Neutral-Earth faults

industryspark · 16 Aug 2007

been testing some industrial workshops today and found loads of neutral to earth faults, i.e dead short zero meg ohm.

no real rcd protection of any circuits so faults gone unnoticed until i stuck my test meter on.

got me thinking about how many of these faults exist within installations, particularly industrial where many circuits make up the installation and how there must be many many out there.

whats the worst effect of this kind of fault that anyones ever seen and how serious do others take this fault?

nozspark · 16 Aug 2007

Just think what would happen if your neutral fell out at the DB....live chassis!!

Spark123 · 16 Aug 2007

It depends how you look at it, if N-E exists and the neutral should go open circuit the CPC will be used as the neutral. The CPC may be smaller than the live conductors (hence has a lower CCC). Should the CPC go open circuit, mains voltage may become aparrent on exposed conductive parts.
Also, on some systems you may get network currents flowing through the fault.

beaten by JohnD!!

JohnD · 16 Aug 2007

not by me!

anyway, the RCBOs would trip.

ricicle · 16 Aug 2007

The plus side is that on industrial installations, especially large ones, there is lots of earthed metalwork about (trunking, conduit, pipes, steelwork etc) so any current that was to flow in the event of a broken neutral via a N/E fault would always find its way back to the Tx via this low resistance earth path.Not ideal, and only probably found when testing, but at least there should be no metalwork that rises to a dangerous voltage.

Adam_151 · 16 Aug 2007

On a similar (but different note)

A story that cropped up on the IEE forum a while ago (sorry, the name of the OP escapes me) was that of a welder that had the 'work' side of the transformer connected to the case (whether intentional or not, no idea), and a metal welders bench that just happened to be bonded, it was only a matter of time before someone discovered they didn't actually need to connect the clamp to the work...

pdcelec · 16 Aug 2007

what type of main earthing is there?

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Neutral-Earth faults

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