Motor protection

[Jraef]

I would agree that a circuit breaker is not an acceptable device for controlling a motor load, but most manufacturers produce circuit breakers with different trip classes (some even adjustable) for inductive loads or motor loads. If he were to get one with a Class 10 rating a 225 would probably do the job.

The devices you are referring to are technically NOT considered "circuit breakers" in the classic UL489 sense because they have adjustable thermals, which is not permitted, but they are often UL 508 listed as Manual Motor Starters.

Of course a 225A breaker would fit the rules, but the way I read the other comments is that it is highly unlikely that a 225A breaker mag trips will allow starting of the motor without nuisance tripping. Even a 225A breaker with adjustable mag trips will top out at 2250A, and a 173A motor may theoretically draw as much as 3800A for a cycle or two, followed by locked rotor current of around 1000A for a few seconds. Most likely that breaker would trip off quite a bit; IF IT WAS USED TO START THE MOTOR QUITE A BIT, and therein lies the issue.

I have actually seen this a lot on larger plant air compressor systems. The basic idea is that the compressor NEVER turns on and off, it runs 24/7/365 and is only shut down for maintenance. The rest of the time it just cycles the load valve on and off. So some OEMs get cheap on them and do the breaker sizing trick, knowing that if it starts, it will not have to worry about RE-starting (unless the power fails). I've never liked that though, its a game in my opinion. The compressor dealers do it because they want not only the order for the compressor, but for the repairs later and they know good and well that poor protection of the motor (but technically legal) is good for their business model.

I personally would put in a motor starter with a solid state overload relay and properly protect that motor. Then you can use the 450A breaker and not worry about it any more.