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Where should fuse be in relation to the power, switch and load? Any suggestions on a better approach or tips on the matter would also be helpful.

POWER > [FUSE] > SWITCH > LOAD

POWER > SWITCH > [FUSE] > LOAD

harayz
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3 Answers3

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The fuse should always be the first thing a power supply hits when it gets to a circuit. The reason is pretty simple. In the event of a fault that blows the fuse, the power is isolated to where it entered the circuit, thus the whole circuit is protected. Using other configurations could allow the supply voltage into other parts of the circuit unexpectedly. There are situations where it's good to fuse both the power supply and the load, but that's another question.

Matt Young
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In most cases, I would prefer to put the fuse immediately after the main power switch. That way, with the power switch off, both terminals of the fuse are "dead", so there is no shock hazard while changing the fuse, providing the switch is off.

If the fuse is before the switch, it will always be "hot", and will potentially be a shock hazard.

For plug-in equipment the order is less important, as you can unplug the equipment while changing the fuse.

Peter Bennett
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  • Two problems with this: What if the switch itself fails? And most fuse holders do not expose the user to live terminals anyway. – Dave Tweed Mar 10 '19 at 14:08
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If the switch itself fails, then there will be no power coming out of the switch, unless you are suggesting that the switch would fail in the on position, ... the answer to that would be to isolate the source of power, & eliminate it, ... the odds of this happening would be quite rare, because if there is/was a powerful enough surge to cause a switch to fail, it would melt the switch itself, & cause the wiring back to the power source to also short out, resulting in an electrical fire, ... understand that the 2 wires that go to the switch are not a common, & ground, ... they are the same power side of the source, ... which makes your question a moot point, ... all a switch does is interrupt the power coming from the source, by flipping a switch “on” you are sending the power from one side of the switch to the other side, like putting a shut-off valve in a pipe of water, turn the valve off then there is no power coming out of the other side of a switch, shut the water off, and the flow of water ceases, ...

John
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