,
Bud <remove.BudNews@isp.com> writes:
> Andrew Gabriel wrote:
>
> When I was doing service work I don't remember a failure caused by a
> wirenut. What do you use to join wires. At devices do you use screw
> tightened pressure contacts instead of wrap around? Anything else?
They're all screw tightened pressure contacts, with no
possibility of the wire escaping as it's tightened. There's
an insulated free-standing type which is used instead of
wirenuts ("chocolate block" connectors, because they come in
strips like bars of chocolate which you break down to the
required number), but we don't use anything like as many, as we
don't use pigtails -- most accessories will not need any extra
connections behind them. If an accessory does normally need
extra wire jointing behind it, in some cases an extra terminal
is included on the rear of the accessory for this purpose.
> 'Heavy duty' US cords have a rubber or plastic jacket over the insulated
> wires - probably the same as sheathed. Would be interesting to see
> actuarial insurance info on electrical causes of fire in the US and UK.
Electrical installation fires in the UK cause around 5 deaths
per year, and electrical appliance fires around 18 deaths/year,
with the figures reducing over time. In perspective, total
deaths from fire in UK homes is around 500/year, the main causes
being smoking (particularly falling asleep whilst smoking),
followed cooking related (oil/fat catching fire). Again, the
trend is figures reducing each year.
--
Andrew Gabriel
| |
| phil-news-nospam@ipal.net 2005-07-24, 9:03 pm |
| On Fri, 22 Jul 2005 15:16:27 -0500 Bud <remove.BudNews@isp.com> wrote:
| Andrew Gabriel wrote:
|
|>
|> One thing most UK people notice when visiting the US is the way
|> your lights get brighter and dimmer when other loads in the house
|> switch on and off. That's very rare here in UK and when it does
|> happen, it will normally trigger a search for a fault, which is
|> probably why it initially alarms visitors to the US.
|>
| I suspect the major cause of dimming is mixing lighting and other loads
| on the same circuit.
And they don't do that in UK?
--
-----------------------------------------------------------------------------
| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
| (first name) at ipal.net | http://phil.ipal.org/ http://ka9wgn.ham.org/ |
-----------------------------------------------------------------------------
| |
| phil-news-nospam@ipal.net 2005-07-24, 9:03 pm |
| On 22 Jul 2005 16:42:56 GMT Andrew Gabriel <andrew@cucumber.demon.co.uk> wrote:
| In article <dbr0hp42oes@news1.newsguy.com>,
| phil-news-nospam@ipal.net writes:
|> On 22 Jul 2005 00:39:29 GMT Andrew Gabriel <andrew@cucumber.demon.co.uk> wrote:
|>
|>| No. That particular type of fault seems to be much more of a
|>| problem in the US than elsewhere. Our approach over the last
|>| 50 or so years was to engineer out the situations which give
|>| rise to arcing in the first place.
|>
|> How has this been done?
|
| I don't claim to know all the areas, but some of the better known
| areas where problems of this sort had been observed...
| Wirenuts ceased to be used (actually, that's over 60 years ago, but
| their use was never very widespread for mains wiring even before then).
| Wrap-around screw terminals have been gradually phased out.
What replaced them? I'm sure it can't be backstabs.
| Plugs and sockets have much larger contact areas, higher contact pressure,
| and firmer grip -- no wobbling around (this is also well over 60 years
| ago, as it was started with the design of our previous round pin plugs).
Mine don't wobble around.
| We didn't use Alumin{i}um wiring in houses.
Good thing, too.
|> A series arc is one example. Twice the voltage and half the current
|> does change the character of the arc. But over twice the distance
|> it can still dissipate the same energy with half the current. That
|> would be an arc that would drop out at a lower voltage.
|
| Arcs are sustained by current. The higher the current they pass,
| the lower voltage they need to sustain them. They aren't ohmic.
But there is a voltage drop within the arc if it dissipates power.
Otherwise it would be an interesting way to get free heat from
electricity (it isn't).
|> Are the cords leading to appliances mechanically protected to avoid
|> stepping on them causing damage? That would be something I'd like to
|> see here.
|
| Yes. All appliance cords are sheathed, since 1960's I think.
| All except low current ones were sheathed long before that.
| They probably get stepped on quite often, but I don't ever
| recall any damage due to stepping on one.
| Unsheathed cords are limited to 50V max, so they can be used
| for LV side of LV lighting.
What kind of sheathing is required?
--
-----------------------------------------------------------------------------
| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
| (first name) at ipal.net | http://phil.ipal.org/ http://ka9wgn.ham.org/ |
-----------------------------------------------------------------------------
| |
| Andrew Gabriel 2005-07-24, 9:03 pm |
| In article <dbvodj29f@news3.newsguy.com>,
phil-news-nospam@ipal.net writes:
>On Fri, 22 Jul 2005 15:16:27 -0500 Bud <remove.BudNews@isp.com> wrote:
>| Andrew Gabriel wrote:
>|
>|>
>|> One thing most UK people notice when visiting the US is the way
>|> your lights get brighter and dimmer when other loads in the house
>|> switch on and off. That's very rare here in UK and when it does
>|> happen, it will normally trigger a search for a fault, which is
>|> probably why it initially alarms visitors to the US.
>|>
>| I suspect the major cause of dimming is mixing lighting and other loads
>| on the same circuit.
>
>And they don't do that in UK?
The fixed lighting is on dedicated circuits, but people routinely
plug table/portable lamps into regular sockets, and we don't get
lights changing brightness even with those, as is common in the US.
So I don't think this can just be blamed on mixing lighting with
other loads on the same circuit, because when we do that, it still
doesn't happen.
--
Andrew Gabriel
| |
| Andrew Gabriel 2005-07-24, 9:03 pm |
| In article <dbvon139f@news3.newsguy.com>,
phil-news-nospam@ipal.net writes:
>On 22 Jul 2005 16:42:56 GMT Andrew Gabriel <andrew@cucumber.demon.co.uk> wrote:
>| In article <dbr0hp42oes@news1.newsguy.com>,
>| phil-news-nospam@ipal.net writes:
>|> On 22 Jul 2005 00:39:29 GMT Andrew Gabriel <andrew@cucumber.demon.co.uk> wrote:
>|>
>|>| No. That particular type of fault seems to be much more of a
>|>| problem in the US than elsewhere. Our approach over the last
>|>| 50 or so years was to engineer out the situations which give
>|>| rise to arcing in the first place.
>|>
>|> How has this been done?
>|
>| I don't claim to know all the areas, but some of the better known
>| areas where problems of this sort had been observed...
>| Wirenuts ceased to be used (actually, that's over 60 years ago, but
>| their use was never very widespread for mains wiring even before then).
>| Wrap-around screw terminals have been gradually phased out.
>
>What replaced them? I'm sure it can't be backstabs.
Straight blind hole for the conductor, with a screw clamp entering
it from the side. These were always more popular than wrap-around
screw terminals in any case, but the wrap-around's have now pretty
much vanished from the scene.
>|> A series arc is one example. Twice the voltage and half the current
>|> does change the character of the arc. But over twice the distance
>|> it can still dissipate the same energy with half the current. That
>|> would be an arc that would drop out at a lower voltage.
>|
>| Arcs are sustained by current. The higher the current they pass,
>| the lower voltage they need to sustain them. They aren't ohmic.
>
>But there is a voltage drop within the arc if it dissipates power.
There is, but an arc naturally seeks to minimise this by increasing
its current density. As the current density increases, the arc
voltage plumits. To keep an arc stable, you need something to limit
the current flow in it.
>|> Are the cords leading to appliances mechanically protected to avoid
>|> stepping on them causing damage? That would be something I'd like to
>|> see here.
>|
>| Yes. All appliance cords are sheathed, since 1960's I think.
>| All except low current ones were sheathed long before that.
>| They probably get stepped on quite often, but I don't ever
>| recall any damage due to stepping on one.
>| Unsheathed cords are limited to 50V max, so they can be used
>| for LV side of LV lighting.
>
>What kind of sheathing is required?
I don't know what the precise rules are, but there's a second
layer of insulation around all flexible cables, tougher the thicker
the cord. Cords are not damaged by standing on them, nor if you
occasionally drive over them (although I doubt the manufacturers
would claim they are designed for that). There are also special
sheaths for different purposes, e.g. silicone for things like
irons and soldering irons, rubber for tools where the cord is
likely to come in for rough use, PVC for most other things.
The figure-of-8 zip cord and other single-insulated cord isn't
allowed for mains use here (or anything over 50v).
--
Andrew Gabriel
| |
| phil-news-nospam@ipal.net 2005-07-25, 9:21 am |
| On 24 Jul 2005 12:01:16 GMT Andrew Gabriel <andrew@cucumber.demon.co.uk> wrote:
| In article <dbvodj29f@news3.newsguy.com>,
| phil-news-nospam@ipal.net writes:
|>On Fri, 22 Jul 2005 15:16:27 -0500 Bud <remove.BudNews@isp.com> wrote:
|>| Andrew Gabriel wrote:
|>|
|>|>
|>|> One thing most UK people notice when visiting the US is the way
|>|> your lights get brighter and dimmer when other loads in the house
|>|> switch on and off. That's very rare here in UK and when it does
|>|> happen, it will normally trigger a search for a fault, which is
|>|> probably why it initially alarms visitors to the US.
|>|>
|>| I suspect the major cause of dimming is mixing lighting and other loads
|>| on the same circuit.
|>
|>And they don't do that in UK?
|
| The fixed lighting is on dedicated circuits, but people routinely
| plug table/portable lamps into regular sockets, and we don't get
| lights changing brightness even with those, as is common in the US.
| So I don't think this can just be blamed on mixing lighting with
| other loads on the same circuit, because when we do that, it still
| doesn't happen.
I see lights dimming here, even on different circuits, so I would have to
agree that sharing the same circuit is not the sole cause of this problem.
This was an issue discussed maybe here a few weeks/months ago, and it
then focused more on the fact that in the USA, most of the loads tend to
be on 120V, and hence draw twice the current as their UK counterparts.
Given that a 100A service is going to have roughly the same gauge wire in
both countries, that means one will see twice the drop in voltage in the
USA as in UK. Then, that twice voltage drop has an even greater impact on
the lower working voltage. If a motor draws enough current on 120V to
cause a 6V drop on some given wiring, that same motor would cause a 3V
drop on the same wiring at 240V. That's a 5% drop vs. a 1.25% drop.
Makes me want to switch to 480V or 600V service :-)
Still, even with that, people here report lights dimming even though the
load in question causing the problem is wired to opposite poles and gets
240V and therefore uses only half the current it would if it had been
wired only to 120V. So there has to be some other factor involved as
well. That may be differences in actual practice by the utilities.
Larger transformers in the UK serving more homes, and smaller transformers
in the USA serving fewer homes, would have a difference in the system
impedance that can affect how the lights dim.
Where I live, one single phase pad mount transformer of unknown capacity
is serving a group of about 8 homes. I don't see or notice (doesn't mean
it isn't there) any flickering or dimming except when I turn on the
garbage disposal unit. That causes a lot of lights to dim rather
dramatically. The GD is on 120V. The air conditioner (on 240V) has never
caused any dimming. And I cannot recall any dimming from unexplained
sources other than what appeared to be line fault problems way upstream.
Trees like to drop branches on, or fall directly on, primary lines around
here. Given the topology, it is nearly impossible to keep trees trimmed
back enough to avoid this in all locations.
--
-----------------------------------------------------------------------------
| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
| (first name) at ipal.net | http://phil.ipal.org/ http://ka9wgn.ham.org/ |
-----------------------------------------------------------------------------
| |
| phil-news-nospam@ipal.net 2005-07-25, 10:21 am |
| On 24 Jul 2005 12:30:38 GMT Andrew Gabriel <andrew@cucumber.demon.co.uk> wrote:
|>What replaced them? I'm sure it can't be backstabs.
|
| Straight blind hole for the conductor, with a screw clamp entering
| it from the side. These were always more popular than wrap-around
| screw terminals in any case, but the wrap-around's have now pretty
| much vanished from the scene.
I'm sitting here holding a receptacle that hasn't been installed. It
happens to be one intended for 240V, 15A, in the USA. It is a duplex, and
each outlet has two horizontal blade holes aligned end to end, instead of
the two parallel vertical ones usually seen. The ground is in the usual
position (above or below or sideways depending on which way you turn it).
It fits the same plate opening as the common 120V receptacles. There are
screw terminals on the side. But there is a plate under the screw that
forms a clamp. The back as an indentation makred "strip gauge".
Stripping insulation off the wire at the length shown would just fit
completely under the clamp. Then the screw would be tightened down
pressing the clamp onto the wire and the wire only the base metal around
the screw hole. The majority of wire contact is the clamp and the base.
The screw may have a slight contact with the wire along the edge of the
threads and that is all. You can't get the wire around the screw for a
few reasons. The screw will not come out all the way. You can't bend it
around the screw under the clamp piece. The clamp has some lips on its
upper side at the back to prevent putting the wire around the screw above
the clamp piece. It seems to be a very good design to me. It is made by
a company called Hubbell.
|>|> A series arc is one example. Twice the voltage and half the current
|>|> does change the character of the arc. But over twice the distance
|>|> it can still dissipate the same energy with half the current. That
|>|> would be an arc that would drop out at a lower voltage.
|>|
|>| Arcs are sustained by current. The higher the current they pass,
|>| the lower voltage they need to sustain them. They aren't ohmic.
|>
|>But there is a voltage drop within the arc if it dissipates power.
|
| There is, but an arc naturally seeks to minimise this by increasing
| its current density. As the current density increases, the arc
| voltage plumits. To keep an arc stable, you need something to limit
| the current flow in it.
I'd say the arc is sustained by ionization, which results from power
dissipated, which as we all know is a function of both current and
voltage.
| The figure-of-8 zip cord and other single-insulated cord isn't
| allowed for mains use here (or anything over 50v).
The zip cord is still used here, but it's found in a lot fewer places
now.
--
-----------------------------------------------------------------------------
| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
| (first name) at ipal.net | http://phil.ipal.org/ http://ka9wgn.ham.org/ |
-----------------------------------------------------------------------------
| |
|
| Andrew Gabriel wrote:
> The current rating marked on the breaker is the max continuous non-trip
> rating of the overload protection component. Typically, a breaker would
> allow twice the marked current rating for a minute without tripping,
> just as any cable is going to handle twice its current rating for a
> minute without coming to any harm. At progressively higher currents,
> the overload trip will operate faster.
>
> The fault current component's trip rating is a multiple of the overload
> trip rating. The multiple is specified by a letter: B is 3-5 times,
> C is 5-10 times, and D is 10-50 times. The magnetic trip is pretty
> instant, disconnecting the supply within a mains cycle (20ms), although
> most makes of breaker actually manage to do it within less than half
> this time.
>
> A ring circuit would normally be protected by a B32 breaker in the
> home (C32 is possible too, but more likely in commercial premises).
> This means the circuit will run continuously at 32A. At 64A, it would
> probably trip after a minute, and at 100A probably within 20 seconds.
> This behaviour allows things like startup surges through, without
> compromising the circuit cable.
> At much over 100A, the fault current protection would kick in and
> disconnect within 20ms. This is intended to very quickly disconnect
> in the event of a short circuit. The circuit designer is required to
> check that the supply impedance and earth fault loop impedance are
> low enough that in the event of a fault current, enough current will
> flow to trip the fault current protection and give an instant
> disconnect. (This is a gross simplification, but you get the idea.)
>
>
I finally found where I hid time-current curves for a circuit breaker.
For comparison a generic curve for Square D breakers (which are probably
typical) are instantaneous at over 10x rating with a maximum clearing
time of 1 cycle. This is right between your B and C rating. For a 2x
overload the clearing time is 9-40 seconds, a lot shorter than I
thought. May have to be faster than UK because we can have #18 wire
rated 7A on a 20A circuit (of course with no fuses in the plug).
Bud--
| |
|
|
Another US quirk - US circuit rating is 80% for continuous loads over 3
hours). My understanding is that this is because fuses and circuit
breakers may open/trip if 100% load is applied over 3 hours. (There is
an exception for 100% rated devices.) Seems like an odd design.
Bud--
| |
| j.l@octa4.net.au 2005-07-26, 10:21 am |
|
Much Snipped
>
> --
> -----------------------------------------------------------------------------
> | Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
> | (first name) at ipal.net | http://phil.ipal.org/ http://ka9wgn.ham.org/ |
>
-----------
Hello all,
Could the difference in lights dimming possibly be to the difference in
size of the pole or distribution transformers? I understand the USA
tends to use transformers for suburban areas of 16 - 50kVA range? And
that in the UK transformers of 300kVA+ are much more common due to
higher density living in a lot of areas? The available short circuit
current at the terminals of the main switch will have an effect of how
much the lights will dim.
Here its not unusual to see lights dim a bit in the suburban areas when
a large airconditioner cuts in, especially if there is some distance to
the pole transformer. In say a medium size block of units (appartment,
condo, whatever they're called elsewhere) where there will be a large
transformer within the building its unusual to see lights dim when
switching on large appliances.
We have similar supply characteristics to that of the UK - 240/415 volt
three phase supplies, but the actual method of delivering it to homes
varies on area. It can be underground, overhead, single phase, three
phase, big transformers or small transformers - whichever is most
economical when the area is being subdivied or developed.
120 volts is most likely best for most household appliances, but 800
volts or so sure would make LV retic, street lights, industrial,
farming or anything where distance are big much cheaper and easier 
Cheers
James
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