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Hi folks
while testing this theatre, i attempted to get a Zs from an emergency exit sign. The steel conduit is being used as cpc.
when i connect my three probes to l,n,earth i'm getting 110v on the screen and when i press test it comes up with about 160 ohms.
i put a voltmeter across and found 110v between L and E but 230v between L and N.
could this be a poor connection on the steel conduit cpc and if so, why does the voltage drop to approx 110v

thanks...its a bit of a puzzle
 
do a R2 test on the conduit end to end. then test to MET.
 
even if it's 3000m you've got to get it right, one way or another. do it in stages with a wander lead.
 
code 1 it and FIX it. you don't put a band- aid on an arterial bleed.
 
probably getting a reading through the damp walls, and forgot to mention, you should not walk away from a code 1, without isolating or rectifying.
 
floating earth?
 
only 76, must have been done on a good day.
 
I assume you are doing a PIR ?
Conduit as CPC 35 years old
76 code 1's so far I guess the recommendation is a full re-wire
As for 110V L-E try testing much closer to the main DB
I guess the conduit is badly corroded at various points and is a very high resistance compared to L-N insulated copper conductors
 
assuming it is a bad earth, can someone please explain the science behind it...how does it become 110v???
If you've got good Zs figures elsewhere you can rule out the earthing conductor itself.
So if we're dealing with a fault on just this one conduit run, here goes:

Let's assume:
The conduit is completely open circuit quite near the origin.
The insulation resistance L-E is 0.5Meg and N-E is 0.5 Meg. (measured at end of circuit)
Voltmeter input impedance is 10Meg.

Think of a potential divider, L to N, with the conduit in the middle
For a 230V supply, you'd get a theoretical 115V
But with the 10 Meg of your voltmeter in parallel with whichever 0.5Meg you were measuring across, the voltage seen would reduce slightly.

Now if you've got a measured Zs of 160 Ohm and 110V L-E, sounds like something is corroded AND full of water

Unless someone's made up an IT system, centre tap earthed through an impedance....

Simon.
 

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