Amp rating of switches.

[Neale]

Personally, I would go with the Maplin toggle switch or equivalent. At least it's rated for 240V AC use, and you will be using it well within its max ratings. The 12V switches aren't necessarily going to be safe for mains use. And an amp isn't an amp when you're comparing AC and DC! With DC, as the switch contacts open, you start to get an arc forming that will continue until the contacts have separated enough stop the arcing. This leads to damage to the contacts fairly quickly, and you need a switch rated for DC operation as it will have some kind of mechanism to stop the arcing. However, with AC, even though it might start to arc as the contacts open (if you do this at the peak of the cycle), as the current drops towards zero any arcing will stop anyway, and by the time the voltage is swinging the other way, the contacts will probably be far enough apart that no new arc forms. That's a pretty simplified explanation, but I hope it helps give a bit of insight in a hand-waving kind of way

(overlapped with Clive but at least we agree!)

[Clive S]

Yes Neale but you said it better.

[Wal]

>Not sure what you are asking here Wal.

Hehe, I'm probably less sure than you are Clive. I guess I was just getting the flavour of amps confused along with how the voltage affects how much current can be handled. Clearly it's always the best idea to use the right gear - in my case stuff that's rated for AC, but out of interest (and I'm unlikely to be trying it at home...) is there a way of ascertaining whether it's safe to use DC rated gear in an AC circuit..? Actually, I might have found the answer - does this get me close?



I used the calculator here. So looking at those results from the calculator, am I right in thinking that the current I'm drawing in my 240VAC application would be equivalent to 3.52A in a 12VDC world, theoretically making the 12VDC switches safe to use..?

Wal.

[Neale]

In this case, that calculator is a red herring. The fact that it mentions AC and DC is not really relevant and is rather misleading. For a switch, you have to look at voltage rating, current rating, and whether it is AC or DC rated. Switches will often have both an AC and a DC rating and you have to look at the appropriate one. If a switch is designed for 12V DC, then pushing it to mains voltage means that you are trusting levels of insulation and safety for which it is not designed. It might be OK, but personally I wouldn't trust it. The contacts might handle the voltage and current (there is no magic threshold that says 12V is ok but 13V is not) but the casing and materials are not rated for mains voltage. Get a low-voltage circuit wrong and you might blow a fuse. Get mains wrong and it can kill. The toggle switch is clearly designed for mains voltage so is the safe choice.