Fused spur - Rating.

2012paddy2012

I see in the attic a supply box for the outside alarm bell box transformer, has a feed taken from the cable that was used for the smoke detector- upstairs -

It’s neatly done - someone mentioned there would be no harm if there had been a fused spur between the smoke detector and the connection to the alarm bell box transformer- this was done before I moved in and there is no issues -

I’m giving thought to putting one in - my question - what rating / app , would be safest -
Thanks
Paddy

2011

Most probably I would feed a transformer such as this from a 2 or 3A fuse.
What is more important in my opinion is the mounting of the transformer so as to ensure that it can cool properly and will not get covered by insulation.

NeuralNetwork

I’d agree, the main risk is how and where the transformer is mounted and that the wiring is done properly.

A 3amp fuse won’t protect against an overheating transformer.

The main reason for the existence fused spurs is to allow connection of fixed devices to 32amp ring circuits. They’re the fixed equivalent of a fused plug, which is only really required because of the ring circuits used in U.K. type wiring. The 32amp rings effectively move the overcurrent protection from the circuit board to relying on fused plugs, as appliance flexes aren’t designed to withstand a 32amp fault.

In terms of rating a fuse, look at the rating on the transformer. It’s very unlikely to be more than a few watts, so 3 amps is more than adequate.

Just bear in mind that if it’s on say a 6 amp MCB for the old smoke detector circuit, you’re not really adding any meaningful protection.

2011

NeuralNetwork wrote: »

A 3amp fuse won’t protect against an overheating transformer.

True, but then again no fuse that will fit in a standard spur outlet can guarantee protecting against this either.

NeuralNetwork

2011 wrote: »

True, but then again no fuse that will fit in a standard spur outlet can guarantee protecting against this either.

I’m not suggesting it will. There’s just a bit of a fixation on local fusing in U.K. inspired wiring regulations.

I’ve seen people argue that a 3amp fuse is essential for electric shock protection, which makes absolutely no sense whatsoever.

Personally, I would prefer to see less active active equipment installed in attics, as they’re an area where fire can spread very rapidly and that can be extremely warm in summer in many homes with bigger roof areas.

It’s not unusual to find transformers for tv equipment, abandoned antenna amplifiers, lighting drivers, even routers etc just sitting on the fibre glass insulation.

2011

NeuralNetwork wrote: »

I’m not suggesting it will.

Fair enough, I thought you were suggesting otherwise.

There’s just a bit of a fixation on local fusing in U.K. inspired wiring regulations.

There are still plenty of homes in Ireland with ring circuits, unfortunately mine is one of them

Personally, I would prefer to see less active active equipment installed in attics, as they’re an area where fire can spread very rapidly and that can be extremely warm in summer in many homes with bigger roof areas.

Some passive kit requires cooling too.

Anyway, I think it depends on the attic and how equipment is installed. Some attics have better cooling than any other area of the house as wind can blow through the gaps in the roof tiles. In these cases once the apparatus is mounted in a suitable manner that allows sufficient cooling it is perfectly acceptable in my opinion.

As house prices continue to climb domestic property sizes are increasing. Combined with this is that demand of kit is increasing. I haven't worked in a domestic installation in a very long time but I expect that more RECs will use the attic to house kit.

It’s not unusual to find transformers for tv equipment, abandoned antenna amplifiers, lighting drivers, even routers etc just sitting on the fibre glass insulation.

Yes, my point exactly.