Spur or new circuit?

[D Skelton]

Hi guys,

My latest customer wants a couple of extra sockets installed. He has no RCD protection and no spare ways in his CU. He is not wanting a new CU so I have concluded that the way I would like to do this job is to spur of an existing 32A MCB into a 1 way RDC board with 6mm cable. Then instal a radial circuit for the sockets from a 20A MCB in the RDC board. Now I can't see a problem with this but can any of you?

Also, am I right in thinking that as my installation would technically be a spur, and not a new circuit, I would only need to complete MWC?

 

[Hawk81]

I have not done much in coleraine. Londonderry would be the closest I was and I used CEF there.

 

[Amp David]

Hi guys,

My latest customer wants a couple of extra sockets installed. He has no RCD protection and no spare ways in his CU. He is not wanting a new CU so I have concluded that the way I would like to do this job is to spur of an existing 32A MCB into a 1 way RDC board with 6mm cable. Then instal a radial circuit for the sockets from a 20A MCB in the RDC board. Now I can't see a problem with this but can any of you?

Also, am I right in thinking that as my installation would technically be a spur, and not a new circuit, I would only need to complete MWC?

What is the consumers unit thats fitted already?

 

[truckster]

aye 1 junction box for each leg. so what is a ring within a ring? you ever done much work down coleraine area, do you know where suppliers is down that direction or what their called. have we job on monday in porststewart??

A Ring in a ring would be where you make a connection between two points of a ring so you effectively have a figure eight instead a zero

 

[i=p/u]

aye im in londonderry at present and id use cef , but i dont know what im going to exactly need. i live ion portstewart now and never get any work,so when i decide to come back upto londonderry, i get phone call to work in portstewart,,,,, not turning it down tho cause the dude is wealthy. my kind of customer some day

 

[D Skelton]

Ok, so you've all replied with various suggestions on other ways I could do the job, which I appreciate, however, what I really wanted to know was whether or not I am conforming to the regs if I choose to complete the job the way I intend. Essentially, I am spurring off a ring, now the regs say do do this for more than one outlet, I need to use a FCU fused at no more than 13A, they make no mention of using an MCB instead of a fuse. Is this permitted? and if so, does it matter what the rating of it is, ie. more or less than 13A?

Edit: Spelling

Also, the cables will need RCD protection so I can't just rely on RCD socket outlets. The make of the CU is AUO, a make I have never heard of and seem unable to find by Googling it. The existing MCB's are a very odd shape which makes the fitting of an RCBO on the existing ring impossible. And remember there are no spare ways. It's a very odd question I know, but thats why I need some help.

 

[truckster]

Take the ring cables through a standalone RCD next to the board. If you are installing more than one socket you can either do as you say use an FCU or extend the ring by running two cables out and joining each to a leg of the existing.

The 13A fuse comes into it as you need to protect the new cable. If you extend the ring you can leave it on the presumably 32A breaker subject to Zs

 

[D Skelton]

So the overcurrent protection will come from the existing 32A MCB and the RCD protection from the new one I install. I see what you're saying, I need not even bother with a new MCB when I can just extend the ring through the RCD. Genius! So what about certs? Edit: As my work does not include the provision of a new circuit. MWC or EIC?

 

[truckster]

MWC as it's an alteration

 

[Amp David]

Thats why I asked what sort the CU is, this is the reason you can buy RCBOs.
Will the CU take an RCBO??? Why make a easy job hard???

And you wont be extending the ring just by putting it through the RCD

 

[D Skelton]

No RCBO I've ever seen will fit this odd construction of a CU, that's why an RCBO is out of the question. And truckster makes perfect sense when he talks about extending the ring through the RCD. I'll have 6mm cable from the 32A MCB feeding the RCD, and then extend the ring from that by taking one leg of the old ring and one leg of the new part of the circuit and joining them together, and then taking the other two remaining legs and stuffing them in the rcd

 

[Amp David]

Just cant see how you can 'extend' a ring circuit with an RCD, thats all.

Extend the ring where you want the new sockets, as truckster says, but you must have both legs in the RCD, not one in RCD and one in MCB.

How will the RCD ever do its job like that?

 

[D Skelton]

Both ends will be in the RCD. I'll be using 6mm cable to bridge the gap between the existing MCB and the new RCD and then essentially putting both ends of the ring into the RCD. I'll take one end of the existing ring and join it to one end of my extention within the CU, then I'll take the other end of my extention and put that in the RCD along with the remaining free end of the existing ring.

Sorry for the rather crude drawing but this is what I mean. Obviously in the drawing I haven't separated L,N & E, but it is just a rough sketch afterall haha.

 

[telectrix]

last post spot on as far as i can see. full EIC for the new circuit, and make sure earthing and bnonding are in place and up to current regs.

 

[D Skelton]

Is it a new circuit though? or just an addition? as I'm only extending an existing ring, not installing a new one. Sorry if my questions sound like I come across as a know it all, clearly I'm not, but I just want to understand it as best as possible. My work at the end of the day will only be altering an existing circuit, so would a MWC not suffice?

 

[PC Electrics]

So the overcurrent protection will come from the existing 32A MCB and the RCD protection from the new one I install. I see what you're saying, I need not even bother with a new MCB when I can just extend the ring through the RCD. Genius! So what about certs? Edit: As my work does not include the provision of a new circuit. MWC or EIC?

I do believe I made this suggestion way back in post #6 !!! Was no-one listening?

MWC.