Consumer Unit Layout (Final)

[Tricky Dicky]

I spoke to the BCO today and the outcome of the conversation is that he insists I include a Surge Protection Device (SPD) in the CU and looking into the calculation required to avoid inclusion and the faff collecting all the info it is probably easier and gets the job moving just to fork out the £44 and be done.

So this is hopefully the final layout of all the protection devices in the CU:

AS the SPD is not connected to the busbar I have included it at the end of the first section containing the Garage MCB and the two RCBO devices. The issue is that it needs feeding from a MCB 16 - 32A. The manufacturers recommend a 32A ring main. So does it matter which of the two devices as indicated on the diagram is used?

Finally, I have added a separate isolator switch and planned initially to feed the tails from it into the bottom of the CU but would now like to fit a socket below the CU and with not much room to play with it would be convenient to feed them through the top? There are suitable knockouts in the top and the instructions say top feeding is possible but with the convention being to bottom feed and CU is situated below a kitchen worktop would anyone raise any objections?

I know I should have asked the BCO but had other things on my mind and I do not want to get into another conversation that will cost me money!

Richard

[Fredxx]

While technically you have 2 lighting circuits on separate RCDs, I would be tempted to split the lighting load more evenly between the 2, not just the kitchen on one RCD.

[Tricky Dicky]

It is a bungalow with only 6 rooms including the hallway, I cannot see any advantage of splitting the lighting any further. The MCB for the kitchen is for the centre light plus some spots around the perimeter to illuminate worktops. The extractor provides a secondary light source on its own.

Richard

[John Rumm]

Hmm, another box ticking exercise for the BCOs...

Yes, you want it to be in circuit all the time. If you feed it from a circuit on RCD1, then should that RCD trip, you would lose surge protection to the circuits on RCD2 and also the non RCD protected section of the CU.

So feeding from a MCB on the non RCD section of the board would be preferable IMHO. I would probably swap the alarm and FF MCB positions and then feed it from the Alarm one, since you probably don't want to add any extra trip risk to the FF circuit.

No, although IP requirements are tighter for cables entering the top. The easiest way is to use a tails gland kit.

Yup, sometimes less conversation is better!

[Tricky Dicky]

Thanks John regards the SPD. ON the tails issue I am using a gland and I would have space on the right hand side of the CU to enter from the underneath my only issue is that it is a MK Sentry CU which unfortunately unlike others is handed in respect that the main switch has to go to the left hand side. This means that I would have to route the tails across the box. The job might be made easier if I am allowed to strip the outer insulation just past the gland to make bending the 25mm2 cables slightly easier, however I do not know if that is permissible as I have only ever seen tails fully sheathed almost to the main switch?

Richard

[spuorgelgoog]

The outer sheating is for physical protection only and can be removed inside an enclosure. Remember though that the meter tails are live even when the CU main switch is off, and a slip of a pointy screwdriver could be nasty.

A lot less of an issue, I think, if you have an isolator external to the CU. In that case there need be no live parts in the CU when working in it.

You can also get 19-strand flexible meter tails type 6183Y to BS 6004 with BASEC approval

They appear to not need ferrules in CU cage type terminals, but might in meter screw terminals.

Owain

[John Rumm]

Assuming its not TT, then you can strip the outer of the tails inside the CU.

Note also you can get flexi tails, which are made with a a larger number of finer strands of wire, and are designed to be far easier to work with in situation where you need to bend them about a bit.

IIRC Toolstation have some...

[ARW]

It "tells" you here how to calculate the risk

Says the electrician who has never actually fitted a SPD.

[ARW]

It's got to be Mr B again:-(

I suppose a conversation mentioning reg 443.4 would be pointless?

[Tricky Dicky]

I have seen that Adam but it is getting the figures to put in the calculation is the issue I know where the substation is and could possibly pace out the distance and like the presenter would have to make quite a few assumptions for L as for environmental factors I simply do not know behind us is the city across the road running past our estate is green fields into the Pennines with just a scattering of villages in-between. The only figure I have with any confidence is lightning strike density which according to the presenters 18th edition is 0.5 per km2. I think someone at the IET came up with that calculation knowing full well that by the time anyone has got all the relevent figures, sat down and done the calculation with time equalling money has probably said "f*ck it, I'll put one in and get doing something that will earn me money". In my case time is not the issue and I was hoping to invoke the get out clause except the BCO was not having it!

Back to practicalities, I will now bring the tails in on the right hand bottom corner and feed them as neatly as possible over to the main switch. I already have the tails so will see how I manage with them first but if I struggle then I will go for the more flexible solution it's only money but this job is for keeps so might as well do it right in the first place.

This is what needs doing

This is the corner of our kitchen and was a small pantry housing the CU and meters. Domestic Management did not like the pantry and wanted a worktop going literally wall to wall on that side of the kitchen. So the CU needs to be moved lower in fact over whatever was there when the house was first built. Got the distributer out who moved the meter to it's somewhat wonky position it is in now. I said to him what was going to happen and asked him to leave me long enough tails to connect to the new CU so he provided the two grey terminal blocks fastened to the small board which was bigger and fastened above until I wrenched it off the wall to make way. Other things that were removed was a pipe passing through to the outside tap and a plethora of junction boxes dangling off wires poking out of the wall which the guy who installed the CU you can see used to connect old wiring to new and the CU. The dangling cables you can see are my new lighting circuits and a longer replacement cable for the shower so all will reach the new CU position. All the cables coming up through the floor will be run in trunking installed where the pantry wall was take a right angle at the new CU before entering through the back. The socket I want to include will be fitted above the meter under the CU against the trunking, this is for the washing machine which will go back in the space beside everything. It is also required for the wall wart of my low voltage landing lights down the side of the drive. To the right-hand side of where the CU will go is the isolator, and for those eagle eyes among us who have spotted it is upside down I can assure you it is already corrected. So the plan is to install the trunking chip out some plaster for the cables capping off those coming from above. Pull the suppliers fuse I have no intention of working live! Whip the old CU off after identifying all the cables. Replace the CU and wire in all the circuits except the kitchen ring main, extractor circuit and the oven and hob circuits which the BCO wants to see at their first fix. I have to replace the old red and black cables to the oven and hob because I am moving the business end of them he wants new cables! So sometime during this week between medical appointments it might get done!

[ARW]

On 16/11/2019 17:27, Tricky Dicky wrote:

Feeding tails all the way through a CU is something I try to avoid at all costs.

Could the socket really not be moved slightly to the right and the tails fed in at the bottom left?

I was going to suggest trunking across the top of the CU and bringing the cables in that way, but I do not think you have room. That is a tight install.

Just one tip. Before you mount the CU flush up to anything, eg socket, trunking or whatever, check that the lid will fit after you have finished......

It has a lip on it.

[Tricky Dicky]

Thanks Adam, the socket is the problem I cannot put it behind the washing machine because the wall wart that powers the driveway lights protrudes to far to allow the machine to go fully back.

I did consider putting it above the CU but the knockout in the case is smack on the meter below and although I have on order a fairly low profile gland I dare not risk lowering the CU.

In its planned position I estimate approx. 80mm gap to the underside of the worktop so no problem opening the front flap and that allows for a batten to be fixed to support the worktop as although the whole thing will be fronted with a base unit it will have to be foreshortened because of the gas meter etc.

There is a possibility of moving the socket to the right but from the position of the isolator the tails will end up across the socket unless I do some fancy bending round it.

Where you see the vertical slot in the plaster I have fitted a 50 × 50 trunking and all the cables coming from under the floor will be housed in it on that side of the CU is a single 32mm knockout which I do not think will cope with the number of cables which are 1 × 10mm2, 2 × 6mm2 and 4 × 2.5mm2 all T&E. The plan is to chip out a cavity behind the CU extending up to the trunking and feed all those cables plus the ones coming down the wall into the back of the CU. There are several 40mm knockouts and I am hoping 2/3 will suffice to feed all the cables into the CU. To preserve the integrity of the CU the plan is to flood the cavity and openings with either intumescent foam or sealant, I think sealant might be more controllable.

Before I fit the CU to the wall and remove any knockouts I will have a play on the bench with it and see how much of a mare the various options are and will report back before I do anything permanent on the CU.

Thanks to all for all the advice up to now!

Richard

[ARW]

Forget using the knockouts. Jigsaw or angle grind them into one big slot[1], superglue on grommet strip and your job will be much easier.

Why chisel into the wall? Mount the CU away from the wall and run the trunking behind the CU with the slot over it so that it sits on the trunking, This will allow you to dress the cables in the correct position into the CU directly above each MCB/RCBO. Depending on your final layout this can also allow you to back entry the tails (no pun intended) directly above the main switch and keep the socket where you wanted it.

will fill the gaps where the cables enter the CU.

A simple CU swap would normally take me an hour. I would want 4 hours to swap and move yours. But all the work is in the preparation. The actual wiring takes very little and it is much easier if every cable is where you want it.

[1]You do not want a load of cables entering a CU just above your RCBOs so maybe slot out the RHS rear knockouts and use the LHS knockout for the tails. Either gland or silicone the entry to these.

All the best with it.

I am only passing on some of the things I have done at work in the past to make things easier for myself and still meet the regs.

I am sure whatever you come up with will be fine.

[Chris Green]

... and then how do you manage the flame retardant seals needed by the latest regulations?

[ARW]

As I said, and will say again, it's all in the preparation.

I swapped two dual RCDs into one all RCBO DB a couple of weeks ago.

That's about 3 hours work. The DB was up and running an hour after the second photo.

[ARW]

[Tricky Dicky]

Back again! I had a little rethink. When we bought the kitchen we were never too accurate on the total distance the pantry made it very difficult to measure up so we factored generous finger spaces for the washing machine and dishwasher and accepted we would have quite generous trimmers at each end of the cupboard run. However paring everything down to the minimum we can now squeeze in a wine rack this would now allow me to fit the socket behind the wine rack which if it does go the full depth I can easily reduce to allow hand space. So the socket can go the other side of the trunking.

As for standing the CU off the wall I thought that had gone by the way with all the focus on maintaining the flame proof integrity of the CU. that makes things an awful lot easier. As the trunking already fitted is below plaster level I will not take it behind the CU but will stand off the CU enough to ease the cables behind. It would be difficult to align trunking with the knock outs as having to come in from the side two of the fixing screws are below the level of the knockouts. I presume that the stand offs need to be fireproof and not like the two wooden battens the present CU is fastened too. I take it from what you said it would still be OK to flood the area of the rear entries with intumescent sealant to maintain integrity.

So it is looking like I am going back to Plan A bring the tails up through the LH knockout, I will leave generous space to fit the socket to the RH side if I have to and just live with the tails being bent round to make space. In the long term it may not be so much of an issue as we will be getting a smart meter fitted and from the ones I've seen they are quite compact and if needs be can be fixed lower down than the present meter is on the DNOs board.

One helpful factor is because I am not fitting the meter tails direct to the CU but to the isolator. I can actually makeup the tails between CU and isolator when I am arranging the MCBs, Main Switch and RCBOs etc. So I can fit them in before hanging the CU on the wall as they will simply fit into the other end of the isolator.

Please confirm this is a workable solution.

Richard

[ARW]

Why do uk.d-i-y posters always over engineer everything?

[ARW]

And very workable.