OT - Fitting RCD in household mains supply

[Sparks]

Where does this stray energy go? All LV Transformers I have seen only have L&N, no earth, so where does it go? Into capacitors??

What use is a 100mA RCD?

You die with a 40mA shock, that's why they make them 30mA

Just like a split load would, but it would only take out the faulty section, not the whole lot. (If it took out the lighing, then there are still table lamps!)

Well I have NEVER had one single nuisance trip on my lighting RCD, and it has been in since the 1980's It has never tripped when a bulb has blown - the only time it did trip was when some d*****ad drilled through a cable (A builder, NOT me!!)

We did however have a fault develop with our "sockets" RCD, this was then tested (along with the lighting one) and it was found to be defective (over sensitive)

Sparks...

[Peter Parry]

Possibly it does, an insignificant number of times. Many more fall down the stairs or perish in fires.

How exactly does this stop the lights going out when you need them most?

[Peter Parry]

Of course there can be, and is. You are forgetting what happens when a bulb goes and the effects of inductance. You are also forgetting the effect of sensitisation by unbalanced noise filters. Indeed it is questionable if simple 30mA protected power circuits have any future because of this alone.

Perfectly serviceable.

Because their most common failure mode is fail on power on and they have poor reliability.

CFL, permanent low level lighting, whatever suits the need.

Any RCD on the lighting circuit is bad, and it is that which you do appear to be suggesting.

[Peter Parry]

Unfortunate, they may figure in the Darwin awards one day.

It is neither, the fitting of RCD's on lighting circuits is deprecated in the IEE regulations. There is no requirement to fit them on power circuits either - only on sockets which may be used by equipment used out of doors. Most electricians simply take the cheap and lazy way out.

The facts on deaths and injuries are plain and speak for themselves, I can't help it if you can't understand them.

Oh good, that will be really useful in a fire.

[Peter Parry]

You don't need resistive leakage to trip an RCD and the problems of pre-sensitisation are become more acute as more equipment includes noise filters.

Indeed not, that is why you chose a lighting type of high reliability whose failure mode is such that it would not trip protective circuits. Incandescent bulbs have poor reliability and less than optimal failure characteristics.

Why? Because they understand the balance of risks better?

Quite reasonable, but risk assessment is about how much work you have to put into circumventing a risk. Removing (or not fitting) an RCD on a lighting circuit is trivial and although the risk of fire is small the consequences are devastating and I suggest the minimal effort is worth it.

What's to fix? I can set up a demonstration to prove an RCD will trip on a bulb blowing on a perfectly serviceable circuit with ease. The point is that an RCD on a lighting circuit does no good at all but potentially may be very harmful, a situation recognised in the wiring regulations. What's the agrement for fitting them?

[Sparks]

When are you specificlly talking about here?

[Niall]

I have seen this interpreted (annoyingly I can't remember where) as meaning that all ground floor sockets should be RCD protected.

[Sparks]

I dont know enough about this to comment, only that as I have said before, in my installation (With incadecent, CFL and LV switchmodes) I have never had the RCD trip on a bulb failure (Including with 500w halogens) - So in my setup I really dont see the added risk. please explain why in my setup it wouldnt be...

Sorry but I totally disagree with that statment. It will stop people getting killed by electrocution.

Please explain, in a property where there are never any nucence tips, whay is it bad?

Sparks...

[Owain]

"Andy Hall" wrote | Non-maintained small fluorescent lights are not very expensive, | although the fittings are pretty ugly. Undoubtedly this could be | improved if there were a consumer premises market for them.

Something like this:

alarm, emergency light and Part L1 compliant.

Owain

[Chris Oates]

I'm quite prepared to be shot down in flames BUT I operate a wet area supplied via 30ma RCDs ..it has 3kw of halogen lighting - failure mode is water spray on tubes. it also has two water pumps many switchmodes many fractional HP motors a large compressor many incandescents several EMI filters many 240v 3 port valves which are damp and the only RCD trip we ever had was from a cable rupture in a pudle of water. MCBs pop often with incandescant failure but never the RCD (it's NICIEC tested regularly)

[Andy Hall]

Hmm. Interesting pair of products.

It would be good if one could have conventional lighting and switch in the fluorescent stuff when the power fails or the alarm goes off.

The technical design seems well thought out though

.andy

To email, substitute .nospam with .gl

[Andy Hall]

No shooting, but was is it?

.andy

To email, substitute .nospam with .gl

[Chris Oates]

cheapest way is to replace the CU switch with an RCD switch but then we don't want the light going out

see separate thread for thaat ;)

[The Natural Philosopher]

Not a bad idea actually.

However I am against having to add two provisions to fix what Peter has probably identified is a non existent problem.

[The Natural Philosopher]

Mmm. Ok, I'll take out the LV transformers. Bercause thinking about mine, they are alos two wrire devices. That is probably why they interfere so badly with radios.

Well it trips if you get a neutral ertha short, or some other appliance problem.

Whether you die at 40mA is not an established yes and no type thing.

Much less applied across the heart can stop it in a vulnerable subject: Much more applied across just a finger, will burn, but not kill.

The problem with 30mA is its proneness to false triggering, especially applied to a whole house.

The other issue is WHAT should be protected. Arguably the most dangerous circuit in the house is lighting, where you have potentially two user accesible terminals, and a (now rigorously earthed) metal housing in close proximity. Grab the housing with one hand, and stck yer other finger in the socket and Whazza! you are across the floor...

Not in my house. They have theor own lighting sockets on the relevant lighting circits.

I like the idea of split loads, but Peter has made me rethink all of this.

Frankly, I cannot see an ideal solution.

I am very happy that the discussion continue - if a general consensus of best practice CAN be established, then a fait accompli could be presented to those who dream up building regs.

[Will Dean]

There's often a requirement to fit one (a 100mA one) covering the whole of a TT installation.

Will

[Will Dean]

JOOI, can you describe the circuit? As I say, I have many years experience of non-nuisance-tripping 30mA whole-house RCDs, and always with a room full of computer equipment somewhere on the circit.

I'm not particularly arguing for the fitting of them against the regulations, only against the received wisdom that A. they'll give you lots of nuisance tripping, and B. that they're the major cause of nuisance tripping on lighting circuits. (Which we can all agree is a bad thing.)

However, my experience of whole-house RCDs is that they've given warning of incipient problems, both with wiring and with appliances. For a start, they detect neutral-earth failures (which one would guess represent about 50% of insulation problems) which are not typically detected by overcurrent protection at all. They also give early warning of thinks like heater sheath failure in immersion heaters and electric showers - I don't consider myself odd in thinking that I'd like to know about an immersed heater failure while there's 50mA flowing to earth rather than 50A.

And, like I say, I know someone personally who had a bad shock off a fixed light fitting, and a teenage girl in the village I went to school in was killed by an electric shock from a light fitting - her parents returned to the house after a holiday to find her dead on the living room floor.

I'm afraid I interpret your gruesome anecdote as a warning about the way one locks ones house at night (not being clear that it has any link to lighting circuit RCDs, anyway), and mine as warnings about earth protection on wiring . No doubt we both feel rather closer to our own cautionary tales.

Will

[Christian McArdle]

It is not explicitly stated as such. However, I think it is considered reasonable to assume that downstairs sockets can be used for outside equipment, unless specific alternative provision is made for outside equipment, such as a weatherproof RCD socket on each outside wall.

However, you should protect all socket circuits. This isn't a requirement, but common sense. It is also common sense to ensure that it is on a different RCD to the outside sockets, as these are quite likely to trip in wet weather.

Christian.

[Christian McArdle]

Firstly, it usually takes about 200mA to be killed. Secondly, a 100mA RCD is not for supplementary direct protection. i.e. it is not intended to prevent electrocution when you touch the live. Its purpose is to rapidly disconnect the supply in the event of a minor earth fault, rather than relying on there being a massive earth fault. Circuits likely to require supplementary direct protection should use dedicated 30mA RCBOs for that circuit only. Whole house RCDs (except 100mA Type S) and even split load consumer units are a bodge.

Christian.

[Peter Parry]

People don't get killed by electrocution from lighting circuits. They may sometimes get a belt from them (which an RCD will reduce but won't prevent) but they do not cause death or injury.

Because in a fire the lights all go out as the RCD trips.

Electrocution in the home kills 25 people a year and causes 2000 minor and serious injuries. I only have access to detailed figures for 1998 and in that year none of the 23 deaths by electrocution involved lighting circuits - all bar 6 were people dismantling live equipment, the remaining 6 were handling faulty supply cords.

In one year 500 people die and 18,000 are seriously injured in fires in the home.

That's why the wiring regulations don't support fitting of RCDs to lighting circuits.