swapping 10mm t&e for 2 x 6mm t&e (and two-CU setup)

[GCarnegi]

Can I substitute two 6mm2 t&e cables in place of a single 10mm2 t&e cable? I need to run approx 4-5m from my old CU to a new CU in my extension, and the electrician has specified 10mm2.

That's fair enough, but I have half a drum of 6mm2 cable in my shed, and although I understand that the load carrying capacity of 2x6mm2 cable exceeds that of a single 10mm cable, there may be other restrictions.

If you don't mind I'd like to ask a couple of questions.
1. I now have an isolator switch next to my meter, so I can safely isolate the old CU. What's the best way to connect the new CU? To the isolator switch (doubleing up with the old CU tails), or piggy-backing onto the bus-bars in the old CU? Obviously, if I connect to the isolator switch, then I'd need to run new meter tails to the new CU, rather than T&E.

2. What is the best solution for running through 20/25mm conduit? 10mm t&e? 2x6mm t&e? 10mm singles? 25mm singles(meter tails)?

many thanks
Guy

 

[holmslaw]

..

 

[Taylortwocities]

Holmslaw speaks wisely. There are a lot of things to consider.

If the distance is more than that allowed by the DNO you will have to use a switchfuse at the supply end.

And as for

piggy-backing onto the bus-bars in the old CU

And as for

Obviously, if I connect to the isolator switch, then I'd need to run new meter tails to the new CU, rather than T&E.

Not obviously, in fact T&E may be better. It depends.

But why are you asking these questions on a DIY forum, if you have an experienced, qualifed electrician who is to do the job? He will design the job, install, test and certify that it all complies with BS7671, trying to save 4 or 5 metres of 10mm isn't going to help the client/electrician interface.

 

[GCarnegi]

I have an experienced, qualified electrician who is going to check and certify the work, which is all that is required here in Scotland. Of course I understand in England it is required that the work is done by a qualified electrician, but here someone with relevant experience can do it without those particular qualifications.

I was just politely asking some advice, but as you say, this is a DIY forum, though I'd hoped there might be some experienced individuals here who might be willing to offer some advice.

Never mind. I'll ask my electrician in the morning, and I'm sure he will advise me accordingly.

Thanks for setting me straight.

 

[flameport]

The problem in giving you or anyone else advice when an electrician is already involved is that the information given here may not be what your electrician expects or wants, even if the info is correct.
There are often several ways to design and install a particular circuit, all of which can be compliant and safe, but ultimately it is your electrician who will be sigining the certificate, so it is up to them which method is used.

Being in Scotland makes no difference to this - electrical work in England and Wales doesn't have to be done by a qualified electrician either.