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Wiring a 240Volt Air Compressor

I am wiring a new air compressor. It is 240volt, 28 amps, 7.5 hp, single phase. Is #6 wire big enough?


240Volt Air Compressor
Electrical Question: I am wiring a new air compressor. It is 240volt, 28 amps, 7.5 hp, single phase. Is #6 wire big enough?

I am wiring a new air compressor. It is 240v, 28 amps, 7.5 hp, single phase. It has a magnetic starter and the motor has it’s own overload protection.
The manufacturer recommends an 80 amp breaker because of the initial startup draw. I am using a 10 hp non fused disconnect to turn it on and off. It is only 10 feet from the breaker panel and wires will be run in conduit.
My question is this, is #6 wire big enough ?
I seem to be getting differing opinions. some say I need #3 because of the 80 amp breaker. Some say because it is wiring to a motor only, it can be much smaller. Even down to #8
Your help would be much appreciated.

This electrical wiring question came from Jeff, a Handyman in Sandwich, Illinois.

Additional Comments: First time visiting – hopefully helpful.

Dave’s Reply:
Thanks for your electrical wiring question Jeff.

How to Wire a 240Volt Air Compressor

Application: Wire a New Circuit for an Air Compressor.
Skill Level: Intermediate to Advanced – Best performed by a Licensed Electrical Contractor, or Certified Electrician.
Electrical Tools Required: Basic Electricians Pouch Hand Tools, Voltage Tester, and appropriate Safety Gear.
Estimated Time: Depends on the personal level experience, ability to work with tools, install electrical circuit wiring, and the available access to the project area.
Electrical Safety: Identify the electrical power source to the Air Compressor, turn it OFF and Tag with a Note before working with the electrical wiring.
Electrical Wiring Parts and Materials: Electrical parts and materials for the Air Compressor should be approved for the specific project and compliant with local and national electrical codes.
Electrical Codes and Inspections: Installing or changing home electrical wiring should be done according to local and national electrical codes as adopted in Sandwich, Illinois. A permit and inspections may also be required.

Wire Size for a 7 1/2 HP 240Volt Air Compressor

Jeff, from what you have described I have come up with the following:

Based upon a 7 1/2 HP Motor, 240Volt, Single Phase:

Full Load Current: 40 Amps.
Minimum Copper Wire Size: #6 – (Wire Types THW, THHN, THWN are Rated at 65 Amps).
Thermal Magnetic Trip Rating: 80 Amps.
Time Delay Fuse Rating: 60 Amps.

You need to keep in mind that the Starting Amperage, and the Running Amperage are the factors.

The Magnetic starter and the Thermal Magnetic Overload Protection help to protect the motor when it is starting, therefore the correct wire size is important.

The Running Amperage is taken into consideration for the wire size and the circuit breaker size.

Most circuit breakers are designed to take the in-rush of starting current that lasts only a few seconds, so generally the circuit breaker should not trip off when the motor is starting as long as everything has been sized properly.

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