80A RCD before main Board?

[walec]

Hello All,

I have just been to a customer who wants down lighters put in their bathroom. The guy who went before me replaced a standard light with some down lighters in a shower room, for protection he split the tails and put a 30ma 80A RCD switch between the meter and the board which has a 100A main switch. I can`t get my head around this, its a standard MCB board, no shower just rings, radials and a cooker. Does this comply?

 

[lazza]

Now that is a head scratcher!! what are the supply earthing arrangments? TT, TN-C etc?

 

[walec]

It`s a TNC and just to complicate it the customer has just phoned and asked for an outside socket and outside lights to be fixed to the outside of the house, can I take supply from existing circuits??? until I can get my head around the first problem I just don`t know, there is also no bonding! anywhere! Just earthing to MET.

 

[Yooj]

It`s a TNC and just to complicate it the customer has just phoned and asked for an outside socket and outside lights to be fixed to the outside of the house, can I take supply from existing circuits??? until I can get my head around the first problem I just don`t know, there is also no bonding! anywhere! Just earthing to MET.

(I am assuming you mean TN-C-S)

I would suggest that an upfront RCD before the CU is an issue purely from the perspective of inconvenience from an earth fault, in that the RCD will trip and knock out everything. Where is this 80A RCBO? Is it easily accessible if it were tripped?

Secondly, are there any other RCDs in the CCU? if so, then there is an issue with regards to discrimination of down-stream devices.

I am not sure that the Single RCD/MCB really contravenes the regs, but it is rather unconventional. And if the installer did this without sorting the Main bonds, then this is not good.

Thirdly, when you say no bonding...do you mean no main bonding? If so, then touch nothing until client agrees to this being installed...if you mean no supplementary bonding, then Supp-Bonding can be ommited, but only when circuits have been RCD's and 'ALL' main bonding is suitably in place.

The outside socket/lights are not an issue if you had a decent 17th Ed. board, or even a split-load board where you could RCBO...But you would still need Main Bonding in place.

Yooj

 

[Sintra]

Hello All,

I have just been to a customer who wants down lighters put in their bathroom. The guy who went before me replaced a standard light with some down lighters in a shower room, for protection he split the tails and put a 30ma 80A RCD switch between the meter and the board which has a 100A main switch. I can`t get my head around this, its a standard MCB board, no shower just rings, radials and a cooker. Does this comply?

I think that this has been done as a quick fix to comply with regs as every circuit now has RCD protection.

Again this set up is sure to incur nusiance tripping putting out the whole installation.

 

[Monkey1984]

It`s a TNC and just to complicate it the customer has just phoned and asked for an outside socket and outside lights to be fixed to the outside of the house, can I take supply from existing circuits??? until I can get my head around the first problem I just don`t know, there is also no bonding! anywhere! Just earthing to MET.

Ideally you want to be getting the PEB in place if its not there already. On the part where your mentioning about working on circuits then surely you can carry out your part of the installation using an RCD Fused spurs surely? Or am I being stupid? This at least covers your work.

I might be wrong as I've been up since friday and just about to crash out haha.

 

[walec]

Yes sorry I thought I had typed TN-C-S.
There is no 80A RCBO just the RCD, easily accessible if tripped.
No other RCD`s in the board or anywhere else.
No bonding, no main or supplementory that I can find, certainly no bonding back to the MET.
The customer was telling me how when the RCD was fitted last month the installer was worried about
going to prison if he did not do it right!

The only way I can see this working is th change the board for a 17th Edition.
I am sure the exisiting set up does not comply.

 

[Yooj]

Yes sorry I thought I had typed TN-C-S.
There is no 80A RCBO just the RCD, easily accessible if tripped.
No other RCD`s in the board or anywhere else.
No bonding, no main or supplementory that I can find, certainly no bonding back to the MET.
The customer was telling me how when the RCD was fitted last month the installer was worried about
going to prison if he did not do it right!

The only way I can see this working is th change the board for a 17th Edition.
I am sure the exisiting set up does not comply.

If it is an MCB board, you might be able to get RCBOs for it. How old is the board, and what type of board, and what make?

However, I would suggest that you identify to the client the need for Main Bonding...this is a must, and you should not do any other work until this is in place. If the main earth connection was lost for any reason, then all fault currents will go through extraneous conductive paths...This is not good and potentially lethal.

Secondly, if you then do the outside work, then you will probably be ok, however, an 80A rated RCD, and a 100A main switch (or fuse), this is not good, since the RCD is not an overcurrent device, and therefore it could fail. Unlikely, but it could.

EDIT: Just reread your post...it is an MCB board, therefore You 'could' get RCBOs for it and dispense with the RCD....however, the biggest concern is no main bonding.

Yooj

 

[Des 56]

Installing the 80amp rcd up front for protection of the non rcd board is a sensible and adequate means of giving rcd protection
Other than the rcd will isolate everything,it is the less expensive and less disruptive means of improving safety instead of insisting on a new probably un needed consumer unit or rcbos or whatever
There is little actual reasoning in domestic situations why there is such importance put by some on this issue
of losing power to all circuits during a fault (occasional power cuts and the meter switching itself off take no heed or regard to the problem)If you feel this is important,perhaps fit 1 or 2 emergency lights

The work you intend to do on the outside should not be tackled until the important issue is resolved ie The Bonding

Rather than emphasise to the customer,percieved problems with the up front RCD(the 80 amp rating can be sorted by making sure the service fuse is 80 or less) be very particular to make the client aware of the dangerous situation that the lack of bonding presents,much more important than the lack or inadequacy of RCDs
Tell him to spend his money on this issue rather than un necessary consumer unit changing

 

[Yooj]

Installing the 80amp rcd up front for protection of the non rcd board is a sensible and adequate means of giving rcd protection
Other than the rcd will isolate everything,it is the less expensive and less disruptive means of improving safety instead of insisting on a new probably un needed consumer unit or rcbos or whatever
There is little actual reasoning in domestic situations why there is such importance put by some on this issue
of losing power to all circuits during a fault (occasional power cuts and the meter switching itself off take no heed or regard to the problem)If you feel this is important,perhaps fit 1 or 2 emergency lights

The work you intend to do on the outside should not be tackled until the important issue is resolved ie The Bonding

Rather than emphasise to the customer,percieved problems with the up front RCD(the 80 amp rating can be sorted by making sure the service fuse is 80 or less) be very particular to make the client aware of the dangerous situation that the lack of bonding presents,much more important than the lack or inadequacy of RCDs
Tell him to spend his money on this issue rather than un necessary consumer unit changing

Totally agree...Do nothing until the bonding is sorted.

Yooj

 

[peteludman]

listern to des 56 he is right with every thing a good sparks

 

[walec]

Cheers Guys, I am calling round later today to discuss the bonding as my first action.