RCD Protection

[timmyquick]

I have been learning a lot about electrics lately. I am having an electrician come out soon. When i have done some overtime that is!.
To sort out having no earth connection as the REC refused until i have called an electrician out.

Is it acceptable to have this on any type of supply installation or is it only allowed on a tt supply only.

http://www.tlc-direct.co.uk/Products/MK6600.html

I also see lots of people on this forum saying that all sockets must be protected on an RCD. Is this really the case as i have put sockets in the loft and ran all the cable down to the CU just needs connecting but there is no space left on the RCD of the CU. Are you allowed to have sockets on a non RCD side if its in the loft as it would be doubtful that it would be used to supply an appliance outside.

 

[plugwash]

on a TT system (which is what it sounds like you are going to end up with) there must be a main rcd (100ma time delay i expect that tlc one is a time delay but for some reason they don't say so might be an idea to get in touch with them) covering everything and a normal 30ma non delayed rcd covering ALL sockets

on TN systems (where the earth comes from the electricity supplier) the 100ma time delay rcd is not needed and only "sockets that can feasiblly supply equipment outside the equipotential zone" need 30ma non delayed rcd protection

 

[Damocles]

Why do you reckon you have no earth connection at the moment? This is unusual.

It is not essential for all sockets to be on a RCD. Regs require that any socket which might be used to power equipment outside must be RCD protected. This is most likely the one just inside your back door. But concievably a lead out of a window. Attick fairly unlikely I would think.

I hope the REC refused on the grounds that they did not believe you, rather than they refused to provide an earth.

 

[ban-all-sheds]

on a TT system (which is what it sounds like you are going to end up with) there must be a main rcd (100ma time delay i expect that tlc one is a time delay but for some reason they don't say so might be an idea to get in touch with them)

It is not a time-delay one, it's just a regular 100mA RCD, so unsuitable for sockets, and unsuitable for whole-installation with a TT supply. Timmyquick - do not buy that one.

 

[ban-all-sheds]

It is not essential for all sockets to be on a RCD.

It is with a TT installation..

 

[Damocles]

Yes but we still have not found out if this is one.

 

[timmyquick]

Why do you reckon you have no earth connection at the moment

?
I have had the old cu cover off traced all earth wire's one 10mm to gas, one 10mm to water. No earth from REC. No earth rod in ground

I hope the REC refused on the grounds that they did not believe you, rather than they refused to provide an earth

.

The REC refused until i have had an electrician to say that my bonding is adequate. The wiring in the house is up to regulation. A letter to say that the supply is adequate for conversion to pme and a sparkys letter to say the wiring is good and a certificate.

 

[Damocles]

Surely whether the supply is Ok for PME is up to them..it's their supply. And refusing to connect an earth when there is already a live up and running seems extremely perverse.

I guess it is superfluous to ask, but are you quite sure there are no tatty bits of old copper wire trailing off to clamp onto the supply cable?

 

[timmyquick]

Surely whether the supply is Ok for PME is up to them..it's their supply. And refusing to connect an earth when there is already a live up and running seems extremely perverse.

I

guess it is superfluous to ask, but are you quite sure there are no tatty bits of old copper wire trailing off to clamp onto the supply cable?

I am certain i have an old pic before the CU was changed. There is no earthing connected to the supply what so ever had mirror underneath floor boards. The earth cable you see in the pic is to gas metre and one more which you can not see berried in the plaster, which has been traced to the stopcock.

http://homepage.ntlworld.com/timothy.lhear/CIMG0849.JPG

The new cu is split load but all circuits have been put on the 30 ma RCD side until i have had an electrician to sort out the earth and no doubt will test all circuits. With the cooker circuit disconnected as no space left on the 30 ma RCD side. So effectively the setup is same as it was with the old cu in place. Depending on what the electrician decides about the earthing arrangement, i assume that the electrician will just put a 100ma RCD before the CU if it is going to be a TT supply. Will find out when i save a few hundred quid. By the way i don't do much cooking so no real loss.

 

[timmyquick]

forgot to mention that the cooker was just connected to the 32amp mcb which was also used to supply the ring circuit for sockets in this terrace house. In the old CU that is

 

[Damocles]

By the way BAS, plug et al, I still have it that even on TT the sockets only have to be on main 100mA RCD, not 30mA. Rule for requiring 30mA being the same as for normal installation..sockets powering or liable to be powering equipment outdoors..

It would also be possible to use non-time delayed 100mA RCD if the split CU is reorganised to have one main switch powering two RCD strips, one 100ma and the other 30mA. This would not be too difficult to do

 

[ban-all-sheds]

Surely whether the supply is Ok for PME is up to them..it's their supply. And refusing to connect an earth when there is already a live up and running seems extremely perverse.

The point is that the two go hand-in-hand.

They won't provide an earth unless it's a PME or TN-S supply. If it's a TT supply then the provision of an earth is not their responsibility, it is the consumer's, and the lack of an earth is the consumer's fault, not theirs.

Timmy has 2 choices.

1) Stick with TT, which means getting an earth rod (properly) installed, and updating his CU to a "TT-spec" one.

2) Getting the DNO to convert his supply to PME, which means that they are entitled to ask questions about the quality of his installation.

 

[ban-all-sheds]

By the way BAS, plug et al, I still have it that even on TT the sockets only have to be on main 100mA RCD, not 30mA. Rule for requiring 30mA being the same as for normal installation..sockets powering or liable to be powering equipment outdoors..

No - ALL the sockets have to be on 30mA - it's nothing to do with inside/outside any more, it's all about 0.4s disconnection times, which are a struggle with a poor TT earth.

It would also be possible to use non-time delayed 100mA RCD if the split CU is reorganised to have one main switch powering two RCD strips, one 100ma and the other 30mA. This would not be too difficult to do

Yes - I guess you could have a normal incomer, and then immediately go to two RCDs, one 100mA, the other 30mA, but it would buy you little, and would probably mean you'd have to build your own board, which is a fun thing to do, but it might not be what you want to do.

Or you could use a normal split-load board, put your 100mA RCD where the 30mA would go, and then use RCBOs on the non-RCD side of the board for your sockets.

Or in either case you could use 30mA RCDs everywhere. The whole point of a 100mA-S as an incomer is to provide discrimination so that a fault which trips the 30mA for the sockets only trips that, and doesn't take out the whole installation. If you've separated them by other means, there's no longer any need for discrimination.

 

[plugwash]

Yes - I guess you could have a normal incomer, and then immediately go to two RCDs, one 100mA, the other 30mA, but it would buy you little, and would probably mean you'd have to build your own board, which is a fun thing to do, but it might not be what you want to do.

as long as the terminal capactiy of the incomer was big enough to deal with the cabling in question i can't see any real diffuculty in modding a CU to do this

 

[timmyquick]

The new CU is already installed with the five existing circuits put onto the 30 ma rcd side of the split load board and one circuit disconnected the cooker. My assumption was that once the earthing was sorted by the electrician, 2 circuits say for example the lights could then go on to the none RCD side making more space on the RCD side to reconnect my cooker. Another assumption i made was that if the electrician goes for installing an earth rod he would simply be able to put a 100amp 100ma time delayed RCD in a separate box before the CU. But if the electrician goes to the trouble of getting the supply converted to pme and sorting out any defects in the existing installation ( required by REC before they will put an PME conversion in ) the 100ma time delayed RCD would not be necessary , or have i made to many assumptions here.