Something missing here...?

[sparkinlee]

Got called out to a tripped RCD yesterday, opened up the consumer unit and...



What, no CPCs anywhere, in any circuit?!

Closer inspection revealed that the whole house is built with singles in metal conduit providing the earthing, and Zs readings are satisfactory, but still a bit of a surprise when I first opened the CU - I expect others have seen this before, but a first for me.

But I have a couple of questions about a socket I need to replace. I found a brass fronted socket where the guts of the socket was not securely fixed to the front plate, and as the earth connection is via the mounting screws and the front plate, the plug earth pin was not getting a good connection. The socket was mounted into its back box using thicker screws than current M3.5 socket screws, so that I cannot use M3.5 screws, and the thicker screws are too thick for the M3.5 holes in new sockets. So:
- any suggestions for how to fix a new socket onto the existing back box (which I do not want to replace as it's a conduit box built into the wall)
- any suggestions for getting a decent earth connection off the back box, which does not have an earth terminal in the back of it (this may depend I guess on the answer to the first question)?

Ideas welcome...

 

[Marvo]

Not sure if it was the same in the UK but when installing sockets into steel backboxes we used to put a wound sleeve over the screw which was the right length. I'm trying to think how to describe it so I'll attach a drawing in a min.

 

[GLENNSPARK]

M4s perhaps?.......

 

[sparkinlee]

M4s perhaps?.......

Possibly, but I'd guess something pre-metric to be honest.

In any event, my basic problem remains - the holes in the back box are too big for modern screws, and the old screws which fit the back box are too big for the holes in the new sockets!

 

[Sintra]

Got called out to a tripped RCD yesterday, opened up the consumer unit and...

View attachment 7454

What, no CPCs anywhere, in any circuit?!

Closer inspection revealed that the whole house is built with singles in metal conduit providing the earthing, and Zs readings are satisfactory, but still a bit of a surprise when I first opened the CU - I expect others have seen this before, but a first for me.

But I have a couple of questions about a socket I need to replace. I found a brass fronted socket where the guts of the socket was not securely fixed to the front plate, and as the earth connection is via the mounting screws and the front plate, the plug earth pin was not getting a good connection. The socket was mounted into its back box using thicker screws than current M3.5 socket screws, so that I cannot use M3.5 screws, and the thicker screws are too thick for the M3.5 holes in new sockets. So:
- any suggestions for how to fix a new socket onto the existing back box (which I do not want to replace as it's a conduit box built into the wall)
- any suggestions for getting a decent earth connection off the back box, which does not have an earth terminal in the back of it (this may depend I guess on the answer to the first question)?

Ideas welcome...

All the accessories should have a fly lead from back box to accessory. If there is no terminal in back box this can be done with a lugged lead and a self tapping screw into back box.

As for the 3.5mm screws the easiest thing to do is drill through existing enlarged screw holes to back of box with a 3mm bit. Then tap with a 3.5mm tap and use long 3.5mm screws.

 

[GLENNSPARK]

could you not cet some waterpump pliers and "collapse" the screw lugs in the backbox a bit then run a 3.5 tap down it to open it up size?..........is it a heavy cast or forged thing? if so then open up the holes and tap it out for a short mild steel bolt then run the bolt in ant tap that so what you have effectively done is created a reducing ferrule? its a faf but you should get a good Zs of that........

 

[wattsup]

Could you unscrew bush/locknut and fit a banjo?

If the box is fitted fairly deep in wall, you could use 3.5 extensions. fix the extension to existing holes with 3.5 nuts.

 

[topquark]

Any chance of replacing the lugs on the existing back box?

 

[Des 56]

I think the earth tail will have to be a self tapper into the back box with a lug

With the front,try bending the existing fixings out of the way,drill holes to suit through the back box,rawl plug them,then use long thin wood screws to fix

 

[GLENNSPARK]

I think the earth tail will have to be a self tapper into the back box with a lug

With the front,try bending the existing fixings out of the way,drill holes to suit through the back box,rawl plug them,then use long thin wood screws to fix

Yep....had to do that one before with an appleby box........

 

[sparkinlee]

Thanks for all the suggestions. I'll go for the self tapper for the earth fly lead.

For the lugs, I'm not sure to be honest without looking again whether they can be folded back, but I don't think they could be replaced. So I think I'll start with Sintra's idea of putting M3.5 holes in the back of the box, and if that's a no go I'll enlarge the holes as Des suggested.

 

[not clever]

You could run in a new cpc.
Drill through the lug into back box, cut a 3.5mm thread in new hole in back box, fix new socket to back box with long plate screws into the new threaded holes in back box.

In your picture it doesnt look like the conduit is connected to the cu by any bushes, the MI is ok but maybe fill the bush where the tails enter the cu if it isnt a sealed gland.
Is the cu itself earthed?

 

[GLENNSPARK]

Rite im off 6am start tommorow. nite guys...

 

[sparkinlee]

You could run in a new cpc.
Drill through the lug into back box, cut a 3.5mm thread in new hole in back box, fix new socket to back box with long plate screws into the new threaded holes in back box.

In your picture it doesnt look like the conduit is connected to the cu by any bushes, the MI is ok but maybe fill the bush where the tails enter the cu if it isnt a sealed gland.
Is the cu itself earthed?

The CU is earthed from the MET. The singles all enter the CU from the back as you can see, but I suspect the conduits are all terminated behind the CU and the earth connections are there (you can just about see a screw and some bare earth wire through the central hole in the back of the CU)

 

[Des 56]

With your consumer unit,I would hazzard a guess that the conduits are made off into a metal clad adaptable box and the newish unit retrofitted onto there
It should have an earth from that box to the consumer unit
It appears that the singles have been brought into the consumer unit without any bushing or grommitt strip as well