Smart Home Switches - Amp Ratings

[jonwestuk]

Hi,

I am going to be installing some smart-home switches for lights. Many are available but there is a common theme even across premium brands like Shelly switches:

1. Single light relay switches are rated at 16 amp
2. Double light relay switches are rated at 10 amps per channel

One of my breakers is 16 amp on my light circuits (1.5mm wiring) and the other is 10amp.
Question - if I buy a double light relay, surely I would need a fuse between the relay and the light fitting rated at less than 10 amp to prevent overload, or to get an electrician to downgrade the breaker?

Really interested in how people approach this.

 

[EFLImpudence]

One of my breakers is 16 amp on my light circuits (1.5mm wiring) and the other is 10amp.

That's odd. They are normally 6A.

Question - if I buy a double light relay, surely I would need a fuse between the relay and the light fitting rated at less than 10 amp to prevent overload, or to get an electrician to downgrade the breaker?

Certainly easier to change the breaker, but...

...do you think a few lights (especially these days with LEDs) are going to overload the circuit?


Have look - your existing switches, if typical, are likely to be only 6A.

 

[Harry Bloomfield]

One of my breakers is 16 amp on my light circuits (1.5mm wiring) and the other is 10amp.

Why is the MCB (breaker) rated at 16amp for a lighting circuit? Most common these days is 6amp.

 

[jonwestuk]

That's odd. They are normally 6A.


Certainly easier to change the breaker, but...

...do you think a few lights (especially these days with LEDs) are going to overload the circuit?


Have look - your existing switches, if typical, are likely to be only 6A.

No way my LED's will overload the circuit, but from a regs perspective don't you have to stick a fuse in if the rating of the appliance/wiring is lower than the breaker?

I think the breaker is way overdue for being changed to a lower rating anyhow, previous owners were running some fans, TV boosters and other stuff off of that light circuit, which may explain it. With all that wiring gone, and having changed to LEDs everywhere, it seems like overkill.

 

[EFLImpudence]

No way my LED's will overload the circuit, but from a regs perspective don't you have to stick a fuse in if the rating of the appliance/wiring is lower than the breaker?

The fuse is to protect the cable; not the appliance.

It would not be possible to do it for the appliance if more than one on a circuit.

 

[Harry Bloomfield]

No way my LED's will overload the circuit, but from a regs perspective don't you have to stick a fuse in if the rating of the appliance/wiring is lower than the breaker?

The fuse/breaker/MCB is to protect the wiring from overload, rather than the appliance, switch or etc., but yes it would be a good idea to derate the MCB. If the cable is 1.5mm T&E, depending on the installation method, then it could be rated up to 20amps.

 

[ericmark]

The regs says no more than 16 amp, but in the main we use ceiling roses as junction boxes and they are rated 5 or 6 amp, so in the main we use 6 amp MCB's.

 

[JohnW2]

The regs says no more than 16 amp, but in the main we use ceiling roses as junction boxes and they are rated 5 or 6 amp, so in the main we use 6 amp MCB's.

Indeed - particularly given that, with LEDs, just 1A (or less) would usually be more than enough.

However, as far as I am aware, the regs are only interested in the protection of cables, not accessories or connected equipment, - and, as has been said, with 1.5mm² cable even 20A protection ('if allowed' for a 'lighting' circuit) would often be adequate to protect the cable.

[ mind you, if (despite someone around here, but fully compliant with BS7671!) one installed a BS1363 socket or two on the circuit, would it then still be a "lighting circuit"? ]

Kind Regards, John

 

[ericmark]

An overload device forms a new circuit. So using a FCU forms a new circuit, the lights does stipulate types, but most need to be protected by an overload device under 16 amp, and many below 6 amp.