Uh oh...shorted MICC. How scr*wed am I?

[johnnyuk]

Ooops, that potentially made the repair a whole lot more difficult!


Forget the multimeter, isolate the cable and IR test it.

thanks dave - when you say isolate, do you mean "turn the circuit off" or do you mean "find the other end of the cable and disconnect it"?

re. sniping the pot off, i'm trying to lower the socket in question so i needed to shorten the cable (fed from below).

 

[UNG]

ok thanks for this. part of the problem is that I can't be 100% sure of the routing of the circuit without pulling everything to pieces as it's all under a concrete slab. I can do an IR test between cores/earth on the open end of the problematic cable. Forgive me a basic question but my confidence has been a bit knocked on this one - do I need to find and disconnect the other end of the "damaged" cable before I test IR? The circuit isn't live but obviously the ring is broken where i cut the cable.

You really need to find the other end before doing an IR test even using a multimeter as you have been without knowing what is attached to the other end of the cable any readings are a bit meaningless
Even if you terminate the open end you will still need to access the other end of the cable to "bell out" the cores to identify which is the live core
Whereabouts in the UK are you it is possible someone experienced with Pyro may be close by and may be able to help you out or offer advice

 

[nicebutdim]

thanks dave - when you say isolate, do you mean "turn the circuit off" or do you mean "find the other end of the cable and disconnect it"?

This circuit isn't disconnected?

 

[freddo]

You said early on it had orange sheath…. Did imperial MICC come with a pvc sheath, or did that come in after the change to metric?

Imperial MICC is listed in all the books I have, available bare or with a PVC sheath coloured orange as standard, also available to order in black.

 

[johnnyuk]

You really need to find the other end before doing an IR test even using a multimeter as you have been without knowing what is attached to the other end of the cable any readings are a bit meaningless
Even if you terminate the open end you will still need to access the other end of the cable to "bell out" the cores to identify which is the live core
Whereabouts in the UK are you it is possible someone experienced with Pyro may be close by and may be able to help you out or offer advice

southwest

 

[johnnyuk]

This circuit isn't disconnected?

yes. I was just clarifying what Dave meant by "isolate"

 

[davesparks]

thanks dave - when you say isolate, do you mean "turn the circuit off" or do you mean "find the other end of the cable and disconnect it"?

I mean open an isolator if available or otherwise disconnect the cable, switching the circuit off does not isolate the cable.
By isolate I mean disconnect all live conductors.

re. sniping the pot off, i'm trying to lower the socket in question so i needed to shorten the cable (fed from below).

I still think it is unwise to cut it until you are ready to reterminate it.

 

[johnnyuk]

ok that's what I thought - thanks Dave.
Thanks to everyone for the help. I'll update when I have more news.

 

[7029 dave]

You need to use an IR tester at 500v

 

[johnnyuk]

A little update for everyone that helped me out before. Feel free to laugh at me:

- It turned out the short on the MICC was actually somewhere else entirely on the circuit. The end I had been testing at on was fine. The short must have already been there before I started testing and disappeared once I traced and disconnected the other end of the leg I was looking at. I feel there's a lesson learned in there somewhere!

Anyway after all that, having belled out the circuit and established exactly what would be required to recommission the MICC for this circuit, I've decided to abandon in and just get a new circuit installed in pvc.

So I was wondering if anyone could advise - what is best practice (apart from pulling out all out) to terminate the abandoned MICC before it gets buried in the walls? It won't be visible in any of the new back boxes as I'm having sockets relocated.

Thanks in advance for any advice.

 

[MDJ]

Anyway after all that, having belled out the circuit and established exactly what would be required to recommission the MICC for this circuit, I've decided to abandon in and just get a new circuit installed in pvc.

That a shame, MICC is one of the greatest ways to wire up a circuit, its life span is several times that of PVC

 

[johnnyuk]

That a shame, MICC is one of the greatest ways to wire up a circuit, its life span is several times that of PVC

Any thoughts on how to terminate abandoned cables before burying? i've heard of joining all three cores and wrapping in tape before burying, but a bit difficult with micc if the gland is missing.

 

[PS Electrics]

Any thoughts on how to terminate abandoned cables before burying? i've heard of joining all three cores and wrapping in tape before burying,

Yes if having to leave redundant cables in situ then short ends out so if the cable ever did somehow become energised it will operate any protective device supplying it.

Not sure where I picked this up from either but believe it is accepted practice.

but a bit difficult with micc if the gland is missing.

Could you use a suitable sized jubilee clip to clamp the cores to the outer sheath?

 

[johnnyuk]

good thinking ps electrics i'll run with that.

thanks