motor protection question (three phase to single?) 2

[rhamm1320]

My background is mechanical engineering, I'm not sure how I should protect the motor below:

http://www.grainger.com/Grainger/items/4F742

I believe the correct term for this motor is single phase? The only power source I have is 230 VAC three phase.

Should I run a two pole circuit breaker like one of these?

http://www.automation4less.com/store/categories.asp?cat=815

Does it have to be fused instead?

Thank you for any help.

 

[waross]

Yess and no.
You can feed the motor from two phases of 3 phase 230 volts.
You may use the circuit breaker to feed the otor and to control the motor but it will not provide adequate protection.
That is it will work, but it will not be code compliant and the installation may be dangerous.
Try a manual motor starter between the breaker and the motor such as this one.

http://www.grainger.com/Grainger/items/3CY89

If you have to ask these questions you should really hire a licenced electrician to do the installation. It is not so much the questions that you have asked as the questions that you haven't asked.

I suggest buying the motor and the manual starter but letting the electrician purchese the two pole breaker to ensure compatability with the exissting panel.

You seem to have done some good research and you are on the right track, but you may be missing something when it comes to a safe installation.
respectfully

 

[sreid]

The motor is thermally protected (a switch in the motor windings opens up if the windings get too hot). I'd use a single pole 10 amp breaker.

 

[waross]

My bad, I didn't scroll down far enough to see the thermal protection spec.
However, you can't legally run a 230 volt motor on a single pole breaker. Some 230(240) volt three phase systems have 120 volts available, but you can't run a 12.2 amp rated motor on a 10 amp breaker.
Also, 15 amps is the smallest standard breaker for load centers. 15 amps is about 245% of running current and should start the motor and be code compliant.
respectfully

 

[rhamm1320]

Thanks for your replies, this is very helpful. A little more background to provide more insight.

The motor is automatically controlled depending upon when vacuum is needed.

Last year I had this same layout and a electrical guy had me replace the three phase breaker with two inline fuses.

 

[waross]

I don't want to second guess the electrical guy. On the one hand you can connect to two poles of a three pole breaker with no problems.
On the other hand, the fuses may have been dual element fuses to provide better protectionfor the motor.
There may have been a reason to use fuses that was not related to the two-pole versus three-pole issue, which is really not an issue.
respectfully

 

[jraef]

I don't want to nit pick here, but technically you can use a 2 pole circuit breaker, but not THOSE circuit breakers shown on your link in particular. They are not UL listed to be used as stand alone circuit breakers, they must have an additional Short Circuit protective Device (SCPD) upstream from them.

I know they saythey are UL listed, but that is misleading because they are listed under UL1077 as "supplemental circuit protectors" or UL508 as "manual motor starters". In either case, they must ALSO have that SCPD I mentioned earlier, i.e. the fuses your previous electrical guy required, or ironically, another circuit breaker!

You can bypass all that crud by just using a proper UL489 listed circuit breaker. However, there are plenty of other issues involved such as interrupting rating, conductor sizing etc. that would require the input of at least a qualified electrician or EE.