Air compressor wiring and selection. 5hp vs 7.5hp

[NoMoreGreen]

I am buying an air compressor in the next several months to a year and considering either a Quincy QT-5, a Quincy QT 7.5 or also possibly the FS-Curtis with the magnetic starters. It’ll come down to Home Depot vs Northern tool and what’s easiest.

My question is, I have a standard 200 amp panel and service. Is a 7.5 horsepower motor even feasible in residential areas? The wire length will be minimal as the panel is right next to where the air compressor will go in the garage.

I read somewhere on here I have to contact the power company for a 7.5 horsepower motor?

What breaker and wire size for 7.5 horsepower?

What breaker and wire size for 5 horsepower?


Sent from my iPhone using Garage Journal

 

[Norcal]

You will need contact your PoCo or might be able to find out on their website if they have one what is allowed. That would be the first thing before going further.

 

[Bert_]

7.5 is no big deal. Could run a bunch of them off a 200A service.

 

[cvairwerks]

Most PoCo's have a single motor limit of 7.5 hp in residential service. With either size motor, I would rather have a mag starter. 5 hp is right at the limit for most pressure switches on compressors and as they wear with age, the margins get smaller and smaller.

With a mag starter, you can easily move over to low voltage controls and have various switches around the garage for control, or add electrically controlled drain valves, or shut offs or whatever you want to add.

 

[bugman-74]

Your mileage may vary, but my PoCo says they want to know if I have anything >10HP.

I recently picked up the QT-7.5 Max package from Northern, and am very happy with it. This unit uses a mag starter. (Max package includes aftercooler, auto tank drain, and low oil pressure switch).

Mine is located nearby my breaker panel. I ran #6-2 NM through the wall to a safety switch, and then #6 THHN from the switch to compressor in conduit. I am using a 2-pole 80A breaker, which is what Quincy recommended (nameplate amps on the Baldor motor is 31A, NEC FLC is 40A)

A couple of notes that might be helpful:

Northern indicated I would receive it faster than I actually did. It was no big deal, but for what its worth I ordered Dec 2 and received it Jan 18.

Consider purchasing the EWK-3 package in the same order as the compressor. If you do, Quincy will extend your warranty.

Plan to need a hoist of somesort to safely lift the unit off the skid. Weighs 700+lbs. I did it with an engine hoist.

The Quincy's never seem to go on sale, but if you time it right with Northern, sometimes they will do a "spend >$999 and get a $200 gift card" sort of deal.

 

[TRWham]

I have a 7.5 hp compressor in my garage on a 150 A service with no issues. It was probably originally a 5 hp but the compressor is larger capacity than most 5s built today (measures about 21 cfm) and I suspect a prior owner found it worked better with the 7.5 hp. It pulls about 28 A at 240 V when running. Wired with 8 AWG THHN in 3/4 EMT on a 40 A breaker (could have used a 50 or larger, but I had the 40 and it runs just fine this way). Starter is a Square D 8911 with a single B45 heater and 240 V coil through a Square D 9013 pressure switch.