Shared neutral

[Carlosfandango]

I was at a job today replacing a db and wiring supplies for an ASHP. The house used to be owned by a company who let them out (there's another 6 houses) as holiday cottages. The supplies were from a central board in cupboard on the site. The houses have been sold off and part of the deal was that they would pay for individual dno supplies and meters in outside boxes at each house . A firm was employed to run supplies from these meter boxes to the existing db's in the house. They have run a 3 core Swa terminated in a tp 63amp mcb using brown for live, black for off peak live, grey for neutral and the armour as the cpc. To me this isn't correct but I'm looking for of you guys expertise. Inside the house it was terminated into a 4 pole isolator and split into seperate db's. I was removing the need for the off peak supply so I fitted a switch fuse and used the Swa using a core as L,N&cpc but the other properties are as described above.

 

[Knobhead]

Is the off peak on another phase? What’s the total loading? How long has it been like this? How could you alter the setup?

 

[Carlosfandango]

It's single phase, not sure how long it's been like this, maybe 6 months. On one of the other houses that's using the new supply (there's been loads of balls ups with getting correct meters fitted so some houses still using the old supplies) theres shower, cooker, 2 storage heaters, immersion, 3 panel heaters. It just doesn't seem right in my head but I could well be over thinking it. I'm not looking to get shot down just seeing if anyone else thinks it's not or likewise if there's nothing wrong!

 

[davesparks]

Was it just the two lives connected to the TP MCB? I cant tell from your post if the neutral was in there too?

 

[7029 dave]

Don't like the idea of 4pole isolator, shutting off both boards, if that's how I have read it.

 

[Carlosfandango]

Neutral in the TP mcb too.

 

[Carlosfandango]

Sorry about the poor explanation guys, wish I'd taken photos. The house that I'm working on is fine now as I've altered it but if it's wrong I think the contractors need to fix it. O have another house on the scheme to do work on and make this Swa live so I need to know your views.

 

[davesparks]

Don't like the idea of 4pole isolator, shutting off both boards, if that's how I have read it.

The regulations require, quite sensibly, that an installation should have one main linked switch or circuit breaker which isolates the installation.

How would you achieve this without the 4 pole isolator (obviously it could be 3 pole in the situation described)

 

[Knobhead]

Neutral in the TP mcb too.

If the neutral is broken it should be late break-early make.

 

[davesparks]

With the neutral going through the TP mcb then there is linked overcurrent protection in the neutral so the cable has adequate overcurrent protection.

But obviously that's not the end of the story.

The regulations require that each circuit has it own neutral and that neutrals not be shared. So is this one circuit or two?
As the two lives are supplied from the one OCPD I think you would technically class it as one circuit and so the setup is ok.

Conceptually I think it is a cost cutting exercise, and would be questioning the bonding arrangements for the properties as the steel armour won't comply as a main bonding conductor.

 

[7029 dave]

Two double pole 100amp isolators, marked as, 24hrs , off peak, not saying you can't use 4pole Dave, just MO.

 

[davesparks]

If the neutral is broken it should be late break-early make.

Is that necessary for SP? I know it is for TP but if I've understood the OP correctly this is going to be a standard 100 SP service with a second switched feed from the meter.

 

[davesparks]

Two double pole 100amp isolators, marked as, 24hrs , off peak, not saying you can't use 4pole Dave, just MO.

But then you don't have a single main switch, which doesn't comply with the regulations.

 

[7029 dave]

But then you don't have a single main switch, which doesn't comply with the regulations.

Is it not upstream, at the meter position TP63amp on front end of this said sub main.?

 

[Carlosfandango]

So the general consensus is that it's ok as it's "one circuit" apart from the size of the main bonding conductor? Still don't really like it but hey ho! What if, for arguments sake the domestic is pulling 50amps and the off peak pulling 50amps. Dont know if I mentioned it is a 16mm cable.