20 Hp air compressor 700' run.

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Hfalz1

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Houston, Tx.
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Electrician
Needing to know wire size and conduit for a 20Hp air compressor that is 700' away. The feed is 3 phase 480v. On a siemens size 1 breaker now. Do i need to go to a size 2? Not sure the breaker size just yet, haven't visited the site just yet. This is just info from a phone call. Will advise when i get more info. Thanks in advance.
 
Cow said:
That sounds about right to me...



I hope he means size 1 starter. To answer the OP's question, that size 1 is the right size for a 20HP motor.
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If there is any standardization to that NEMA size 1, 2... I know that Square D NEMA starters would need to be a size 2 for 15, 20 and 25 HP @ 480 volts three phase.
 
ptonsparky said:
Furnas, now Siemens, used to make 1/2 sized starters. Don't know if that is still true or not.
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I think it was mostly just size 3.5, and I think they still have it, works for 60 and 75 HP (@ 480 volts anyway) where a size 4 works up to 100 hp.
 
Jraef said:
NEMA starter sizes are the same regardless of brand. Size 1 is 10HP max. at 480V. You need a Size 2 starter.
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You're absolutely right. I had it in my head a 100HP was a size 3, and I worked backwards from there to a size 1 for a 25HP.:slaphead:
 
Yes, they (Siemens) still have tweener sizes, 1-3/4 2-1/2 and 3-1/2. NEMA standards do not have sizes in between the whole numbers, this was just a marketing ploy of Furnas that Siemens inherited and continued.

The NEMA starter size numbering system was conceived of by the automotive industry to streamline the process of setting up new or reconfiguring old production lines when there were major changes in model year designs. Trained and qualified electricians can just pick out a NEMA size and not have to wait for an engineer to decide on the size based on what it will be used for etc, because the NEMA design can take any abuse you can throw at it.
 
Jraef said:
Yes, they (Siemens) still have tweener sizes, 1-3/4 2-1/2 and 3-1/2. NEMA standards do not have sizes in between the whole numbers, this was just a marketing ploy of Furnas that Siemens inherited and continued.

The NEMA starter size numbering system was conceived of by the automotive industry to streamline the process of setting up new or reconfiguring old production lines when there were major changes in model year designs. Trained and qualified electricians can just pick out a NEMA size and not have to wait for an engineer to decide on the size based on what it will be used for etc, because the NEMA design can take any abuse you can throw at it.
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Even a D-9 Caterpillar? I guess most of us probably can't throw a D-9 though:)
 
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