What's allowed on a lighting circuit.

[deskpro]

I have a problem with power shower blowing a fuse whenever it is switched on.

The fuse blown is a 5amp wired fuse in the main box for the house which also cuts out all the upstairs lighting.

It turns out that the central heating also shuts down.

Power shower was installed with a new bathroom about 9 years ago and central heating is a new condensing boiler installed June 2010.

So,my question relates to what is allowed in a lighting circuit and should I get one or both(power shower pump and central heating) changed to a different circuit?

 

[sparkwright]

I assume you mean the power shower, lights and central heating are on the same 5 amp fuse, and it's not an RCD tripping. ?

Typically you wouldn't have the central heating or power shower on a lighting circuit, though not dangerous as such.

The power shower and heating would normally be wired from the socket circuit, via separate switched fused spurs.

Or they could be on their own circuit from the fuse box.

How many lights on the circuit?

 

[EFLImpudence]

As a rule 5A = 1150 watts.

So, unless there are lots of downlights upstairs it should be alright.

As it has been working since June 2010, perhaps the motor in the shower is wearing out - Does it work as it always has?

 

[imamartian]

Firstly Deskpro, i'm a DIYer, so in this forum, treat what i type as a further question rather than a statement of fact.

But my first question to you is what wattage is the shower? (i'll assume 8KW as a minimum after a quick google)...

According to my book: volts x amps = watts,

so 240v (our electric) x amps = 8000watts (your shower) and with a bit of maths....

amps (or fuse size) = 8000 / 240
" " " = 33.33 amps

So to me, you're 5amp lighting fuse is totally inadequate.

However, what i don't understand (and hopefully i'll get shot down here by numerous sparkies) is that i reckon your main fuse box (consumer unit) only has a 30amp fuse/trip ?

But to answer your question, i think you need a separate feed for the shower... but get someone in

 

[RF Lighting]

If it's a power shower as the OP states, then all it will be is a pump which pumps hot water from the cylinder, and cold water from the storage tank. It does not actually heat the water, and they are typically rated somewhere around 50W

 

[riveralt]

The OP said power shower not electric shower .
Mira power showers use about 150w so that is not going to break the bank.

 

[westie101]

Though I did once come across a house with a 7.5kW shower connected to a lighting circuit!

 

[imamartian]

Thank you.

That's why i'm a user here, not a contributor !!

But i still think asking what wattage the shower is would be the first question to the OP?

 

[imamartian]

so leading on from this....a 10kw shower, on 240/250v needs a 40amp fuse? right?

 

[EFLImpudence]

At 240V a 10kW shower is 41.66A which is what the manufacturer will state.

At nominal voltage of 230V it will be 39.9A.

 

[riveralt]

so leading on from this....a 10kw shower, on 240/250v needs a 40amp fuse? right?

Maybe 45Amp depending on Manufacturers instructions.

And it will need 10mm T&E cable.

 

[EFLImpudence]

6mm² T+E method C = 47A

Edit - just noticed 'fuse'