Safety relay advice please

Hi Guys,

I have a circuit containing a 10A 250VAC 05V Songle Relay (SRD-05VDC-SL-C).

It is controlling the power to a standard light fitting through the NO terminal.

Can I add a second light to the same terminal safely? Or do I need a second relay?




The question is the same for 1 or 2 lights:

  • What is the voltage and current needed for the light?

  • If the current needed for 2 lights is less than 10A you should be OK..

Probably. What's the actual voltage? This is power-line voltage, right?

Power (Watts) is calculated as Volts x Amps. So for example, in the U.S. a 100W light bulb is about 1A, and if you live in a 230V country a 100W bulb is about 1/2 Amp. Your relay can handle up to 10A (although it's a good idea to leave some safety margin).

I am actually advising a friend who has taken the circuit to Sweden with her, so I dont have the lights to hand but can assume they are 220V in Europe I think?

Sounds like its all ok then. Great, thank you guys.

If the relay you are using is attached to one of the many hobby relay boards available out there, it will not take a full 10A. These relay boards are only as good as there weakest link. This could be the thickness of the circuit trace itself, or in many cases the terminal block. These terminal blocks are only rated for 7A or 8A max. You also have to make sure that the distance between the traces is adequate to keep from arcing. Safety is a big concern with these relays. I always recommend using a "certified" remote control relay instead, for mains power use.

Tungsten bulbs have a high inrush current, so you should derate somewhat to allow for this, especially for tunsgsten-halogen bulbs which take longer to heat up.

Generally lighting is less than 1A anyway...

Old style fluorescent light fittings with ballast coils are inductive, those need special consideration.

So when you said "standard light fitting" you actually omitted useful information as there is no standard.