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I was wondering if the amperage ratings of devices, say, for instance, circuit breakers, add in parallel or series. For example, if I hooked up 5 20 Amp circuit breakers in parallel, would it take 100 amps to trigger them all? Or would it take 100 amps with them in series to trip them all? I'm not sure about this because I have used two 1 amp solid state relays in series to switch loads well above 1 amp, but it seems more logical for them to only do that if they were connected in parallel. Also, whatever the answer to my question is, does it apply to all devices? Circuit breakers, Triacs, etc? Thanks!

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use the water pipe analogy: It fits for 'most' intents and purposes:

Amperage is current, flow,
Voltage is pressure
Resistance is how narrow the pipe is - only so much can get through at a given pressure
Power (watts) is 'total electrons from a to b' over time

So....High amperage low voltage = wide pipe flowing slowly = sewer pipe, or a river
High voltage, low amerage = pressure washer. super soaker - water willing to jump long distances (think sparks, lightning)

1 volt at 100 amps is the same total power as 100 volts at 1 amp = 100 watts

To answer your question: 2 20 amp connections in series...doesn't offer any additional flow. Think 2 20cm pipes in series - they can handle the same flow as 1 20cm pipe by itself.
Now think 2 20cm pipes in parallel - it can handle twice the flow.

In theory, 5 x 20A breakers in parallel would trip at 100A. In practice, due to small differences in manufacture one would take slightly more current than the others and you'd probably have the first trip out at lower than 100A, then the others would cascade out immediately as the load through each one increased. Connected in series, the first one would trip at 20A and break the circuit leaving the others untripped.

The 20A breakers trip at ~20A. If you had 5 in parallel you'd be able to run upto 100A through them (5 x 20A).
It's generally applicable to conductors, but all devices would surely include some exceptions.

L