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#199918 - 03/14/11 11:06 AM What are the heaters for in a motor starter?
strantor Offline
New Member

Registered: 03/12/11
Posts: 3
Loc: TX
I have a 600V contactor here and no heaters. It's for a 480V pump controlled by a limit switch. It would switch maybe 100 times over a 12 hour run. I need to get it setup today but I don't have any heaters. Is it ok to use it without heaters for a while? I'm assuming that all they do is keep the contacts from burning up too fast; am I close?
Thanks

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#199919 - 03/14/11 11:42 AM Re: What are the heaters for in a motor starter? [Re: strantor]
ghost307 Offline
Member

Registered: 05/09/05
Posts: 748
Loc: Chicago Illinois USA
The heaters are critical for providing electrical protection for the motor.
A contactor without heaters is comparable to a fusebox with a penny in it.
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#199927 - 03/14/11 01:20 PM Re: What are the heaters for in a motor starter? [Re: strantor]
sparkyinak Offline
Member

Registered: 07/08/07
Posts: 1188
Loc: Alaska
The heaters if properly sized will protect the motor from over loading and trips the circuit. All do respect, it sounds you button off more you can chew at this time. You may want to get some help on the ground with you
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#199928 - 03/14/11 02:33 PM Re: What are the heaters for in a motor starter? [Re: strantor]
renosteinke Offline
Cat Servant
Member

Registered: 01/22/05
Posts: 5032
Loc: Blue Collar Country
There is a difference between "over-current" protection and 'over-load' protection of the motor.

"Over-current" protection is supposed to act FAST. With motors, the amount of over-current protection we can provide is limited by the high amount of current needed to get the motor started.

"Over-load" protection is what we use to keep the motor from working too hard for any period of time. This is what the heaters provide. It will, say, keep you from asking that 1-hp motor from providing 2-hp for any length of time. The breakers or fuses for that same motor, by contrast, won't kick in until you're asking that motor to give you six horses - which will be long after that motor is trash.

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#199938 - 03/14/11 07:22 PM Re: What are the heaters for in a motor starter? [Re: renosteinke]
strantor Offline
New Member

Registered: 03/12/11
Posts: 3
Loc: TX
Originally Posted By: sparkyinak
The heaters if properly sized will protect the motor from over loading and trips the circuit. All do respect, it sounds you button off more you can chew at this time. You may want to get some help on the ground with you

I agree there are better guys for the job, but the unfortunate reality is that I was the only guy available & this had to be done ASAP. I'm not an electrician, I'm an "electronics technician" (overpaid mechanic) & our electrician on vacation. I figured it was better to ask the stupid question from you guys who don't know me than burn up a motor or worse hurt myself. Don't worry, I installed the properly sized heaters; had them hot-shot in.

Originally Posted By: renosteinke
There is a difference between "over-current" protection and 'over-load' protection of the motor.

"Over-current" protection is supposed to act FAST. With motors, the amount of over-current protection we can provide is limited by the high amount of current needed to get the motor started.

"Over-load" protection is what we use to keep the motor from working too hard for any period of time. This is what the heaters provide. It will, say, keep you from asking that 1-hp motor from providing 2-hp for any length of time. The breakers or fuses for that same motor, by contrast, won't kick in until you're asking that motor to give you six horses - which will be long after that motor is trash.


So, is it like a super slow-blow fuse? if one trips, does it "burn out" and I need to replace it?

Thanks for the input guys!

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#199941 - 03/14/11 07:42 PM Re: What are the heaters for in a motor starter? [Re: strantor]
renosteinke Offline
Cat Servant
Member

Registered: 01/22/05
Posts: 5032
Loc: Blue Collar Country
The 'heater' differs from a fuse in that it will never, ever react to a short circuit. And, no, they do not 'burn out' when they trip.

First off, they are brand-specific to the type of starter they're in. You can't use Square D heaters in an Allen Bradley starter.

The older style used various mechanical means - springs, solder pots, etc- to react to heat build-up. When they got hot enough, they would open an internal contact, which would cause the starter coil to lose power and open the power contacts. You would have to wait for them to cool before you could press the 'reset' and then start up everything again.

The newer ones are electronic.

Whatever the type, you can set them / get them in settings very close to the actual operating current of the equipment. That is, a motor that normally drew 7.3 amps might have heaters set at 7.4 amps. The idea was to protect the equipment as best you could. (That same motor might have 50A fuses protecting it, and an 8FLA on the nameplate).

Another way to look at it: Fuses protect the wires, heaters protect the motor.


Edited by renosteinke (03/14/11 07:43 PM)

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#199944 - 03/14/11 08:42 PM Re: What are the heaters for in a motor starter? [Re: strantor]
Tesla Offline
Member

Registered: 06/16/04
Posts: 1178
Loc: Sacramento, CA
Contactors either come set up absolutely requiring heaters -- to complete the circuit...

Or have a heater module as an add on, in which case you can eliminate it and make a direct connection.

Personally, I've never found an urgency so great that I'd compromise my work.

After you've 'let the smoke out' there'll be plenty of time to correct the fiasco.

All of the urgency will have been lost.
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