air compressor combo starter

[StitzieJ]

I am working on my EPEC training and need some advice on where to start.

I need a combination starter for a 20HP motor (air compressor) in a 120/208v system protected by a 3 Pole, 80 amp breaker.

Any ideas of where to start looking? What kind specs should I be looking for. I am unsure of the FLA of the compressor as it isn't specified, nor am I sure whether or not I may need some sort of transformer to voltage specs.

 

[augie47]

I would start by obtaining a spec sheet on the compressor and verifying the facility voltage.
As far as the starter, once you verify the voltage the starters are HP rated. The comprssor spec sheet might give you guidance on fuse/ breaker size.

The 80 amp breaker is a but of a red flag for me. Possibly undersized for a 20HP 208v compressor.
Code will allow a 150 amp so you are on the low end of the scale.

 

[petersonra]

I would start by obtaining a spec sheet on the compressor and verifying the facility voltage.
As far as the starter, once you verify the voltage the starters are HP rated. The comprssor spec sheet might give you guidance on fuse/ breaker size.

The 80 amp breaker is a but of a red flag for me. Possibly undersized for a 20HP 208v compressor.
Code will allow a 150 amp so you are on the low end of the scale.

My handy-dandy Square D sliding calculator from 1987 says the FLA is 62 and suggests a 100A CB.

I am generally inclined to up size more than the 30% the 80 A CB would be, just to reduce the chances of nuisance trips. We don't like them.

 

[Jraef]

For this exact reason, a long time ago, people in this country came up with the concept of NEMA sizing of starters. You can select a NEMA Size 3 starter and it is good for anything from 15 to 25HP at 208V, and whatever breaker they put in there will be UL listed for that purpose. The only thing you need worry about then is conductor sizes, which you determine from the charts in the NEC, and OL heater elements or settings, depending on what brand you end up with and read in their instruction manual. Easy peasy.

Or... you can fret and worry about all of the details ahead of time to save a few dollars on parts, but possibly make a mistake and pay for it through the nose later.