house smoke alarm false warning

[charles]

but it is.

[Lieutenant Scott]

Unless the fitting comes loose exposing wires that aren't supposed to be exposed.

I've had shocks within one hand and across my body from one hand to the other. I guess I don't have a weak heart.

Kinda puts a damper on the belief by some that they are safer than fuses. More convenient yes, but not safer.

I have fitted MCBs ONLY to my lighting circuit. This because I have automatic lights, the sensors are very susceptible to surges, and putting a fuse carrier back in is not a clean switch on.

And the majority of those have nothing to do with unexpected darkness.

As stated earlier, 240 volt shocks are not life threatening to healthy people.

I tell you what would be safer though - not earthing so many things. Imagine this - you touch something live, you get a tingle. Now imagine you are leaning against an earthed sink, washing machine, etc, etc. Now you are a circuit. Why did people think an earth was a good idea?

RCD/MCB in the same part is what I see installed in commercial premises. Although the cost may be higher than domestic installations....

Oh, incompletion. Not a fire :-)

[charles]

yes, I've seen them there, but we have no pavement on our side of the road. the cable is simply under the carriageway.

[Ghostrecon]

dont want nuisance trips to take out lights or freezer seemed sensible to put smoke alarms on non rcd - garage conversion and so u room lighting waere done last year so the lighting is still on non rcd need to get a new busbar to move the rcd in the cu- whilst 240 volts across a dry body contact may not kill I would rather not be in the circuit especially if a wet contact is possible

fail due to a fire in the wire before your meter. Happened to my neighbour due to loose connection. Electric board too stupid to fuse this wire at substation.

yes interlinked and battery backed up - think that was in the op that started this sub thread

[The Natural Philosopher]

I went up to 100mA slow blow on total house to get rid of nuisance trips.

I ought to put RCBO's on the 13A rings, esp the ones that go outside..

Round Tuit etc..

fail due to a fire in the wire before your meter. Happened to my neighbour due to loose connection. Electric board too stupid to fuse this wire at substation.

Unlikely in my case, since it would blow the substation fuse - and has.

Comes out of de ground and into the meter box..think that's where the company 'house fuse' is...

[John Rumm]

Even less likely - but again, you are in a situation where you are unlikely to be well earthed. If you made contact with both live and neutral then you would get a nasty shock to the hand, but it would not be through any major organs. Also the effect of the jolt / passing out etc will tend to break contact which minimises the duration.

Light fittings are exceedingly rarely a cause of electrocution.

Weak or otherwise, the wrong set of circumstances will either stop it, or more likely result in ventricular fibrillation.

Depends on the type of fuse... compared to BS3036 rewireable ones they perform better, and hence one does not need to design circuits with a current derating on the cable for installation. Also there is no chance an ill informed user can rewire them with the wrong wire / tin foil etc.

Compared to a cartridge fuse, then they are no better (and in some cases once could argue not as good (i.e. they are more likely to trip on a incandescent bulb failure than a fuse). However they are certainly more convenient.

You ought not be re-energising under load anyway... not good for fuse or MCB contacts.

(note there is a mistake in what I said above... the 20 deaths/year are from *all* sources of electrocution including misuse of portable appliances - those from fixed wiring typically used to amount to one or two a year (although there is evidence that this is now increasing following the introduction of part P of the building regs (as you would expect)))

Probably true, however it was found that there were sufficient number of serious falls in darkness that resulted from nuisance RCD trips to cause a revision of the guidance on RCDs originally included in the 15th edition of the regs.

That is complete and utter bollocks.

For several reasons....

Firstly 240V shocks can and do kill perfectly healthy people every year.

Secondly there is a much larger class of people who will be seriously injured and suffer permanent after effects as a result of shocks.

There are an even greater number of will suffer serious but recoverable injury, and still more that will be hurt to various degrees.

Research conducted by the National Safety Council shows that in the UK there are something like 1 million hospital visits resulting from electrical shocks per year. (obviously these include minor burns cuts and bruises, right up to cardiac damage, severe burns / disfigurement etc, and deaths).

You seem to be misunderstanding the whole purpose of earthing. It is not there to reduce the shock potential difference you might be exposed to. It is designed to operated in conjunction with a circuit protective device to de-energise a circuit in the event of a fault.

If a wire falls off in some appliance and makes the metal case live, the earthing connection to the case will ensure enough fault current flows to blow a fuse or trip a MCB - thus limiting the maximum shock duration to something survivable.

The argument that you are safer with no earths around is true, but only when you can ensure there is *no* access to any independent earth. If there is, then you need to make sure that the earth is "good" or else you may not get adequate fault current flowing to operated the CPD while at the same time having an earth good enough to kill you.

If you want to seek to reduce the magnitude of potential difference that you might be exposed to, you need equipotential bonding. This is typically used in location where people are highly vulnerable to electric shock (e.g. when wet / naked / barefoot etc as in bath and shower rooms).

RCDs add another layer of protection by limiting shock duration by detecting current imbalance. They work particularly well for people (mis)using appliances outside etc or any other situation where you have unwittingly become part of a circuit.

Yup, that is a RCBO. (Residual current Circuit Breaker with Overload protection)

Details here:

>>>> BTW I take it the smoke alarms are ok on batteries, because all the

Either way - the duration of the former is significantly longer than any fire one is likely to encounter.

[ARWadsworth]

It was God's idea.

We just use it.

[John Rumm]

Or stick all the outside / outbuilding circuits on their own CU and with its own (time delayed) RCD (TT Here)

[The Natural Philosopher]

I'm a tad less rural/farm than you are John :-)

[John Rumm]

Putting outside circuits on their own CU was really a way of making sure they could have no influence on the house electrics - even to the point of not sharing RCD leakage budget.

Really, I had visions of you out in the sticks a bit... How long would it take you to walk to the nearest shop? (probably about 15 mins from here)

[The Other Mike]

was an old house. The hot wire ignited the rafters.

loudly and thrown sparks for a full 10 minutes. Also the electric board guy confirmed it when I asked him. He said it was "too expensive to fit them".

Possible facts:

You saw a fire Maybe that fire was caused by electricity

Definite facts:

The cable was fused at the substation to protect the cable There is no way to bypass the fuse carrier at the substation

Possible fact:

The fuse rating may have been incorrectly chosen

Definite non fact:

Fuses are not too expensive to fit

Definte fact:

Fuses cost less than half a dozen metres of cable

The End

[The Natural Philosopher]

similar, but I don't have lossa outbuildings

[John Rumm]

Me neither (yet - got some planned though). Got a feed to garden sockets and pond, another to garage/workshop, and one for outside lights/PIRs (+ one low current socket). The garage has its own split load in it, and that also has a feed to a shed.

[Lieutenant Scott]

Have done it with both. With wet hands all the muscles jump - the only danger is falling off something, or bashing your head against something hard or sharp.

Do tell us then, and show off your knowledge....

[ARWadsworth]

Considering that dennis posts here that is quite a statement:-)

[Lieutenant Scott]

A fuse could be place there.

[Lieutenant Scott]

Except when some health and safety twatt insists the fitting gets earthed. Hold the fitting with the left hand and change the bulb with the right....

The heart has approximately 5 signals to keep it going. It's not easy to stop it.

What's with no amperages matching up? 5 amp fuse, 6 amp breaker, and the "lighting" cable in Wickes is 13 amps!

I'd prefer them to trip when an incandescent fails. My fuse didn't and the buggered halogen spot took out the automatic light switch circuitry.

Very inconvenient not to. And impossible for me. My light switches are automated.

IN creasing?

We need to get rid of these paper pushers.

All 20 of them. Big deal.

So why am I still in one piece?

990,000 of them because their finger is a bit sore.

Er..... if everything is earthed, they ARE at the same potential.

I've had a few shocks from mowers in the rain etc. Never done me any harm.

One would hope so!

[Tim Watts]

Joints used to be ferruled and soldered. These days they are more often crimped, I believe.

Fuses exist in "link boxes" which are in the road, accessible with a visible lid (obviously) and more often occur when a feed splits off to service a side road, but not always (could be a solid joint, or you could have a link box somewhere along a straight section of road). The fuses which are fitted in 3's (3 phases) vary from typically 300A to 500A.

Having a visible box marked "SEEBOARD" or some such is no guarantee of presence of fuses - it could also be a fuse box fitted with solid links (copper bars) if the engineers decided a fuse at that position was not actually useful, or wanted the option to fuse later.

This is why, if you put a spade through the cable under your drive that feeds your house, you'll get a not inconsiderable bang.

[Tim Watts]

And why the British system is superior to say, the Chinese system. My son got a belt unscrewing an ES lamp from a fitting in China due to:

1) It being an ES fitting[1]; 2) China, in common with a lot of countries has no enforcement of polarity so in this case the cap happend to be live rather than the tip[2]. [1] Modern British ES fittings disengage on the first turn or so, the old ones of course just had an all metal recepticle. However, even in Britain, plenty of the older type exist. [2] Even if the British regs demand the tip be live and the cap be neutral, there's no guarantee some pillock hasn't wired it up wrong.

Which is why I hate ES fittings, and regard BC as generally a better idea.

[Lieutenant Scott]

So is it just a matter of they found it cheaper to fit 500A cable to each house than to fit 100A cable and a fusebox? I would have thought thicker cable up everyone's driveway was very expensive.

And require the purcahse of a new spade.