ask the electrician
Electrician Training Electrical Certification wiring recessed light fixtures Electrical Wiring Electrical Troubleshooting and Electrical Repairs wire outdoor light fixture Home Electrical Wiring Diagrams
wiring home generator and transfer switch wiring a 220 volt range cord outlet Wiring for GFCI Outlets Wiring Outlets and a Switched Outlet Wiring and Installing Ceiling Fans and Remote Controls wire dimmer switch wiring diagrams for switches wiring a dryer cord and 220 outlet circuit breaker panel
Electrical Wire and Cable

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?

Home Electrical Wiring Video

How To Hook Up a Generator to the House Panel
Using a Circuit Breaker Interlock Kit
for Backup Power

NOTE: A List of All my Helpful Videos
Will Display at the End of This Video
So Keep Watching So I Can Help You Wire it Right!

Check out my YouTube Channel:
» AskTheElectrician «
and Subscribe!

Learn more about Home Electrical Wiring
with my online Video Course:
Basic Home Electrical Wiring by Example

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. This electrical project is best performed by a licensed electrical contractor.
est 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.

The following articles that may assist you as well:

220 240 Volt Air Compressor Wiring

Wiring a 220 Volt Air Compressor

More about Wire a New Circuit a Air Compressor

Electrical Code for Conduit Fill

Guide to Home Electrical Wire

Electrical Wire for the Home

Complete listing of electrical wire types and parts used for home projects with electrical code information serves as selection guidelines.

Home Electrical Codes for Main Service Panels
Electrical Wiring Codes

Home Electrical Circuit Breakers

Home Electrical Circuit Breakers

A guide to home electrical circuit breakers and how they work to protect your electrical wiring. When properly installed, your home electrical wiring is protected by a circuit protection device.

240 Volt Wiring Diagram
240 Volt Wiring Diagram

Wiring 240 Volt Electrical Outlet

Home electrical wiring includes 110 volt outlets and 240 volt outlets and receptacles which are common place in every home. See how electrical outlets for the home are wired.

How to Install Workshop Electrical Wiring

Work Shop Electrical Wiring

Fully Explained Photos and Wiring Diagrams for Workshop Electrical Wiring with Code Requirements for most new or remodel projects.

The following may also be helpful for you:

Dave's Guide to Home Electrical Wiring:

» You Can Avoid Costly Mistakes! «

Here's How to Do It:
Wire It Right with the help of my Illustrated Wiring Book

Great for any Home Wiring Project.
  electrical wiring  

Complete Guide to Home Electrical Wiring

Perfect for Homeowners, Students,
Handyman, Handy Women, and Electricians
Wiring GFCI Outlets
Wiring Home Electric Circuits
120 Volt and 240 Volt Outlet Circuits
Wiring Light Switches
Wiring 3-Wire and 4-Wire Electric Range
Wiring 3-Wire and 4-Wire Dryer Cord and Dryer Outlet
How to Troubleshoot and Repair Electrical Wiring
Wiring Methods for Upgrading Electrical Wiring
NEC Codes for Home Electrical Wiring
....and much more.

Learn more about Home Electrical Wiring
with my Online Video Course:
Basic Home Electrical Wiring by Example

Be Careful and Be Safe - Never Work on Energized Circuits!
Consult your Local Building Department about Permits and Inspections for all Electric Wiring Projects.

Electrical Tips to Help You Wire it Right

The Safest Way to Test Electrical Devices and Identify Electric Wires!

The Non-Contact Electrical Tester
This is a testing tool that I have had in my personal electrical tool pouch for years, and is the first test tool I grab to help identify electrical wiring. It is a Non-contact tester that I use to easily Detect Voltage in Cables, Cords, Circuit Breakers, Lighting Fixtures, Switches, Outlets and Wires. Simply insert the end of the tester into an outlet, lamp socket, or hold the end of the tester against the wire you wish to test. Very handy and easy to use.

The Quickest Way to Check for Faulty Electrical Wiring!

The Plug-In Outlet Tester
This is the first tool I grab to troubleshoot a problem with outlet circuit wiring. This popular tester is also used by most inspectors to test for power and check the polarity of circuit wiring.
It detects probable improper wiring conditions in standard 110-125 VAC outlets Provides 6 probable wiring conditions that are quick and easy to read for ultimate efficiency Lights indicate if wiring is correct and indicator light chart is included Tests standard 3-wire outlets UL Listed Light indicates if wiring is incorrect Very handy and easy to use.

Strip Off Wire Insulation without Nicking and Damaging the Electric Wire!

The Wire Stripper and Wire Cutter
My absolute favorite wire stripping tool that I have had in my personal electrical tool pouch for years, and this is the tool I use to safely strip electrical wires.
This handy tool has multiple uses:
The wire gauges are shown on the side of the tool so you know which slot to use for stripping insulation.
The end of the tool can be used to grip and bend wire which is handy for attaching wire onto the screw terminals of switches and outlets..

The wire stripper will work on both solid and stranded wire. This tool is Very Handy and Easy to Use.

More articles about Air Compressor, Electrical Wiring and Home Electrical Wiring:
« Previous Next »
Lightning Strikes and Electrical System Protection How to Troubleshoot Incorrect Voltage for a Stove