Wire size for compressor replacement question.

[Carla]

Hello, Garage folk,

We're planning to replace a 3hp compressor with a 5hp unit, with a wiring run of approx 30 ft from a 50A breaker (230VAC, of course, and single phase).

The model of compressor we mean to use might be considered a 'hard starting load' for the motor. Its a Quincy 350, which has its unloaders operated by oil pressure, so that it won't pump air until it comes up to speed, but the sheer mass/weight of the large pump is, I'm told, a tough starting load for a 5hp single phase motor.

The pump is a Quincy factory rebuilt unit, and seems to turn over quite easily when spun over by hand.

The motor we have in mind would be a new Baldor #L1508T, which is rated for 27A full load.

What wire size, using copper wire, is needed for that length of run?

I was told by one person who claims to be knowledgeable about electricals that the starting draw of such a motor on a relatively hard starting load would surely trip a 50A breaker.

Should I call the Quincy Co. to enquire about this setup? One would be tempted to think that since the pump is listed at 5hp min, belted for min pump rpm, that one could follow the spec sheet safely.

What, in your opinion, should we do?

Thank you

cheers

Carla

 

[Norcal]

10 AWG & a 50A breaker, IF suitable motor overload protection is used. Motor rules are different, in the example shown the fuse/circuit breaker is only providing short circuit protection. If no O/L protection, 6 AWG & a 50A breaker.

 

[Aceman]

10 AWG & a 50A breaker, IF suitable motor overload protection is used. Motor rules are different, in the example shown the fuse/circuit breaker is only providing short circuit protection. If no O/L protection, 6 AWG & a 50A breaker.

How did you come up with #10 when no mention of wire type was made?

THHN would be OK.
NM would not.

 

[sberry]

8/50 for the diy crowd, cant miss. Simple.

 

[Charles (in GA)]

Hello, Garage folk,

We're planning to replace a 3hp compressor with a 5hp unit, with a wiring run of approx 30 ft from a 50A breaker (230VAC, of course, and single phase).

The model of compressor we mean to use might be considered a 'hard starting load' for the motor. Its a Quincy 350, which has its unloaders operated by oil pressure, so that it won't pump air until it comes up to speed, but the sheer mass/weight of the large pump is, I'm told, a tough starting load for a 5hp single phase motor.

The pump is a Quincy factory rebuilt unit, and seems to turn over quite easily when spun over by hand.

The motor we have in mind would be a new Baldor #L1508T, which is rated for 27A full load.

What wire size, using copper wire, is needed for that length of run?

I was told by one person who claims to be knowledgeable about electricals that the starting draw of such a motor on a relatively hard starting load would surely trip a 50A breaker.

This won't begin to trip the 50 amp breaker. I have a 7.5 hp on a 50 amp and it draws 190 amps for a split second then falls off. Common breakers are inverse time type, in that the shorter the load time, the higher it can go (within reason). In reality, the quincy, due to its unloader design, probably starts easier than most, as I suspect it take a couple of revolutions of the pump to build enough oil pressure to close the unloader. Pumps that use the pressure switch to operate the unloader start out with the unloader closed.

Charles

 

[EOC_Jason]

Yeah a 5HP unit really only needs a 40AMP breaker... Your current 50AMP circuit should be fine.