Largest Motor

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fifty60

fifty60

Senior Member
Location
USA
I need to specify the largest motor in my system. I have a 3 phase 230V refrigeration compressor that is 1.5HP with an RLA of 4.9A. This is my largest HP motor.

I also have a single phase fan motor that is 0.5HP, but operates at 115V and 8.8A. this would be my largest Amp drawing motor load. the 115V is derived from a 230V/115V single phase transformer.

What would the installer be most interested In knowing? That the largest motor is 1.5HP, or that I have a motor, through a transformer, that draws 8.8A.

None of this, relative to this question, affects the FLA. I know the FLA for the system, and now am trying to determine what the installer needs in regards to the largest motor load.
 
Jraef

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
fifty60 said:
I need to specify the largest motor in my system. I have a 3 phase 230V refrigeration compressor that is 1.5HP with an RLA of 4.9A. This is my largest HP motor.

I also have a single phase fan motor that is 0.5HP, but operates at 115V and 8.8A. this would be my largest Amp drawing motor load. the 115V is derived from a 230V/115V single phase transformer.

What would the installer be most interested In knowing? That the largest motor is 1.5HP, or that I have a motor, through a transformer, that draws 8.8A.

None of this, relative to this question, affects the FLA. I know the FLA for the system, and now am trying to determine what the installer needs in regards to the largest motor load.
Click to expand...
Motor size, not amp draw. It's about kVA requirements from the supply source.
 
Smart $

Smart $

Esteemed Member
Location
Ohio
Jraef said:
Motor size, not amp draw. It's about kVA requirements from the supply source.
Click to expand...
That's incorrect. The motor with the highest rated-load current is the largest motor [440.7].

That said, the 115 would not be the largest because it only draws 4.4A on the primary side of transformer.
 
Smart $

Smart $

Esteemed Member
Location
Ohio
Jraef said:
As would be evidenced by the kVA draw...
Click to expand...
kVA is not an accurate method of determination. It's about the motor that draws the most line current when more than one motor is supplied by that line conductor. A 1? motor with 10A RLC has a lower kVA than a 3? motor with 8A RLC. The 3? motor likely has a higher HP rating, too, given the same supply voltage. Yet the 1? motor is the largest according to 440.7.
 
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