No RCD on cooker, Why ?

[bernardgreen]

Perhaps I am being over protective but

Why is it not necessary to have an RCD on the supply to the cooker.

If the protective earth to the cooker failed for some reason and the cooker developed a live to chassis fault ( leaking element ) then the chassis is live. Some ones touches the cooker with one hand and an earth bonded piece of metal with the other. As the cooker chassis is live that person has the immediate need of an RCD dis-connect.

Also the 30 ( 0r 100 ) mA fault current that would trip the RCD in a fault condition is not going to cause any damage where as a fault current that could reach 30 amp before the MCB tripped could do damage to metal work or wiring not designed to carry 30 amp. Not all wiring in cookers is capable of sustained passage of 20 amps or more.

( our oven IS on an RCD and the kitchen lights are on a different RCD )

Bernard
Sharnbrook

 

[dingbat]

By that reasoning, Bernard, every circuit would have to be RCD-protected. Maybe not a bad idea in principle, but given the alarmingly high in-service failure rate for RCDs, it would be foolish to rely on them.

Our principle method of protection from indirect contact is still EEBAD.

 

[sm1thson]

i agree bernard, but i guess its a ballance of practicality, as when the earth leakage ads up the oven is likely to cause nuisence trips. i guess this is where rcbo's come in, but they are expensive, the price will drop when they are used more -but thats a chicken/egg scenario!. i got the impression that the 17th edition is going to have more requirements for RCDs so hopefully that will drive the use of rcbo's and bring the price down.

alternatively is there some merrit in people using a 100ma RCD on the incommer like a TT setup?

 

[JohnD]

If you use a 100mA then it needs to be time-delayed, otherwise it will probably trip at the same time as a 30mA RCD.

The disadvatage of using any RCD as a main switch is that you will lose all circuits, including lighting, which is certainly inconvenient and can bring danger.

RCBOs are great! You could always use a 100mA RCBO on the cooker to reduce nuisance trips. Another advantage of RCBOs is that they protect individual circuits so do not suffer from cumulative small leakages per circuit reaching the trip point