Manual motor starter vs magnetic.

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nizak

Senior Member
I don't use a lot of motor starters in the line of work I normally do. I have a question regarding starters.

Will a manual motor starter serve the same purpose as a magnetic type?

I'm looking to put together a price for wiring a number of 3 phase 460 volt motors.

They will be basic one direction on/off applications.

There is considerable cost difference between the two types.

If sized properly for the load, is one way better than the other.

There won't be considerable starting and stopping. Units will be turned on at start of shift and off at end of shift.

Thanks
 

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
The main difference is that with an MMS, your finger pressing the button is what directly closes the contacts. So there is a size limit involved in that as the motor current increases, the force it takes to keep the contacts closed or to open them if they are closed increases beyond reasonable expectations of human strength. So a push button MMS will stop at the 460V equivalent of 10HP. IEC types will go up to 63A, but use a rotary mechanism to operate. Above that, you can get molded case circuit breakers with adjustable thermal trips that are qualified as an MMS, so a toggle mechanism. The thing is with the larger rotary and toggle mechanisms is that they don’t lend themselves well to repeated operations day in and day out, they are not made for that.

Aside from the size issues, a mag starter also provides the ability to use what’s called “3 wire control”, a safety function in that means if the power fails, the mag starter drops out and someone must push the start button again to restart. A simple MMS will remain closed on a power loss so the motor restarts on its own when the power comes back on, which is usually dangerous. You can add an Under Voltage Coil to an MMS that will do the same thing, but then the cost starts to go up.

A mag starter also provides for the ability to electrically interlock one motor starter with another, or with other control elements or safety devices. That’s difficult to implement with an MMS.

They both have their place in the grand scheme of things.
 

kwired

Electron manager
Location
NE Nebraska
As Jraef mentioned larger sized motors becomes more impractical to use a manual starter on.

For a motor that runs 24/7 and almost never gets turned off a manual starter may be ideal.

If you want to control the motor from a remote location or via any kind of automation process, a magnetic starter becomes a necessity.
 
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