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Both Dual Bound electrical contractors and Hager are claiming that George Wimpey has taken a major safety step in offering 30 mA earth leakage protection across all electrical circuits in its homes. They claim that the move significantly reduces the chances of a homeowner receiving an electric shock.

The size of the consumer unit used depends on the size of the home and the number of electrical circuits it has. A typical configuration splits circuits to reduce homeowner inconvenience (see box, over).

Clearly, nuisance tripping is a potential bone of contention. In a more conventional distribution system, lighting circuits have no rcd protection and others such as the upstairs, kitchen and utility ring final circuits, as well as those dedicated to the immersion heater, smoke alarms, cooker and fridge freezer, may not be included. These decisions are left to the electrician who uses the Wiring Regulations standards and common sense.

Hager has in the past argued for complete rcd protection across all electrical circuits (‘Total protection', EMC, May 2004). Then, however, the argument was to help prevent electrical fires caused by arcing in high resistance earth faults.

Its suggested solution was to use a 30 mA residual current device (rcd) for circuits where there is a greater chance of direct or indirect contact and a 100 or 300 mA rcd for additional protection against the risk of domestic fires. This, argued Hager, provides additional protection without the issue of nuisance tripping. If the 100 or 300 mA rcd tripped, then you should investigate the cause in any case.

Even at the time of the article two years ago, Hager and Dual Bound were exploring a more radical approach with George Wimpey. "The argument against using twin rcd protection is obviously nuisance tripping," says Dual Bound's md Martin Corney. "In practice, this is not a problem. The circuits can be arranged so that if an rcd trips you don't lose all lighting or power. In addition, the loads are roughly equal on each side of the board to minimise tripping."

For a six by six split-load board Corney suggests having circuits for the cooker, ground floor ring main, first floor lighting, conservatory, immersion heater and a ground floor lighting circuit on one rcd. For the other he suggests the circuits could be kitchen ring main, first floor ring main, a second ground floor lighting circuit, heating and garage. This leaves a spare outgoing way, which could also be used for a smoke or burglar alarm.

"Naturally we came up against a lot of arguments and had several meetings with people from George Wimpey and fellow contractors that carry out their work nationally," continues Corney. "For instance it has been stated that smoke alarms should not be placed on a circuit protected by an rcd for safety reasons. In fact, even if the circuit did trip the smoke alarm has to have a battery back-up, which typically has a life of 12 months.

"In any case, now that George Wimpey has had twin rcd protection for two years many of the arguments about nuisance tripping have become redundant. We deal with George Wimpey Northern region and have not had a single call-out due to a tripped rcd. From what I can gather, other regions are experiencing similar success.

The argument against using twin rcd protection is nuisance tripping. In practice this is not a problem

"In many cases the cause of an earth fault current tripping the rcd is due to a faulty portable appliance. We find that the public is aware of such problems, so they either unplug the equipment themselves or don't use it. If there is an earth fault it should be investigated anyway," concludes Corney.

Product marketing manager for Hager Steve Dyson argues that George Wimpey has taken a responsible approach in offering its customers additional protection against electric shock. "The DIY culture of today's society can pose its own dangers," says Dyson. "For instance, many modern houses use metal partitioning for internal walls. I have heard of rare instances when this partitioning has become live - someone putting a screw or a nail into the metal stud of a wall is then at major risk. Also, unless safety lampholders are used, one of the few areas where there are exposed parts free to touch is the lampholder.

"On a more cautious note, you should always remember that a rcd should not be used as the sole means of direct contact with a live conductor. Just because there is complete rcd protection across all circuits, complacency should not set in.

"Personally I do not think that this is the case. George Wimpey is not actively marketing the rcd protection to its customers; it is merely there as an extra safety precaution against both electric shock and fire. Also, an IEE (now IET) report states that other than certain groups, typically men over 35, many people are unaware of what an rcd does. Most people remain rightly cautious about electricity.

"Using 30 mA protection across all circuits provides additional protection against electric shock for the workforce on site during the final stages of construction. Again the same proviso against complacency applies, but that is not an argument against providing such supplementary protection."

Asked to comment on a move to 30 mA rcd protection across all circuits in the home an IET spokesperson stated: "We urge that all installations meet the Wiring Regulations. These state that every installation shall be divided into circuits as necessary to avoid danger and minimise inconvenience in the event of a fault."

Dyson and Corney argue that George Wimpey has taken a positive and proactive step towards improving safety in the home for both its customers and workers and meets regulations. "After two years without any problems of nuisance tripping using twin 30 mA rcds, we have clearly met and exceeded the requirements of the Wiring Regulations," Dyson concludes. "George Wimpey is to be applauded for such a move. It is time for electricians and housebuilders to reconsider how they use rcd protection."