Extending a radial circuit

[richierich81]

Hi All,

I am looking for some advice in extending the radial circuit in a room in my house. I've never extended a radial circuit before so I'd just like to check a few things.

I have done a diagram of the existing and proposed extension.
View media item 67651
I'd like to add 3 double sockets into a bedroom.
1 of the double sockets will power a desktop computer and monitor.
2 of the double sockets will be for either side of a bed, so will be used for a lamp etc.

The wiring in my 1965 house is a radial circuit which supplies both the downstairs and the upstairs. (There are 3 circuits in total at the Consumer unit, 1 for the lighting, 1 for the sockets and 1 for the cooker).

Firstly I'm going to tidy up the wiring where someone at some point has moved the socket. I then intend to run a new cable to the first double socket, onto the second and third and then rejoin the radial circuit using a junction box, which will be accessible under a trap in the wardrobe.

I'll obviously be removing the separate 3 individually wired spur (is that common?!) I also found a nice unsheathed earth wire in the socket, I guess different standards have applied down the years!

I just want to double check with regards the radial circuit does all the above and the diagram look ok? Also will it be 4mm I need to use for the cabling, or will 2.5mm be ok? Will a 30Amp JB be sufficient?

Thank you for your help.

Richard

 

[richierich81]

Oh and I will be removing the existing wiring between the single socket and the new junction box.

I meant to ask is my diagram the best way of extending? Or would it be better running the radial as a branch or even a star radial?

Thanks again

 

[PrenticeBoyofDerry]

Are you sure it is a radial circuit and not ring final?

 

[ericmark]

First question is what size fuse/MCB/RCBO is feeding the radial?

If it is a 30/32 amp then 4 mm² is required and to be frank not easy to get three x 4 mm² into terminals in a socket. I would also be checking all wiring to ensure no one has messed up in the past and used 2.5mm² in error. Also remember you can take 2.5mm² spur from a radial in the same was as from a ring so cable sizes are really important to check.

If using a 16 - 20 amp then 2.5mm² but now length becomes a real problem. The volt drop on radials is greater than with rings so should be measured.

With all new sockets RCD protection is now required and if not at the consumer unit already then either special cable feeding new sockets or surface cable is required it will also mean the earth loop impedance as well as volt drop becomes important.

As electricians we carry three meters in the main.
Combined loop and prospective short circuit current meter.
Combined low ohm (200ma) and insulation (500v) meter.
RCD meter.

These are expensive to even hire but there is a plug in loop tester which costs around £50 although not as good as out meters it will show if the socket is out of spec. Problem is you can only test once fitted which is a bit late to find out it's out of spec.

Some times the old PIR or new EICR will give the loop readings of sockets and you can look and see what spare capacity you have.

The earth loop allowance varies with size and type of MCB/fuse used so for example where a B20 MCB is used changing to a B16 will allow some extra length however clearly more likely to be over loaded and trip.

For the DIY man often the compromise is using RCD FCU to power extra sockets as unlikely to exceed the values when using them.

So first question has to be what protects the radial at the moment.
Second why do you think it's a radial.

 

[knowall]

If you are adding sockets and lifting floors ect, I would convert the radial into a ring and be done with it. That way you remove joint boxes and can use 2.5mm and you have upgraded your wiring for the same labour .

Regards,

NA

 

[EFLImpudence]

I would be grateful if it was a radial.

 

[ban-all-sheds]

for radials.

 

[knowall]

Ring a Ring a Roses

 

[ban-all-sheds]

Feel free to make sensible posts.

 

[richierich81]

View media item 67684
That's the consumer unit. Yes it needs replacing!

I'm starting to think I might leave this to a pro, I'm a confident diyer with a guiding hand but electrics is something I don't want to get wrong . after the questions on here I'm not sure if it's a ring or radial, there seem to be spurs and dead ends all over the house.
Guess this will have to wait a few months now (money as always is the problem).
Thank you for all your replies.

 

[ban-all-sheds]

Also, you (essentially) may not add any more sockets or any concealed cabling, as there's no RCD.

 

[knowall]

View media item 67684
That's the consumer unit. Yes it needs replacing!

I'm starting to think I might leave this to a pro, I'm a confident diyer with a guiding hand but electrics is something I don't want to get wrong . after the questions on here I'm not sure if it's a ring or radial, there seem to be spurs and dead ends all over the house.
Guess this will have to wait a few months now (money as always is the problem).
If the circuit you are referring to is the one without the fuse it's a radial ( it has one cable ). You also appear to have a ring.

regards,

NA

 

[Taylortwocities]

Dear knowallnot

Please research the previous posts before typing!
The OP said

The wiring in my 1965 house is a radial circuit which supplies both the downstairs and the upstairs. (There are 3 circuits in total at the Consumer unit, 1 for the lighting, 1 for the sockets and 1 for the cooker).

So that's three circuits , not four. Do you think he removed a fuse just to take the picture? I'll bet that is the feed to a (now) disused immersion heater. The circuit to the right of it is the ring final for the sockets.

Now, that circuiut without a fuse IS a radial and COULD power the additional sockets if the end could be discovered. But, as stated above, an RCD will be needed to protect new wiring and sockets.

PS And please learn how to use the quote button. Previewing your posts might help?

 

[knowall]

Maybe the OP will supply the answer

NA

 

[richierich81]

You are totally right the fuse that was removed was for an immersion heater. I think the wires terminate in the airing cupboard/room just off our main bedroom. This circuit also supplied the hall wall light that stopped working once the plumber had disconnected the fuse. Seems to be strange wires everywhere, I can only think that half the sockets are spurs off the ring but without taking up floorboards I'll guess I'll never know!

The circuits from left to right are...

Lighting
immersion heater (fuse removed)
Downstairs and upstairs sockets
cooker (which also seems to feed two separate sockets in the kitchen think for the kettle and another)

I wonder which circuit supplies the garage?!

I've just ok'd it with the wife for a new csu and for the sparky to finish off the sockets that I've chopped out of the wall ready.

Thanks again for your replies

Richard