Three phase switch for single phase?

Hi group. I have a big vertical bandsaw that I would like run with a single phase motor. The saw came with a three phase motor and switch. I would like to use the existing switch for 220 volt single phase power. I know enough about electricity to get me into trouble. The existing switch looks to be a single throw, triple pole type. Can I just use two of the three sets of contacts for my 220 volt single phase?

the specifics of the switch are as follows: 30A 250V AC 20A 600V AC Motor Ratings 2HP 110-600V AC 3-phase "manual motor starter" Arrow-Hart and Hegeman Elec. Co Hartford, Conn USA

The old 3-phase motor is 1HP The new single phase motor is 2hp, full load amps = 12 both motors are 1725 rpm

Thanks for any insight you may have, Andy Hall Lynn, MA

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andy wrote:

Sure, just use 2 of the 3 contacts for your single phase motor. - GWE

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I think that his question mainly revolved around the switch 2 HP rating (for what voltage?), and the fact that a three phase motor could draw less current per leg than same HP single phase motor.

So, I am not sure if his 2 HP 3 phase rated switch is capable of handling a 2 HP single phase motor.

It probably will work fine, but perhaps would last less than the lifetime it was designed for. Which could be just fine in a home shop where equipments is not used constantly.

i

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"Ignoramus30285" wrote: (clip) Which could be just fine in a home shop where equipments is not used constantly. ^^^^^^^^^^^^^^^ Two actions by the switch are hard on the contacts. On startup, the current is very high. Avoid turning the motor on and then right off again. You are not likely to switch the motor off under load, which is the other action that is hard on a switch.

What's the worst that could happen if you use this switch? You might have to replace it eventually. That's not worse than replacing it now. Go for it.

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Thank you for the replies. My original question was whether or not it would work. But your point of "it will work but not for as long as it should" is appretiated.

Also, what will happen when the swich fails? in theory of course. switch stops working obviously. garage burns down? Andy gets electrocuted? motor gets damaged?

any thoughts? Andy

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I think that "it will work but not for as long as it should" would be an accurate summary, IF the rating indeed is for 2 HP at 230V. That's what I am not sure of, usually contactors have different HP ratings depending on voltage, and you gave only one HP rating. Are you sure that it is rated for 2 HP at 230V?

It would possibly get stuck closed, that is, your bandsaw would not turn off when you decide to turn it off one day. Which is no big deal, usually, just turn off curcuit breaker and replace the contactor or its contacts.

It might also start arcing or buzzing, I am not sure how likely that is (I think that it is very unlikely).

Contactors are inexpensive these days, for a few bucks you can find a size 1 contactor.

http://tinyurl.com/npbuj

3 HP at 230v, single phase, $15.

I highly recommend that seller, his name is John (there is also lisa_ctrsurplus, they are a great company).

i

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"As a bit of an aside, do make sure to properly ground the motor. I assume you at least know this much, but the ground should NEVER be switched. " Understood.

i: thanks for the contactor link. Do you know of a good primer on setting something like that up? I would imagine that that is a component inside a box with a start and stop pushbutton? For now i will just use my existing switch, but down the road it may be nice to have a start-stop pushbutton setup with the saw's brake hooked up to the stop circuit. Stomp on the brake and a. the circuit is opened, and b. the wheels stop.

are the boxes modular? lots of questions. Thanks again, Andy

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A contactor is a device that engages contacts by means of a mechanical action, which is set in motion by electric field. There is a coil inside a contactor. When power is applied to the coil, magnetic force created by the coil moves main contacts and closes them. When power is removed from coil, a spring opens main contacts again. That happens very quickly and such contactors can be controlled with tiny switches, possibly from distance, instead of having big handles when switching manual switches.

Whether a given contactor would fit a given box, is something that you would need to check.

i

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Thanks for the explanation. I will have to read up on them. Actually I am vaguely familiar with them, as I used to assemble them years ago at a previous job. Back then, I didn't care what it did or how it did it. I just followed a "recipie". Pretty sad. They were used to start blowers.

I guess the joke is on me. Andy

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Can you simply retype and post here the entire dataplate of your mag switch. It should, hopefully, be clear after that.

i

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I think I lead you astray. The switch that I have looks like a large version of a household light switch. The info printed on the switch is: "30A 250V AC 20A 600V AC Motor Ratings 2HP 110-600V AC 3-phase "manual motor starter" Arrow-Hart and Hegeman Elec. Co Hartford, Conn USA" based on the responses to this post, I have decided to use it with my single phase 2 hp motor.

Thanks, Andy

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Aha - Manual Motor Starter. It should be OK with a 2HP 1-phase, as it isn't going to be over 30A except during the start surge.

And considering the name, that MMS Switch has to be ancient - Cooper Industries has owned them for quite a while...

If this is the type that has overload heaters, make sure they're the right size for the motor.

--<< Bruce >>--

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Bruce L. Bergman, Woodland Hills (Los Angeles) CA - Desktop
Electrician for Westend Electric - CA726700
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andy wrote:

It will be fine.

As a bit of an aside, do make sure to properly ground the motor. I assume you at least know this much, but the ground should NEVER be switched.

JW

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