Pyro Cable Tripping RCD

[sl1210]

Went to a job in a church hall today where one of the power circuits was tripping the rcd. There seems to be 4 bad legs of pyro in the circuit, as I get a dead short in my IR tests between line/neutral, line/earth.

Is it common for pyro cable to do this after a certain time, or could a fault have caused this?

I have disconnected all the faulty legs and managed to keep the rcd on with only one socket working. I'm going to have to re-link the damaged pyro with new cable.

Was wandering if I could use 2.5mm FP cable clipped direct, or whether because its a church hall i would need to run it in plastic conduit???

Cheers

 

[vjsmarwick]

why are you using a makeshift extension lead ? your tester should be enough to test the cables not energizing a known faulty cable !!!!

 

[Silly Sausage]

Have you isolated/completely disconnected each length at both ends and IR tested each one separately?

 

[GLENNSPARK]

when i disconnect the piro from the connector block with singles going to the consumer unit the rcd holds. as soon as i touch the piro line to the single line. rcd trips.

i'm sure its damp too but really wouldn't know how to dry it. and i'm sure it could happen again anyways

i`v told you how to dry it already.....
drive the damp out with a heat gun...

 

[sl1210]

yep and once i dry it out. who's to say it wont happen again in a week or two???

 

[Silly Sausage]

You make a proper repair to the electrics for starters, then if there's a water problem, you or someone else locates the source and get that dealt with. It's really not that difficult!

 

[Knobhead]

The pyro's been there for years, why should it develop several faults all at the same time.

I think it's time you looked at your testing method.

 

[UNG]

yep and once i dry it out. who's to say it wont happen again in a week or two???

I'm sorry but you are just showing a total lack of knowledge of the cable system you are working on here

 

[Engineer54]

Why are you not using your made for purpose test equipment to trace any potential faults on this circuit??

Well i have to say i'm very dubious that 4 separate legs of a MICC cable run suddenly go down together, all with suspected damp ingress!! As for replacing those legs with FP200, words escape me... lol!!

 

[Sparkii]

HaHa i can see megger bring one of those out, a plug with a bit connector block on the end! classic

 

[ackbarthestar]

Its very rare, I've never known it, for Pyro to go down all at once like the OP has suggested, unless a disgruntled member of the congregation has 'spiked' it along its route.

Have you checked the physical condition of the actual cable, rather than the pots ?
If moisture has got in it will most likely be at the point of termination .
Have you checked the quality of the sfcu/skts. M/C outlets often become corroded and can fail because of the moisture.

Having said that, unsheathed pyro is not difficult to heat and repot, although only having made one off at college, you'll have fun on your first one......

 

[tony mc]

my megger only goes up to 450v.

nope trips straight away. its so strange because there are three runs of pyro on the left of the hall doing it, and one run on the right of the hall.

i think i will just replace it anyway because, i'm guessing theres a chance it will get damp and trip again anyways even if i did dry it. now that you have said that i'm always certain that it is a damp issue. but would damp cause a dead short???

What sort of megger do you have which only put out 450v on a IR test ?

 

[Deleted member 26818]

I'm assuming that these four bad legs, are in fact two lengths of cable linking between three socket-outlets.
If so, could you inform us of the state of play at the midle socket-outlet?
Is it damp or corroded, do the two links into the socket-outlet run together, are they damaged?

 

[Golden_Boy]

yep and once i dry it out. who's to say it wont happen again in a week or two???

You make the ends off properly .... Simples...

 

[sl1210]

like i said i have disconnected all of the socket faces and it still trips, so can't be the socket/spur plates.

tony mc i've got a megger mft1710 and only IR tests at 250v and 500v, so to answer your question no it doesn't test at 1000v.

tony its all very well you saying i should look at my testing method without actually giving me any advise on what you would do?

like i said i've identified where the first leg is, disconnected it and done a 450v IR Test??? as soon as i reconnect the line to the db it trips.

 

[Golden_Boy]

like i said i have disconnected all of the socket faces and it still trips, so can't be the socket/spur plates.

tony mc i've got a megger mft1710 and only IR tests at 250v and 500v, so to answer your question no it doesn't test at 1000v.

tony its all very well you saying i should look at my testing method without actually giving me any advise on what you would do?

like i said i've identified where the first leg is, disconnected it and done a 450v IR Test??? as soon as i reconnect the line to the db it trips.

Can you please tell us EXACTLY whay readings you are getting on these cable runs. If IR tests show low readings what are they? DEAD SHORT means nothing.... We are here to help but need more information as to the readings you are getting...