On Tue, 16 Dec 2003 20:29:09 -0000, "Will Dean"
wrote:

"Peter Parry" wrote in message
.. .

Can you propose a mechanism for this? The only one which comes to mind
would be that you already had a neutral-earth leakage fault, and the rise in
neutral current caused by the bulb-failure arc was sufficient to create a
leak to earth.

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.

As has been pointed out the danger is in using inappropriate
lighting. If the design of the house or the condition of the
occupants makes a fall likely don't fit incandescent bulbs in lights
needed for safe navigation of stairs.

It wouldn't matter what kind of lamp illuminated the stairs if the lighting
circuit had tripped.

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.

My experience is of lifting the burnt corpses of family out of the
way of the locked front door they had died against while trying to
break it down to escape the fire which killed them.

Yes, but you're a (former?) member of the emergency services, aren't you?

No.

As such, I have every sympathy with the gruesome sights you might have had
to deal with in your chosen profession, but I do believe that members of
such services are uniquely *ill* placed to give general advice about risks
to ordinary people.

Why? Because they understand the balance of risks better?

To a fireman, a horrible death in a house fire is a common occurence

Actually it isn't.

- to
me, as a resident of a non-smoking household, it's extremely unlikely to be
the cause of my, or my family's demise. Personally, if I'm doing the
neurotic parent bit I worry about road safety a darn sight more.

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.

TBH, if you know of a property that has an RCD which trips when light bulbs
blow, then you ought to advice the occupants to get the wiring fixed.

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?

--
Peter Parry.
http://www.wpp.ltd.uk/