How many lights off one switch?

[AdamCH]

Hi

Can anyone tell me how many lights / total wattage I can switch through a single switch?

Thanks
Adam

 

[ColJack]

that would depend entirely on the rating of the switch and the rating of the lamps..

a 6A switch could manage 70ish 20W lamps..
a 20A switch could manage 9ish 500W floodlights...

simple maths..

( rating of switch x 240 )
wattage of lamp

 

[mikhailfaradayski]

that would depend entirely on the rating of the switch and the rating of the lamps..

a 6A switch could manage 70ish 20W lamps..
a 20A switch could manage 9ish 500W floodlights...

simple maths..

( rating of switch x 240 )
wattage of lamp

simple, yet somehow quite confusing

perhaps to make it even easier, you could say that the current capacity of the switch (in Amps) should not be exceeded.
You can calculate the current that will be drawn by the connected load with this:-

total wattage of all lamps (W) / 240 (V) = Current (A)

some might prefer to use 230 instead.

 

[Chri5]

plus consideration for the circuit fuse rating..........

So a 6a circuit would limit the circuit to a 6a load


Add all the wattages for all lights on the circuit (except the switch and lamps your asking about). If the circuit is fused at 6a x 230v = 1380w minus the laod you have added up gives the potential max watt load available to the new switch / light requirement.

 

[Taylortwocities]

A single switch may cope with the load of 6amp or 10amps worth of load

BUT

you also will need to look at the fuse/contact breaker that protects the lighting circuit.

It is very likely 5 or 6 amps and (broadly speaking) that will be the limit for the entire circuit.

1 amp = approx 230watts.

WHat, exactly, are you trying to do?

Edit: Curses Chri5. I was a nanosecond too slow...

 

[AdamCH]

What I'm doing is adding a couple of extra lamps in the loft. There are already 2 wired off one switch & I was looking to add another 2 off the same switch. Looks fine to do that if I've understood correctly & I'll just daisy chain them to what's there.

Intersting point about total circuit lioading though. We've added lights over the years and there are a couple that are multi halogens now rather than single bulbs and floods have been added front and back of the house - although only the front is switched on. Adding up the loading without taking acount of energy saving bulbs would come to 1200w including the extras in the loft which looks ok for the 5A circuit, but adding in the floods would raise it by 500w a piece and take it way over.

Should I be looking at splitting away the floods? Blown fuses haven't been a problem - maybe 2 in 15 years.

 

[mikhailfaradayski]

Do you know that the flood lights are connected to the lighting circuit?

Its not uncommon to find they are fed from a socket outlet circuit.

 

[AdamCH]

Floods are definately on the upstairs lighting circuit.

Same hope had occured to me but there is no access to the socket ring in the loft space (socket rings are all done from the first floor) so it's been connected in to the lighting.

Switching to LED floods might help?

 

[Chri5]

Thing is, when would every light on the circuit be on at the same time ?

Rarely, I'd imagine.

Then there's the over head on the circuit fuse. They won't trip out at exactly 6a of load, it varies from MCB type and manufacturer. The fuse might handle between 6a-9a for a period.

 

[Taylortwocities]

adding in the floods would raise it by 500w a piece and take it way over.

The 500W floods will be 2 amps each. So two of those will be a big whack if they both come on together.

Do you really need 500W - is that Wembley stadium you've got there?

 

[AdamCH]

Rather than wire in more lights I've switched the loft to 2 x 58w flourescents. GIves me more light and saves wattage over the 150w + 100w bulbs that were in there before.

Adjusting the overall circuit wattage calc for low energy bulbs brings the total down and makes just about enough room for 1 x 500w flood - probably why the fuse copes. But plan to swap the floods for energy saving lamps or if that's no good, LEDs.

Thanks for all the advice.

 

[mikhailfaradayski]

you can also apply diversity to you load calculations. As a rule of thumb, which is at the discretion of the designer, it could be assumed that only 66% of the loads will be switched on at any one time.