Broken CPC on ring final

[skamuk]

My friends downstairs sockets are tripping the RCD. First thing I did is unplug everything on the circuit, switched on the MCB and the RCD tripped. Tested continuity of L-L N-N CPC-CPC between the legs. CPC has no continuity whatsoever. Could anyone advise me what would be my next step to determine where the break in the cpc is? Thanks

 

[markc123]

OK, the CPC being split is highly unlikely to be the cause of your RCD fault, however, here is a very quick way of finding your earth fault.

Get a socket tester (3 neon variety)

Unplug everything from the ring main

Disconnect 1 leg of the CPC at the CU

Go around each socket in turn with the tester, at some point you will go from a fully serviceable ring to a 'no earth' indication. Or vice versa.

Stop and investigate further

Simples......

I like your style, Sergei.

 

[markc123]

Really? I didn't realise there was a difference between r1 r2 and R1 R2. My bad! What does the capital letter version stand for?

There isn't much of a difference, people just tend to get a little bit muddled up with the terminology

r1 is the end to end of the line conductor
r2 is the end to end of the CPC.

R1+R2 is cross connecting the two and testing together.

r1+r2 is a myth

 

[HandySparks]

Really? I didn't realise there was a difference between r1 r2 and R1 R2. My bad! What does the capital letter version stand for?

Only reason we've not got "Gasp..." and "I'm out of here...", is that it's late.

r1 and r2 are end-to-end resistances of ring circuit line and cpc conductors. R1 and R2 are resistance from origin of circuit to furthest point (in the case of a ring, this is the centre) of line and cpc. Not the same thing at all!

 

[skamuk]

Oh wow! I didn't know that. Thanks! I'm not an electrician just yet as you have all probably gathered, I'm still at college so I'm learning every day. I have another question, slightly off topic: I was having this debate with my teacher/lecturer... He says that if you have a conductor, say 50m long, and you measure continuity between one end and the mid point (25m) you will get half the ohms value of measuring the full length of the cable. I thought that the extra copper would effect the half way reading? Would the value be half?

 

[44ALLAN]

Google.............'resistances in series mate'

 

[telectrix]

it should be exactly half. look in the osg, there is a table giving the resistance/m of all the cable sizes in milliohms/m. just multiply that value by the length , dvide by 1000, and that will give the resistance of X metres.

 

[skamuk]

it should be exactly half. look in the osg, there is a table giving the resistance/m of all the cable sizes in milliohms/m. just multiply that value by the length , dvide by 1000, and that will give the resistance of X metres.

Ah ok, thanks!

 

[GLENNSPARK]

Have done this. All connections are present and terminated ok. I now need to determine where the break is, bearing in mind all cpc are twisted together at each socket. Would I untwist all of them and test continuity between each socket?

prove that every point served on the ring has R2 present.....do the adiabatic then move on to the RCD issue...
dont waste time arsin about looking for broken R2...as long as every point served has R2 available...

 

[telectrix]

you might get lucky and find that some ham-fisted dork has snapped one when twisting them. and what's the betting he's put 2 in 1 sleeve. aarrggghhh.

 

[skamuk]

you might get lucky and find that some ham-fisted dork has snapped one when twisting them.

Lol. I won't be fixing the problem any more I'll be there for a month doing a couple of days worth of work!! I'm not capable yet, he's getting a sparks in to do it.

 

[DPG]

Let us know what the fault was if you find out. Daz

 

[skamuk]

Let us know what the fault was if you find out. Daz

Will do.

 

[Wayne Gollop]

Is it a split load board? Do you have the correct CPCs for that ring at the board? Not been mixed up.

 

[Hawkmoon]

Just a thought...

Name - Skam UK?
Instrument will test ze but not zs?
Questions simple series resistance of length of cable?

Does the term 'windup' mean anything to anyone?

 

[skamuk]

SkamUK is my artist name. I produce music in my spare time. Www.soundcloud.com/skamuk

I question these things because I am still learning!

 

[skamuk]

It's a split load board. Yes I had the right cpcs.

 

[Octopus]

SkamUK is my artist name. I produce music in my spare time. Www.soundcloud.com/skamuk

I question these things because I am still learning!

Really!

 

[guest119]

Why is this in the general forum, not diy?

Boydy

 

[skamuk]

I posted in the general forum because I have a general electrical enquiry. I'm not sure what the definition of 'DIY' is. An electrician, plumber, builder whatever will do their own work themselves? Do it yourself doesn't make sense to me.. I assume it's used here for people who aren't well educated on the subject, which in turn means there will be a lot of blind leading the blind going on there...

 

[skamuk]

Electrician and his mate went round there yesterday and after 3 hours of searching, found a damaged length of t&e although I'm not sure where they found it or why it was damaged. Problem sorted though.