Is a new metal CU needed...?

[ClockPie]

Hello all

I had a conversation with an electrician 18 months ago, and I'm sure he said that any changes to a circuit would mean I need a new metal CU (from a modern plastic one). I'm not sure if there were other reasons for this or not.

But I've since read that if you are changing an existing circuit (such as adding sockets to a ring) or adding a new circuit in an existing free space, then you do not need to replace the CU - you can use the existing plastic one.

My CU is standard 10yo with 30mA RCD on the rings.

I just want to confirm details before I get someone in to deal with a new socket or two on an existing ring.

Thanks

 

[flameport]

If you are installing a new CU, it would be a metal one.

It is not necessary to fit a new CU as part of extending or altering existing circuits.

any changes to a circuit would mean I need a new metal CU

Wrong. Probably spouted by those who wanted to make extra money by doing a load of work which was not necessary.

 

[JohnW2]

But I've since read that if you are changing an existing circuit (such as adding sockets to a ring) or adding a new circuit in an existing free space, then you do not need to replace the CU - you can use the existing plastic one. ... My CU is standard 10yo with 30mA RCD on the rings.

That is true. For the past requirements year it has been a requirement that any newly-installed CUs be made of 'non-combustible material' (which most people take to mean metal), but there is no requirement to upgrade an existing CU to a metal one, no matter what is done to the installation.

Kind Regards, John
Edit: Typo (fingers thinking ahead of brain!) corrected.

 

[EFLImpudence]

The regulations could be better in a lot of respects but they do relate to (the very rare) common sense in some respects.
Not that they are 'legally' enforceable anyway.

That you could not have a new socket unless you also have a new consumer unit would be so obviously ridiculous as to be farcical.

Why isn't 'gullible' in the dictionary?

 

[ClockPie]

lol

Thanks for that clarification.

We were talking about other things too, so there may have been another reason for their comment which I forgot, and only this bit stuck in my head. (I omitted that from above post to simply thyngs).

I was also talking about changing 2x other circuits (cooker & lighting) which are on the 100A/100mA RCD side, and perhaps if these are changed they need to go to the 30mA RCD side? And if so, there is only one space so he may have said you need a new metal CU for the new circuts.. But now, I'm only needing new cooker feed and ring change so enough room on 30mA side regardless,

But the clarity above is great

Thanks

 

[JohnW2]

I was also talking about changing 2x other circuits (cooker & lighting) which are on the 100A/100mA RCD side, and perhaps if these are changed they need to go to the 30mA RCD side?

That's a rather unusual arrangement - do I take it that you have a 'TT' earth (i.e. your own earth rod, rather than an earth supplied by the electricity company)?

And if so, there is only one space so he may have said you need a new metal CU for the new circuts.. But now, I'm only needing new cooker feed and ring change so enough room on 30mA side regardless,

Fair enough. If you add any new sockets they would need to be on circuits on the 30mA RCD side (unless you installed RCD sockets), and any circuits with any new wiring which was buried in walls etc. would also have to be on the 30mA side. ... and if you made any material changes to any circuits in a bathroom (e.g. lighting circuit) that would also have to be on the 30mA side.

However, if any of that additional work does happen, you could discuss with your electrician the possibility that the 100mA RCD could be changed for a 30mA one (which would very probably be possible), in which case all circuits would then have 30mA RCD protection.

Kind Regards, John

 

[ClockPie]

Great response John, and that is ringing true.

Yes, overhead cables and own earth rod, TT type.
For the planned changes, new sockets will be on 30mA side already.
Bathroom - no changes planned.
Cooker is full new wire, switch n outlet - so guess that needs to move from 100mA RCDside to 30mA side (fine - there is room)

This is an old house and I am not sure I want it all tested (!) which would happen if we changed the 100A/100mA RCD to 30mA (I guess). That was mentioned IIRC. It was all tested on install 10 years ago when current CU was installed by previous owners and I have the paperwork which.

So from the responses, I'm happy that I now know what is needed, so once I've finished my bits I can speak the electrician with a clearer head.

Thank

 

[JohnW2]

Great response John, and that is ringing true. Yes, overhead cables and own earth rod, TT type.

Thanks for confirming.

For the planned changes, new sockets will be on 30mA side already. Bathroom - no changes planned.

Fair enough - that's fine then.

Cooker is full new wire, switch n outlet - so guess that needs to move from 100mA RCDside to 30mA side (fine - there is room)

Fair enough. There is actually no requirement for a cooker circuit, per se, to have 30mA RCD protection, BUT if there is new buried wiring, that would require 30mA protection.

This is an old house and I am not sure I want it all tested (!) which would happen if we changed the 100A/100mA RCD to 30mA (I guess). That was mentioned IIRC. It was all tested on install 10 years ago when current CU was installed by previous owners and I have the paperwork which.

If it was only 10 years ago, I don't think you have any reason to be nervous about having things tested (or is it perhaps just cost which concerns you?), and I see no obvious reason why the 100mA RCD couldn't be changed to a 30mA one - which could avoid the need for a new (metal!) one in the future.

Kind Regards, John

 

[ClockPie]

New Cooker wiring will have a run of buried cable to/from the switch (from below worktop height vetical to switch) , and to the outlet plate. So looks like it will be the case to move to 30mA side.

And no reason to be nervous - (!!!!). Well, this house is old, gone through numerous generations of cabling and standards, and work done by a mixture of monkeys and experts and idiots like me in between. And if changing 100mA RCD to 30mA requires every circuit testing in full, including every fitting and socket, then there is probably a minefield ahead which I'd rather not know about yet lol. One job at a time (I do have test from 2007 and nothing done since then, but I am aware of things that tested OK that aren't perfect).

Old houses - love 'em!

 

[JohnW2]

New Cooker wiring will have a run of buried cable to/from the switch (from below worktop height vetical to switch) , and to the outlet plate. So looks like it will be the case to move to 30mA side.

Indeed so.

And no reason to be nervous - (!!!!). Well, this house is old, gone through numerous generations of cabling and standards, and work done by a mixture of monkeys and experts and idiots like me in between. And if changing 100mA RCD to 30mA requires every circuit testing in full, including every fitting and socket, then there is probably a minefield ahead which I'd rather not know about yet lol. One job at a time (I do have test from 2007 and nothing done since then, but I am aware of things that tested OK that aren't perfect). Old houses - love 'em!

My house is also old (some parts 125 years old, and the remainder 200+ years old) and, like yours, has gone through countless generations of alterations! However, if your electrics all tested OK in 2007 and nothing much has been changed since then, I'm not too sure what you're so nervous about!

In any event, you could always commission a testing (an 'EICR') and see what it reveals, and then decide whether to ask for the 100mA RCD to be changed to a 30mA one. Apart from the cost of the EICR, there would be nothing to loose - and, in any event, excatly the same testing would be undertaken if you went for a CU change.

Kind Regards, John