Strange Readings......

[Crosswire]

Ok , am currently doing dead testing on 150 new build flats. Apart from the usual faults, every so often a strange phenomenon crops up which has me stumped.

When doing end to end continuity tests on ring final circuits, I am finding that the cpc has LOWER resistance than the line and neutral!

For example I am getting 0.74 on line and neutral, then 0.64 on the cpc..., where I expect to see the cpc 1.67 times higher than the lives.(Wired in standard 2.5 twin and earth).

Out of 100 odd flats this has happened 2 or 3 times and cant fathom it.

All connections I've checked are fine and tight - good sparks are doing the work


Can anyone suggest why this might be?

Thanks guys.

 

[li150pacemaker]

Are the batteries in your tester o.k? My Kewtech can give strange results when the batteries start to run low!

 

[telectrix]

or a possibility is a bit of gunge on the lead plugs.

 

[Crosswire]

Hmmm, maybe the batts...

But same tester on lives and cpc's within a couple of secs...

will change batteries and see if this continues.

 

[sedgy34]

Hmmm, maybe the batts...

But same tester on lives and cpc's within a couple of secs...

will change batteries and see if this continues.

you could have a few dodgy socket outlet plates out of that amount of points eg terminal screws cross threaded

 

[Edd]

parrallel earth path through a boiler spur or somthing. Any fixed item with a bonded earth will give a lower reading.

 

[oldtimer]

Yep Megger the same when it gets to 9v its meant to work ok but it can dip in and out when first switched on.

 

[lamb]

I used to get this on new build flats. It was the parallel earth path where the steel k/o boxes were fixed to the tin of the metal frame walls.
The walls were fixed to the metal frame tin from the ceiling, creating a big parallel path for all sockets.

 

[the pict]

Like Edd says something is "bigging up" (an apprentice expresion I heard on a job )the earth somewhere. as in "if ye dinnae dis the the supply earth it'll big up yer ZE readin"
Pict

 

[Crosswire]

I used to get this on new build flats. It was the parallel earth path where the steel k/o boxes were fixed to the tin of the metal frame walls.
The walls were fixed to the metal frame tin from the ceiling, creating a big parallel path for all sockets.

This might well be it! The whole thing is metal framed. It would certainly explain things... Thanks dude.

 

[lamb]

No worries. IMO that is probably the least of the problems you will encounter on new build flats (normally because the men are agency on price).

 

[jdd]

Do an IR test between cpc and MET to verify this, if not parallel path from other circuit sounds likely.