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Home > Archive > Electrical Engineering > April 2006 > Arc fault Circuit Interupter Breakers
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Arc fault Circuit Interupter Breakers
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| AFCI breakers are now mandatory in new construction. I've never used one
but I see that the neutral wire passes thru the breaker instead of going to
the neural buss directly. I assume that it maybe monitoring the current
passing thru the white wire and then what? What is the actual working
principles for this breaker? How does it differ from a GFI? (I understand
the distinct purposes between the two, I am not asking about function, I'm
asking about the guts) (gfi trips at aprox. 5ma of current passing thru the
ground (not white wire)). Since a switching power supply or an arc welder
presents themselves as a rapid succession of shorts, why wouldn't a afci
misinterpret those as arcs? I think the response time to the shorting
pulses would have to be slower than 10 kHz (.0001seconds)
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| electrician@electrician.com 2006-04-11, 4:21 am |
| Just go to the site of the inventor:
http://www.zlan.com/
You will find just about everything you want to know.
It took the inventor a long time to program a chip to know the
difference between a good arc like in a light switch from a bad arc
like a hot to neutral arc in the wall.
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| n wrote:
> AFCI breakers are now mandatory in new construction. I've never used one
> but I see that the neutral wire passes thru the breaker instead of going to
> the neural buss directly. I assume that it maybe monitoring the current
> passing thru the white wire and then what? What is the actual working
> principles for this breaker? How does it differ from a GFI? (I understand
> the distinct purposes between the two, I am not asking about function, I'm
> asking about the guts) (gfi trips at aprox. 5ma of current passing thru the
> ground (not white wire)). Since a switching power supply or an arc welder
> presents themselves as a rapid succession of shorts, why wouldn't a afci
> misinterpret those as arcs? I think the response time to the shorting
> pulses would have to be slower than 10 kHz (.0001seconds)
>
AFCIs include a 30 ma GFCI - I believe the idea is that if there is a
ground wire, an H-N arc will rapidly also become a H-G arc.
You are right that there are a lot of arcs an AFCI should'nt detect.
They include operating any switch, which commonly bounce on make
producing arcs, opening a switch, light bulb burning out which commonly
includes the broken filament remaking at shortened length, motor start,
light bulb start. I suspect you might not want an series AFCI for an arc
welder.
Arcs can be parallel (H-N, H-G), or series (loose connection). AFCIs
only detect parallel (surprised me but note the "fault" in AFCI). Those
produced (sold?, installed?) after 1-1-2008 will have to detect both
series and parallel. Series arcs are limited by the load (the current
will not excede the load current). Parallel arcs are limited by the
available fault current at the arc - obviously much higher.
Parallel arcs, because they are not a clean fault, have currents can be
somewhat intermittent and are lower than for a fault. The result is that
the current is low enough that a breaker may take significant time to
trip or not trip at all. 30 seconds may be a very long trip time
compared to the time it takes to ignite a fire. IIRC the arc "signature"
that AFCIs look for is large current pulses, around 80 amps. The
detection is sophisticated to separate from normal arcs. I presume a
series arc is much harder to detect and separate from a normal arc.
A good paper from the Consumer Product Safety Commission on AFCIs is at
http://www.cpsc.gov/volstd/afci/AFCIFireTechnology.pdf
It includes the rationalle for using AFCIs and information on how they
work.
bud--
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| n wrote:
> AFCI breakers are now mandatory in new construction.
Not every breaker in the panel - just for the bedrooms.
I've never used one
> but I see that the neutral wire passes thru the breaker instead of going to
> the neural buss directly. I assume that it maybe monitoring the current
> passing thru the white wire and then what? What is the actual working
> principles for this breaker? How does it differ from a GFI? (I understand
> the distinct purposes between the two, I am not asking about function, I'm
> asking about the guts) (gfi trips at aprox. 5ma of current passing thru the
> ground (not white wire)).
No. The GFCI trips when the current on the white wire and
the current on the black wire differ by ~ 5 mA or more.
You do not need a ground wire at all in order for a GFCI
to trip, and the fault current which causes the GFCI to trip
does not have to flow on the ground at all.
Ed
Since a switching power supply or an arc welder
> presents themselves as a rapid succession of shorts, why wouldn't a afci
> misinterpret those as arcs? I think the response time to the shorting
> pulses would have to be slower than 10 kHz (.0001seconds)
>
>
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"ehsjr" <ehsjr@bellatlantic.net> wrote in message
news:ERW_f.3606$yg2.2249@trndny02...
(gfi trips at aprox. 5ma of current passing thru the
>
> No. The GFCI trips when the current on the white wire and
> the current on the black wire differ by ~ 5 mA or more.
> You do not need a ground wire at all in order for a GFCI
> to trip, and the fault current which causes the GFCI to trip
> does not have to flow on the ground at all.
>
> Ed
> Well Ed, you're simply restating what I said. If there is a difference
between the white and black it can only be because 5ma is finding some
path to ground. I suppose I did not make myself clear. But thanks for
clearing that up.
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| Michael Moroney 2006-04-12, 3:21 pm |
| "n" <no@no.no> writes:
>"ehsjr" <ehsjr@bellatlantic.net> wrote in message
>news:ERW_f.3606$yg2.2249@trndny02...
>(gfi trips at aprox. 5ma of current passing thru the
[color=darkred]
>between the white and black it can only be because 5ma is finding some
>path to ground. I suppose I did not make myself clear. But thanks for
>clearing that up.
The way you originally wrote it implies there is something measuring the
ground current. There isn't. Anyway, no ground is necessary to trip a
GFCI. A high resistance from the hot (of another circuit or upstream of
the GFCI) to either the black or white downstream of a GFCI will trip it.
The test button in a GFCI outlet just connects a resistor, and not to
ground, it just causes a >5mA difference. Also, I once miswired two
adjacent GFCI breakers in a panel by switching the white wires. When I
applied a load to one circuit, BOTH breakers tripped. One saw a current
flow on the hot with none on the neutral, the other saw current on the
neutral and none on the hot. No ground involved.
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| Ben Miller 2006-04-12, 6:21 pm |
| "n" <no@no.no> wrote in message news:123p5peecuqvn22@corp.supernews.com...
> between the white and black it can only be because 5ma is finding some
> path to ground. I suppose I did not make myself clear. But thanks for
> clearing that up.
A shared neutral with only one black going through the GFCI will also trip
it, as will any other situation where some current finds a path around the
GFCI. True, most of the time it will be a path to ground, but it doesn't
need to be. It is better to think in terms of a difference in current, and
leave the ground out of it.
Ben Miller
--
Benjamin D. Miller, PE
B. MILLER ENGINEERING
www.bmillerengineering.com
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| phil-news-nospam@ipal.net 2006-04-16, 4:21 am |
| On Tue, 11 Apr 2006 10:36:59 -0500 Bud-- <remove.BudNews@isp.com> wrote:
| Arcs can be parallel (H-N, H-G), or series (loose connection). AFCIs
| only detect parallel (surprised me but note the "fault" in AFCI). Those
| produced (sold?, installed?) after 1-1-2008 will have to detect both
| series and parallel. Series arcs are limited by the load (the current
| will not excede the load current). Parallel arcs are limited by the
| available fault current at the arc - obviously much higher.
|
| Parallel arcs, because they are not a clean fault, have currents can be
| somewhat intermittent and are lower than for a fault. The result is that
| the current is low enough that a breaker may take significant time to
| trip or not trip at all. 30 seconds may be a very long trip time
| compared to the time it takes to ignite a fire. IIRC the arc "signature"
| that AFCIs look for is large current pulses, around 80 amps. The
| detection is sophisticated to separate from normal arcs. I presume a
| series arc is much harder to detect and separate from a normal arc.
I read the target was 70 amps. Minor difference.
But it would need to be amps with some kind of intermittent waveform,
else some motors could cause problems, such as air conditioner start.
I notice very little dealing with potentials of radio transmission
interference caused to the AFCI device. I know uch an issue exists
with GFCI receptacles.
--
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| Phil Howard KA9WGN | http://linuxhomepage.com/ http://ham.org/ |
| (first name) at ipal.net | http://phil.ipal.org/ http://ka9wgn.ham.org/ |
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