Current in earth

[Inspector]

Does anyone know what the max permissible current reading in earth is?
If so please provide references.

 

[breezer]

surely it should be 0v? 000.0000mA (that is should be in an ideal world)

also in refence to what?

 

[Inspector]

In the perfect world it is the case that there is 0A on the main incoming earth but in large installations there can be a small measurement of current on the main earth (usually below 1A) when measured with a calibrated clamp ammeter. This may be traced through to several final circuits which each have a small amount on their respective earth.

It is something which electrical engineers are expected to measure (not sure if this includes the NICEIC, but then ... mmm) during an inspection.

By references I mean in the IEE regs, guidance notes, etc.

 

[kendor]

Agreed Inspector, Large Load installations can and usually do suffer from "Earth Leakage" one example is the television studios at the BBC which run hundreds of 5KW and 10 KW loads simultaneously the studios incorporate an earth leakage system that monitors the earth and alarms if this current gets too excessive whereby the lighting rig would have to be reduced to bring levels back within acceptable levels.

 

[Inspector]

So my question is what is the level at which it becomes a defect. 0.0001mA??? and is there a reference in the regs etc for this level?

 

[kendor]

Not sure of the max permissable level allowed, perhaps it's one of those grey areas unless someone can shed light on it.

 

[Big_Spark]

This is a constant problem in the City and Docklands where large installations suffer leakage onto installation earths from all manner of equipment in the buildings, electronic control gear in discharge lighting, computer systems, in fact anything with electronic controls of any description by and large.

It is recommended that this level should not exceed 20mA, the current capable of killing a person through ventricular phibrilation, however as we all know this is a pipe dream.

Whilst I have never seen it about 1.2A, I have heard of installations where up to 8A was measured at the main earth!

I think one of the problems in large installations, especially when they are multi-occupancy, the Engineers invariably are only concerned with their part of the overall picture, and consequently they are happy with the 20 to 60mA that they measure on their installation, but by the time you get 50 or 60 clients in a large building add their say 20mA, it doesn't take long to get to potentially dangerous levels.

There is nothing in the Regs about this..it is yet another omitted grey area.

 

[securespark]

Don't worry about references, everybody. Insp. is taking the mick out of me......sad get!