Multiple Motor Feeder Calc?

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jahilliard

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I am adding 5 - 3 HP mototr loads to an existing 200 Amp panel. The question is how should I figure the added load? I don't do load calcs often at all and in this case I'm not sure the best way to calculate the new load. These motors are 240V single phase, 5 minute rated motors for car hoists. Any suggestions would help thanks.
 
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jahilliard

Senior Member
the biggest question is if I'll need to upgrade the existing panel based on the new load from the motors. Simple calculation would suggest an additional 85A load at 100%...but considering these are 5 minute rated hoist motors I thought there may be a DF that can be applied that I'm not aware of??
 
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petersonra

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Location
Northern illinois
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engineer
jahilliard said:
the biggest question is if I'll need to upgrade the existing panel based on the new load from the motors. Simple calculation would suggest an additional 85A load at 100%...but considering these are 5 minute rated hoist motors I thought there may be a DF that can be applied that I'm not aware of??
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I don't think you can claim anything short of having some kind of interlock that would prevent them from operating simultaneously.

220.60 might offer you an out, but usually when the code uses the word "unlikely" it really means "impossible", just as when it uses the word "likely" it really means "there is a remote chance". :)
 
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Smart $

Smart $

Esteemed Member
Location
Ohio
Your only [compliant] options are doing a complete load calculation or using the exception to 220.87, which essentially requires monitoring the existing load for 30 days and compensating the result for any loads that were not energized at all during that period.
 
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petersonra

Senior Member
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Northern illinois
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engineer
given how conservative load calculations are, one would think the NEC would have some kind of dispensation for cases like this for a motor that may run for 20 seconds a few times a day.
 
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