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Discussion Starter #1
I don't really work with motors, so forgive any ignorance below...

I am working on a grain bin for a family member and there are two grain augers that I need to supply. I planned to run a 100A circuit to a subpanel near the augers with a 2P 50A breaker for each motor. I want to have a switch to control the motors (preferably at the same time, since they need to be turned on in order or simultaneously, but it can be separate).

The two motors are identical 7.5HP, 230V single phase, (Nameplate says 36A) with built-in overload protection. We don't want to use breakers as the switch.

What would you guys use as an on/off switch option? I'm having a hard time coming up with an inexpensive single phase switch for that HP motor. Is there an option for one switch to run both? (Of course, outdoor application, needs to be enclosed from grain dust, rain, etc.)

Thanks for any advice!
 

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zap
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I don't really work with motors, so forgive any ignorance below...

I am working on a grain bin for a family member and there are two grain augers that I need to supply. I planned to run a 100A circuit to a subpanel near the augers with a 2P 50A breaker for each motor. I want to have a switch to control the motors (preferably at the same time, since they need to be turned on in order or simultaneously, but it can be separate).

The two motors are identical 7.5HP, 230V single phase, (Nameplate says 36A) with built-in overload protection. We don't want to use breakers as the switch.

What would you guys use as an on/off switch option? I'm having a hard time coming up with an inexpensive single phase switch for that HP motor. Is there an option for one switch to run both? (Of course, outdoor application, needs to be enclosed from grain dust, rain, etc.)

Thanks for any advice!
You need a mag and a few other goodies. I get the impression you're not an electrician and should be asking this question on a DIY site not a professional forum.
 

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Discussion Starter #3
You need a mag and a few other goodies. I get the impression you're not an electrician and should be asking this question on a DIY site not a professional forum.
Thanks. I am a licensed electrician, but I don't practice anymore, and like I said, I don't know much about motors.
 

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zap
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Thanks. I am a licensed electrician, but I don't practice anymore, and like I said, I don't know much about motors.
Keep in mind you have a dust ignition hazard also to contend with, look into a "pump" panel, most wholesalers will stock these. You can piggy back the start stop so both mags close together. Also fill out your profile, welcome.
 

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Discussion Starter #8
Thanks for the suggestion on the pump panel, I will research. (And fill out profile)

It won't let me hyperlink to motor since I have less than 20 posts...

Teco-Westinghouse Farm Duty Single Phase TEFC Motor S7/54

It has a manual overload reset on it and the spec sheet includes it.
 

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Discussion Starter #11
Have a Baldor motor almost identical to that one, but it's in a different location and has it's own control that a manufacturer added.

joe-nwt, that looks perfect, it doesn't switch both at the same time, but I think it would work. Thanks!
 

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John R retired electrician from Fed Gov

I agree, Mag starters with overloads. Also I not sure that a 50A breaker will be able to start a 7.5 HP SP motor. My SD cheat card says a 80A is required for a 7.5 HP. Most SP motor of that size do have overload already. I do not like them but they are better than nothing.
 

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I've owned such motors -- and not one of them had O/L integral to their design.

I think you are entirely mistaken on this point. You want heaters in your contactor.
Integral O/L are common for FRACTIONAL horsepower motors -- not for these beasts.

I know of no device that could easily be stuck inside them. ( Klixons won't do. )
Telsa,

Sometimes I think you're stuck in a bubble.

They do put thermal overloads in single phase motors every day of the week. I see them at work, my folks have one in a 7.5HP 230v single phase vacuum pump for a milking parlor.

The fact you tell people they are mistaken, when YOU just don't know, is baffling to me.

Please stop googling your answers just so you can respond to posts and act like the authority on all things electrical. It does get old.

To answer the OP's question, we'd most likely use pump panels.

The pump panels we use regularly are all 3 phase, so it takes a pretty good sized 3 phase pump panel to run a 7.5HP single phase motor. Probably a size 3.
 

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Farm Duty motors usually have thermal OL protection built-in, that's one of the things that make them different.


So you don't really need the OL relays in a starter. It's just that a Pump Panel is a known inexpensive way to buy an outdoor rated motor controller. Each one will have a Fused Disconnect or Circuit breaker, properly sized for the circuit, a contactor, an overload relay, an H-O-A switch and a Start-Stop Push Button (some use an H-O-A-Start switch, no PB). that gives you everything you need to make this work, all you would do is tie the Start circuit together so that starting one starts the other one at the same time.


You will need a NEMA Size 2 Pump Panels for 7-1/2HP 230V single phase motors. You will need one for each motor because if you combined them to try to use one Size 3 PP, the SCPD in the controller would be too large of one motor. Each Pump Panel will be rated for 45A, so you will need a 90A circuit to feed them.
 

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Use a nonfused 60 amp 3r knife switch. This is a farm, dust tight is not required and has never been a problem outdoors. a Sq D standard duty sw # DU322RB is 10 hp rated. I agree that contactors are a best practice for controlling but they are not required. The farm world is a very different beast than the industrial world. Most farmers will have a heart attack when you try to sell them a pump panel to start and stop a motor that does not need automatic or remote control.
 

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Use a nonfused 60 amp 3r knife switch. This is a farm, dust tight is not required and has never been a problem outdoors. a Sq D standard duty sw # DU322RB is 10 hp rated. I agree that contactors are a best practice for controlling but they are not required. The farm world is a very different beast than the industrial world. Most farmers will have a heart attack when you try to sell them a pump panel to start and stop a motor that does not need automatic or remote control.
Do not do this. Starting a motor this big with a knife switch will ruin the knife switch. You will have a lot a arcing every time you start or stop the motor
 

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you are right. but these guys have been controlling silo unloaders for many many years 2 times a day this way. Starting and stopping under almost full load. Dirty wet corrosive silage. I have seen enclosures almost gone and the switch still works. Dangerous yes. We fix them when we see them.
 
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