Considering CU update

[EFLImpudence]

Not according to the 3 sparks I've had in.

Find one who knows what he is doing.

I can double check with them.

That would seem to be pointless.

9kw hob, and 3kw oven.

That's 12kW which at 240V is 50A.

With cooking appliances, what we call diversity is applied.
That is the first 10A and 30% of the remainder.


So 10A plus 30% 0f 40A is 10A + 12A = 22A.

4mm² T&E has a current carrying capacity of 37A (as long as it is not run through thermal insulation).

So the 32A breaker and 4mm² cable is fine.


Despite this people tend to still (for historical reasons) use 6mm² cable. Are you/they sure it is 4mm²?

 

[dormermike]

Find one who knows what he is doing.


That would seem to be pointless.


That's 12kW which at 240V is 50A.

With cooking appliances, what we call diversity is applied.
That is the first 10A and 30% of the remainder.


So 10A plus 30% 0f 40A is 10A + 12A = 22A.

4mm² T&E has a current carrying capacity of 37A (as long as it is not run through thermal insulation).

So the 32A breaker and 4mm² cable is fine.


Despite this people tend to still (for historical reasons) use 6mm² cable. Are you/they sure it is 4mm²?

Thanks. Does cable length factor into that? Its (very approx) 25m long. It does not go through insulation for the majority of the run, just perhaps 2 metres or so of 100mm rockwool type stuff.

I'll power off the circuit this evening and pop the cover off the isolator and take a look to see if it is 4mm or 6mm. Nobody has checked, we've just assumed as the breaker / rcbo is 32amp.

 

[EFLImpudence]

Thanks. Does cable length factor into that? Its (very approx) 25m long.

Not unless it is very long.

It does not go through insulation for the majority of the run, just perhaps 2 metres or so of 100mm rockwool type stuff.

That would have an effect of reducing the current rating but as only 22A is the circuit requirement 4mm² might still be alright and 6mm² definitely would be.
I presume you have been using a cooker or oven and hob until now with no problems.

I'll power off the circuit this evening and pop the cover off the isolator and take a look to see if it is 4mm or 6mm. Nobody has checked, we've just assumed as the breaker / rcbo is 32amp.

Ok.

6mm² was required for a 30A rewireable fuse and people still use it from habit but since 32A MCBs/RCBOs took over 4mm² is fine.

 

[dormermike]

Well well, looks like 6mm² cable after all?

 

[EFLImpudence]

Looks like it.

Just to be sure; is the bare CPC(earth wire) 2.5mm² - 1.78mm diameter.

 

[Adam_151]

What would be top tier these days? I don't mind spending extra.

Schneider Acti9 Isobar P Type A SPN Board, Expect to pay About £70 per RCBO and another couple of hundred for the board itself and incommer

.... Well you did ask!

 

[flameport]

Also they fit "fusebox" consumer units -

A brand which gets others to advertise it's wares all over social media and shovels out pink coloured merchandise on a regular basis.

are these better or worse or same as

They all comply with the same standards for use in the UK

Just like all cars comply with the same standards for use in the the UK.

 

[dormermike]

Looks like it.

Just to be sure; is the bare CPC(earth wire) 2.5mm² - 1.78mm diameter.

Bingo! Thank you so much for your help.

 

[dormermike]

Schneider Acti9 Isobar P Type A SPN Board, Expect to pay About £70 per RCBO and another couple of hundred for the board itself and incommer

.... Well you did ask!

Yikes. Little over budget, think i'll leave the electrician to fit his preferred brand. Thanks!

 

[dormermike]

A brand which gets others to advertise it's wares all over social media and shovels out pink coloured merchandise on a regular basis.


They all comply with the same standards for use in the UK

Just like all cars comply with the same standards for use in the the UK.

Thanks, makes sense. I guess beyond long term support there is probably little to distinguish between CU's purchased at the regular places like screwfix and so on. I won't be fitting it myself, so as a consumer, as long as it does what its supposed to do... i shouldn't need to care too much what brand it is.

 

[Murdochcat]

I would ask the sparks which brand(s) they fit. Most of us have distinct favourites. And always carry spares for the units in my van all the time

If any of them don’t have a favourite and fit the cheapest at the time , I would see that as an issue.

 

[plugwash]

Just like all cars comply with the same standards for use in the the UK.

AIUI cars require type approval from government (it looks like we are currently in the process of trying to seperate our type approval system from that of the EU). I don't think there is such a requirement for most electrical goods. Fusebox do seem to have sought third party testing even though I don't believe they are required to do so.

The Schneider isobar stuff has some nice features (including the headline "isobar" feature itself which makes it much safer to add and remove devices from a live board), but you don't half pay through the nose for it.

 

[dormermike]

Find one who knows what he is doing.


That would seem to be pointless.


That's 12kW which at 240V is 50A.

With cooking appliances, what we call diversity is applied.
That is the first 10A and 30% of the remainder.


So 10A plus 30% 0f 40A is 10A + 12A = 22A.

4mm² T&E has a current carrying capacity of 37A (as long as it is not run through thermal insulation).

So the 32A breaker and 4mm² cable is fine.


Despite this people tend to still (for historical reasons) use 6mm² cable. Are you/they sure it is 4mm²?

Hi again. Electrician saying diversity for an oven and hob on same circuit is hard to justify, as they're frequently operated together. Also that "12000 / 230v gives approx 52.2 amps, therefore 6mm cable not suitable under any installation method, as max current is 47A, even before derating to 35A for being in a wall/conduit and not clipped".

AS they're the one signing off I think I'm going to have to get a new 6mm or even 10mm circuit put in "10mm flat cable max current for ref method c is 64 amps, and for ref method 102 is 47 amps".

 

[Murdochcat]

Hi again. Electrician saying diversity for an oven and hob on same circuit is hard to justify, as they're frequently operated together. Also that "12000 / 230v gives approx 52.2 amps, therefore 6mm cable not suitable under any installation method, as max current is 47A, even before derating to 35A for being in a wall/conduit and not clipped".

AS they're the one signing off I think I'm going to have to get a new 6mm or even 10mm circuit put in "10mm flat cable max current for ref method c is 64 amps, and for ref method 102 is 47 amps".

That’s not a competent spark

 

[EFLImpudence]

Hi again. Electrician saying diversity for an oven and hob on same circuit is hard to justify, as they're frequently operated together.

Has he ever heard of a 'cooker'? An oven and hob in one and what the label on the circuit breaker states.

Also that "12000 / 230v gives approx 52.2 amps,

Well, the ratings will be quoted at 240V, at 230V the Wattage will be less - but that doesn't make much difference.
As I have shown you, the design current of the circuit is 22A.
I don't blame you for being wary but the system has been in use for decades - and works.

therefore 6mm cable not suitable under any installation method, as max current is 47A, even before derating to 35A for being in a wall/conduit and not clipped".

35 is more than 22 so fine.

AS they're the one signing off I think I'm going to have to get a new 6mm or even 10mm circuit put in "10mm flat cable max current for ref method c is 64 amps, and for ref method 102 is 47 amps".

You could get a new - or probably better would be an older - electrician.

10mm² is used for the supply cable to many premises to supply everything; cooker, heating, shower, everything; as they (and you might) only have a 60A main fuse.
I wonder how that works.