I guess this is place to ask anything right? :)

So here it goes...

Let's say I have an appliance that has an on/off switch on it (e.g. kettle, active monitor speakers, etc.)

These appliance is plugged into the mains, the mains socket switch is turned on, but the on/off switch on the appliance is set to off.

Does the appliance draw any power down the lead that connects it to the mains socket?

Traditional switches were mechanical, which is clearly evident from their symbol. They literally cut the wire in half, so electric current was broken. Same effect as if plug were pulled out.

There is then a whole separate class of different kinds of switches, relays, transistors are one of them.

In general, a switch breaks electric circuit, so electricity cannot flow (excluding obscure dielectric effects or whatyouhave in there). That is the very definition of the switch.


Many today's devices however use soft switches. With those, devices still draw some minimal amount of power, usually to power some standby system, such as remote control sensor, or they keep some part of electronics warm (literally or figuratively) to make powering on faster. While they are made to look the same, they are technically not switches. They toggle different power states.

Such devices, even when turned off, they still draw power.


In general, mechanical switches physically break the circle. Switches on monitors or TVs frequently do not, nor do any devices which still offer some function after turned "off", perhaps time display or some LED indicator.

Thank you for the detailed info.

Would this count as a mechanical switch?

External power supplies can draw quite a lot of power when not even connected to the device they're supposed to power (depending on how well they've been designed). This extends to chargers and the like. If you're in a country that puts a switch on each socket (such as the UK) then it's generally a good idea to use that to switch off all power to the device when you're not using it.

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Original post by Spa8nky Thank you for the detailed info. Would this count as a mechanical switch?

Most likely, it definitely looks like it.

To know for sure, the best way is to use a volt meter or one of those plug-in watt meters.

There's always that weirdly-wired device which bypasses the switch to do something funny. But it's unlikely.


A possibly related word of warning.

CAPACITORS.

Before messing with electronics that contains them, make sure to understand the risks. They store charge that remains there for minutes or more not only after the device was turned off, but also after being unplugged. Touching them can, in theory, kill a person. Getting shocked by them happened from time to time with CRT monitors and TVs, but they can be found elsewhere, just typically not as strong. There's a lot of other funny stuff, some capacitors can charge themselves over time even if not plugged in. This isn't as much of a problem these days, but back in the day of CRTs, computer repair shops had staple tools for discharging them as well as grounding bracelets.

Awesome. Thanks for the help guys. Looks like a decent plugin watt meter is way forward!

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Original post by Spa8nky Looks like a decent plugin watt meter is way forward!

heh. So I was reading this thread and was wondering what if you planned to keep it plugged in for a long time. You'd want to get a low power one. I came to the conclusion that a good way to test it would be a another watt meter. >_> (yo dawg)