high current in main earth

[Dean Williams]

Hi
i'm testing a very large office complex. at the source, a 800A busbar system, i put my clamp on the main earth and found 7A. Would this be due to the high number of computers used throughout the building, and is the 7a dangerous/not compliant with the regs.

also i put my clamp around a couple of SWAs and found 3A, i'm surprised as i thought the currents in the live and neutral would balance each other out. can anyone explain this.
note: the installation is the old MEM Exel stuff and is 40 years old.

thanks

 

[snowhead]

First one, is your clamp calibrated?
Second was it zero'd at the time of test?

 

[Chr!s]

is it TNC-S? if so prob diverted neutral current.

 

[Amp David]

Can your meter measure when clamped around a multi core cable?

 

[Darkwood]

Ive had similar currents in main earthing conductors on office blocks, it common with large no' of computors, electronic lighting ballasts, patch panel systems etc its a functional earth and all the mA leakage adds up.

 

[Knobhead]

L&N will cancel each other so you’re measuring the leakage. With an 800A supply I wouldn’t worry about 7A. It’s probably higher, the average clamp meter doesn’t cope with harmonics very well. Is you’re meter calibrated by the way?

 

[Marvo]

I also wouldn't worry about 7 Amps leakage current on a 800A office complex supply as long as there's no elevated voltage developing on the N or E.

 

[plugsandsparks]

Had 14amps on a 400A supply, eventually tracked it down to fluorescent lights, 40 odd 6ft doubles.
I was surprised TBH.

 

[emzach]

this thread also helping in my case.