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.

 

[richy3333]

Why can't god make it better, it's his house?

 

[Silly Sausage]

Why can't god make it better, it's his house?

If it's Catholic, he'll want paying.

 

[GLENNSPARK]

confession time...
i peed into the pyro......when he wern`t lookin....

 

[Stroppy]

Dirty boy! Anyway 'He' sees everything.

 

[UNG]

I find it strange that four lengths of Pyro have gone down at the same time and can't help but feel the OP's lack of any useful experience with Pyro is not helping in identifying the problem or it's cause

It would be interesting to have sight of the last PIR / EICR to check the IR values of the circuit in question when it was last tested

 

[Silly Sausage]

I suspect lack of experience here, something he said earlier (hate criticising people I don't know)
Deeper testing required. Pictures would be good too.

 

[nikmet]

im thinking a possible load still connected and out of sight maybe, have you got a clear view of the entire pyro run or does it disappear into a wall, roof void, floor etc?

 

[ayjay]

oh, god is my father, pyro my son
thou art be with me, and every-one--
fp200, a bodge up to make, but boys have to make-- a holy mistake?

 

[Guest55]

im thinking a possible load still connected and out of sight maybe, have you got a clear view of the entire pyro run or does it disappear into a wall, roof void, floor etc?

a connected load would almost certainly show a poor L-N reading rather than a N-E short.

 

[Guest55]

church walls are mostly solid rather than cavity and as such are virtually permanently damp , so i'd go with water ingress at a possibly hidden j.b's / counduit boxes somewhere.

 

[Silly Sausage]

I was best man the other week in church and all the walls and micc looked perfectly fine to me.

 

[vjsmarwick]

i would have thought dampness at first read too but if the ends were made of correctly and have been there for years i would suspect either there has been someone that knows nothing about pyro turning the pot after its been made off or some other damage else where but find it very strange that 4 cables go all at one time.

 

[sl1210]

hi guys. like i said i can trace the pyro from the first socket to a metal conduit box on the other side of the wall of the consumer unit, where it then joins singles in a connector and then to the consumer unit.

so my readings cant be because of a connected load as i had separated all the cables.

like i said as soon as i plugged my make shift extension lead into the suspect pyro's they trip instantly. only a couple held.

 

[GLENNSPARK]

it`l be damp will that...

 

[sl1210]

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

 

[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...

 

[sl1210]

o ohms

 

[telectrix]

try your tester on continuity. a reading of 0 meg. on a IR test could be several kohms. you need about 8 kohms or less to trip a 30mA RCD.

 

[MDJ]

i'm sure its damp too

Na can't see that, if the pot and seal were fitted properly and they obviously were due to the age of the circuit damp probably won't be the reason, you could stick a pyro under water and run over it with a steam roller and it will still work, also I very much doubt 4 legs are down, that seems almost impossible, unless alterations have been carried out by someone not familiar with MICC.

 

[Deleted member 26818]

Is it actually four legs though?
If you have a length of cable and damage one end, both ends would read as being damaged.
The OP appears to state that this is a single circuit supplying sockets.
It could be that the cable goes into the side of the first socket, then out the other side to th next socket.
Or it could be that the cable is run up at ceiling height and there are drops down to each socket.
One loop in and one loop out.
It may be that a pair of cables to a socket have been damaged, and the OP is reading it as four damaged legs, when in fact it's just two damaged cables.

 

[Knobhead]

Well having had a read through his previous started posts, I'll leave you gentlemen to it.