Kitchen Electrics FAQ?

[unopened]

Well, I suppose the question is: why did the RCD trip? We seem to have ascertained that DIN rail RCDs do not stay tripped on power loss only - they will re-energise the circuit after a power failure so long as no fault is detected, so the RCD having tripped and stayed tripped indicates a fault of some sort. Are you happy for your fridge freezer to be on a faulty circuit?

Of course, if the fridge/freezer shares the circuit with other appliances which may potentially generate leakage currents in excess of the RCD trip margin, then I see the problem, so there is a good argument for putting a fridge/freezer on its own spur from the consumer unit.

I have received a mains shock off an appliance (in this case, a washing machine) where the flex had worn entering the appliance, rendering the casing live. It was not on an RCD protected circuit. I don't know if that particular w/m was double insulated.

I don't know how much of a problem nuisance trips are in reality. It would certainly be irritating to lose a freezer full of food as a result of a nuisance trip just after you left for a fortnight's holiday. Perhaps (taking things to extremes), one should have two sockets - an RCD protected one for when you are in, and a non-RCD protected one for when you are away for long periods. That said, the British populace seem to have survived the decades without RCD protection for their freezers quite well, so one might argue the absolute level of risk is small enough to ignore. Your choice, really. It is a perennial topic with no satisfactory resolution.

Regards,

Sid

[John Rumm]

Not wrong as such, but there are a couple of points to bear in mind. Firstly there are some items of fixed equipment that you don't really want to be disconnected unless there is a real fault. Freezers, boilers, fish tank heaters, smoke alarms, life support systems etc.

Secondly some equipment like washing machines etc can have naturally high leakage currents. If they are sharing a RCD with too many other items you increase the nuisance trip likelihood since the extra leakage can lead to sensitisation of the RCD.

Your post does raise an interesting point about the NVR function of some plug in RCDs though. I will add that to the wiki on the subject:

[Lurch]

On Mon, 30 Jul 2007 13:01:56 +0100, John Rumm mused:

And if you're like me, you buy a new machine with 9, 12 and 24mm tape in all different colours, use the appropriate colours as above then when they start running out don't actually remember to replace them and then just stick any colour anywhere. 24mm black on yellow looks good for labelling spurs in kitchens. ;)

[Lurch]

\On Mon, 30 Jul 2007 06:02:45 -0700, [e-mail] mused:

I never said I did, I meant if you for instance go away for a weekend and the power trips out an hour after you leave. Obviously the circuit would be repaired upon your return but I'd rather have a happily working fridge\freezer on a slightly faulty circuit than a non working fridge\freezer on a faulty circuit thawing the contents and pissing itself all over the floor for 2 days.

Yes.

I don't think I've ever seen a class II washing machine.

Getting a bit over complicated now, bear in mind 99% of the UK population do everything on price and don't care how well it doesn't work or how many flaws a plan has, as long as it's cheap.

[David W.E. Roberts]

Thanks for all the useful advice so far - I have been ill (man flu) for a week but have now resumed operations.

[meow2222]

People dying by electrocution from ff casings: 0. People getting ill and dying from dodgy food: many.

Odds of an electrically leaky ff killing you: from the above figures, close to zero. There are other safety layers designed to take care of such faults, maybe this is why.

Therefore as a safety measure fitting RCD ''protection'' to a ff feed is counterproductive. Satisfactory resolution achieved.

NT

[meow2222]

no, on several counts.

I wish

only if you define good order as not tripping an rcd, or having near zero leakage, which I dont. I define it as safe, ie not killing people. Millions of RCD tripping loads have been used perfectly safely in both domestic and commercial premises, and a huge number are in use today.

This is just another illustration of the difference between what one might imagine and what electrocution figures tell about the real facts. For some reason what people commonly imagine about electrical safety tends to be unrealistic fairly often.

Whats it going to cost to put these in every property in the land? (added cost at rewire time only) How many deaths per year will it prevent? What does that cost the nation per life saved? If youve answered those qs it should be fairly evident that other measures using that money could save 100x as many lives.

NT

[unopened]

Purely to satisfy my curiosity, could you say briefly what the other safety layers are? I imagine they are quite effective. As a side note, on my trips to visit friends and relatives abroad, I've noticed a lot of equipment is not earthed/grounded and protected (apparently) only by cartridge fuses. However, they do use washing machines (and dryers) in (wet floor) bathrooms - and on inspection these use sockets that are earthed/grounded and in addition come with warning labels to say that only double insulated equipment should be used in them. (Belt & braces?) On that basis, I think w/ms available in Europe are probably double insulated.

Cheers,

Sid

[Owain]

Yebbut nobbut Part P...

Owain

[John Rumm]

My own experience with RCD protected systems is that with working appliances and a well designed system, nuisance tripping is a non issue.

Zero leakage is not a requirement. Reasonable estimates of likely leakage can be made, and adequate leakage budget allocated on the circuit.

The electrocution figures tell us that injury of death resulting from fixed wiring installations is a tiny proportion of total injuries and fatalities. The vast bulk happening with portable appliances. This is one area where changes to the fixed wiring (more widespread use of well designed RCD protected circuits) could have a big positive impact on safety.

I understand that of all the accident and injury risks we face in our homes, that of electrocution is one of the less likely ones. That does not seem to be justification to abandon any efforts at improving the electrical design and safety, just because you are more likely fall over your part P extension lead, or lacerate yourself on your nanny approved round ended kitchen knife.

As a proportion of the total cost of a rewire? Cube root of sod all.

For each property equipped in this way, that is another one where it would become very difficult to electrocute yourself with a faulty or misused appliance.

I don't follow your argument really. If you are rewiring anyway you

*will* be including RCD protection in the required places since that is a current regulatory requirement. All Andy is suggesting is that you opt for better design practice and implement this in such a way as you reduce the likelihood of, and impact from, any nuisance trip that does occur.

The total cost difference between a basic compliant design, and a better one with improved discrimination, is unlikely to be less than £100 extra. Looked at as a proportion of the cost for a full rewire at say £2,500 - £4000 that is pretty insignificant.