Unisaw Switch Issue

Our delema: Changed a 3 phase motor to a 4 hp single phase. Bought a standard Unisaw switch for single phase, 220 volts. We either have something wired wrong or the 4 hp motor requires a different switch. Too late to call out an electrician for help.
Do 4 hp motors require a different switch? And/or does a 4 hp motor require a different breaker. We have a 20 amp breaker.
Otherwise, I think we wired the switch wrong.
There is no LVC box on this saw. The wiring from breaker to socket seems to be ok. When we plug the saw into the socket, the breaker trips. The motor came wired, but not to the switch, since there was no switch.
Any comments are welcome.
Sonny
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 5/18/2012 5:09 PM, Sonny wrote:

I think you will need a starter for a 4 HP motor. Perhaps an electrician will help out on this. If I recall, anything bigger than 1 /12- 2 HP needs a magnetic starter.
Here is some information: http://www.emsco.net/faq.htm http://www.southlandelectric.com/motor_starter_sizing_chart_for_s.htm
--


___________________________________

Keep the whole world singing . . .
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Thanks Dan. We probably should put a LVC on it, to be safe. I had always understood an LVC was required for commercial use, but a private saw didn't have to have one. I really don't know, though. I've never had this problem.
I suspect this 4 ph mptor needs a larger breaker, like 40 amps. Leeson motor, Cat# 120998.00, model - C145K34FB16D. This model motor may be discontinued, as it is not listed on the Leeson website. There is a model C145K34FB16E, though (same Cat#)..... only difference is the last letter - D & E.
We were hoping to get this thing fixed and running today/this weekend. We may have to wait until Monday, when electricians are available, for help.
*Oh, no matter if the saw switch is turned on or off, with the saw plugged into the socket and then the breaker is turned on, it trips.
Sonny
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

This particular Leeson is nameplated at 17.6A, but 4hp@230v gives a nominal 12.8A draw. You might need to go to a heavier breaker, but I doubt it. Then again, the engineering toolbox rule of thumb is 7 amps per horse at single-phase 230v.

You have -definitely- wired it incorrectly, Sonny. With the switch off, it shouldn't EVER be able to blow the breaker.
Did you ground the saw and motor, then wire the two 120v phase leads through the switch so -both- interrupt when it's off? It's a DPST (or DPDT) switch, right?
Have you ohmed it out yet? That will show you where your trouble is if you understand a VOM and the circuit.
-- The reasonable man adapts himself to the world; the unreasonable one persists in trying to adapt the world to himself. Therefore, all progress depends on the unreasonable man. -- George Bernard Shaw
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Yep, I am now sure we wired something wrong. But there may be something else amiss....

I didn't do the actual wiring, but Jonas was sure he had done so correctly. He did comment that the wires may be positioned to make the saw turn backwards, so that would be tested and reversed if need be. Also, he thought maybe he had wired the "on" button as actually "off", and 'off' to 'on', but said this shouldn't have made the breaker trip.

We have an ohm meter. I don't know how to operate an ohm meter, but Jonas seems to know. I don't know what all Jonas may have ohmed or why. I am confident in wiring a 220 outlet, but not a switch, as this.
There may (unlikely?) be another reason for our problem. The motor (discontinued model, maybe?) was recently purchased via Amazon, so it is new. It came with a cord already wired into it, whether this cord would go directly to the switch or to an LVC box, first. Since there is no LVC box on the saw, Jonas ran this cord to the switch. If Jonas did wire the switch correctly, then this motor's cord may be (the unlikely aspect?) incorrectly wired inside the motor. He was confident his wiring of the power cord (from the switch to the plug/ outlet) was correct. I don't know if he tested all of this with the ohm meter.... at this stage of our unknowing, I was searching online trying to troubleshoot the issue.
We may play with it again today. Yesterday, we spent most of the day working on the whole of the saw, so some fatigue, late in the day, may have played some role in whatever is screwed up. We may be a little more clear-headed today. I vote to have an electrician check it out, though.
This has been a good learning experience for me. Sonny
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Are you certain it's a single-phase motor, not 3-phase?

If I didn't know how to use a VOM, I wouldn't feel comfortable wiring anything, be it switch, outlet, or motor. It's a very good time to learn how to read and use one, Sonny. It could save your life.

He should have opened the little cover to see exactly how the motor was wired. I hope you find an electrician. The stuff you two are toying with can kill ya.

Excellent idea. Dead shorts which blow 40A of breaker are dangerous.

Good. Keep learning and stay very careful, please.
-- The reasonable man adapts himself to the world; the unreasonable one persists in trying to adapt the world to himself. Therefore, all progress depends on the unreasonable man. -- George Bernard Shaw
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 5/18/2012 5:09 PM, Sonny wrote:

See if this helps:
http://media.ptg-online.com/media/dm/OwnersManuals/20040331153155_En438-01-655-0002-04-01-04.pdf
--
www.eWoodShop.com
Last update: 4/15/2010
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

If the breaker trips *immediately* when you plug the saw in, with the saw switched _off_, you obviously have something wired VERY WRONG.
A 4hp single-phase motor on a 20A 220v circuit is 'iffy', at best.
The running power consumption is within the limits for a 'plug in' device on a 20A circuit, but 'start-up' power draw is -much- higher.
A 30 A circuit, with 10 ga (minimum!!) wiring is recommended.
FURTHER, check the power rating _on_the_switch_. It should state the maximum number of amps, _and_ the max. horsepower rating of a motor, that it can be used to control. DO NOT EXCEED those ratings -- if you do, the device may NOT TURN OFF when you turn the switch 'off'.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On May 18, 6:08pm, snipped-for-privacy@host122.r-bonomi.com (Robert Bonomi) wrote:

Okay, our problem may, in part, be some of these issues.
We did read the switch load and compare it to the motor. It does appear the switch may be too weak. I'll double check that tomorrow.
We did wire it with 12-2 wire, not 10 guage wire.
We probably wired it incorrectly, anyway. I think we need to call in an expert. This is definitely not my or my friend's field.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

A friend of mine referred to calling in the professionals early as "keeping the repair bill small." If you're not sure, call in the expert early so he doesn't have to fix what you screwed up.
Puckdropper
--
Make it to fit, don't make it fit.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

And you don't know the NEC. <grin>
The OP has since posted that the moter is plated at 17.6 A.
For 'plug' items, you are limited, by NEC to 80% of the breaker capacity. 80% of 20A is 16A. 17.6 A definitely exceeds the 'legal' limit.

An 'unloader' on a _table_saw_?? *snort*
I've measured transient start-up current draw of motors, under no load, at well over 2x the rated 'full load" draw.

Your 'belief' doesn't change the reality of the situation. :)
First off, we're not dealing with a compressor.
Second, you admit you haven't done the math. You should have. Using 'real world' efficiency numbers, not 'theoretical' 100% efficiency conversions. For a 'plug in' device, the 'legal limit' on a 20 A circuit is 3-3.5 HP.
Lastly, 12 ga _is_ sufficient for the load, BARELY. Running the saw as a 'plug in' device requires _more_ than a 20 A breaker, however -- because it has a 'plate' draw that is more than the allowable 80% of the breaker rating. The next larger standard breaker is a 30A one. Or you can pay through the nose for a 25 A one. Either way, you have to upgrade to 10 ga wiring though -- because 12 ga, in conduit, is not rated for even 25A. And the wiring must be of a size sufficient for the rated breaker ampacity.
Now, if this was a 'permanently wired' device, you'd be 'legal' with 12 ga wiring on a 20 A breaker. BUT, the start-up draw would still be a potential issue. It depends tremendously on the 'small overload' characteristics of the breaker -- how quickly it trips at what level over rated ampacity.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Although there are additional considerations, the above is much more practical advice ... advice that actually reflects many of the realities of the issues involved.
--
www.ewoodshop.com

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
snipped-for-privacy@host122.r-bonomi.com (Robert Bonomi) wrote in

Apparently, you don't know it as well as you think you do.

No, you are not. The 80% limit applies only to "continuous loads", which is defined in the Code as "a load where the maximum current is expected to continue for 3 hours or more."
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Site Timeline

Related Threads

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.