575 Volt Heater - Can you run at 480 Volt - even thought 30% less KW output??? - Electrician Talk - Professional Electrical Contractors Forum
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Old 06-25-2016, 08:22 PM   #1
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Wink 575 Volt Heater - Can you run at 480 Volt - even thought 30% less KW output???

I've been told by a company that makes an explosion proof 'forced air heater' that I've purchased,(year old surplus)>>>>that I can run this heater that is
configured: 10KW - 575V - (controls are 120 Volt) 60 Hz - 3 Phase.....I've been told I can run it at 480 Volt and will loose about 30% of KW bringing it down to then a 7KW Heater.....which is still plenty for our needs.....
I'm wanting to hear from some electricians about this idea of running 575V Heater at 480 Volts?
There is a small 1/2 hp motor that blows through the coils and the vent that would run at a slight less speed as well! All comments and thoughts are appreciated?
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Old 06-25-2016, 08:33 PM   #2
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Get it in writing from their engineering dept. on company letterhead or else it didn't happen.
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Old 06-25-2016, 08:40 PM   #3
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The only question I would have is the controls.
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Old 06-25-2016, 08:43 PM   #4
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NEC 110.3 Equipment must be installed in accordance with any instructions included in their listing or labeling requirements.

I believe that equipment is intended for a 347/600v 3 phase system.
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Old 06-25-2016, 08:48 PM   #5
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[quote=22422;2958210]I've been told by a company that makes an explosion proof 'forced air heater' that I've purchased,(year old surplus)>>>>that I can run this heater that is
configured: 10KW - 575V - (controls are 120 Volt) 60 Hz - 3 Phase.....I've been told I can run it at 480 Volt and will loose about 30% of KW bringing it down to then a 7KW Heater.....which is still plenty for our needs.....
I'm wanting to hear from some electricians about this idea of running 575V Heater at 480 Volts?
There is a small 1/2 hp motor that blows through the coils and the vent that would run at a slight less speed as well! All comments and thoughts are appreciated?[/quote

Heating elements will still work at a lower voltage,although less heat.
Motors again will work on lower voltages with less HP out,
So depending on the load the motor could overheat,
But I would try it and monitor the motors temp.
What else is involved ?
Is there any control circuitry ?
Any solinoids or relay ?

But remember just because it may work technically
there are other issue's to consider such as legal liability
should some thing go wrong
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Old 06-25-2016, 10:13 PM   #6
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It'll work just fine. It's a heater, running it at a lower voltage will actually extend the life of the elements.

The blower motor and controls may have to be revamped though.

Or just replace the heater with one of the right specs.
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Old 06-25-2016, 10:25 PM   #7
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As noted, the elements will work just fine but with around 30% less heat.

A 575 volt motor will run on 480 but since it's a fan, it'll very likely be overloaded at the lower voltage. Technically, the lowest voltage it would run on would be 517.

The control transformer might have a 480 tap.

Since the fan and controls are single phase, you could get a 480 - 48 volt buck-boost transformer and boost the 480 up to 528. This would be ok for both fan and controls and since it's a buck-boost, it'd be a fairly small transformer.
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Old 06-25-2016, 10:46 PM   #8
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Quote:
Originally Posted by nownojin View Post
NEC 110.3 Equipment must be installed in accordance with any instructions included in their listing or labeling requirements.

I believe that equipment is intended for a 347/600v 3 phase system.
575 three phase is a normal system voltage. I worked in a plant that was setup like that.
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Old 06-26-2016, 09:24 PM   #9
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Okay bare with me here, I'm just an apprentice so correct me if I'm leading this discussion the wrong direction. But in school I remember reading this awhile back out of my school books. I'll type the paragraph word by word, just found the text...

"Although it is theoretically possible to control the speed of an AC motor by varying the voltage, it is not a good way to change the speed of the motor. In fact, if the voltage is changed by more than plus or minus 10%, the motor may be damaged. If less than nameplate voltage is applied, torque and full load speed decrease while the full load current and winding temperature increase. Regardless of applied voltage, a motor still wants to deliver rated HP. Keep this in mind before connecting a 208-volt circuit to a motor rated to operate at 230 volts. If more than nameplate voltage is applied, torque and full load speed increase while the full load current and winding temperature decrease. The two practical methods of AC motor speed control are to change the number of poles to change the frequency."

Edit: More info I found. Looking back on one of my homework questions.

The speed of a single-phase AC motor can be easily controlled by changing the frequency and number of poles. Even though OP is talking about 3 phase, maybe the theory still applies. Idk...

Last edited by JasonCo; 06-26-2016 at 09:30 PM.
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