Creating a 'non-RCD' way in a twin RCD board

[dhutch]

I currently have a wylex box with a main switch and a pair of RCDs, 10 5 ways each, but no non RCD ways.

Im planning get a feed added to my garage and it has been mentioned that I would be better coming out preRCD, even better out of a dedicated switch fuse, but if a 40amp mcb is used in t eh house CU, with 16amp mcb's in the garage CU, there should be suitable discrimination.

Anyway, I need to get a electrician in, but while im at work and thinking about it, how feasable is it to shuffle the lot along an make and non-RCD way?

Currenly my box looks like this (image from google) with two cables coming from each of the main switch load terminals, running round one each into the RCDs, with a neutral bar each.
http://www.ctm.co.uk/gallery/Home_Page/Changing a consumer unit.jpg (blokes hands covering half of it sadly)
http://www.ukelectricalsupplies.com/images/uploads/prod/vc712c1t.jpg (less good image, but the same cable routing)

This is an image of a box with a non-RCD way, which clearly has slightly differenct cable routing and one less N bar.
http://sparkydirect.s3.amazonaws.com/N/NHRS10SSLHI_2.jpg

As I only want one single non-rcd way, could you just link it out of the top of the first RCD

Like this

Untitled

• dhutch
• 31 Jan 2013
• 1

How allowable is that out of curiosity. I dont really see to much issue with it coming out post RCD as the risk to the house of that RCD tripping is fairly small and the inconvience of going to the house to reset it if ti should trip is also fairly small.

The garage CU will i suppose only have a single RCD so it you would already loose you lights if the power tripped.


Daniel

 

[JohnW2]

IAs I only want one single non-rcd way, could you just link it out of the top of the first RCD ... How allowable is that out of curiosity.

I see nothing particularly wrong with that, electrically, but it may well then not qualify as a 'type-tested' CU, if that concerns you. I guess that a lot will depend upon your electrician's feeling about it.

Kind Regards, John

 

[dhutch]

Fair enough. Largely agrees with my own thoughts. Obviously its acceptable to have more than one cable per terminal and the live is only really whats done elsewhere, although the neutral is less as you would expect it obviously.

Alternatively, would anywhere stock the missing neutral bar to add to the box?

Obviously it would also be slightly nicer to link the live over with a bit of bus bar, but short of loping a pair of ways (rather than just one) off the existing busbar that too would depend on its avialabilty.

Really should think about this less, and do more of my work, but heyho!


Daniel

 

[JohnW2]

Fair enough. Largely agrees with my own thoughts. Obviously its acceptable to have more than one cable per terminal and the live is only really whats done elsewhere, although the neutral is less as you would expect it obviously. Alternatively, would anywhere stock the missing neutral bar to add to the box?

I really don't personally see the point in even thinking about a further neutral bar for just one MCB. After all, that neutral bar would have to be fed by a cable from the top of an RCD (per your proposal)(or from the load side of the main switch) - so why not just connect the one non-RCD circuit to that place,per your proposal?

Obviously it would also be slightly nicer to link the live over with a bit of bus bar, but short of loping a pair of ways (rather than just one) off the existing busbar that too would depend on its avialabilty.

You say 'nicer', but what you probably really mean is "more like the way they do it in a custom-built 'high integrity' CU". In electrical terms, I don't think a bus bar offers any particular advantage over an (adequate) bit of cable.

Kind Regards, John

 

[dhutch]

Well yes indeed, all of that is true.

 

[EFLImpudence]

I don't see anything (i.e. there is nothing) wrong with what you want to do.

Personally I would use a piece of busbar if the new mcb is next to the main switch (just prefer it).
However, it could be placed on the left in which case a piece of wire would have to be used.
I would use 10mm² to ensure a good connection.

I think you may find some detractors later on as this method seems frowned upon for some reason.

Just as an aside - with high integrity boards (three N bars) I do not like the practice of looping the N conductors at the first RCD (as in your third link) as all the current flows through the first.
This is probably alright in most installations but may not be.

 

[AndyPRK]

whats the model number of your CU ?

 

[ban-all-sheds]

Im planning get a feed added to my garage and it has been mentioned that I would be better coming out preRCD, even better out of a dedicated switch fuse, but if a 40amp mcb is used in t eh house CU, with 16amp mcb's in the garage CU, there should be suitable discrimination.

By the time you've paid him to disconnect every device from the bus-bar, remove it, saw the end off, move devices along the DIN rail, move the affected N cables to their new numbers on the neutral bar, replace the bus-bar, install an MCB in the gap, provide a length of suitably terminated tri-rated cable to connect it to the RCD and then do whatever testing he feels is appropriate after that jiggery-pokery, he could have put a switchfuse in.

http://www.ctm.co.uk/consumer_unit.htm

I wonder how he isolated the supply before removing the tails from the old fusebox?

I dont really see to much issue with it coming out post RCD as the risk to the house of that RCD tripping is fairly small and the inconvience of going to the house to reset it if ti should trip is also fairly small.

And if it won't reset because of a fault on the cable to the garage?

The garage CU will i suppose only have a single RCD so it you would already loose you lights if the power tripped.

Well then don't have a garage CU like that.

 

[PrenticeBoyofDerry]

deleted
invalid information

 

[AndyPRK]

Yes it will.

It's the same connections just at a point where there is space in the terminals.

 

[PrenticeBoyofDerry]

Yes it will.

It's the same connections just at a point where there is space in the terminals.

Indeed missed that, need coffee to wake up!

 

[PrenticeBoyofDerry]

The distribution cable from the consumer unit to the garage, when non RCD will need to be then compliant of that of a non RCD protected cable.
Rather than giggling the CU around, which can be time consuming, it would be worth considering and connection external to the consumer unit via fused switch or small RCD unit.

 

[AndyPRK]

A lot depends how tidy you want your area by your cu.

Neither are great options.

Putting an rcbo and a small busbar into the cu is probably the tidy and sensible option

 

[dhutch]

By the time you've paid him to disconnect every device from the bus-bar, remove it, saw the end off, move devices along the DIN rail, move the affected N cables to their new numbers on the neutral bar, replace the bus-bar, install an MCB in the gap, provide a length of suitably terminated tri-rated cable to connect it to the RCD and then do whatever testing he feels is appropriate after that jiggery-pokery, he could have put a switchfuse in.

Yes, and to be honest my plan is just to have him to use one of the RCD protects MCBs.

If it fails because of a cable fault, it would take out half the board, ie, upstairs lights and the conservatory, the one ring main and the only other lighting circuit being on the other rcd. Worst case, you remove the garage from the box and call and electrician!

You could have a dual rcd consumer unit in the garage, or a stack of rcbo's, but where do you draw the line. While it doesnt excuse bad design, my parents have a single RCD as the main switch, which runs the whole house and the garage, and in the 25 years thats been there, most of which I have been living there as ive grown up, theres not been a nuisance trip. Although the supply into the box goes down about once a year.

I have no idea how the person who changed the consumer unit did so, but it understand its not imposable to do it 'live' and that its not uncommon for installers to wrongly remove the cutout. Either way, it was prior to my buying the house. Said board is as per the one in the first photo, two rcd plastic wylex job.

PrenticeBoy makes a valid point about the cable used to the garage then having to comply with the requirments of being non-RCD protected.

As said, im am quite genuinly just thinking aloud to while away the hours.

Daniel

 

[ban-all-sheds]

my parents have a single RCD as the main switch, which runs the whole house and the garage,

30mA?

I have no idea how the person who changed the consumer unit did so, but it understand its not imposable to do it 'live'

No, just dangerous and illegal.

and that its not uncommon for installers to wrongly remove the cutout.

Photos show it still in place, and the seals look intact.