Earth Leakage

[slippyr4]

Hi all,

Small office supplied with single phase PME. About 7 computers on, 1 KW of fluorescent lighting, a kettle, a portable A/C unit and loads of wall-wart type ac adaptors are pretty much the only loads.

Clamping the main earth electrode at the service head reads an average current of about 7 amps.

Is that normal? or is there likely a fault in there somewhere?

Cheers

slip

 

[Taylortwocities]

Possibly, hard to tell. And you havent measured during peak times..
Dont forget that the kettle will be near on 13A by itself!

Why do you ask these questions grasshopper? Is there a problem or is this just an acedemic query?

 

[mikeyd]

Most definitely a fault.

I take it you have no RCD.

TTC - I think you may have mis-read the original post.

 

[securespark]

Main Earth Electrode @ 7A?

If so, then there's definately a fault! If you meant to put 7mA, then probably not, depending on what's running.

 

[slippyr4]

hi all,

it was partly academic.

our electricity bill in the office seems to have gone up a lot recently so i brought my clamp meter in to try and isolate any funny unidentified loads.

just out of interest i stuck it on the main earth and got this reading.

Do you think we should get a spark in to find the problem then?

Slip

 

[slippyr4]

Main Earth Electrode @ 7A?

If so, then there's definately a fault! If you meant to put 7mA, then probably not, depending on what's running.

definately 7 amps. not milliamps.

indeed, we have no rcd.

 

[mikeyd]

Sounds like it could be a Neutral-Earth short (Not good)

Unplug appliances one at a time and see it the earth current drops to zero (to rule out a faulty appliance). If not get a sparky in.

EDIT - Forgot to say, this is probably not the cause of your high bill though.

 

[Spark123]

Main earth electrode or Main earth conductor?
What happens to the current if you turn the CU off?
I take it all the MEBs are in place? Is the current travelling through these or from the CU via the main CPC?

 

[Taylortwocities]

TTC - I think you may have mis-read the original post.

Oh yes i did!

TTC

 

[slippyr4]

Main earth electrode or Main earth conductor?
What happens to the current if you turn the CU off?
I take it all the MEBs are in place? Is the current travelling through these or from the CU via the main CPC?

Main conductor. It's a PME installation. I clamped the earth conduction between the PME service head and the CU.

All MEBs that i have ever seen are in place. Gas and water are bonded in the cupboard with the CU (their incomers are in there too) and the metal staircase is also bonded.

Clamping on the MEB's only ever reads 0.0 - 0.1 amps - which is about the margin of error of my clamp meter.

When the CU is off, the current in the earth conductor is 0.

also:-

Phase current = Neutral current + Earth current, approximately.

Does sound like a earth/neutral fault, doesn't it.

 

[Spark123]

Yeah, it is sounding like you have a N-E short or something miswired (i.e. phase-earth instead of phase-neutral) somewhere.

 

[Softus]

Apart from the obvious fact that any fault causing this should be found and remedied, is there actually anything else inherently dangerous in this situation?

 

[Spark123]

An open ckt CPC could result in mains voltage becoming aparrent on exposed conductive parts I suppose.

 

[Softus]

Er, I didn't think this CPC was open circuit though. Was I wrong?

 

[Spark123]

Not at the moment, though that is probably one of the biggest risks using the CPC as a live conductor.
Also, the CPCs are often smaller than their associated live conductors hence their current carrying capacity is not as high.