Dedicated Air Compressor Circuit
#1
Dedicated Air Compressor Circuit
I just bought a 20 gallon 2HP air compressor (Ingersoll Rand P1.5IU-A9) and the manual says the breaker should be twice the rating of the motor. The motor is 15A, so this means a 30A breaker. This seems overkill to me. I just powered on the compressor for the first time a few moments ago on a 15A circuit (which was powering my cable modem and router) via a 10 ft extension cord and the breaker didn't trip. I will be running a dedicated circuit tomorrow, and planned on using 12/2 and a 20A breaker. FYI, the compressor has a 3-prong 110V plug. How do they expect the user to use a 30A breaker with 10 gauge cable and a standard 110V receptacle?
#2
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Bah, a 20 amp breaker will be fine for a dedicated line. Clamp on an amp meter with it running and you won't see near 15 amps steady state. There is probably a jumper on the compressor if you want to run it 220v.
-=Phyber
-=Phyber
#4
I hate to rain on your new tool but that motor will only deliver 2 horsepower in a highly overloaded state. Look at the nameplate and I'll bet it says "compressor duty" or something like that and also that it has a rotational speed of about 3450 rpm. A REAL 2 horsepower motor will draw approximately 24 amperes at 115 volts so that makes the 15 ampere maximum of your motor more in line with a one horsepower motor. The manufacturer can get away with the labeling because the motor WILL develop close to 2 horsepower for a limited time before it burns up the windings AND because it actually exceeds 2 electrical horsepower in its power consumption. Further, the "compressor duty" signifies that the motor is NOT rated to deliver full power except in a cycling operation.
But don't get too excited over this news as ALL compressor manufacturers do the same and it is even used as a marketing ploy with industrial compressors. The ONLY time the compressor will normally have to utilize the full starting torque of the motor is when it re-starts at the cut-in pressure of the pressure switch and even then most compressors will have a device (unloader) that relieves the tank pressure from the starting load.
The ONLY specification that is truly important is the delivered CFM at a usable pressure. That usable pressure is different for different tools. Most paint spray guns use a pressure between 40 and 60 psi while most tools need a minimum of 90 psi at the tool for proper operation. You will notice that as the pressure rises the delivered CFM will fall and it will fall significantly on a single stage compressor once the pressure exceeds about 100 psi. Over 100 psi a single stage compressor's volumetric efficiency drops off rapidly, as low as about 50% at 150 psi. For this reason multiple stages of compression are called for if your pressure needs exceed about 120 psi.
But don't get too excited over this news as ALL compressor manufacturers do the same and it is even used as a marketing ploy with industrial compressors. The ONLY time the compressor will normally have to utilize the full starting torque of the motor is when it re-starts at the cut-in pressure of the pressure switch and even then most compressors will have a device (unloader) that relieves the tank pressure from the starting load.
The ONLY specification that is truly important is the delivered CFM at a usable pressure. That usable pressure is different for different tools. Most paint spray guns use a pressure between 40 and 60 psi while most tools need a minimum of 90 psi at the tool for proper operation. You will notice that as the pressure rises the delivered CFM will fall and it will fall significantly on a single stage compressor once the pressure exceeds about 100 psi. Over 100 psi a single stage compressor's volumetric efficiency drops off rapidly, as low as about 50% at 150 psi. For this reason multiple stages of compression are called for if your pressure needs exceed about 120 psi.
#5
This is my first compressor and I realize it's not the best. It was a really good deal and should suffice for what I'm doing. If in time I find it isn't, I won't hesitate to upgrade at a later date.
So 12/2 and 20A breaker is fine?
So 12/2 and 20A breaker is fine?
#7
Here's a test. Plug the machine into a 20 ampere circuit that you can turn off any other loads, essentially making it a "dedicated" circuit. Pump the tank up to just under the point where the pressure switch would shut off the motor and while still running unplug the cord. Wait a few seconds and then plug it back in and if it starts without popping the circuit breaker then a 20 ampere circuit will be fine. At any rate, run your dedicated circuit with #12 copper wires and if the 20 ampere CB becomes problematic you CAN use a 30 ampere CB.
#8
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The NEC requires that motors have a "name-plate" that displays certain specific information ,such information including the HP rating , so I suggest you base your circuit design criterion on the motor name-plate info.