Fire risk

[Stockden]

Originally Posted by MichaelR

Proof of the pudding is if you had a fire you would admit to the Insurance company if asked that you had left certain electrical equipment switched on because they do work on statistics.

Yes I would. As Kat has said, the clock radio, like most domestic appliances, was designed to be left plugged in continuously.

You are right to point out that insurance companies work on statistics. They use those figures to calculate the chance of them having to pay money to their customers. The fact that the annual premium is a small fraction of insured value (0.2% in my case) shows that they deduce from those statistics that the probability of fire caused by an electrical appliance are acceptably low (at least to them).

Of course you do need to use common sense and operate appliances in the way they were designed for. I would not, for instance, leave a hot air gun switched on and running continuously nor would I dry my coat by draping it over an electric fire.

[russell_w_b]

I opine that you're more likely to have a fire through leaving a concave mirror, or a bottle of liquid in view of a non-north-facing window.

If it's designed to be left energised (and is in good condition with the correct fusin in place under the plug-top), it'll be fine. Others have described the risks more eloquently, so I shan't repeat them.

[Boom]

Originally Posted by Kat Manton

That relies on the live and neutral (and earth) wires being cut to the correct length; the live wire should be short and run straight to its terminal, the neutral wire should be longer and have some slack in it (and the earth wire, if present, longer still and also slack.)

That is what I would have thought too but....

A few years ago I took City and Guilds 236 (electrical) and the instructor was adamant that doing this on a practical test would result in a fail. The wires all had to be the same length.

Dave

Note:- By 'same length', I mean that they all had to have equal reach to the connections.

[Kat Manton]

Hi David,

Originally Posted by David Tilley

Note:- By 'same length', I mean that they all had to have equal reach to the connections.

I think we must be describing the same thing. As an engineer, I use the term 'length' in an absolute sense. If two things are the same length, they measure the same (within some tolerance) in some unit of measurement (mm, inches, etc.)

Clearly, if all three wires were cut to the exact same absolute length, the live wire in a typical mains plug would have to be coiled up to fit and the neutral wire less so. The earth wire would be the first to disconnect if the cable was to be pulled out, followed by the neutral, and the live last. That circumvents the designed-in safety feature of UK mains plugs and is a bit dangerous...

Regards, Kat

[Station X]

When I was being trained as an apprentice starting in 1967 I too was taught that the earth wire in a plug should be the longest. The reason given was that it pulled out first it would leave a "live" appliance uneathed and there was a possibility that the disconnected wire could contact the live pin rendering metal parts of the appliance live. Also if the L or N pulls out first someone is likely to investigate what's wrong whereas a disconnected earth wire can go undectected.

We were also told that it was extremely rare for an appliance to require a 13A fuse. I have bags of spare fuses and most of them are 13A ones which I've removed because they've been fitted where only a 3A was needed.

[russell_w_b]

Originally Posted by Station X

When I was being trained as an apprentice starting in 1967 I too was taught that the earth wire in a plug should be the longest.

Same in the BBC Engineering Training Dept. Makes perfect sense to me.

[ted_ntsx]

Originally Posted by paulsherwin

A typical small appliance like a clock radio will contain lots of low rated components. If these components fail they may burn out, but this will happen too quickly to start a fire outside the unit, or the heat generated will be insufficient to start a fire.
....

Paul

It is rather surprising what CAN catch fire. Most unusual but...

I saw a simple TV remote handset catch fire. Powered by just a normal PP3 battery, it actually produced flames! It was on a solid workshop bench so nothing else happened, but supposing it had been left on on sofa...

Ted.

[kalee20]

Originally Posted by Kat Manton

Many years ago, the wiring on my sister's hairdryer failed (spectacularly!) Due to repeated movement, the wiring fractured. This caused internal arcing which blew out a chunk of both inner and outer insulation, leaving a hole in the side of the cable and only the neutral wire attached, just where the cable exited the plug.

That happened to me once, with a fan heater. The heater drew enough current so that, once the conductor fractured, there was a sufficient internal arc to puncture the insulation and flash over live-neutral. There was a loud bang and the fuse blew - but not before a ball of molten copper shot out of the side of the cable.

I always use minimum-rated fuses in mains plugs. I leave quite a lot of equipment (VCR, DVD-recorder, radio alarm clock) permanently 'on'. As for vintage equipment - mains transformers do have the potential to die due to enamelled-wire breakdown, and if wax impregnated could catch fire. Luckily, I've only had 2 transformers do this, and I've been present each time, and not waited for the flames. Conversely, AC/DC equipment with a mains dropper does not have this mechanism to self-destruct under power, and so although running hotter, could also be said to be safer!

[russell_w_b]

Originally Posted by ted_ntsx

It is rather surprising what CAN catch fire. Most unusual but...

I saw a simple TV remote handset catch fire. Powered by just a normal PP3 battery, it actually produced flames!

I could understand this in a mobile telephone (hence the reason they are not to be used on a filling-station forecourt, lest they are dropped and the battery shorts), and I'm wary of leaving my laptop on near the furniture because of the large battery capacity and the fault-energy available within.

I've had a couple of 'U2' cells get extremely hot in a faulty flashlight, and then there's the old trick of touching a PP3 onto a brillo pad...

[Richard]

Hi

I recently did a commercial kitchen refurbishment job for an insurance company after a fire, caused by a domestic fridge used to keep deserts.
Looking at the remains, the terminal block on the compressor caught fire, which set fire to the insulation above it, which in turn set fire to the plastic wall cladding behind the fridge, which then went through the ceiling/floor and the whole place needed gutting.

The TV remote is a scary one, they end up down the side of the sofa etc all the times.

On the point of fuses, when I did my PAT testing course we were taught that there are only 3 recognised fuse values; 13, 10 and 3 amp, because they are all identified by the colour of the fuse; brown, black, red.
Personally I use 1, 2, 3, 5, 7, 10, and 13 selecting the lowest for the job.

The strangest thing I have seen catch fire was a small rechargeable torch which was in my tool bag and caught fire while it was in the boot of my car, I was driving and smelt the smoke, and found the cotton / canvas bag smoldering, next to my plastic spare tin of petrol .
The torch was totally melted, I assume the wiring shorted out and the nicads can provide a big short circuit current.

Richard

[Michael Maurice]

Modern electronic equipment can and sometimes does on occasion catch fire.

Some Philips TV's had a problem with their mains switches which could cause a fire, worst still the only thing protecting it was the fuse in the plug. What did most people do, they simply changed the original 5A fuse to a 13A because that's what they had to hand. They then wondered why the thing went Bang!

Sony had a problem in the mid - late 80's with the Preh type power switches, but having discovered the problem, they had a massive recall program to fit new type switches.

I wrote an article for Television on this subject, in some ways it is still relevant today. I'll try and dig it out and post.

Going back to the original question, I think we can keep these clock radios on and still sleep soundly.

[avro]

We leave our DAB radio on for the doggies (Radio 2), but I wouldn't do the same with a valve radio. Much better to be safe than sorry.

[Mr Moose]

Hello,
As others have said the risk of fire from a clock radio is very small and probably less than the risk of fire from the house wiring or other appliances that are on all the time like a fridge, so unless you switch your electricity off at the mains switch you wont be reducing the fire risk much by switching off the clock radio.
Fitting the right fuse in the plug (and any other plugs) and having the mains supply protected by an RCD will reduce any risk.
Shutting doors will stop the spread of smoke and fire and you should have smoke alarms fitted and tested regularly.
Yours, Richard

[Brian R Pateman]

This thread has gone too far from the straight and narrow to be salvageable.

Thread closed.

[crockhamtown]

The thread on fire risk was closed before I could comment on the responses to my query.

I was overwhelmed by the expert advice offered and am most thankful.