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

 

[telectrix]

you can use whatever the church authorities will accept, as long as it also complies with regs.

 

[Golden_Boy]

We once experimented with pyro and a BIG hammer. The cable was almost completly flat in CSA before the conductors shorted out.

There must be some extreme damage ( possibly cuts ) somewhere...

Continuity measurements shoud indicate roughly how far away the short circuits are from the CU ( thats length of cable NOT actual distance as the cable could follow a long route to get a short distance.

 

[sl1210]

not that i can see mate.

basically what i did, was create a temporary plug top on a lead with a connector block. i then plugged this into a working socket via an extension lead, to see what didn't trip.like i said 4 pyro cables tripped the rcd when connected. really strange, cos i know that pyro is normally made for life right???

i need to relink 4 sockets. just not sure whether to use fp2000 clipped direct or plastic conduit with metal surface boxes???

 

[GLENNSPARK]

you havn`t got any connected loads have you that may be causin this?....
or has the pyro been left unterminated...and has been exposed to damp?.....if so you can drive out the damp with a blowtorch....

 

[sl1210]

nope no loads. and i removed all the faces and was testing open ends. they are internal exterior walls they run along. you think it could be damp????

 

[GLENNSPARK]

maybe.....
or theres a shard of copper thats doin it.....badly wound off maybe....

 

[telectrix]

it's quite possibly damp. stick your IR test on the cable/s , use 1000V if your tester will do it, and leave it connected for a minute. if the reading improves, then it's probably damp.

 

[GLENNSPARK]

i mean does the RCD hold....for about 10 secs....then let go?......

 

[sl1210]

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???

 

[Silly Sausage]

Remember a dead short on your IR tester could be in the order of several 10K ohms.

 

[telectrix]

good call. a continuity test might be advantageous.

 

[ayjay]

just replace the micc with new silicone impregnated micc
old micc is notorious for ingress of moisture at the pots
if its bare micc you can gently remove the seals and compound then unscrew the pots and drive the moisture out with a blowlamp
but u need to be about 60(me) to know what your doing
sticking some other cable inbetween is a crap bodge up imo

 

[ayjay]

if the minerel has been there for years glenn how would a shard be present?

maybe.....
or theres a shard of copper thats doin it.....badly wound off maybe....

 

[sl1210]

unfortunately i'm nowhere near 60 and only done pyro in college for 1 lesson. i really don't know much about it.