UK Building a frankenboard

partplonker · Sep 5, 2022

I've got a bunch of old single phase BS88 1970s fuseboards in the communal areas of a converted building. All the wiring is MICC and it's buried in the walls. The fuseboards all have a back box that's flushed into the walls where the pyro cables are glanded into, so the metal fusebox is the only part that's accessible. The fuseboards are then inside custom made wooden cupboards (it's a listed property). I want to upgrade them to modern switchgear.

The obvious approach would be to take out the fuse carriers and busbars, and turn the existing fuse boxes into junction boxes and run cable extensions out to a modern board.

I'm not overly keen on this idea because the boxes are quite big already and there's no free space in the cupboards as they were built to house the existing boards alone.

One thought I had was to take out the old busbars and ceramic holders and replace them with DIN rails. After all a metal box is a metal box and these 1970s ones are much thicker steel than modern ones. I could then put modern switchgear in the old box. The boxes have an existing neutral bar and the copper sheathing of the pyro is used as the earth. Some boards have a few circuits in twin and earth, but there are already earth bolts in those boxes that I could ring crimp a fly lead onto and use earth DIN rail terminals.

There's plenty of space inside the old boxes and they have a thick steel door. These boards are all 12 foot off the floor and are only ever operated by skilled and instructed people anyway since it's very easy to touch live parts in them the way they are right now.

Can anyone think of any reason that would make it a bad idea? I can't think of any regs it would contravene off the top of my head. Maybe manufacturer/type testing, but all the switchgear and any busbars would match, it's just the metal box that wouldn't.

Thanks.

UNG · Sep 5, 2022

Have you looked at the skeleton consumer units that are available

Have you got any pictures of what you are trying to replace

snowhead · Sep 5, 2022

The problem is going to be when the next person comes along and does an EICR, are they going to accept the D.I.Y solution?

As above maybe something like this,

10 Way Dual RCD Configurable Flush Metal Clad Consumer Unit

10 way configurable consumer unit

www.cef.co.uk

partplonker · Sep 5, 2022

UNG said:
Have you looked at the skeleton consumer units that are available

Good call. I've had a look at the Wylex ones, but 320mm is just a little bit too wide.

UNG said:
Have you got any pictures of what you are trying to replace

I'll add one when I'm back there later.

partplonker · Sep 5, 2022

snowhead said:
The problem is going to be when the next person comes along and does an EICR, are they going to accept the D.I.Y solution?

Absolutely agree that this could be an issue. I would have thought to fail an EICR though, the inspector is going to have to at least come up with a reg that is being violated or a reason for potential danger?

snowhead said:
As above maybe something like this,

10 Way Dual RCD Configurable Flush Metal Clad Consumer Unit

10 way configurable consumer unit

www.cef.co.uk

Thanks, that's a really good suggestion. That specific one is a bit on the wide side, but it's a great idea and I could look at flush mount ones with fewer ways. Thanks!

UNG · Sep 5, 2022

partplonker said:
Good call. I've had a look at the Wylex ones, but 320mm is just a little bit too wide.

You haven't said how many ways the boards you are trying to replace the 320mm is the fixing centres for a 13 module unit the base is only 286mm wide

Have you looked at

https://www.electrium.co.uk/media/l5mdd4jj/wylex-domestic-circuit-protection-catalogue.pdf

Page 47 gives all the measurements for the range of skeleton CU's so you might find one that will fit

Whatever unit you go for I suspect it will need a little bit of modification to get the best fit

littlespark · Sep 5, 2022

I did this with a church heating board… old MEM fusebox, retrofitted with din rail and rcbo’s.

partplonker · Sep 5, 2022

UNG said:
You haven't said how many ways the boards you are trying to replace the 320mm is the fixing centres for a 13 module unit the base is only 286mm wide

Have you looked at

https://www.electrium.co.uk/media/l5mdd4jj/wylex-domestic-circuit-protection-catalogue.pdf

Page 47 gives all the measurements for the range of skeleton CU's so you might find one that will fit

Whatever unit you go for I suspect it will need a little bit of modification to get the best fit

Thanks, that's very useful info - I only checked the Wylex skeleton boards they had on CEF. The old fuse boxes are laid out in 3 rows of 5 (or possibly 6, can't remember) carriers, so they are taller than they are wide. I'll get a pic later and check the measurements. By eye, I'd guess the boxes are maybe 350mm tall and 250mm wide. I had thought originally that I might put 2 DIN rails in to make use of the space.

I've got 5 boards to look at sorting. 4 of them have 6 ways in use.

The most populated one has 11 ways used, but I think it could get away with only requiring 6 as quite a few items in there can be doubled up. There are 4 individually fused double sockets for example - completely unnecessary since the most load they will ever see is a hoover. One room off that board has the lighting circuit split into 3 because it used to run many large fluorescents and now just has a few chandeliers with LED lamps, etc.

So, I guess I'm looking for something 8 modules wide, 2 for the switch and 6 for RCBOs.

partplonker · Sep 5, 2022

Boards are a bit roomier than I thought. 280mm (W) x 430mm (H) x 90mm (D).

I've never had one of these off the wall, so I'm not sure what the full construction of the box is. The pyro cables behind have to be glanded into the box somewhere and the conductors come from above, so there must be a second box flushed into the wall behind what we can see here (the back of the box that you can see here is level with the plastered wall) and the glands have been plastered over. The inner conductors from the pyro come down and in through the rear.