Board upgrade but cpc woes???

[Foxmeister]

Was asked to install a mains powered smokie and new cu. Will be fitting an 8way with 30mA main RCD, but upon opening the (very) old unit to be stripped out i have discovered only 2 circuits are earthed at the board. Then on further inspection theres no real connection for board to main income earth. The supply to the flat is old style MICC 2 core cable.

Firstly, which is the best way to obtain the earth from MICC income cable, heard of using a Tenby clamp but not sure if this is good practice??? Dont come up against this type of supply often.

Secondly, with the majority of the circuits not having the cpc present at the cu, is this a re-wire job only as i was reluctant to change the cu and re-connect circuits? Is there a requirement for these cables(twin+earth) to have and utilise its own earth at all times, and have supplementry bonding secondly if required? (i.e flying leads on socket boxes)

Have checked a couple of sockets which do have earthing at the points but unsure if its picking up the earth at a point under the floor somewhere as it doesnt have it at the board.

 

[batty]

Little concearned why you are using 30ma RCD main switch board which does not comply with regs unless there are more than one consumer unit. Not sure about why there is no main earth would need dno to sort probably.

 

[green-hornet]

The CPC "circuit protective conductor" must be present for all circuits. This would be a major worry for me.

First do a Ze test at the old cu, this will verify if there is indeed an earth external to the property. Then test out all circuits to find what has happened to the earths, it may be a very old earthing arrangement involving the use of a looped braided cable.

From the basic description you have described I would think it is possible that a full rewire may be required.

 

[m4tty]

It's not earthed through conduit is it ?

Prob not but just a thought

 

[ProDave]

It's not earthed through conduit is it ? Prob not but just a thought

Good thought.

A picture of the CU might help.

Which circuits DO have a CPC? is it just lighting that does not?

 

[binky]

Firstly, which is the best way to obtain the earth from MICC income cable, heard of using a Tenby clamp but not sure if this is good practice??? Dont come up against this type of supply often.

and have supplementry bonding secondly if required? (i.e flying leads on socket boxes)

Have checked a couple of sockets which do have earthing at the points but unsure if its picking up the earth at a point under the floor somewhere as it doesnt have it at the board.

Earthing Micc is basically the same as earthing 2 core SWA, and of course its was normal practice to use steel fuse boards, so earth is staraight to steel casing.

Flying leads are not a requirement on socket back boxes, unless you have steel conduit system where conduit is earth, that's if I understand you correctly.

You may have bits of unsleeved steel wire floating around the system - these are the CPCs

 

[Foxmeister]

As far as i could see, the cooker and another 5amp which would be lighting were the only with cpc connected to main point on steel cu.

The sockets i managed to look at werent conduit system and definately no conduit at the board.

Bit of a catch 22 as i would really need to remove the cu to investigate further, but dont want to go to the point of no return, then have to inform landlord that re-wire may be required as i dont know if it would be getting done immediately if required, flat is occupied presently.

 

[ianmacd]

Whats the Zs from the sockets?

 

[jl-heating]

rewire ..... there is to much thought going into this ..

time is money ,.

my crystal ball says dont just make good . make safe.

 

[ProDave]

As far as i could see, the cooker and another 5amp which would be lighting were the only with cpc connected to main point on steel cu.The sockets i managed to look at werent conduit system and definately no conduit at the board.

So are you saying no CPC on sockets???

If so, definitely a rewire.

But I find it hard to imagine sockets really being wired with no CPC, are you sure it's not conduit?

 

[initforthemoney]

If the sockets have no cpc present, then it will be wired in conduit, which in effect is your earth path. It could be similar for the lighting. No need for a rewire.

Test the conduit to make sure it is continuos.

 

[kme]

If the sockets have no cpc present, then it will be wired in conduit, which in effect is your earth path. It could be similar for the lighting. No need for a rewire.Test the conduit to make sure it is continuos.

And you know this how, exactly?

In an ideal world, and with all things being "to the book", you may be right. But please don`t presume to to advise that "there is no need for a rewire"; unless you`ve actually seen the job in question??

Not good advice, IMHO

KME

 

[Foxmeister]

There is no obvious conduit at the board, and the existing wiring is in twin and earth which is visible protruding from the plaster of wall at the top before it enters the board.

Possible that its conduit system that is set into a junction box inside the wall where might have a central earth point, but strange why there is 2 circuits utilising the board earth stud also, possible these have been re-wired at an earlier time maybe but unsure. Will try re-arrange another visit for more info and some pics hopefully.

 

[Evans Electric]

Foxy , from your OP you say there are no socket earths at the board , the ones at the plugs may be a bare earth wire system connected to the water main.

I think the place needs upgrading TBH.

If the main earth is the pyro sheath then fit a metal C/U .

 

[kme]

If the main earth is the pyro sheath then fit a metal C/U .

Unless the earthing system is TT; in which case you can`t use a metalclad

 

[initforthemoney]

And you know this how, exactly?In an ideal world, and with all things being "to the book", you may be right. But please don`t presume to to advise that "there is no need for a rewire"; unless you`ve actually seen the job in question??

Not good advice, IMHO

KME

Did you read my post properly???

I said "IF" and "test".

Two key points there.

Plus, you CAN use a metal clad CU providing certain conditions are met.

Please dont give inaccurate information.

 

[Evans Electric]

If the sockets have no cpc present, then it will be wired in conduit, which in effect is your earth path. It could be similar for the lighting. No need for a rewire.Test the conduit to make sure it is continuos.

He says there is no conduit at the board , Init.

 

[jl-heating]

see already to much time wasted ... i do a walk by and decide what to do its very rare its the wrong decision i always aire on caution and usually its a full or partial rewire

i would deffo rewire this property as the client never wants to pay for any tests etc ....

the other option i do is offer a pir to evaluate the install so at least you get paid for you inspection.

the upgrade would be charged on top of the pir .

 

[initforthemoney]

He says there is no conduit at the board , Init.

Fair enough:^O

 

[ProDave]

He says there is no conduit at the board , Init.

But some of us are questioning that.

There may be no conduit VISIBLE at the board. Doesn't mean it's not there.

I did a CU change on a conduit install a while back, where all the conduit terminated into a metal box sunk flush into the wall. The CU completely covered the sunken box, so you could not see it.

The conduit singles exited through the back of the CU into this sunken box and then into the conduit.

A SINGLE earth conductor was bolted to the sunken conduit box and was terminated inside the CU.

This sounds very very very much like the OP is reporting, seemingly an installation with only one or 2 CPC's connected and no visible conduit.

IF it is like this, and IF all the earthing, insulation, continuity etc tests okay, there is no need for a rewire.

But unless the OP comes back and tells us more, we will never know if it is like this or not.