4mm Radial and re-wire Dillema

[adsmith]

Hi new to the forum and thanks for any help,

Parents have bought a typical 1930s 3 bed semi which had a rewire in the early 70s. I’m guessing the consumer unit has been updated since then because all circuits are protected with RCBO’s ( 2 x 6amp lighting circuits 1.5mm cable, 2 x 16amp radial socket circuits 2.5mm cable, 4 x 32 amp radial socket circuits 4mm cable)

I’m considering doing a re wire to update the cables and sockets also need adding to circuits etc, however I’ve hit a bit of a dilemma. I was considering upgrading the 16amp RCBOs to 20amp using 2.5mm cable, is that ok?

Also because I really seem to struggle a bit with 4mm cable ( room in back boxes, 2 cables in oval conduit issue, fitting 2 cores easily in sockets terminals etc) I was thinking of downgrading the 32 amp breakers to 20 amp and using 2.5mm cable radial circuit. However I’m unsure if 20 amp is enough. One circuit would be upstairs sockets (approx 11 double sockets) and the other circuit would be downstairs living rooms and hallway (approx 11 double sockets also) these sockets will only have the usual appliance plugged into them with the occasional use of an iron/hairdryer/straiteners being the highest power. Would 20amp be enough or am I best just dealing with the 4mm cable and 32amp RCBOs to prevent any worry of overload.

Also if I was to change the 4 RCBO’s that would cost in the region of £120-160. Would I just be best buying a split board RCD consumer unit and just using ring circuits for sockets or would you recommend paying the extra for the RCBO’s and use radial circuits?

Hope this all makes sense and sorry for it being long winded. Appreciate any feedback and help!

 

[Gavin John Hyde]

Dont know why but my DIY radar is pinging..
Are you competent enough to be doing this work?
Its notifiable to building control. you either A) need to be part of a scheme such as Niceic. Stroma etc .. B) hire an electrician or C) do it yourself and pay the fees to building control to inspect it afterwards. Usually a couple hundred quid.
If you do it yourself then you need to test it.. Are you able to do this? A multi function tester is needed.
Do you have access to the required regulations?
You will also need to isolate supply if changing the CU.. Do you have a isolator or are you going to get the dno out to turn off supply?
Get it wrong and you could kill yourself or your parents at worse or be left with a big bill when you need an electrician to lut it right.
I think they are points we need to consider before giving you tips on a full rewire.

 

[Richard Burns]

Make sure you as a trainee? are competent and capable of doing the work to a safe and regulatory compliant standard.
Ensure that you are aware of at least the basics required such as requirements for cable size and circuit breaker coordination.
A full rewire may be a bit of overkill, but if renovation is going on then it is probably a good idea to update numbers of socket outlets, so a partial rewire may be good.
So long as the radial circuits are not heavily covered with insulation then 16A to 20A radials should be fine.
Similarly if the circuits you want to convert to 20A from 32A are just general room sockets and not kitchens or work rooms then 20A should work fine. Alternatively you could convert them to rings and extend the existing circuit in 2.5mm² cable, but some would say using two different size cables on one circuit is not a good idea.
Do not downgrade from RCBOs to dual RCD boards, you have a good system there.

 

[adsmith]

Hi thanks for the rapid reply.

I’d like to deem myself competent enough to carry out the works. Domestic electrics is not field however I am a qualified industrial maintenance electrican in a power station therefore I do understand how to safely work on circuits etc and domestic circuits. However I do not hold any formal domestic qualification. I was under the impression that I was ok to carry out the works and as the house is not a new build it does not require to be notified to building control and comply fully to current regs. Am I not right in thinking this? I do however have an electrician I know who can carry out the inspection and testing of the job once complete. Is that ok?

Replying to your comment Richard I thought myself that a full re wire seems unnecessary and just to add sockets where needed and just carry out a partial re wire however I thought whilst the house is getting a full renovation am I best to change the lot and start from scratch or would you still think that is a waste of time.

Thanks again for the quick reply’s!

 

[Chris86]

I have found myself in the same situation as you, I am an industrial maintenance engineer in the automotive sector. My brother has bought a new house which needs a full rewire and I feel competent enough to take this on.

You will definately need to notify this work to your local council building control department. Regardless of if a house is new build or not, certain works come under the scope of part p of the building regs and must be notified. Look up part p, far to much to write on here.

I am based in Birmingham and notifying was easier than I thought. I have now been given a reference number which I can use to contact a local electrial contractor who will inspect at first fix and then again on completion when a certificate will be issued.

One thing I will say is get yourself a copy of bs7671 or at least the on site guide and read up on the subject like crazy. There are also some good books out there on inspection and testing which are invaluable. Christopher Kitcher's practical guide to inspection and testing has helped me no end. I have learnt so much in the last few months and got a lot of satifaction from the work i have done (so far anyway)

ATB

Chris

 

[mhar]

I would reference table 4D2A re the ccc of the 4mm radials. I tend to use a 25A OCPD but there are only a couple of manufacturers who make B curve 25A rcbos (eaton, live)

 

[Pete999]

L

Hi new to the forum and thanks for any help,

Parents have bought a typical 1930s 3 bed semi which had a rewire in the early 70s. I’m guessing the consumer unit has been updated since then because all circuits are protected with RCBO’s ( 2 x 6amp lighting circuits 1.5mm cable, 2 x 16amp radial socket circuits 2.5mm cable, 4 x 32 amp radial socket circuits 4mm cable)

I’m considering doing a re wire to update the cables and sockets also need adding to circuits etc, however I’ve hit a bit of a dilemma. I was considering upgrading the 16amp RCBOs to 20amp using 2.5mm cable, is that ok?

Also because I really seem to struggle a bit with 4mm cable ( room in back boxes, 2 cables in oval conduit issue, fitting 2 cores easily in sockets terminals etc) I was thinking of downgrading the 32 amp breakers to 20 amp and using 2.5mm cable radial circuit. However I’m unsure if 20 amp is enough. One circuit would be upstairs sockets (approx 11 double sockets) and the other circuit would be downstairs living rooms and hallway (approx 11 double sockets also) these sockets will only have the usual appliance plugged into them with the occasional use of an iron/hairdryer/straiteners being the highest power. Would 20amp be enough or am I best just dealing with the 4mm cable and 32amp RCBOs to prevent any worry of overload.

Also if I was to change the 4 RCBO’s that would cost in the region of £120-160. Would I just be best buying a split board RCD consumer unit and just using ring circuits for sockets or would you recommend paying the extra for the RCBO’s and use radial circuits?

Hope this all makes sense and sorry for it being long winded. Appreciate any feedback and help!

ook at Appendix 15 in BS7671 that will help you design your circuits.

 

[Pete E]

Hi new to the forum and thanks for any help,

Parents have bought a typical 1930s 3 bed semi which had a rewire in the early 70s. I’m guessing the consumer unit has been updated since then because all circuits are protected with RCBO’s ( 2 x 6amp lighting circuits 1.5mm cable, 2 x 16amp radial socket circuits 2.5mm cable, 4 x 32 amp radial socket circuits 4mm cable)

I’m considering doing a re wire to update the cables and sockets also need adding to circuits etc, however I’ve hit a bit of a dilemma. I was considering upgrading the 16amp RCBOs to 20amp using 2.5mm cable, is that ok?

Also because I really seem to struggle a bit with 4mm cable ( room in back boxes, 2 cables in oval conduit issue, fitting 2 cores easily in sockets terminals etc) I was thinking of downgrading the 32 amp breakers to 20 amp and using 2.5mm cable radial circuit. However I’m unsure if 20 amp is enough. One circuit would be upstairs sockets (approx 11 double sockets) and the other circuit would be downstairs living rooms and hallway (approx 11 double sockets also) these sockets will only have the usual appliance plugged into them with the occasional use of an iron/hairdryer/straiteners being the highest power. Would 20amp be enough or am I best just dealing with the 4mm cable and 32amp RCBOs to prevent any worry of overload.

Also if I was to change the 4 RCBO’s that would cost in the region of £120-160. Would I just be best buying a split board RCD consumer unit and just using ring circuits for sockets or would you recommend paying the extra for the RCBO’s and use radial circuits?

Hope this all makes sense and sorry for it being long winded. Appreciate any feedback and help!

Whats the colour code of the wires in use in the house?

 

[Octopus]

I would test the house properly.

The enemies of 1970's wiring are DIYers and rodents - unless there is green go coming out of the cable.

 

[The Ghost]

I think in principle you are thinking along the right lines subject to the caveats as stated above looking at the tables to ensure the CCC of the circuits proposed. What about bonding and earthing have you considered that and the need to possibly upgrade if it is '70s installation? You are on the edge of what the cable will carry taking into account the C factors Ci Ca etc. RCBOs' are becoming the ideal way of installing as they take out the worry of too many ccts going out together with dual RCD. But in any event if you are stuck you can always ask here. It is ironic that in truth you are the real electrician and you are having to justify yourself. If you take on the work it is a legal requirement to notify BC at least 48 hours prior to undertaking work. There can be complications when selling the house and for insurance purposes when not doing things in exactly the right way/order. Any outside power?

 

[davesparks]

Why do you want to update the cables? Is there something wrong with the existing installation?
Rewireing a house when all it really needs is existing circuits extended is just a waste of the natural resources we are running short of.

 

[Strima]

My house was built in the 70's and there's nothing wrong with the cables.

Testing is the only way to be certain.

 

[mhar]

@DavidSpark what is the dumb bit of post no 6?

 

[Midwest]

Rewire, OP can do whatever he wants, its his (parents) money.
If I moved into a 70's house, I'd be tempted to rewire, regardless of what some meter told me.

 

[Midwest]

As regards notification to local building control. Speak to them, they might accept your qualifications as an electrician.