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Home > Archive > Electrical Engineering > February 2008 > LV Earth Fault
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| Samuel Chan 2008-02-18, 9:25 am |
| Anyone know if the earth terminal is talking about 10 Ohm impedance, TN-S earrthing. How can we perform earth fault protection in Main switchboard?
| |
| Andrew Gabriel 2008-02-20, 3:25 am |
| In article <47b98553$1_2@rain.i-cable.com>,
"Samuel Chan" <threecat@i-cable.com> writes:
> This is a multi-part message in MIME format.
Please don't do that.
> Anyone know if the earth terminal is talking about 10 Ohm impedance, =
> TN-S earrthing. How can we perform earth fault protection in Main =
> switchboard?
You call your supply network maintainer to get it fixed - 10 ohms is too high.
--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]
| |
| Tomi Holger Engdahl 2008-02-20, 9:25 am |
| "Samuel Chan" <threecat@i-cable.com> writes:
> Anyone know if the earth terminal is talking about 10 Ohm impedance, TN-S earrthing. How can we perform earth fault protection in Main switchboard?
If the earth impedance is high then earth fault protection
can be made using residual current device
http://en.wikipedia.org/wiki/Residual-current_device
"A residual current device (RCD), or residual current circuit breaker
(RCCB), is an electrical wiring device that disconnects a circuit
whenever it detects that the flow of current is not balanced between
the phase ("hot") conductor and the neutral conductor. Such an
imbalance is sometimes caused by current leakage through the body of a
person who is grounded and accidentally touching the energized part of
the circuit"
"In the United States, the National Electrical Code, requires GFCI
devices intended to protect people to interrupt the circuit if the
leakage current exceeds a range of 4.6 mA of current (the exact trip
setting can be chosen by the manufacturer of the device and is
typically 5 mA) within 25 milliseconds."
"GFCI devices which protect equipment (not people) are allowed to trip
as high as 30 mA of current. In Europe, the commonly used RCDs have
trip currents of 10-300 mA."
--
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at
http://www.epanorama.net/
| |
| Stuart 2008-02-20, 9:25 am |
| In article <lajwsozuc52.fsf@sahrami.niksula.hut.fi>,
Tomi Holger Engdahl <then@sahrami.niksula.hut.fi> wrote:
> "GFCI devices which protect equipment (not people) are allowed to trip
> as high as 30 mA of current. In Europe, the commonly used RCDs have
> trip currents of 10-300 mA."
I have a 10mA trip protected socket on my electronic test bench and a 30mA
trip on the mains between the supply authority fuse and my consumer unit.
I have never seen an RCCD with a trip higher than 30mA on sale in the UK
although earth leakage trips in industrial switchboards can be a lot
higher than this.
--
Stuart Winsor
From is valid but subject to change without notice if it gets spammed.
For Barn dances and folk evenings in the Coventry and Warwickshire area
See: http://www.barndance.org.uk
| |
| Samuel Chan 2008-02-20, 9:25 am |
| Usually I posted on news group, no reply is back. THANKS!
The final circuits are protected by RCD. However, the main switchboard can't
perform E/F protection. That is the problem, as if there is a earth fault in
main riser (say busbar), the value is talking about below 50A. Main CB will
not trip but a 50A flow continuous from one phase to earth as leakage>energy
loss>thermal>voltage drop?
Samuel Chan
"Stuart" <SW_NOSPAM@dsl.pipex.com> wrote in message
news:4f74122daaSW_NOSPAM@dsl.pipex.com...
> In article <lajwsozuc52.fsf@sahrami.niksula.hut.fi>,
> Tomi Holger Engdahl <then@sahrami.niksula.hut.fi> wrote:
>
>
> I have a 10mA trip protected socket on my electronic test bench and a 30mA
> trip on the mains between the supply authority fuse and my consumer unit.
>
> I have never seen an RCCD with a trip higher than 30mA on sale in the UK
> although earth leakage trips in industrial switchboards can be a lot
> higher than this.
>
> --
> Stuart Winsor
>
> From is valid but subject to change without notice if it gets spammed.
>
> For Barn dances and folk evenings in the Coventry and Warwickshire area
> See: http://www.barndance.org.uk
| |
| Stuart 2008-02-20, 9:25 am |
| In article <47bc216a$1_2@rain.i-cable.com>,
Samuel Chan <threecat@i-cable.com> wrote:
> Usually I posted on news group, no reply is back. THANKS! The final
> circuits are protected by RCD. However, the main switchboard can't
> perform E/F protection. That is the problem, as if there is a earth
> fault in main riser (say busbar), the value is talking about below 50A.
> Main CB will not trip but a 50A flow continuous from one phase to earth
> as leakage>energy loss>thermal>voltage drop? Samuel Chan
Well, as someone else has already pointed out, an impedence of 10ohms to
earth is way too high and needs rectifying as a matter of extreme urgency.
However, as I understand it, earth fault protection does not depend on the
quality of the earth at your switch-board, as an earth leakage won't
neccessarily put current down the earth continuity conductor to your
switch board anyway.
Earth leakage is measured by summing the currents in all your live
conductors, with due regard to phase, and the answer should be zero. The
neutral conductor should be regarded as a live conductor in this context.
I assume your switchboard has an earth-fault relay built into it and you
can see what it is set at. It may also have an earth leakage meter. If you
are worried, carefully [1] connect a load between a phase conductor and earth
at your swithboard and see if either you get a reading on your meter or an
E/F trip. If you have a meter, a light bulb should be sufficient to give
you an indication.
This advice is given in good faith based on my understanding of the
situation but I accept no resonsibilty for any harm, hurt or damage which
may occur to persons or equipment or the consequences of such.
[1] That means with all due regard to your own and anyone else's safety.
--
Stuart Winsor
From is valid but subject to change without notice if it gets spammed.
For Barn dances and folk evenings in the Coventry and Warwickshire area
See: http://www.barndance.org.uk
| |
| John McLean 2008-02-20, 5:25 pm |
|
"Stuart" <SW_NOSPAM@dsl.pipex.com> wrote in message
news:4f74122daaSW_NOSPAM@dsl.pipex.com...
> In article <lajwsozuc52.fsf@sahrami.niksula.hut.fi>,
> Tomi Holger Engdahl <then@sahrami.niksula.hut.fi> wrote:
>
>
> I have a 10mA trip protected socket on my electronic test bench and a 30mA
> trip on the mains between the supply authority fuse and my consumer unit.
>
> I have never seen an RCCD with a trip higher than 30mA on sale in the UK
> although earth leakage trips in industrial switchboards can be a lot
> higher than this.
>
> --
> Stuart Winsor
10, 20 and 30mA ratings are used for personell or livestock protection,
there are also higher rated units of 100,300 and 500 mA units available for
the domestic scene - these are installed at the main incoming point and have
a time delay, to give discrimination with e.g. 30mA downstream. These units
provide fire and property protection - not personnel protection.
| |
| Samuel Chan 2008-02-21, 8:25 pm |
| I worked for a project somewhere in the world and this area's Supply
Regulator stated 10 Ohm. (That is the root of my question)
I am also know that there is many possible ways for the leakage current to
leak away...
The Supply Regulation also stated that it is possible to provide some
warning (aud./vis.) instead of protection. (I think this is their local
experience on this matter).
Anyway as an electrical engineer, I am trying to find any possible
protection method (As I born/live/work in HK, I think that this is my stupid
or something that I haven't met/learnt before...)
Many thanks!
Samuel Chan
"Stuart" <SW_NOSPAM@dsl.pipex.com> wrote in message
news:4f741b79c0SW_NOSPAM@dsl.pipex.com...
> In article <47bc216a$1_2@rain.i-cable.com>,
> Samuel Chan <threecat@i-cable.com> wrote:
>
>
> Well, as someone else has already pointed out, an impedence of 10ohms to
> earth is way too high and needs rectifying as a matter of extreme urgency.
>
> However, as I understand it, earth fault protection does not depend on the
> quality of the earth at your switch-board, as an earth leakage won't
> neccessarily put current down the earth continuity conductor to your
> switch board anyway.
>
> Earth leakage is measured by summing the currents in all your live
> conductors, with due regard to phase, and the answer should be zero. The
> neutral conductor should be regarded as a live conductor in this context.
>
> I assume your switchboard has an earth-fault relay built into it and you
> can see what it is set at. It may also have an earth leakage meter. If you
> are worried, carefully [1] connect a load between a phase conductor and
> earth
> at your swithboard and see if either you get a reading on your meter or an
> E/F trip. If you have a meter, a light bulb should be sufficient to give
> you an indication.
>
> This advice is given in good faith based on my understanding of the
> situation but I accept no resonsibilty for any harm, hurt or damage which
> may occur to persons or equipment or the consequences of such.
>
> [1] That means with all due regard to your own and anyone else's safety.
>
> --
> Stuart Winsor
>
> From is valid but subject to change without notice if it gets spammed.
>
> For Barn dances and folk evenings in the Coventry and Warwickshire area
> See: http://www.barndance.org.uk
| |
|
| "Samuel Chan" <threecat@i-cable.com> wrote:
>I worked for a project somewhere in the world and this area's Supply
>Regulator stated 10 Ohm. (That is the root of my question)
>I am also know that there is many possible ways for the leakage current to
>leak away...
>The Supply Regulation also stated that it is possible to provide some
>warning (aud./vis.) instead of protection. (I think this is their local
>experience on this matter).
>Anyway as an electrical engineer, I am trying to find any possible
>protection method (As I born/live/work in HK, I think that this is my stupid
>or something that I haven't met/learnt before...)
>Many thanks!
>Samuel Chan
>
You may be mixing up two different things
a ground rod, to infinite earth ground resistance is often specified
at 10 ohms or less.
THat is a completely separate issue with the bonding resistance, which
is intended to be as close to 0 as possible.
jk
| |
| Rowbotth 2008-02-24, 1:25 pm |
| In that case, you need to put some relaying on your neutral leg of the
incoming power supply and do something around Zero Sequence protection.
H.
==========
In article <47bc216a$1_2@rain.i-cable.com>,
"Samuel Chan" <threecat@i-cable.com> wrote:
[color=darkred]
> Usually I posted on news group, no reply is back. THANKS!
> The final circuits are protected by RCD. However, the main switchboard can't
> perform E/F protection. That is the problem, as if there is a earth fault in
> main riser (say busbar), the value is talking about below 50A. Main CB will
> not trip but a 50A flow continuous from one phase to earth as leakage>energy
> loss>thermal>voltage drop?
> Samuel Chan
>
>
> "Stuart" <SW_NOSPAM@dsl.pipex.com> wrote in message
> news:4f74122daaSW_NOSPAM@dsl.pipex.com...
| |
| Samuel Chan 2008-02-25, 9:25 am |
| At the very beginning of this matter, I've thought about zero squ. relay.
But a moment later, I turned down it. As 1st, I do not have experience on
this, 2nd it is a long time & hard to get it, 3rd as discussed before, it is
possible that the leakage current leak away in some other paths (may be I'm
wrong)?
The likely solution is No E/F relay (just O/C relay) w/ E/F detector that
pass out the warning signal.
Many thanks.
Samuel Chan
"Rowbotth" <rowbotth@telusplanet.net> wrote in message
news:rowbotth-60FF97.12224224022008@news.telus.net...[color=darkred]
> In that case, you need to put some relaying on your neutral leg of the
> incoming power supply and do something around Zero Sequence protection.
>
> H.
> ==========
> In article <47bc216a$1_2@rain.i-cable.com>,
> "Samuel Chan" <threecat@i-cable.com> wrote:
>
| |
| Rowbotth 2008-02-27, 5:25 pm |
| That is OK as long as you realize that you cannot count on it working
with the same degree of certainty as if you had relaying on your neutral
leg.
H
==============
In article <47c2ce7c$1_2@rain.i-cable.com>,
"Samuel Chan" <threecat@i-cable.com> wrote:
[color=darkred]
> At the very beginning of this matter, I've thought about zero squ. relay.
> But a moment later, I turned down it. As 1st, I do not have experience on
> this, 2nd it is a long time & hard to get it, 3rd as discussed before, it is
> possible that the leakage current leak away in some other paths (may be I'm
> wrong)?
> The likely solution is No E/F relay (just O/C relay) w/ E/F detector that
> pass out the warning signal.
> Many thanks.
> Samuel Chan
>
> "Rowbotth" <rowbotth@telusplanet.net> wrote in message
> news:rowbotth-60FF97.12224224022008@news.telus.net...
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