Adding non Rcd protected circuit to split consumer unit

[edexlab]

I've a possible job coming up where I'd need to add a circuit to a domestic property which has several spare ways both protected by 30mA rcd's the circuit I will be installing can't go on a 30mA rcd and will be surface ,usually in conduit/trunking and so I'll get a split load kit for it and add it next to the main switch and change the labelling etc
this is a problem I've had before in which case I've installed a one way consumer unit but occasionally there is no space for this

So the question is if you have this scenario on a consumer unit where you can't source the correct kit ,is it acceptable to take a flexible tail direct from the outgoing main switch side to the Mcb and lose one of the spare ways from the Rcd side and fit a neutral block to the back of the consumer unit and place the new circuit Mcb in the middle of the CU ie between the Rcd protected circuits ( to avoid reconfiguring the whole board ) assuming that its clearly labelled as a non Rcd circuit
It seems a bit of a bodge and was suggested by an another Electrician quoting for the same job ,but could be a solution and I'm interested to hear any views on this.

 

[topquark]

You could convert one of the RCD's (with the least number of MCB's) to RCBO's and add the MCB to that neutral. May be a bit pricey depending on the number of MCB's to convert.

You may be able to move some of the MCB's across to the other RCD to reduce the cost.

 

[GLENNSPARK]

You could bury the cable if at a depth greater than 50mm...........

 

[GLENNSPARK]

or run it in an earthed metallic conduit and bury it that way......

 

[GLENNSPARK]

would not an ip rated box be suitable and site the MCB in that...........

 

[edexlab]

This is not the issue the circuit will be run surface ! (assuming TN system TT it would go on a 100mA Rcd) therefore no Rcd protection required
As for the IP rated box if i can use one of these then I could probably fit a one way Cu in the same space in the op the point was that space was limited

 

[GLENNSPARK]

This is not the issue the circuit will be run surface ! (assuming TN system TT it would go on a 100mA Rcd) therefore no Rcd protection required

No probs mate...

 

[GLENNSPARK]

This is not the issue the circuit will be run surface ! (assuming TN system TT it would go on a 100mA Rcd) therefore no Rcd protection required
As for the IP rated box if i can use one of these then I could probably fit a one way Cu in the same space in the op the point was that space was limited

Yes well we have this problem loads ...tryin to get an RCD board to cover our work next to BS3036s and stuff.....you could put another section of neutral bar as TQ sugests so in a way its like a high integrity and take a feed from the incomer....

 

[Deleted member 26818]

One of the problems with altering a CU, in an unorthodox way, is that it would then not conform to the applicable British Standard.
As such, it would be doubtfull that the modification would comply with BS7671.

 

[Octopus]

why is the new circuit not going on a rcd?

 

[topquark]

Dist circuit I suspect. For the record, I never said anything about altering the CU or adding a neutral bar

 

[SPARTYKUS]

I've a possible job coming up where I'd need to add a circuit to a domestic property which has several spare ways both protected by 30mA rcd's the circuit I will be installing can't go on a 30mA rcd and will be surface ,usually in conduit/trunking and so I'll get a split load kit for it and add it next to the main switch and change the labelling etc
this is a problem I've had before in which case I've installed a one way consumer unit but occasionally there is no space for this

So the question is if you have this scenario on a consumer unit where you can't source the correct kit ,is it acceptable to take a flexible tail direct from the outgoing main switch side to the Mcb and lose one of the spare ways from the Rcd side and fit a neutral block to the back of the consumer unit and place the new circuit Mcb in the middle of the CU ie between the Rcd protected circuits ( to avoid reconfiguring the whole board ) assuming that its clearly labelled as a non Rcd circuit
It seems a bit of a bodge and was suggested by an another Electrician quoting for the same job ,but could be a solution and I'm interested to hear any views on this.

One thing to watch out for with the highlighted bit is the cable you take from the main switch, don't be tempted to stuff a bit of 2.5mm2 in there, or most other sizes in fact - chances are they will not have the CCC to match the only protective device back down the line - the main fuse. I'm assuming there's nothing else inbetween.

 

[edexlab]

Absolutely agree with that it would only be done with same size tails as existing,and only if there was capacity in the terminal for another ,However the non conforming to a British standard is a problem when its an old unit,ie getting the ok from the manufacturer

Its actually a Pv job cables either surface conduit or Swa so no need for RCD (tn system)

 

[mark_]

One thing to watch out for with the highlighted bit is the cable you take from the main switch, don't be tempted to stuff a bit of 2.5mm2 in there, or most other sizes in fact - chances are they will not have the CCC to match the only protective device back down the line - the main fuse. I'm assuming there's nothing else inbetween.

Interesting that you say that as I would always do the same BUT- Wylex make specific PV board now with a mcb, double pole isolator and a generation meter all within a 17th edition board. The problem being that "they" at manufacturing stage have linked the primary main switch to the PV mcb in what looks like no bigger than 4mm. Strange!