6mm kitchen sub-main

[bro8284]

Howdy All,

just after a 2nd opinion as i'm doubting myself.
I went to a property to look at replacing the ccu, I noticed what I thought was a 6mm cooker circuit on 32a
But found it was feeding another ccu in the kitchen (Extension)
I couldn't open the ccu as it was boxed very tightly!!
it has 4 circuits feeding the kitchen and rooms above. Bedroom/bathroom
cooker 32a (hob 5.5Kw & oven - unsure of Kw)
sockets 32a
radial 16a (unsure)
Lights 6a

I recommended upgrading the cable to 10mm and on 45a due to the loads
The cable is run above the ceiling
They don't wanna replace as its "working fine and always has been"!!

I just want others views.
appreciate any reply's

 

[davesparks]

I'd side with the customer on this one, 6mm cable suitably protected by a 32A MCB and no apparent history of tripping.

 

[bro8284]

I'd side with the customer on this one, 6mm cable suitably protected by a 32A MCB and no apparent history of tripping.

Cheers pal for your reply, this is the reason I wanted a 2nd opinion

 

[7029 dave]

IMO it's pure luck that this sub circuit (32A) has not gone pop feeding 4 circuits some of which are of substantial size, any cable feeding between to cu's is not a sub main, it's a sub circuit just like any other circuit fed of a CU. Technically the circuit is sized correctly to the cable. Terrible circuit design and undersized for what it's supplying. A genuine sub main would be better. Out of interest what protective devices are there in both CU's.?

 

[DPG]

Seems likely that the OCPD could well be running over its rated current quite often.

 

[7029 dave]

Seems likely that the OCPD could well be running over its rated current quite often.

Yup well worked 6mm cable lol

 

[bro8284]

IMO it's pure luck that this sub circuit (32A) has not gone pop feeding 4 circuits some of which are of substantial size, any cable feeding between to cu's is not a sub main, it's a sub circuit just like any other circuit fed of a CU. Technically the circuit is sized correctly to the cable. Terrible circuit design and undersized for what it's supplying. A genuine sub main would be better. Out of interest what protective devices are there in both CU's.?

Cheers for your reply, the protective devices in each CU are 3871, was looking at changing the CU's to add RCD protection.

 

[pc1966]

Seems likely that the OCPD could well be running over its rated current quite often.

It probably comes down to if they use plug-in heaters or not.

The 32A upstairs rooms' sockets probably draw an amp or two normally otherwise. Cooker can be above 32A of course but not normally for long periods. The 16A radial is more of a worry as it might be immersion heater so a real long-term draw. Lights largely can be ignored.

But I agree with the above, a proper sub-main in SWA fed from fused-switch would be better design. But why, why, WHY? Surely the house should have been wired from the normal CU for everything unless it is truly massive!

 

[bro8284]

It probably comes down to if they use plug-in heaters or not.

The 32A upstairs rooms' sockets probably draw an amp or two normally otherwise. Cooker can be above 32A of course but not normally for long periods. The 16A radial is more of a worry as it might be immersion heater so a real long-term draw. Lights largely can be ignored.

But I agree with the above, a proper sub-main in SWA fed from fused-switch would be better design. But why, why, WHY? Surely the house should have been wired from the normal CU for everything unless it is truly massive!

There’s no electric heaters, I couldn’t verify but I think the 16a radial could be an oven or boiler.

As for the sockets it’s not just the upstairs sockets it’s also the kitchen sockets.

I’m guessing when they put the extension on they they decided to use the old cooker cable, then new circuits from there.

 

[davesparks]

IMO it's pure luck that this sub circuit (32A) has not gone pop feeding 4 circuits some of which are of substantial size

It's not luck, it's diversity.

, any cable feeding between to cu's is not a sub main, it's a sub circuit just like any other circuit fed of a CU.

Neither submain nor subcircuit are correct terminology. Circuits are either distribution circuits or final circuits.

 

[7029 dave]

It's not luck, it's diversity.


Neither submain nor subcircuit are correct terminology. Circuits are either distribution circuits or final circuits.

 

[7029 dave]

Well you would say that, being quite a newcomer to the trade, I don't say CPC ethier lol

 

[davesparks]

Well you would say that, being quite a newcomer to the trade, I don't say CPC ethier lol

It's nothing to do with being a newcomer, it's keeping up with changes in terminology and regulations etc.

 

[7029 dave]

It's nothing to do with being a newcomer, it's keeping up with changes in terminology and regulations etc.

Does it really matter if old terminology is being used, the OP and other members knew exactly what I was saying.
You are a guy with great knowledge but I feel sometimes you try and bait an argument for arguments sake, shame really.

 

[Midwest]

Does it really matter if old terminology is being used, the OP and other members knew exactly what I was saying.
You are a guy with great knowledge but I feel sometimes you try and bait an argument for arguments sake, shame really.

I don't think davesparks does it intentionally, he's just a bit picky.