Upgrading main earth on old metal rewireable fuse box

[Smugley]

Doing some minor work on an old installation which will first require upgrading the main earth and bonding.

The existing earth terminal is a bolt through the bottom of the metal fusebox, hidden down the side. There is no possibility of loosening the nut without dismantling the board and removing the main switch (why were they ever designed like this!).

As expected, the bolt is overloaded with various bonding wires, old main earth and various CPCs. I've added a new MET outside the box to terminate the new gas & water bonding cables and main earth but I still need to extend the main earth to the box.

I was going to go ahead and spend some time dismantling it and adding the earth to the existing terminal. However it may be quicker to drill another hole in the box and attach it to a new bolt with locking washers etc. However I'm uncertain if this would be an acceptable way to ensure a good earth connection. Any thoughts people?

 

[telectrix]

i would imagine that you would have to change the board. i assume that there is no RCD fitted, i would not entertain upgrading anything unless it was to 17th. CYA every time

 

[Sintra]

Nothing wrong with drilling a new hole, clean off any paint use serated washers inside and out and it will be fine.

 

[telectrix]

what is the earthing arrangement. is it TT or TN?

 

[Sintra]

Only your alterations need comply with the current version of the regs.

 

[telectrix]

true, but i would not like to leave an installation with no RCD protection, regs. or no regs.

 

[Sintra]

Neither would i if it was a TT but we don't know that yet.

 

[Smugley]

Supply is PME. The client requested the absolute lowest cost option. Earthing and bonding will be up to scratch, and the extension to the ring main will be several sockets on an RCD fused spur. He is aware that a CU upgrade is recommended and intends to do so once he has the money.

 

[malcolmsanford]

Then your fine. As the system is PME the metalclad box is fine. Metal clad boxes are frowned upon for TT as you know unless you do all manner of things to them, bushing tails into the box etc.

As your just extending the the ring with a RCD FCU then again fine as your work meets the current regs, and all main bonding and earthing upgraded spot on.

Your MWC filled out. Personally I would also include a cover letter outlining the condition of the installation and offering a PIR at a very reasonable price.

Just an aside on your first post you noted that on the existing earth bolt there were CPC's attached to it. I know that some of the old 60's boards never had an earth bar, is this one of them ?

 

[Smugley]

I can't see an earth bar, as far as I can tell there is only the earth 'bolt' through the casing.

The board is a very tight fit in the casing, but since I can see the bonding, earth and CPCs attached to it I assume there is no other bar.

 

[POWERFULL]

Never assume, because it makes an --- out of U and ME.
Until mid 60's Metal Clad consumer unit mainly had a Bolt Through Earth Connection, where all earth wires conected.

From Approx 1968 they started to have Earth Bars . Some Electricians terminated these by fitting Lugs on the wires, but most used ( Shell Clamps ) for ALL wires.
We have come along way since then, thank God