Air Compressor for Pneumatic Tools

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Jeff80

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I have a single phase air compressor with name plate rating of:7.5HP, 230volts, 31.4amps, 37 sf amps, and service factor of 1.15.

I am installing this to single phase 208volts. I dont do many motor calcs and I am a bit confused. I need help with wire size, breaker size, and heaters.

I think this is 55amp wire, 60 amp breaker.
 
before I would begin to guess with the information provided, I would need to know what is the overall distance from the source to the compressor. Voltage drop can be a major factor with a single phase motor that big.

your guesses seem to be in the right neighborhood (assuming distance is less than 75 feet or so), but I think I would use a 70A OCP at the source (I think an 80A is the max allowed by code in this case with the same assumption).


Mods --- Is it OK to post a link to a Manufacturer's web site to get this person a useful motor calculator??
 
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Here is a link to an electrical formula page you might find useful:
http://www.electrician2.com/calculators/elcal.html

when using the motor calculation be sure to scroll to the bottom and complete the voltage drop section since, as poboy relates, it can have a significant impact.

In your situation, I would be concerned about the 208 v source. Compressors are often designed so close on HP that you very well may find the 230 volt motor is not going to perform on the 208 system.
 
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For the reason Augie47 states is why I have wound up going back to "FIX" compressors like that by adding in a buck/boost transformer.

They MIGHT work for a little while, but the motors soon burn up and the saddest part is that many times a motor replacement on those single phase compressors costs almost as much as new compressor, often times MORE when you add in the cost of the buck / boost. Customers do not like to hear news like that at all.
 
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