Moving a Consumer Unit. Cable extension "best practice" question. [PING Andy Gabriel]

[Vortex4]

Hi,

I need to move 6 circuits from an old CU (which will be removed) to a new one (which is already installed).

2 x ring main (32 Amp) 1 x Simple spur (15 Amp, to boiler and controls) 3 x lighting (5 Amp)

The problem is that I will need to extend the existing cabling by about 2 feet to the new CU.

I intend to use IMO DIN components / IP66 enclosure which I will install at the location of the (old) CU.

My question arises from this pic I found (posted by Andy)

and concerns the ring main circuits:

QUESTION

Given that the CU and the DIN rail will be separated, should I extend the ring circuits using 2 x 2.5mm T&E cables so they meet at the new CU? Or is it valid to run single 4.0mm T&E from junction box to new CU (essentially as in the picture)?

D

[Andrew Gabriel]

You can use 4.0mm T&E (although I actually used 6mm, and that's going to be better where you might have cable grouping, and it's more common).

One concern might be the single earth, whereas a ring has two separate earth routes. However, what's not so obvious in the picture is that all the DIN rail earth terminals also connect to the DIN rail, so actually there are 4 paralleled earth connections from the DIN rail back to the main earthing terminal. Were it not for this, I would say that if you are using a single 4mm or 6mm T&E branch to a ring circuit, I would add a second earth connection in parallel with the integral earth in the T&E for redundancy.

The other suggestion I would make -- use one size larger DIN rail terminal than you might think you need, particularly where multiple conductors are being connected. When a DIN terminal says 2.5mm (or whatever), it really means it - there's no spare space in the terminal at all.

Also, it would have been easier if I'd used a larger box for making the cable connections at the top.

[Tim W]

Andrew Gabriel wibbled on Tuesday 27 October 2009 13:46

Andrew,

How do you rate the electrical integrity of the DIN rail to earth clamp?

I have bought some RS terminals for my lighting junction boxes, and I was considering relying on the DIN rail to common the earth terminals. Whilst this appears to be the intention, do you consider it sufficient?

Cheers

Tim

BTW - to the OP:

The RS own brand DIN terminals are very well made and are one of the best priced I could find.

[Vortex4]

Thanks for the input Andrew,

I had not considered the earth redundancy via the DIN rail.

D

[Andrew Gabriel]

I wouldn't rely on it without finding a suitable product spec and/or BS/EN reference.

[Tim W]

Andrew Gabriel wibbled on Thursday 29 October 2009 12:59

Hmm. Suppose I'd better daisychain some link wires down one side. Wish I'd saved the money and just used simple 30p yellow terminals :(

Unless there is a BS/EN reference. Any tips on how I might go about searching for this - is there a BS for "Earthing Integrity"?