How do you choose the breaker for a motor?

[crazrRobot123]

Hi,

Our team is trying to figure out how do your electronics team decides the breaker that a motor is going to have.

Thanks.

[ngreen]

I think drive motors or things that will have high current draw to high current motors all go on 40 amp circuits.

You may be able to estimate the current draw of other mechanisms either from design calculators or other estimates, and can go with smaller breakers when it clear that the smaller current is sufficient for what you need. In FIRST, the circuit breaker corresponds to the wire gauge size needed, so if you are able to use a smaller breaker you can route smaller wires, which might be an advantage.

If you have a smart controller like Spark Max or Falcon 500/TalonSRX, you can also set current limits in the controller itself, and should for some mechanisms (like the recommendation for NEO550s at 20 amps). You can use a current limit with a similar breaker, but that knowledge is based on expected current draw and the motors stall current, etc.

[AriMB]

Honestly, unless you’re specifically trying to protect the branch from an over-current situation, you should probably put everything as high as it’ll go (all 40A for PDH, half 40A half 30A for PDP). The downside is pretty minimal, just a bit of extra weight from the heavier wire, but the upside of not worrying about losing functionality from tripping breakers is substantial.

[Ryan_Blue]

@AriMB

half 30A for PDP

You can go full 40a with the rev breakers.

[Domtech]

The breakers are a safety device to protect the wires, your choice of breaker decides the minimum wire size (maximum gauge number) that you are allowed to use on that channel. If you want to run a smaller wire then you need to use a smaller breaker, however you are free to use a larger wire than the minimums stated in the manual.

Using too small a breaker for a given load increases the risk of it tripping, so generally for any larger motor you will want to use the largest possible breaker.