moving meter head and consumer unit

jazzbhatia · 14 Mar 2012

I am looking to have my consumer unit moved in addition to the meter head. They will still remain close to one another.

When extending the circuits should the electrician use a single cable per circuit between the consumer unit and the junction box? The guy I spoke to said that this is acceptable

Im not convinced

riveralt · 14 Mar 2012

jazzbhatia said:
I am looking to have my consumer unit moved in addition to the meter head. They will still remain close to one another.

You are responsible for everything electrically after the meter - everything else belongs to the DNO and you must not under any circumstances move it without contacting them.

jazzbhatia said:
When extending the circuits should the electrician use a single cable per circuit between the consumer unit and the junction box? The guy I spoke to said that this is acceptable
Im not convinced

This sentence is confusing. What junction box are you talking about?
Are talking about a service cable connector block?
In which case 25mm2 single tails will be used for L & N - so the electrician is correct, though your wording is wrong.
Be aware though some DNO's do put a limit on the length of meter tails.

jazzbhatia · 14 Mar 2012

I have already contact the electric board to arrange moving the head, would snot have it any other way.

What I am referring to is once the consumer unit has been moved to the new location all the circuits will be too short to reach the consumer unit (lighting circuit, ring main etc).

What has been proposed is the following

For example, with the lighting circuit on the ground floor there will be two live, two neutral and two earth cables terminating in circuit 1 of the consumer unit.

The electrician has proposed to connect these three cables in a junction box and then add ONE cable going to circuit 1 in the consumer unit.

What this means is where circuit 1 had two cables terminating in the consumer unit it will now have only one.

JohnW2 · 14 Mar 2012

jazzbhatia said:
What has been proposed is the following
For example, with the lighting circuit on the ground floor there will be two live, two neutral and two earth cables terminating in circuit 1 of the consumer unit.
The electrician has proposed to connect these three cables in a junction box and then add ONE cable going to circuit 1 in the consumer unit.
What this means is where circuit 1 had two cables terminating in the consumer unit it will now have only one.

It is quite unusual, although not impossible/forbidden, to have two cables going to the CU for one lighting circuit. However, if that's what you have (two cables going to same lighting circuit MCB), it would probably be theoretically acceptable to do as suggested, although it could create some problems/confusions for anyone subsequently undertaking tests on the installation. For the sake of a bit of cable and junction box (or a 6-way JB rather than a 3-way one), far better to extend the two cables separately.

The same cannot be done with any ring final circuit supplying sockets (which do have two cables returning to the CU). In that case, the two cables going to the CU must be extended separately. If any 'electrician' you've spoken to doesn't understand that, I think you should seriously question whether you should be using him/her.

Kind Regards, John

riveralt · 14 Mar 2012

jazzbhatia said:
For example, with the lighting circuit on the ground floor there will be two live, two neutral and two earth cables terminating in circuit 1 of the consumer unit.
The electrician has proposed to connect these three cables in a junction box and then add ONE cable going to circuit 1 in the consumer unit.

Okay I understand - you actually had two lighting circuits or perhaps a bell and lighting circuit coming into the old Consumer Unit single fuse.
There is nothing wrong with what the electrician proposes since the lighting circuits are radials this is just an extension of the radial circuit.
Unless there is no other option it is not the way I would do it though.
I've got a similar type of job to fit a replacement CU in a house next week and some of the cables need extending. I prefer to extend the cables by crimping and run the extended cables in trunking to the CU - but each to their own.

TicklyT · 14 Mar 2012

Lighting circuits usually follow a branching or radial topology, so it's usual to find just one cable at the CU - unless one of the branches originates at the CU - so there would be nothing unusual in what your electrician proposes.

Ring circuits for sockets follow a ring topology, so both cables must be extended to the CU to maintain the ring.

Better still to replace the cable between the CU and first accessory than extend it by criming or a junction box, but that isn't always practical.

Taylortwocities · 14 Mar 2012

So, you are going to end up with a lot of junc.tion boxes, or one big one with lots of connections inside it.

Where will this/these JBs be situated?
Will you be able to get at it/them later on if there are problems?

jazzbhatia · 14 Mar 2012

I intend to have the meter head and consumer unit moved from under the staircase with a view to fitting a WC and wash hand basin.

I am keen to have the connections crimped as the junction boxes will indeed take up too much space.

I will leave an access panel which will make access easy for maintenance.

As I will be supplying the electrician and contractors with all the materials, where can I purchase some good quality crimps.

Thanks

ban-all-sheds · 14 Mar 2012

JohnW2 said:
It is quite unusual, although not impossible/forbidden, to have two cables going to the CU for one lighting circuit. However, if that's what you have (two cables going to same lighting circuit MCB), it would probably be theoretically acceptable to do as suggested, although it could create some problems/confusions for anyone subsequently undertaking tests on the installation. For the sake of a bit of cable and junction box (or a 6-way JB rather than a 3-way one), far better to extend the two cables separately.

The same cannot be done with any ring final circuit supplying sockets (which do have two cables returning to the CU). In that case, the two cables going to the CU must be extended separately. If any 'electrician' you've spoken to doesn't understand that, I think you should seriously question whether you should be using him/her.

Kind Regards, John

JohnW2 said:
ban-all-sheds said:

BAS Towers may need to have it's CU moved, with circuits extended using DIN rail terminal blocks.
Now - I know I said this: //www.diynot.com/forums/viewtopic.php?p=165038#165038
but I'm sitting here thinking yes, it's unconventional, and yes it makes testing more awkward, but is there really any great merit in extending ring final line conductors with 2 terminals and 2 x 2.5mm² cables into the CU rather than putting both legs into one terminal and running a single 4mm² to the breaker?

Click to expand...

I think that you (with your old thinking!) and I also crossed swords over this one in the past, but I agree with you (new thinking!) and Eric that there seems to be nothing intrinsically wrong with doing as you suggest. There would obviously be less scope for argument if, as Eric suggests, you used 6mm², rather than 4mm², cable - since (although one can stage some sort of argument by analogy with a 32A radial final) there is otherwise obviously the scopr for people to start fussing about the 'CSA reduction' from 2x2.5mm² to 4mm².

In fact, I inherited a situation like this in my house, and happily lived with it for several years. A 6mm² (well, imperial equivalent) cable which appeared to have originally been supplying a second cooker circuit in the (large) kitchen had been diverted into the (large) cellar and used as the start/finish points for a 2.5mm² (imperial equivalent) ring final circuit. As I say, I happily lived with that for a good few years, until I eventually treated the cellar to a sub-main and its own CU.

As you know, I do my best to play at Devil's Advocate, but I find it hard to come up with any 'sensible' objections that anyone could raise, particularly if you used 6mm² cable. You should, of course, label your CU appropriately, so that anyone coming across it knows what is going on, and knows where to find the ends of the ring for testing etc.

Kind Regards, John.

ban-all-sheds · 14 Mar 2012

jazzbhatia said:
As I will be supplying the electrician and contractors with all the materials, where can I purchase some good quality crimps.

1) Why do you want to make the job cost more by paying more for the materials than the electrician will?

2) Why do you want to give the electrician the cast-iron excuse of poor materials provided by you if there are any problems?

riveralt · 14 Mar 2012

jazzbhatia said:
I intend to have the meter head and consumer unit moved from under the staircase with a view to fitting a WC and wash hand basin.

I take it you have your quote from the DNO to move the meter and you still have enough money left to employ electricians.

jazzbhatia said:
As I will be supplying the electrician and contractors with all the materials, where can I purchase some good quality crimps.

There are specialist crimping tools that have their own brand of crimps.
So the person who is crimping the cables is the best person to answer that question not us here.
Also since he will be designing, installing, testing and notifying your new installation to your Local Authority Building Control, the cable runs, cable terminations, access points etc should be left to him.

JohnW2 · 14 Mar 2012

ban-all-sheds said:
JohnW2 said:

the simple and conventional answer.

Click to expand...

a good while ago said:

<a less conventional, and more controversial answer, culminating with .... As you know, I do my best to play at Devil's Advocate, but I find it hard to come up with any 'sensible' objections that anyone could raise, particularly if you used 6mm² cable. You should, of course, label your CU appropriately, so that anyone coming across it knows what is going on, and knows where to find the ends of the ring for testing etc.

Click to expand...

I still see no real engineering problem with the latter (and, as I said, happily lived with a cellar supplied in such a fashion for a good few years) - but I can see that it might be 'controversial', and I can even imagine some people questioning whether it actually qualified as a ring final which attrcated the 'special considerations' given to such circuits by the regs. However, I would not even discuss that possible approach with someone who was not already conversant with all the issues and regs, and the OP in this thread obviously does not come into that category (given the questions that are being asked).

Kind Regards, John.

ban-all-sheds · 14 Mar 2012

Fair enough, but there's a big difference between that position and

"The same cannot be done with any ring final circuit supplying sockets (which do have two cables returning to the CU). In that case, the two cables going to the CU must be extended separately. If any 'electrician' you've spoken to doesn't understand that, I think you should seriously question whether you should be using him/her."

JohnW2 · 14 Mar 2012

ban-all-sheds said:
Fair enough, but there's a big difference between that position and
"The same cannot be done with any ring final circuit supplying sockets (which do have two cables returning to the CU). In that case, the two cables going to the CU must be extended separately. If any 'electrician' you've spoken to doesn't understand that, I think you should seriously question whether you should be using him/her."

If you wish to think so - it seems that you are at a loose end today and want to find some thread in which to introduce some argument. As I said, the big difference is the person to whom the words were directed. In theory, you should be flattered by the implications, but I don't suppose you will see it like that.

Although my previous discussion with you was academically interesting, I seriously doubt whether any electricians would consider installing a 'banjo' like ring final, either by first intent or in the context of extending for a CU move, even if the cables were appropriately rated.

Kind Regards, John.

ban-all-sheds · 14 Mar 2012

The point is that you can't see anything really wrong with it, I can't see anything really wrong with it, and IIRC nobody else could see anything really wrong with it.

It's possible that the OP's electrician won't see anything wrong with it, and decide that it's appropriate.

But despite the fact that you know it's his call, and despite the fact that you can't see anything really wrong with it, you've told the OP (who doesn't cross your threshold of understanding) to have nothing to do with such an electrician because it cannot be done with ring finals because the cables must be extended separately.

On the one hand you believe electricians should actually think about what they are doing, and on the other you tell someone to reject an electrician who does do that if his thinking results in something unconventional but soundly engineered.

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moving meter head and consumer unit

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