Questions About Modern Electrical Installation

[TheScullster]

Hi all

Just out of interest really.............. A colleague recently bought a new Barratt house and one or two things were puzzling me. The house is split over three floors being one of these trendy "town-house" style buildings. He showed me the electrical inspection document which lists the circuits, protection measures etc. There are 2 lighting circuits, ground floor then first-and-second floor. Each of these was labelled as run in 1.0mm2 with a 1.0mm2 cpc. I thought that the use of 1.0mm had been dropped, or was it just the stuff with a

0.75mm2 cpc? Second question.......... In his kitchen there is a panel of grid type switches which isolate the below-worktop sockets for washer/dryer, fridge etc. This implies that principle power users are all tapped-off the same point on the ring - I thought that this was generally to be avoided. From memory I don't think the kitchen had a separate ring although the same argument would apply either way.

Any comments appreciated

Phil

[Andy Hall]

1mm^2 seems to be the common lighting size.

It can still be part of the ring.

The arriving cable goes to switch1, then 1 goes to 2, 2 goes to 3, 3 goes to 4,.... until the last one where the departing cable is connected. It's still a ring, but the wiring accessories are simply very close together. It would be a problem if the arriving and departing cables both went to 1 and then 2,3,4 were connected to that as well at a single point. However, the conductors probably wouldn't fit in the terminals of 1 since there would be 5 in this example. Maintain the architecture of the ring and it's two as normal. There isn't anything specificying the minimum distance between wiring accessories on the ring as long as they part of it, AFAIK.

[John]

Reminder to self: Must get shares in stairlift companies.

[John Rumm]

1mm CPCs were phased (pun not intended) out on 2.5mm^2 T&E power cables since it was not always effective under fault conditions with 30+A protective devices.

For lighting circuits protected at 6 or 10A, a 1mm^2 CPC is fine (and normal for 1mm^2 T&E cable)

Much would depend on how they wired it.... but you are right, it could be a bit dodgy. You could do it use a lighting style "loop in wiring" on the sockets. The difficulty there being you would need a pair of switch drop wires per socket to give you proper isolation switching since you need to break both poles. Using a single wire would only break the live to each socket.

Taking the face plate off one of the appliance sockets would probably tell you. A single cable would indicate they had done what you suspect.

[Owain]

Which could lead to imbalance on the two legs of the ring.

However, the circuit might also be a radial, in which case I hope it's a

30A one in 4mm

Owain

[Dave Plowman (News)]

What are all the appliances? A fridge or freezer doesn't use much power - and washing machines etc don't take a high load for long. And I doubt it would make much difference in practice if they were all high loads given the switch panel is likely to be near the centre of the ring, if the CU is at the front door as in most new builds.

[scullsterhome]

"Owain" wrote

The circuit according to the spec is fed with 2.5mm cable so I assume it's a ring.

Phil

[scullsterhome]

"Dave Plowman (News)" wrote

Good point Dave

[Andy Wade]

The Schedule of Test Results should positively identify all/any ring circuits as such (in column 8, under the heading of "continuity" if forms based on the standard model have been used).