MOTOR AIR COMPRESSOR DETERMINE THE SIZE OF THE BREAKER

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surgegs430

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SO I CANT FIGURE WHAT SIZE BREAKER TO USE FOR MY INSTALL, HERES WHAT I GOT ITS A 3.7 HP SINGLE PHASE 230V WITH FULLY LOAD AMP 17.2A AND ITS CONTINOUS. I WNET TO 310.15(B)(16) THHN FOR MY WIRE SIZE 125%X FLA=21.625 SO THEREFORE I CAN GET AWAY WITH A COPPER 12AWG BUT I GOT 10"S IN THE CONDUIT ALREADY NOW I FIGURE WHY NOT A 2POLE 30A BREAKER BUT I LOOK INTO IT AND 430.52 MAXIMUM RATING MOTOR BRANCH CIRCUIT 250%XFLA= 43.25A SO NOW I WOULD GO WITH A 2POLE 50A NOW IM NOT SURE WHICH ROUTE TO TAKE DO I PUT A 2POLE 50A WITH #8"S OR CAN I GET AWAY WITH 2POLE 30A & #10"S
 
Please take off the caps-lock and add some punctuation, that was very hard to read.

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I can't figure what size breaker to use for my install. Here's what I've got-- it's a 3.7 hp single phase 230v with fully load amp 17.2a and it's continuous. I went to 310.15(b)(16) THHN for my wire size (125% x FLA=21.625) so therefore I can get away with a copper 12awg but I got 10's in the conduit already. Now I figure why not a 2pole 30a breaker but I look into it and 430.52 maximum rating motor branch circuit 250% x FLA = 43.25a so now I would go with a 2pole 50a. Now I'm not sure which route to take, do I put a 2pole 50a with #8"s or can i get away with 2pole 30a & #10's.
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That seems like an odd-size motor. Is it part of a machine?
 
What kind of equipment has a 3.7 HP motor? That is not a standard size in tables of Article 430.
 
zbang said:
Please take off the caps-lock and add some punctuation, that was very hard to read.

Reformatted and edited--


That seems like an odd-size motor. Is it part of a machine?
Click to expand...
If you want to be pedantic, it should be 230V and 17.2A.
And your first sentence should be two with a full stop after "punctuation". " that was very hard to read." should be a new sentence.

But I take your point..........:D
Yes, it seems an unusual rating for a motor but they can be made any rating. I thought the 230V might indicate a European rating and it would equate to about 2.8kW which is available. I'd be looking at 4mm2 conductors.
 
Split the difference and go with 40A MOCP and your already installed #10.

istm you are forgetting that 240.4(D) allows motors to be on larger breakers that wouldnt be allowed for other loads. You cannot use a 50A breaker; 45A are available and next size up from 43.25A. And that is a MAXIMUM size, not a REQUIRED size.
 
infinity said:
What kind of equipment has a 3.7 HP motor? That is not a standard size in tables of Article 430.
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A single phase air compressor is very common to see odd HP ratings. Some other power tools are this way also.

All one can do with those is go by rated amps on the motor itself, when determining minimum conductor size needed and overcurrent protection device selection.
 
surgegs430 said:
SO I CANT FIGURE WHAT SIZE BREAKER TO USE FOR MY INSTALL, HERES WHAT I GOT ITS A 3.7 HP SINGLE PHASE 230V WITH FULLY LOAD AMP 17.2A AND ITS CONTINOUS. I WNET TO 310.15(B)(16) THHN FOR MY WIRE SIZE 125%X FLA=21.625 SO THEREFORE I CAN GET AWAY WITH A COPPER 12AWG BUT I GOT 10"S IN THE CONDUIT ALREADY NOW I FIGURE WHY NOT A 2POLE 30A BREAKER BUT I LOOK INTO IT AND 430.52 MAXIMUM RATING MOTOR BRANCH CIRCUIT 250%XFLA= 43.25A SO NOW I WOULD GO WITH A 2POLE 50A NOW IM NOT SURE WHICH ROUTE TO TAKE DO I PUT A 2POLE 50A WITH #8"S OR CAN I GET AWAY WITH 2POLE 30A & #10"S
Click to expand...

12 AWG conductor would be fine. 30 amp breaker may be marginal as to whether it will allow starting, 35 amp breaker probably holds most of the time. NEC would allow up to 45 amp breaker before it must fail to start before you go any higher.
 
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