CU Replacement - Upstairs and Downstairs Rings Connected

[SW1970]

Hi, newbie here. Done a domestic PIR and Consumer Unit replacement is required (damaged, lighting circuit not earthed or RCDd, plus other reasons). However, another finding was that the upstairs and downstairs ring final circuits are connected (currently installed as the 2 live cables going into the circuit breaker).

Cable size is 2.5mm2.
Total floor area served is 85m2.
Circuit breaker is 32A (RCD protected).

After finding out rings were connected I did cross connected line conductor resistance test at each socket and it looks like the rings are connected at the extremity and not bridged half way round. I've deduced this as the resistance readings are almost identical to within 0.01ohm.

Customer doesn't want to fund sorting out the rings (tricky as laminate flooring and fitted furniture everywhere).

I'd appreciate views on whether it OK to proceed with CU replacement and re-energise with the rings remaining connected as they are now? Clearly it doesn't meet the suitable segregation of circuits requirement, but this appears to be the only failing. Any thoughts?

Many thanks
SW

 

[Octopus]

How many circuits are there in the house in total? If there aren't many maybe you should go down the RCBO route.

 

[topquark]

Are you sure it's two rings connected. Many older houses only had one RFC.

 

[SW1970]

Hi, CU replacement is required anyway because the existing one is damaged, but circuits are:

Cooker
Downstairs lights
Upstairs lights
Garage lights
Garage sockets
Upstairs and downstairs sockets
Utility room sockets

Cheers
SW

 

[SW1970]

Topquark - could be. House is 1963 build. Utility room is an extension so that would explain why it's on a separate circuit.

 

[Octopus]

I'd talk to the customer about a set of RCBO's, rather than a dual RCD unit.

 

[topquark]

As your readings are all pretty much identical my first guess would be only one ring. How many cores do you have back at the CU?

 

[Des 56]

As your readings are all pretty much identical my first guess would be only one ring. How many cores do you have back at the CU?

(currently installed as the 2 live cables going into the circuit breaker).
SW
Same question as topquark,
I dont quite get what that description is suggesting

 

[Guest123]

Definitely sounds like a single ring final serving up & down.

 

[SW1970]

Two 2.5mm2 cores going into the MCB labelled sockets upstairs and downstairs. So if it is a single ring installation, ok to proceed with CU replacement and identify the segregation deviation from BS7671? Cheers, SW

 

[IQ Electrical]

Two 2.5mm2 cores going into the MCB labelled sockets upstairs and downstairs. So if it is a single ring installation, ok to proceed with CU replacement and identify the segregation deviation from BS7671? Cheers, SW

If you have 2 other socket circuits, then I wouldn't even be concerned, I don't see a safety issue on a nuisance trip?

The
'departures' box is strictly relating to your work only and if you did feel the need to make a note, it should be recorded in the 'comments on the existing installation' box.

 

[Des 56]

Well you have segregation to a certain level because of the seperate utility sockets
An household ring and a kitchen or utility ring where most of the heavy loads are sited would satisy the segregation of circuits requirement in my opinion

 

[IQ Electrical]

Sorry to sound pedantic but this is 'division' of circuits rather than segregation.

 

[SW1970]

Fab! Many thanks for your help.

 

[Des 56]

Sorry to sound pedantic but this is 'division' of circuits rather than segregation.

Sorry to sound pedantic but this is 'division' of circuits rather than segregation.

Point noted


quote Sw
Clearly it doesn't meet the suitable segregation of circuits requirement

It is sometimes just as well talking the same language

 

[SW1970]

To segregate and conquer.
The Segregation Bell.

He he he.

 

[IQ Electrical]

Point noted


quote Sw
Clearly it doesn't meet the suitable segregation of circuits requirement

It is sometimes just as well talking the same language

Mais oui monsieur!

 

[topquark]

exactement!

 

[telectrix]

or aqs inspector clusseau would say " c'est que ces't votre minky"

 

[SirKit Breaker]

Hi, newbie here. Done a domestic PIR and Consumer Unit replacement is required (damaged, lighting circuit not earthed or RCDd, plus other reasons). However, another finding was that the upstairs and downstairs ring final circuits are connected (currently installed as the 2 live cables going into the circuit breaker).

Cable size is 2.5mm2.
Total floor area served is 85m2.
Circuit breaker is 32A (RCD protected).

After finding out rings were connected I did cross connected line conductor resistance test at each socket and it looks like the rings are connected at the extremity and not bridged half way round. I've deduced this as the resistance readings are almost identical to within 0.01ohm.

Customer doesn't want to fund sorting out the rings (tricky as laminate flooring and fitted furniture everywhere).

I'd appreciate views on whether it OK to proceed with CU replacement and re-energise with the rings remaining connected as they are now? Clearly it doesn't meet the suitable segregation of circuits requirement, but this appears to be the only failing. Any thoughts?

Many thanks
SW

Have you done r1, rn, and r2 end to end, if you have, and r1, and rn are the same, and r2 is about 1.67 times the value of either r1 or rn then you have one circuit, R1+R2 at every outlet will then show up any spurs, reverse polarity, interconnections (ring within a ring etc),and any faults like loose connections.

Cheers.......Howard

 

[topquark]

Everyone should "own" their own monkeys (problems)

 

[SW1970]

Hi Howard, yes, measurements are as you point out. Alas there is one ring! Thanks!

 

[topquark]

As it's a fairly old build you may well find a lot of it (mainly lighting) is wired as radial as well. Often done with a couple of large junction boxes (one in the loft and one under the first floor landing). Very often with dodgy cpc connections ... just the bundle of cpcs twisted together with no sleeving!

 

[telectrix]

As it's a fairly old build you may well find a lot of it (mainly lighting) is wired as radial as well. Often done with a couple of large junction boxes (one in the loft and one under the first floor landing). Very often with dodgy cpc connections ... just the bundle of cpcs twisted together with no sleeving!

nice and easy to get a croc clip on without undoing the JB though.

 

[SPARTYKUS]

Hello SW1970

like has been said already, wouldn't worry too much, houses are laid out all sorts of ways with their socket circuits. You have more than one, plus you didn't install it, plus I agree an RCBO board would not really cost much more than a 'pain in the rear' dual RCD board.

Electrical Components and Equipment Assemblies, inc. basic, passive, marine, etc - ECD UK

I have heard these sell good stuff at good prices. Bought some myself.

I've seen houses with rings and radials all over the place, some bedrooms with three different circuits serving the sockets in that bedroom - this may make one exclaim but I think it is actually a great idea. As long as the DB is labelled / legended correctly this layout provides a higher level of 'separation' and ....resilience I suppose is the word.

 

[SW1970]

Hi Spartykus, thanks for the input. Being new to the game I have wondered why dual RCD units are so popular compared to a unit with RCBOs. I'm aware from other posts that RCBOs can sometimes give a benefit of less nuisance tripping due to combined leakage not having so much of an effect, and are generally more convenient and perhaps more expensive, but can you guide on any reasons why a dual RCD is a pain in the rear?

 

[topquark]

Units with RCBOs are preferable because each circuit is independant from a leakage detection perspective. Dual RCDs, or indeed any RCD that covers more than one circuit may cause nuisance tripping due to the cumlative effect of multiple circuits (as opposed to multiple devices on a circuit).