Ring main.

[JKMRK1]

Question I have is, is it ok to have x2 ring main circuits on one 32amp type B MCB??

If so does this meet the current regs.

TIA.

 

[pc1966]

right or wrong what's the common response to finding a Ring on a 20A MCB or wired in 4mm??

Both are rare but not in any way dangerous.

4mm is needed if the end-to-end length is over about 106m, but on a multi-floor building you could have a fair amount of that used up in the CU-to-floor run up and down so it need not be a ridiculously large area covered.

I have seen 20A BS3036 rewireable fuses used for the ring before so there may be some historic reason for that, and it is quite possible that a CU upgrade just copied the existing fuses with the nearest MCB.

 

[7029 dave]

Its still only one circuit , the only danger I could see if you lost a couple of legs off this multi RFC.

 

[Mark Wright]

Both are rare but not in any way dangerous.

4mm is needed if the end-to-end length is over about 106m, but on a multi-floor building you could have a fair amount of that used up in the CU-to-floor run up and down so it need not be a ridiculously large area covered.

I have seen 20A BS3036 rewireable fuses used for the ring before so there may be some historic reason for that, and it is quite possible that a CU upgrade just copied the existing fuses with the nearest MCB.

Yeah my first Response to OP questions was NO! this is Dangerous but thinking about it can't really find how although A break in 2 rings would be very bad.

But then looking at it the other way round 20A or 4mm that's actually safer but not considered standard - so what response would this cause.

 

[pc1966]

But then looking at it the other way round 20A or 4mm that's actually safer but not considered standard - so what response would this cause.

The Best Practice Guide #4 has various things mentioned that are departures or non-compliance with the standard that are not unsafe so don't merit a code.

Probably you would add it as a comment, more so the 20A MCB as it might be prone to nuisance trips if it serves several power hungry things (washing machine, tumble dryer, dishwasher, etc).

 

[Pete999]

Are we not going off piste Lads and Lasses? the original scenario was 2 separately wired RFCs connected to a single OCPD, this constitutes a single circuit, no matter how you twist and turn with it which is not only bad practice but in my opinion a dangerous situation, Discuss.

 

[ipf]

But then looking at it the other way round 20A or 4mm that's actually safer but not considered standard - so what response would this cause.

None, to my mind. Certainly not the 4mm. The 20amp...only if load problems.

 

[SparkyChick]

Are we not going off piste Lads and Lasses? the original scenario was 2 separately wired RFCs connected to a single OCPD, this constitutes a single circuit, no matter how you twist and turn with it which is not only bad practice but in my opinion a dangerous situation, Discuss.

We're not denying it's bad practice, there is seemingly unanimous support for that view, but dangerous... if they are both sized and installed correctly in every other aspect, how are they dangerous?

I'm not being facetious Pete, I'm genuinely trying to understand the thought process behind the statement.

 

[Mark Wright]

Going to Lollipop and other non standard circuit territory.

Could a break in a Ring cause a fire?
Possibly but probably not

Could a break in 2 Rings on a single 32A MCB cause a fire ??? that is the main thing I'm thinking now.

 

[ipf]

Are we not going off piste Lads and Lasses? the original scenario was 2 separately wired RFCs connected to a single OCPD, this constitutes a single circuit, no matter how you twist and turn with it which is not only bad practice but in my opinion a dangerous situation, Discuss.

Take one leg out of each ring and link 'em (properly, of course). That'll make it miles safer

 

[SparkyChick]

Going to Lollipop and other non standard circuit territory.

Could a break in a Ring cause a fire?
Possibly but probably not

Could a break in 2 Rings on a single 32A MCB cause a fire ??? that is the main thing I'm thinking now.

A break in a ring is definitely a safety issue regardless of other factors such as the supply arrangements for the circuit. And yes, a break in a ring can cause a fire.

If a ring is running on a 32A MCB and it has a break in a live conductor you should look at downgrading the MCB to 16A/20A.

 

[Pete999]

We're not denying it's bad practice, there is seemingly unanimous support for that view, but dangerous... if they are both sized and installed correctly in every other aspect, how are they dangerous?

I'm not being facetious Pete, I'm genuinely trying to understand the thought process behind the statement.

SC I have stated my point of view, and although an interesting post I really have nothing more to say on the subject, you questioned the dangerous statement, which is your prerogative, I just think sticking two separate systems on one OCPD forming one circuit out of two systems is inherently dangerous, I have no other arguments to continue, what next a lighting system added to a RFC circuit OCPD? or vice versa?

 

[Ed Evans]

Question I have is, is it ok to have x2 ring main circuits on one 32amp type B MCB??

If so does this meet the current regs.

TIA.

It does not meat the regs BUT. if you exceed the loading I will be surprised but if you do the breaker will trip, ie doing its job.

 

[littlespark]

Has it been proven by testing that this is in fact two rfc’s?
It may be 1 rfc, and a spur was added at source.... then another added.

how many sockets does this 1 OCPD protect?

I think it’s right, if it is 2 rings coming out, to move one into the spare way... but end to end continuity must be found to know you’ve got the right legs of each ring into the same breaker.

My other worry is that there has been work done in the house which has somehow linked the 2 ring together. Rather than investigating, they’ve just bundled everything together

 

[Mark Wright]

SC I have stated my point of view, and although an interesting post I really have nothing more to say on the subject, you questioned the dangerous statement, which is your prerogative, I just think sticking two separate systems on one OCPD forming one circuit out of two systems is inherently dangerous, I have no other arguments to continue, what next a lighting system added to a RFC circuit OCPD? or vice versa?

Don't start that one but if the lighting is wired in 2.5 it's not actually dangerous is it

I'll get my coat.....

 

[SparkyChick]

SC I have stated my point of view, and although an interesting post I really have nothing more to say on the subject, you questioned the dangerous statement, which is your prerogative, I just think sticking two separate systems on one OCPD forming one circuit out of two systems is inherently dangerous, I have no other arguments to continue, what next a lighting system added to a RFC circuit OCPD? or vice versa?

So in essence, it's a 'I just don't like it' kind of situation and that's fair enough Pete thanks

I feel the same way about it, I don't like it, I'm not sure I can qualify why I don't like it other than 'it feels wrong'.