induced current.. i think

[chris day]

Hello guys

I am a little puzzled with a job I am currently working on.

A hotel we currently do work for had an EICR carried out by what appears to be quite thorough firm with regards to their items highlighted which all appear understandable with the exception of one on which we can’t get to the bottom of.


On 3 (3phase 18 way) consumer units each located at differing locations within the hotel we had highlighted “Higher than expected earth leakage”, each board has between 2.8a supposed leakage.


After clamping my amp meter around all 3 lines & N I had the same values highlighted being between 2-3a on each board on the sub mains. (Nothing down the earth)


We suspected the final circuits to have earth leakage from equipment plugged in however after isolating the DB the 2-3a remained.

We then isolated the sub mains to each board and the number was still 2-3a on each board.


I suspect induced current on the sub main as with the supply isolated to the sub main the same 2-3a remained on each board.


Whilst I can’t conclude the source of this possible induced current I cant see any issues with it or am I wrong?


Thanks guys will be interested to hear any punts.

 

[Pete999]

Hello guys

I am a little puzzled with a job I am currently working on.

A hotel we currently do work for had an EICR carried out by what appears to be quite thorough firm with regards to their items highlighted which all appear understandable with the exception of one on which we can’t get to the bottom of.


On 3 (3phase 18 way) consumer units each located at differing locations within the hotel we had highlighted “Higher than expected earth leakage”, each board has between 2.8a supposed leakage.


After clamping my amp meter around all 3 lines & N I had the same values highlighted being between 2-3a on each board on the sub mains. (Nothing down the earth)


We suspected the final circuits to have earth leakage from equipment plugged in however after isolating the DB the 2-3a remained.

We then isolated the sub mains to each board and the number was still 2-3a on each board.


I suspect induced current on the sub main as with the supply isolated to the sub main the same 2-3a remained on each board.


Whilst I can’t conclude the source of this possible induced current I cant see any issues with it or am I wrong?


Thanks guys will be interested to hear any punts.

Did you clamp the earth conductor?

 

[Bobster]

He did, nothing was measured.

What meter are you using to measure the current, and how much current is on this sub main you're measuring. Are you sure it's not just an erroneous meter reading.

2 -3 amp is enough for most meters to pick it up accurately on a single conductor.

 

[Pete999]

He did, nothing was measured.

What meter are you using to measure the current, and how much current is on this sub main you're measuring. Are you sure it's not just an erroneous meter reading.

2 -3 amp is enough for most meters to pick it up accurately on a single conductor.

Oh yes didn't notice that

 

[Wilko]

"We then isolated the sub mains to each board and the number was still 2-3a on each board"

Hi - if I'm understanding this correctly, you measured a current in a board that had no supply connected?

 

[chris day]

Hi - if I'm understanding this correctly, you measured a current in a board that had no supply connected?[/QUOTE]

Yes correct Wilko

 

[Wilko]

Yikes !
What is the earthing arrangement?

 

[chris day]

He did, nothing was measured.

What meter are you using to measure the current, and how much current is on this sub main you're measuring. Are you sure it's not just an erroneous meter reading.

I am using a fluke clamp meter, the testing company tested the sub main using the same method which consisted of putting the clamp around all lines and N whilst live.
on one board for example they highlighted 2.8a.
after repeating the same method i am yielding the same results even when the sub mains supply has been isolated.
in my opinion I cant see an issue as i suspect induced currents?

 

[chris day]

What is the earthing arrangement?[/QUOTE]
From the dedicated sub station within the building we a ring of mains with a TN-S earthing system

 

[Andy-1960]

Did you clamp the individual cores - I.E L1, L2,L3 & N ?

 

[HandySparks]

I suspect induced current on the sub main as with the supply isolated to the sub main the same 2-3a remained on each board.

Whilst I can’t conclude the source of this possible induced current I cant see any issues with it or am I wrong?

Was the neutral isolated, or just the lines?

Unless there's a complete circuit, you can't have an induced current, just an induced voltage.

 

[chris day]

Unless there's a complete circuit, you can't have an induced current, just an induced voltage.

I need to remove the neutral once I return to site and re/test. I should have picked that up myself.

 

[Andy-1960]

My thoughts here are that the neutral is not bonded at the transformer.....

 

[Wilko]

My thoughts here are that the neutral is not bonded at the transformer.....

Yes - something v. strange for current to be flowing in a board that has no supply ...

 

[Bobster]

My thoughts here are that the neutral is not bonded at the transformer.....

That would cause far too many other issues to just have this as a fault.

Current can't flow without potential.

The guy is measuring with the same type of instrument the previous testers used. My money, it's an issue with the meter.

 

[Andy-1960]

That would cause far too many other issues to just have this as a fault.

Current can't flow without potential.

The guy is measuring with the same type of instrument the previous testers used. My money, it's an issue with the meter.

I was thinking.. is the current flowing in the neutral conductor from other supplies? I have seen boards with quite high voltages on the neutral even with the board isolated.. all due to a neutral not being bonded