Electric motor question

[bbergami]

I'm building a cyclone dust collector and I just got a chance to power it up. It blew the breaker after about a second. I'm using a Harbor freight 3hp (5hp compressor motor) rated 15A @ 230V. Why they have the 2 different ratings on the motor I don't know. I've got it on a 30A breaker. Are there special breakers required to run a motor of this size? Thanks

[Al_The_Man]

There are usually two ratings indicating 110 or 230v, if you have it on the correct connection, then if it is an impeller type dust collector,(vacuum cleaner like), then cover the intake or exhaust while starting until up to speed and see if that makes a difference, as the load will be removed from the motor.
I assume it is single phase?
Al.

[bbergami]

The motor is single phase 220-230v only. No option to wire it for 110v. It is an impeller type. I just covered the intake and it still blows the breaker.

[Al_The_Man]

Does it at least appear to get up to speed and then blow the breaker? I would have expected a 30amp breaker to hold.
Al.

[bbergami]

No....I would guess it might get up to about 500-600 rpm then blows.

[Al_The_Man]

If it is a capacitor start motor, which it probabally is, it sounds like the start windings are not switching out via the centrifugal switch, If they stay in then there is alot more continuous current draw.
What does the motor say exactly for the ratings.
Al.

[bbergami]

It say's
208vac@16a, 230vac@15a, 60 Hz single phase 3HP(5 hp locked rotor) ccw 3,450 rpm. It is a capacitor start.

[Al_The_Man]

Normally, perception wise, a motor of this size, off load, is virtually impossible to tell the acceleration, especially a 3450rpm motor, to tell when its at 500 rpm tells me the motor is not coming up to speed fast enough.
If this were an existing motor in use doing this, I would say it had a shorted winding, or as I mentioned the starting switch.
I trust you have confirmed your motor terminal connections etc and the capacitor/start winding is connected correctly?
Al.

[bbergami]

It's wired according to the plate on the motor. 2 hots and a ground. Not a whole lot of room for error. It's new out of the box and I don't think there are any options to wire the windings differently.

[Al_The_Man]

It's new out of the box

It's possible, I guess you have a dud, You mentioned in the first post that it blows after 1 second, I would expect that motor to be up to just about full speed by that time.
Make sure it is totally off load, and if you can see a fairly DISTINCT acceleration rate then I would start to suspect the motor. Also this is assuming you have the proper gauge wire, if it is a long run, then 14g will be pushing it.
If you really suspect the breaker, you could temporarilly swing it over to another like a 40amp stove breaker to try it.
Al.

[ViperTX]

I would definitely suspect the breaker....I believe your running current is 16 amps, but your startup current is much higher...

[ger21]

You mentioned in the first post that it blows after 1 second, I would expect that motor to be up to just about full speed by that time.

With the impellor, I would think it should take at least 2-3 seconds to get up to speed, as it's pushing a lot of air. Our Cylone at work takes about 3-4 seconds with a 10HP motor.