Three phase switch for single phase?

Have a question or want to show off your project? Post it! No Registration Necessary.  Now with pictures!

Threaded View
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


Re: Three phase switch for single phase?
andy wrote:
Quoted text here. Click to load it

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

Re: Three phase switch for single phase?
Quoted text here. Click to load it

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


Re: Three phase switch for single phase?

"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.



Re: Three phase switch for single phase?
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


Re: Three phase switch for single phase?
Quoted text here. Click to load it

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?

Quoted text here. Click to load it

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

Quoted text here. Click to load it


Re: Three phase switch for single phase?
"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


Re: Three phase switch for single phase?
Quoted text here. Click to load it

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


Re: Three phase switch for single phase?
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


Re: Three phase switch for single phase?
Can you simply retype and post here the entire dataplate of your
mag switch. It should, hopefully, be clear after that.

i

Quoted text here. Click to load it


Re: Three phase switch for single phase?
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


Re: Three phase switch for single phase?

Quoted text here. Click to load it

  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 >>--

--
Bruce L. Bergman, Woodland Hills (Los Angeles) CA - Desktop
Electrician for Westend Electric - CA726700
We've slightly trimmed the long signature. Click to see the full one.
Re: Three phase switch for single phase?

andy wrote:
Quoted text here. Click to load it

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


Site Timeline