# New Consumer Unit

#### Sherbertlion

He fitted a 16a to make he installation safe

I think the only way to make a broken ring safe if there is no continuity on live or neutral is to drop out the faulty leg as there is no telling what the fault is. Only time I think it's acceptable to down rate the MCB is if there is no continuity on the CPC.

#### Iggifer

He fitted a 16a to make he installation safe
Only time I think it's acceptable to down rate the MCB is if there is no continuity on the CPC.

I don't see how changing from a 32a to a 16a makes a broken CPC any safer. A broken CPC may indicate no CPC at a socket outlet, which is unacceptable on any MCB

The proper thing to do is locate and repair the fault, if the break is in a cable you cannot replace then break the ring into two 16/20a radials, but obviously repairing the break is the best thing to do

#### JohnW2

Only time I think it's acceptable to down rate the MCB is if there is no continuity on the CPC.
Did you really mean to write that? If all one knows is that there is no CPC continuity, there's no telling how many breaks in the CPC there may be, so to use the circuit with any MCB could be leaving some sockets with no earth connection at all.

Edit: whoops - somehow missed the previous post. At least there are at least two people of like mind!

Kind Regards, John

#### Sherbertlion

He fitted a 16a to make he installation safe
Only time I think it's acceptable to down rate the MCB is if there is no continuity on the CPC.

I don't see how changing from a 32a to a 16a makes a broken CPC any safer. A broken CPC may indicate no CPC at a socket outlet, which is unacceptable on any MCB

The proper thing to do is locate and repair the fault, if the break is in a cable you cannot replace then break the ring into two 16/20a radials, but obviously repairing the break is the best thing to do

Obviously you test the circuit to prove that each point has a cpc present.

#### phatboy

He fitted a 16a to make he installation safe
Only time I think it's acceptable to down rate the MCB is if there is no continuity on the CPC.

I don't see how changing from a 32a to a 16a makes a broken CPC any safer. A broken CPC may indicate no CPC at a socket outlet, which is unacceptable on any MCB

The proper thing to do is locate and repair the fault, if the break is in a cable you cannot replace then break the ring into two 16/20a radials, but obviously repairing the break is the best thing to do

Obviously you test the circuit to prove that each point has a cpc present.

You seem to have a fundamental mis-understanding of electrics I'm afraid.

How does lowering the MCB size make a ring with a faulty CPC any safer? A 6amp current is going to kill you, just as a 32amp one will.

Do you understand what a CPC is? It seems that you may be confused........

#### JohnW2

How does lowering the MCB size make a ring with a faulty CPC any safer? A 6amp current is going to kill you, just as a 32amp one will.
I've been struggling to understand, too, but I think I may have worked out what he's trying to say, particularly since he has now said "Obviously you test the circuit to prove that each point has a cpc present."

If there is a CPC present at all sockets, but the CPC ring is broken, the Zs may have become too high to achieve required disconnection times with the MCB in question. Reducing the MCB size ('temporarily') would improve, maybe rectify, that situation.

However, I think most of us would agree that if a break in the CPC ring is detected, it should be located and rectified, rather than adopting some measure to make the installation 'safer' in the presence of that fault. I suppose the latter might be justified (and perhaps even laudable) as a very short-term measure pending rectification of the fault, but I'm not sure I would be comfortable with even that. People should really not be using a circuit with a btoken CPC ring!

Kind Regards, John

#### Sherbertlion

Yes John, thank you. That's pretty much what I was trying to say. I'm afraid I don't seem to be able to go into enough depth or articulate myself properly when posting!
I too would always advocate tracing a fault and rectifying and 9.5 times out of 10 the customer is happy for this to happen, occasionally though it doesn't and all I was trying to say was that I don't think it is acceptable to just down rate a 32a ring using a 20 or 16a MCB without dropping out the faulty leg, unless its the cpc broken.....back to previous posts! Anyway, probably not explaining myself very well again!

#### JohnW2

Yes John, thank you. That's pretty much what I was trying to say. I'm afraid I don't seem to be able to go into enough depth or articulate myself properly when posting!
You're welcome.
I too would always advocate tracing a fault and rectifying and 9.5 times out of 10 the customer is happy for this to happen, occasionally though it doesn't ...
Fair enough. However, the process of confirming that every socket has an acceptable CPC connection (which, as you say, you're going to have to do, anyway) ought to get you pretty close to locating the break.

Kind Regards.

#### mickl66

Sorry guy's but this seems to be moving away from my original query,(see my posts), there never was a problem with the earths or the neutral side of the ring only the Live showed no continuity (according to the electrician),which is now showing continuity, so does this mean I should get the electrician back to recheck everything or should I just replace the 16amp mcb with a 32apm one and leave it at that.
Many thanks for all your feedback
Regards Mick.

#### securespark

You need to make sure (ideally with certified test gear) that the readings are aOK for a ring final before committing to a 32A breaker.

Get your chap back to give it the once over.

#### ban-all-sheds

all I was trying to say was that I don't think it is acceptable to just down rate a 32a ring using a 20 or 16a MCB without dropping out the faulty leg, unless its the cpc broken
Actually that's the worst of the 3 to lose. With L or N broken you have got a (bizarre) radial circuit, but had it been designed and installed as a radial, i.e. no continuity on any conductors, would be absolutely fine on a 16 or 20A breaker. 2 breaks in L or N could leave you with some sockets not working but not unsafe, whereas 2 breaks in a cpc could leave you sockets working but unsafe.

#### riveralt

so does this mean I should get the electrician back to recheck everything or should I just replace the 16amp mcb with a 32apm one and leave it at that.
If he fitted the new CU then he should have conducted the appropriate tests before he started the installation and informed you of his findings before going ahead and fitting the new CU.
What does it say on the electrical installation certificate - how can he inform your LA building control - get him back to sort out the problem.

#### JohnW2

Actually that's the worst of the 3 to lose. ... 2 breaks in L or N could leave you with some sockets not working but not unsafe, whereas 2 breaks in a cpc could leave you sockets working but unsafe.
To be fair, he did add "Obviously you test the circuit to prove that each point has a cpc present." - so ought to be avoiding a situation in which there was more than one break (potentially leaving live socket(s) with no CPC connection). Provided that the resultant Zs was low enough to provide for acceptable disconnection times (which might require downrating the OPD), that's then presumably no less safe than a break in L or N (with downrating of OPD for CCC, if not also Zs, reasons).

Kind Regards, John

#### ban-all-sheds

I know he said test - I was just challenging the notion that somehow it's less serious to lose the cpc than either L or N

#### JohnW2

I know he said test - I was just challenging the notion that somehow it's less serious to lose the cpc than either L or N
Fair enough. I agree that there's not much to choose between all three. I think/hope that we all agree that if any of them in a ring final are 'broken', the break should be located and rectified, rather than taking measures to render the 'broken ring' (whichever conductor) situation 'safer'.

Kind Regards, John

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