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How to Test Electrical Circuits for a Home Generator

Home Generator Circuits Explained – Electrical load testing for home generator circuits can produce some puzzling results, especially when measuring incandescent lighting loads and other 120 volt circuit loads.

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Understanding Home Generator Circuits

Home Electrical Troubleshooting Repairs Question: When testing a Cutler Hammer 8 space main lug sub panel for its current usage (for a generator set up)with a Greenlee digital “Amprobe”, I detected 37 amps on one supply leg, 25 amps on the other supply leg, and 12 amps going through the leg to ground.
I do not understand the 12 amps going to ground, what the source of the “ground” might be, or how to find the problem if in fact it is a problem.
There is a 100 amp double pole breaker used as the “main” for the sub panel itself, a 30 amp double pole breaker for a water heater, and four 20 amp single pole breakers for lighting. The water heater lines tested 17 amps each, which i consider reasonable usage (did not notice the size of the water heater)….the 4 lighting circuits tested 2 to 3 amps each- a conglomeration of incandescent and cfl bulbs are on those circuits.
Can you shed some light on this one for me? (no pun intended)

This home electrical repairs question came from: TOM, from Oaks, Pennsylvania

See more about Home Electrical Repairs for Pennsylvania

Dave’s Reply:
Thanks for your electrical troubleshooting question TOM

Home Generator Circuits Explained

Testing Generator Circuits

Electrical load testing for home generator circuits can produce some puzzling results, especially when measuring incandescent lighting loads and other 120 volt circuit loads.
As described in this question you will notice that the ground connection for the main generator is also serving as the neutral for the 120 volt circuits. The 20 amp 120 volt circuits are providing power for the incandescent lighting circuits, therefore the 12 amp reading on the ground wire may be due to the incandescent lighting loads of the 120 volt circuits where the return power is being measured at 12 amps. You can verify this by measuring the amperage of the ground and turning off one or more of the 20 amp lighting circuits and you should notice the amperage drop down if the incandescent lighting is in fact being used at the time of the test. Make sure that the ground and neutral system of the generator and main panel are properly bonded. When connecting 120/240 volt circuit loads to a generator it is best if the generator has a 4-wire connection.
IMPORTANT: All generator power connections must be made using an approved transfer switch or approved circuit interlock device to safely allow only one source of power at any given time and provide a disconnection from the main electric utility company power source.

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Complete Guide to Home Electrical Wiring

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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.

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