electrics...whole house RCD?

andyox

If you already have a consumer unit with miniature circuit breakers for all circuits, is it necessary (for safety) to have a whole house RCD - which will shutdown everything?

Andy

sjc_2

They are normally built in to the newer Consumer Units as standard and have a split to put your light circuits the other side of the RCD protected circuits. So when it does trip your lights will stay on so you can see what you are doing.

They offer very good protection against shocks and dodgy appliances etc. Highly recommended.

We had all sorts of problems when ours first went in with the washing machine tripping the RCD. Called out washer man and it turned out when the spin kicked in a wire had been rubbing against the chassis and had worn through the insulation so the RCD was detecting an earth drain and tripping out.

moonrakerz

An MCB and an RCD are totally different animals.

An MCB will trip if there is excessive current flowing through the circuit. An RDC will trip if there is current (a very small one) "leaking" to earth, possibly through you!
Don't forget, you can electrocute yourself just as easily from a light socket as you can from a 13 Amp socket.

christhesparky_2

whole house needs rcd protection when the supply is via overhead lines

HugoSP

christhesparky wrote: »

whole house needs rcd protection when the supply is via overhead lines

I assume from your username that you are employed as some sort of electrician?

The reason I make that statement is because I am afraid I consider that you are wrong, as you were with your answer to equipotential bonding.

An RCD at the origin of supply (ie after the meter) is only necessary when a TT earthing system is employed. There are broadly 4 types of earthing systems available. The TT system is the only type that is NOT provided by the distributor. It is infact a copper or steel rod into the ground that has a 10mm earth cable attached to it from the consumer unit. Such a system has a much higher earth loop impedance and hence needs the RCD to trip in the case of an earth fault. The earth loop impedence (resistance of the earth circuit) in all the other earthing systems can cope with earth leakages that may occur due to an appliance or an installation fault.

In the case of a TT supply an RCD is often fitted as the main switch. This RCD has a higher residual current setting o 100mA, as opposed to the 30mA unit fitted on a split load board.

If the OP needs more information I can go to my copy of th IEE On Site Guide and get it.

The specification of RCDs has nothing to do with whether or not the supply is overhead or not.

Christhesparky, I respectively ask you to learn your trade before you start providing answers to these questions. Either of the two answers you have given could kill someone:eek:

HugoSP

andyox wrote: »

If you already have a consumer unit with miniature circuit breakers for all circuits, is it necessary (for safety) to have a whole house RCD - which will shutdown everything?

Andy

As I said in my previous post an RCD at the origin of supply is necessary if you are on a TT system. A single core earth wire down to a steel or copper rod in the ground will provide some indication, alterntively you could contact your distributor.

The current regs require you to protect with an RCD any socket that could reasonably be expected to provide power outside. Common practice is to split the load. Lights, smoke alarms and doorbell would not be protected whereas sockets, perhaps the cooker, electric shower and maybe the immersion heater would be protected.

andyox

HugoSP wrote: »

As I said in my previous post an RCD at the origin of supply is necessary if you are on a TT system. A single core earth wire down to a steel or copper rod in the ground will provide some indication, alterntively you could contact your distributor.

The current regs require you to protect with an RCD any socket that could reasonably be expected to provide power outside. Common practice is to split the load. Lights, smoke alarms and doorbell would not be protected whereas sockets, perhaps the cooker, electric shower and maybe the immersion heater would be protected.

Thanks hugo/everyone for replies.

Apparently (from NICEIC certificate) our downstairs sockets MCB has an integral RCD. Given that the old whole house RCD has been removed when the new consumer unit was installed - I wonder if the upstairs socket should have RCD protection as well...

Andy

HugoSP

andyox wrote: »

Thanks hugo/everyone for replies.

Apparently (from NICEIC certificate) our downstairs sockets MCB has an integral RCD. Given that the old whole house RCD has been removed when the new consumer unit was installed - I wonder if the upstairs socket should have RCD protection as well...

Andy

No, not normally necessary Andy.

Upstairs sockets are not normally expected to power appliances that are used outside. If you fancy powering up Christmas lights from a bedroom window and consuming half the out put of the national grid, as a lot of people tend to aim for these days, then you would need an RCD for this outlet at least.

You can get RCD sockets as a one off.

From what you've told us you should be OK provided you do NOT have a TT supply.

HTH

ffym

HugoSP wrote: »

An RCD at the origin of supply (ie after the meter) is only necessary when a TT earthing system is employed.... The earth loop impedence (resistance of the earth circuit) in all the other earthing systems can cope with earth leakages that may occur due to an appliance or an installation fault.

I am rather confused by these comments. Whilst I agree that certain supply configurations need RCDs to clear electrical faults efficiently are you suggesting that RCDs are unnecessary as a safety device (for human protection)? In my opinion a RCD is one of the most important pieces of electrical protection (human) on any earthed electrical system.

Nobleck

Another alternative would be to replace the normal mcb's (socket circuits, shower circuit) with RCBO'S , this is normally considered to be a cheaper alternative to a fuse board change.
HugoSP is spot on with his comments as usual and it's nice to know that a few people on here actually take time to sit down and study before posting replies. Well done!!.

Avoriaz

christhesparky wrote: »

whole house needs rcd protection when the supply is via overhead lines

Is 230 volts via overhead wires more dangerous than 230 volts via underground cables or is there some difference in the earthing?