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Why are main on/off switches in electronic circuits/appliances (any small, low power electronics) always placed on the positive wire (in case of DC circuits) between the power supply (batteries, adapters, etc.) and the circuit regardless of the low operating voltage?

Does it affect the efficiency and makes any difference in power consumption when it's turned off?

Wouldn't placing the switch on the negative wire between the power supply and the circuit just work the same?

MarkU
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Yudhi G.
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  • Except for the issue that "if you place the switch on the negative terminal (and negative terminal is grounded), then the entire circuit would be at a potential (when the switch is open)", there is really no difference. A switch in series will stop current, no matter where it is. – Duck Dodgers Aug 12 '19 at 09:19
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    @Yudhi: See my answer to https://electronics.stackexchange.com/questions/445740/does-it-matter-if-a-fuse-is-connected-to-the-negative-or-positive-terminal-of-a/445745#445745. We recommend that you don't accept an answer for a day or two to encourage others to post answers (unless it really is the complete answer to your question). You might get a better one or one that gives you other insights. – Transistor Aug 12 '19 at 09:28

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Why do main on/off switches in electronic circuits/appliances (any small, low power electronics) are always placed on the positive wire (in case of DC circuits) between the power supply (batteries, adapters, etc.) and the circuit regardless of the low operating voltage?

Mostly, convention. You connect ground to the negative supply, because that's what all the ICs expect. Then, you decide that it's easier to switch the pole that is not ground.

Isn't placing the switch on the negative wire between the power supply and the circuit just works the same?

usually, yes.

Marcus Müller
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  • I'm not sure this fully answers the question. Let's say we are testing a circuit using a external DC power supply with a earthed return. Measuring waveforms on a scope. Switching the positive removes power from the circuit but switching the negative may not as the scope provides a return path. If your supply is floating this should not make any difference however. – Warren Hill Aug 12 '19 at 11:18
  • Well, that's true, and I'm happy you mention it. But: that'd be a lesser concern for a mass-produced appliance (which I assume OP asked about). – Marcus Müller Aug 12 '19 at 11:32
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It would (current wouldn't flow) but then you still have voltage on the appliance (or on the circuit). And in case of malfunction (a live wire touching metal housing) there is still chance of eletric shock if you touch the housing.

Benjamin Rajner
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