Replacing fuse box with consumer unit

[Michael Chare]

There is a fault in the neutral of one of the cables going to my six way fuse box. To find this fault I am likely to have to remove the fuse box so that I can inspect the incoming cables and maybe replace one of them.

This makes me wonder whether I should replace the fuse box with a modern consumer unit, probably 8 way.

Can anyone recommend a suitable unit. One of the problems that will inevitably occur is that the house wiring cables will be to short. So ideally I would like a unit that has all the terminals close to the cable entry point would be a bonus.

[tabbypurr]

Type of earthing? Metal or plastic? Cheap or deluxe? 2 RCDs or RCBOs?

NT

[Andy Wade]

No option there any more. Amendment 3, must be metal.

[Andrew Gabriel]

A new domestic one pretty much has to be metal now.

[dennis]

I think it says non flammable, but most manufacturers are using cheap pressed steel.

Changing the consumer unit is, along with some bathroom stuff still notifiable so don't DIY if you are selling soon.

[John Rumm]

Pick any of the well known brands and you should be fine. MK is nice but can be pricey - although sometime you will find package deals for a CU and a selection of MCBs that are not bad.

Hager have a good range of stuff, also good quality. Contactum is cheap and "ok". I tend to avoid the wholesalers own brands since its not always obvious what you are getting or what the spares availability will be like.

You are likely to find that all 8 way boxes have a very similar layout and that is likely to be different from your current CU. So arm yourself with some suitable lengths of wire, and decent quality crimps (+tool) so that you can extend the ones you need to. (you can also het a bit of wiggle room by choosing the ordering of the MCBs to suite the wire lengths you have).

For more on brands, see:

for changing one:

[ARW]

You are not the only one:-)

Although you can often gain extra cable by moving the box up or down.on may installs.

Screwfix had an offer on a BG populated RCBO CU last week - I believe it had 8 ways and 6 RCBOs. They are not bad CUs. I cannot check that ATM as the Screwfix site is down. All RCBOs on a small unit may help with the existing cable lengths on the L and N but do be prepared to have to extend the earths.

Whatever CU you buy (it will need to be metal if you are meeting the 3rd amendment regs) then you can often forget about using the existing knockouts and just jigsaw whatever entry points you need and then use grommet strip. Depending on how the tailes enter the CU then a gland pack such as

is essential.

[Mike Tomlinson]

En el artículo , Michael Chare escribió:

Beware that doing this can show up faults, such as shared neutrals, that don't affect fused CUs. They can result in an RCD that trips and won't reset.

[Michael Chare]

Thanks, I just bought a Screwfix crimp tool to mend my hob!

Would these be suitable crimps:

Any need for additional insulation such as tape and/or heat shrink?

Are RCBOs a good idea?

[Brian Gaff]

But of course nobody bothers anyhow, from what I've heard. If he has to extend the cables he is also going to need some certified connection system as well. I know its done as someone I visit in a block ogf flats has the wires going into some form of connection block in a box and new cables emerge the other side. Brian

[spuorgelgoog]

I wouldn't buy crimps from China. The last lot I bought from B&Q [1] were so soft I could deform them with finger pressure.

Owain

[1] I know, but I only wanted 10 and it was a bit an emergency.

[Dave Plowman (News)]

There is generally only one incoming neutral to a CU. All the others are outgoing.

And any fault is far more likely to be elsewhere in the house - unless work has recently been carried out on the CU.

[Dave Plowman (News)]

Is there a need to use a crimp to extend a cable within a CU? After all it will remain accessible, in terms of the regs. And I've seen more badly made crimps than I'd like.

[John Rumm]

They look like the right kind, however for this application I would play safe and order something branded from CPC

Not when extending individual wires inside the CU - only if you are crimping cables outside.

Yes. All RCBO setups are a top end solution - but it will cost more. It gives the best levels of RCD discrimination available. (i.e. the effect of a fault will be limited to the single circuit on which it occurs)

You may find a "high integrity" CU is a good compromise - that's one where it has at least a couple of banks of MCBs with their own RCD, but them also a couple of additional non RCD ways that you can fit RCBOs in. So you can stick circuits with high leakage risk on their own RCBO, but still lump together low risk circuits on shared RCDs.

[John Rumm]

You can use chockie block if you prefer (or Wagos etc). The only real advantage of crimps is they are slim and easy to thread through a rats nest of wires if needs be.

Yup, then again, I have met rather too many chock block terminals made of cheese also!

I think I would probable go for Crimp, Wago, then Chock block in that order of preference.

[Dave Plowman (News)]

But I'd guess less common than cheap crimps and an even worse crimp tool. Before any finger trouble.

I'd be inclined to use a decent chocolate block connector large enough for the wires to overlap so both screws bite on both wires. Tighten till it groans using the correct size screwdriver, and insulate with heatshrink. That's what I did when fitting my replacement CU for the few wires which wouldn't reach - if they couldn't easily be replaced. And I've not had any problems.

I personally hate those pre-insulated Red Blue and Yellow terminals - especially bought from an unknown source. They may be just about acceptable where the wire size is a tight fit, but when at the other end of the stated sizes, give an extremely poor crimp. To see what I mean do a trial one then carefully cut off the insulation. It looks terrible. Simply squashed like you could do with pliers. Not a proper crimp at all - to me. Of course like all domestic wiring it may never get near its stated maximum load. But I'd not trust it for a circuit which does.

[Andy Wade]

You're supposed to test and assess each circuit before connecting it to the new CU.

This is a useful guide:

[David]

+1 for the RCBO; the extra up front cost may well save you loads of aggro down stream.

Earth/neutral trips were the bane of my life, before I discovered RCBOs!

[Major rewire may have helped, of course.]

Cheers

Dave R

[Graham.]

For the record, that's the technique I always adopt with chock-block, but I've never seen it done by a professional, or inside a manufactured appliance.

[tabbypurr]

I always do that when practical. Much better reliability & safety. Plus in situations where it's permissible you can also ignore the connector's curre nt rating if you've got 2 copper cables pressed well against each other - m ost of the current bypasses the chocblock. That does not include house wiri ng of course.

For the record one can overtighten these things. Go too far and the cable e nds become flat thin weak things that fracture readily.

NT