Whole house rewire questions

[jelliott]

Hello,

I am renovating a house. I am rewiring myself. I am getting an electrician to install a new consumer unit & test all my work. I'm looking for a sanity check before I run all the cables. I want to do first fix and get the house plastered. Some of the cable colours in the diagrams are wrong as I changed my mind half way through of going from 2 core to 3 core.

My questions are:
Downstairs light circuit
1) Is 1.5mm 3 core and earth suitable for all the downstairs lighting circuit, 6A fuse?
2) Can I use internal 1.5mm 3 core for the outside lights, as long as the cable goes directly into the light & not run along any walls?
3) Can the smoke alarms come off the downstairs light circuit. My idea was that if they were on their own circuit. I wouldn't know if a fuse had gone. Additionally, can I just run 1.5mm to connect the 3 smoke alarms together.
4) Does the kitchen fan need it's own separate isolation switch?

Upstairs light circuit
1) All this okay on 1.5mm 3 core and earth, 6A fuse?
2) Can I just run a cable off a junction box to a wall light with it's own internal switch
3) Same as 2) for the bathroom cabinet with light/shaver socket

Living room plugs and Kitchen plugs
1) Can i use 2.5mm twin core on a 20A fuse? Originally, the electrician said 32A ring, but I don't see the advantage.

Bed/Dining plugs
1) Can i use 2.5mm twin core on a 20A fuse?
2) Can I just spur the boiler circuit to a 3A isolation and worry about it later? I haven't done the heating design yet. There are multiple zones, underfloor heating etc.

Kitchen
1) Can I use 6mm twin core for the cooker on a 32A fuse?
2) What do I do with induction hobs? I can't get a straight answer on this. Can I just extend the cooker isolation switch to another isolation switch (opposite side of the kitchen) and worry about connecting it up later? I'm looking at a 32A hob, I don't like the idea of the smaller ones.

 

[James]

You really need your electrician to be involved in the planning stage.
there are so many things that could go wrong here if you try to specify it yourself.

it’s rare for me to use 1.5 for lighting unless it’s a Comercial job with long runs or big lights.

lso, i would not provide an installation certificate for a job like that unless I was involved from day one with regular site visits.

 

[jelliott]

You really need your electrician to be involved in the planning stage.
there are so many things that could go wrong here if you try to specify it yourself.

it’s rare for me to use 1.5 for lighting unless it’s a Comercial job with long runs or big lights.

lso, i would not provide an installation certificate for a job like that unless I was involved from day one with regular site visits.

I've got an electrician on board. I'd like to get as much as I can of the design sorted before talking to him.

 

[littlespark]

Answers in italics....


Downstairs light circuit
1) Is 1.5mm 3 core and earth suitable for all the downstairs lighting circuit, 6A fuse? 1.0mm is sufficient with LED loads. Modern practice is cables to switches, not looped at lights.
2) Can I use internal 1.5mm 3 core for the outside lights, as long as the cable goes directly into the light & not run along any walls? You canjnot use flat grey cable exposed outside as it is not UV stable. Take to a small joint box, then flex to light fitting.
3) Can the smoke alarms come off the downstairs light circuit. My idea was that if they were on their own circuit. I wouldn't know if a fuse had gone. Additionally, can I just run 1.5mm to connect the 3 smoke alarms together. Sensible to come off a lighting circuit, but again, 1.0mm will suffice. Twin to first detector, then 3 core between. Check requirements for number of detectors.; will possibly need heat detector in kitchen as well as smokes in hallways.
4) Does the kitchen fan need it's own separate isolation switch? wall mounted fan? part of cooker hood? Ask your electrician about Part F and see if it applies.

Upstairs light circuit
1) All this okay on 1.5mm 3 core and earth, 6A fuse? As above.
2) Can I just run a cable off a junction box to a wall light with it's own internal switch yes. just need a live/neutral/earth
3) Same as 2) for the bathroom cabinet with light/shaver socket check instructions... might require a fuse.

Living room plugs and Kitchen plugs
1) Can i use 2.5mm twin core on a 20A fuse? Originally, the electrician said 32A ring, but I don't see the advantage. kitchen has a lot of high loads. sensible to be 32A ring. Kitchen on its own.

Bed/Dining plugs
1) Can i use 2.5mm twin core on a 20A fuse? Yes
2) Can I just spur the boiler circuit to a 3A isolation and worry about it later? I haven't done the heating design yet. There are multiple zones, underfloor heating etc. Yes. but get the heating planned out, as there will be cables for it running around the house for room thermostats etc.

Kitchen
1) Can I use 6mm twin core for the cooker on a 32A fuse? How big is the cooker?
2) What do I do with induction hobs? I can't get a straight answer on this. Can I just extend the cooker isolation switch to another isolation switch (opposite side of the kitchen) and worry about connecting it up later? I'm looking at a 32A hob, I don't like the idea of the smaller ones. If you're rewiring, then put it on its own circuit.



Im ignoring the terminology such as "fuse" instead of "circuit breaker"

But i will also add that what's been said above is good advice.
Get your electrician involved now... not suddenly say, "oh can you do my consumer unit and test all this?"

Theres much more than just about getting cables of the right size to where they need to be...

 

[jelliott]

Thanks for the replies. I am definitely getting an electrician on board at all stages. I'm paying for consultancy as well as the consumer unit and testing. I'd rather get it all right first time and not have to pay for extra consultancy to fix my mistakes

I'll drop down to 1mm 3 core for the lighting.

The outside cable won't be 'exposed' to the elements. Only through the hole in the wall direct into the light. Same with the outside plug socket. It seemed overkill to buy additional cable.

I have got 3 smokes in the plan. 2 in the hallways and a heat detector in the kitchen.

The kitchen fan will be part of the cooker hood.

The kitchen is on its on circuit. There are 3, north house, south house and kitchen. What I really wanted to know was the reasoning behind a 32A ring , rather than a 20A radial. My understanding is that we get more power out of a 20A, as the 32A is split.

The bathroom cabinet is easy, I can run the cable into the loft and worry about it later when I buy the thing and read the instructions.

For the heating, I was thinking of just cabling the thermostats myself and letting the plumber/electrician deal with the rest. The underfloor heating comes with it's own wiring centre, so it can't be that hard. It's the upstairs radiator zones I don't have a plan for. The two will need to be linked.

I haven't bought a cooker. Future proof?

 

[littlespark]

Oh look. Someone hit the “disagree” button by accident again.

 

[Lucien Nunes]

What I really wanted to know was the reasoning behind a 32A ring , rather than a 20A radial. My understanding is that we get more power out of a 20A, as the 32A is split.

I don't know what you mean by this. A 32A circuit can supply 32A whether it is run as a ring in 2.5mm² or a radial in 4.0mm². The choice of cable configuration is a matter of convenience for a particular location or socket layout, but it makes no difference to the usage or available current.

IMO 20A is too low for a kitchen unless the major appliances are fed from a separate appliance circuit. For the sake of one extra home run of cable to the CU, make it a ring, give yourself the full 32A and avoid nuisance trips.

 

[mainline]

I don't know what you mean by this. A 32A circuit can supply 32A whether it is run as a ring in 2.5mm² or a radial in 4.0mm². The choice of cable configuration is a matter of convenience for a particular location or socket layout, but it makes no difference to the usage or available current.

IMO 20A is too low for a kitchen unless the major appliances are fed from a separate appliance circuit. For the sake of one extra home run of cable to the CU, make it a ring, give yourself the full 32A and avoid nuisance trips.

I personally would separate the kitchen sockets from the appliances using a pair of 4 mm radials.

 

[mainline]

For the heating, I was thinking of just cabling the thermostats myself and letting the plumber/electrician deal with the rest. The underfloor heating comes with it's own wiring centre, so it can't be that hard. It's the upstairs radiator zones I don't have a plan for. The two will need to be linked.

Or save on wiring and use wireless.

I haven't bought a cooker. Future proof?

If you want to future-proof, then a pair of 6 mm.

 

[Lucien Nunes]

I personally would separate the kitchen sockets from the appliances using a pair of 4 mm radials.

Even better. This not only gives lots of elbow-room for total loading but spreads the earth leakage between two circuits reducing the chance of nuisance leakage trips. I always think of it as a bit of a luxury to have the two circuits, having been brought up in the tradition of 'a 30A ring is enough for anything' but it does make sense.

 

[jelliott]

For interest. Here are my revised designs. I'm going to leave the kitchen off for now. I want to buy a second hand kitchen, then do the electrics based on what I get.

 

[James]

You realy need to be discussing this with your electrician.

I would not normally expect anything other than a 1 bedroom flat to be wired using only 4 circuits, and even then, it would be an unusually small amount.

the lighting circuits in 3 core are of an unusual design looping 3 core through everything.
although it would work.

 

[jelliott]

You realy need to be discussing this with your electrician.

I would not normally expect anything other than a 1 bedroom flat to be wired using only 4 circuits, and even then, it would be an unusually small amount.

the lighting circuits in 3 core are of an unusual design looping 3 core through everything.
although it would work.

Hello, there are more than 4 circuits,

Not shown are the kitchen circuits, heating circuits, cooker circuit, hob circuit. I have additional for expansion too. Our house is fairly small.

For the kitchen, I was thinking of taking in the suggestion of separating the appliances from the sockets on 4mm radials. Until I know what is going in the kitchen, it is hard to plan.

 

[brianmoooore]

Any design that incorporates 4 pole junction boxes is a fail!

 

[jelliott]

Any design that incorporates 4 pole junction boxes is a fail!

Tough crowd. I assume you mean to favour the Wago type connection boxes.