Faulty RCD...

Nemo

mercurystar999 wrote:

As it is on the inside of the house changing it should be no problem for you. In the above posts they suggest upgrading the fuse board, is the rest of your sockets protected by another main RCD? Do you know what type of fuse board it is?

Just checked and it's one of these:-

http://www.tlc-direct.co.uk/Products/WY604.html

I think I'll just go for the RCD socket option. Even considered replacing it with a standard double-socket, and using a plug-in RCD, but for an extra tenner or so I know I should do it properly.

ffym

gromituk wrote:

You are very, very unlikely to get a live-earth shock from a ceiling light. Even if you stick your fingers in the bulb holder, you will get a live-neutral shock, which won't trip the RCD.

Earthed wall lights might present you with slightly less of a challenge, but still nothing like portable appliances.

My point about protecting the lighting circuits is not one of electrocution but one of fire hazard. If you have new wiring with energy efficient lamps then the risk is virtually nil anyway. Old wiring buried in the loft under various forms of heat insulation is a worry though - particularly if multi lamp chandeliers have been fitted with high wattage bulbs.

gromituk

But an RCD is designed to protect against electrocution, not fire. It will do absolutely nothing to protect against overloaded wiring. That is what MCBs/fuses are for.

ffym

gromituk wrote:

But an RCD is designed to protect against electrocution, not fire. It will do absolutely nothing to protect against overloaded wiring. That is what MCBs/fuses are for.

Disagree!
First symptom of overheating is insulation degradation, in all (correct) fixed wiring the live / neutral are individually insulated, the earth wire is not. When the wiring cooks it faults to earth first - not live to neutral.
MCB's / fuses will protect against large overloads such as shorts but for insulation degredation due to excess heat the RCCD will trip first every time. Iron leads are a classic example, they get warm, they get twisted, the insulation breaks down and then they fault - live to earth - RCCD trips, no fuses blown!
At the fault levels that take out a RCCD it's most unlikely that a fire will occur, it's quite possible to feed a high resistance earth fault to combustable levels when protected by a 6A MCB, with a 32A fuse flames are virtually certain.

gromituk

Iron leads are not the same as wiring in lofts. Do you have some references to back up your theory?

beefster

Simmer down......... you are both right.

An RCD detects some, but not all, faults in the electrical system and rapidly switches off the supply, reducing the potential for injury caused by a common type of electric shock. To reduce the likelihood of injury to people the RCD should have a tripping current of not more than 30 milliamps (mA). RCDs with higher tripping currents are unlikely to prevent injuries to people, but can protect against fire.

http://www.hse.gov.uk/electricity/electricequip.htm#rcd

ffym

beefster wrote:

Simmer down......... you are both right.

An RCD detects some, but not all, faults in the electrical system and rapidly switches off the supply, reducing the potential for injury caused by a common type of electric shock. To reduce the likelihood of injury to people the RCD should have a tripping current of not more than 30 milliamps (mA). RCDs with higher tripping currents are unlikely to prevent injuries to people, but can protect against fire.

http://www.hse.gov.uk/electricity/electricequip.htm#rcd

Thanks Beefster, we were getting a bit off the original thread but thanks to gromituk as I think it is a useful discussion.
It's interesting that the figures produced from the Office of the Deputy Prime Minister on the causes of domestic fires show that, all the causes of combustion due to electricity all are going down apart from "electrical distribution" which is on the increase (2003 are the latest available figures - link here: http://www.odpm.gov.uk/embedded_object.asp?id=1124894)
I know statistics can prove anything and that even though increasing, fires caused by electrical distribution are a small proportion of the total.
My own standpoint is that RCCDs can help reduce this figure, but obviously the risk needs to weighed against the cost. Certainly in most homes it would be well down the priority list behind getting rid of cigarettes etc, chip pans and candles!!

beefster

The safety aspect far out weighs the cost implication in my view........ fit them and you will be very unlucky to get a fatal shock or an electrical fire on the circuits covered.