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How to Wire a Generator Transfer Switch


By Dave Rongey - Summary:

The Basic Wiring Configuration for a Generator Transfer Switch: Each Wiring Termination must be correct for the Power Conductors of the Line or Load.
Neutral conductors are attached to the Neutral Terminal Block. All enclosures and equipment must be grounded and bonded. Common Misunderstandings or Mistakes when Wiring Generator Transfer Switches.


Generator Transfer Switch Wiring

Electrical Question about a Transfer Switch:
I had a Reliance 31410RK manual transfer switch put in by a licensed electrician about a year ago. Powering it with a Honeywell 7000 watt generator. After a power failure the other day I started up the generator, connected the cord into the twist lock inlet outside to the switch, then went inside and started one by one transferring load to the generator. At first the overhead light in the cellar went on, but dimly. But after that I wound up blowing up 3 power strips that had little or no load on them, blowing out 2 light bulbs, frying a TV cable box, and blowing out the ignition module of my gas boiler. Sparks were coming out of 2 of the power strips and one caught on fire.
After that the switch would not work at all and nothing shown on the meters when the generator is running. Funny thing is once before when I used it when the electrician had put in about half the circuits- sparks flew out of the boiler ignition (the box that steps down house current to 26 volts to light the boiler). After that time, the switch would not work, but after he returned to finish up wiring all the circuits, everything worked fine and we inspected it while using all the circuits. The same things were hooked up and everything worked fine. But after the transfer switch failed now, I just hooked up the generator with a 25′ long 30 amp generator cord that inserts into the very same twist-lock receptacle on the generator, everything works fine. In other words, not using the transfer switch, just running a heavy generator cord into the house and plugging things into that, no problems. My electrician is puzzled, he has not looked at it yet, what could cause this?

This home electrical repairs question came from: Frank, from Madison, New Jersey.

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

Generator Transfer Switch Wiring Configuration

Skill Level: Advanced – Licensed Electrical Contractor, Not Recommended for Homeowners.
Tools Required: Electricians pouch of hand tools and the various power tools necessary for installing the generator and transfer switch.
Estimated Time: Depends on the type and size of the generator and transfer switch and the available access to the project area.
Precaution: Any existing electrical wiring within the immediate area that may interfere with the installation of the generator transfer switch may need to be relocated if necessary.
Important: Installing a generator and transfer switch must be well thought out and performed with a permit with all of the work being inspected.

The Importance of Proper Wiring Configuration and Isolation

The Basic Wiring Configuration for a Generator Transfer Switch:

  • LINE  (top) – The power from the Electric Utility Company – Normal Power.
  • LOAD (center) – The Connection to the Home Electrical Panel.
  • LINE (bottom) –  The Power from the Generator – Emergency Power.

Each Wiring Termination must be correct for the Power Conductors of the Line or Load.
Neutral conductors are attached to the Neutral Terminal Block.
All enclosures and equipment must be grounded and bonded.
NOTE: Some transfer switches may have the provision for transferring the Neutral Conductors.

Common Misunderstandings or Mistakes when Wiring Generator Transfer Switches
Not understanding the difference between:

  • LINE and  LOAD.
  • L1 and L2 or Line1 and Line2.
  • Not Terminating the Neutrals Correctly.
  • Not Grounding and Bonding the Electrical System.

Alternatives to a Generator Transfer Switches

  • UL Approved Circuit Breaker Interlock Kit – When installed properly allows only one power source to be on at a time, is more economical and great for smaller generators and portable generators.
  • Designated Generator Panel – A separate panel for generator circuits only, may be for 120 or 240 volt circuits, such as a Reliance Pro-Tran or equivalent.

IMPORTANT: All generator transfer switches and generator panels should be installed by a licensed electrician and all work must be inspected.

Portable Generators for Immediate Emergency Power

Portable generators are great for powering up a few devices by using appropriately sized extension cords without connecting to the home electrical system. Refer to the Operating Manual which comes with the Portable Generator for specific details and Safe Operation.

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