The lights are on, but nobody is home

Home Inspector with Charles Buell Inspections Inc.

A heads up on the use of 3-light circuit testers.

Whether you are a home inspector or a real estate agent, you have likely either used or seen used, these common place 3-light testers.  They are designed to give the user a quick diagnosis of circuit wiring and can find some of the common defects associated with receptacle outlets.

However, like any tool, the user must understand their limitations.

A common misuse of these testers is relying on the information given by the tester when testing receptacles that have something else plugged into the receptacle at the time of test.

When something else is plugged into the receptacle it can confuse the tester.

In this first picture, the tester tells us the circuit has reversed polarity---time to the electrician!

3 bulb tester

For example, a washing machine might be incidentally or intentionally grounded but not from the circuit it is plugged into.  Being plugged into a three-prong receptacle improperly installed on an ungrounded circuit will feed that ground information to the receptacle and the tester will see that and will interpret the condition as “reversed polarity.”

When the washer is unplugged from the receptacle, the tester will correctly indicate that the circuit is “ungrounded," as can be seen in the second photo.

3 light tester

Understanding this difference is important because it means there is either NO issue (other than you might want to upgrade the older wiring) or an electrician gets called to fix something that isn’t there to fix.

So the person at home needs to make sure the right lights are on.

Charles Buell, Real Estate Inspections in Seattle

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Anna Banana Kruchten - Phoenix Homes Sales
Phoenix Property Shoppe - Phoenix, AZ

Charles we just ran into this very issue with an older listing built in the 70's. . The home inspector called out a bunch of receptacles but when our electrician went over the 'fix' the issues there were no issues to fix. Glad you wrote this post today!

Jun 16, 2016 02:37 AM #1
Jay Markanich
Jay Markanich Real Estate Inspections, LLC - Bristow, VA
Home Inspector - servicing all Northern Virginia

That's pretty good info Charlie! 

And what I really like is how that tester heats up and scorches the wall!  Cool!

Jun 16, 2016 10:21 AM #2
Fred Hernden, CMI
Superior Home Inspections - Greater Albuquerque Area - Albuquerque, NM
Albuquerque area Master Inspector

I have had some clients that the power is on but nobody's home... 

Jun 17, 2016 01:29 AM #3
Rene Fabre
First American Title - Seattle, WA
Marketing in the Digital Age

Thanks for this post Charlie! I understand polarity, but I did not know if you had something plugged in it could confuse the tester. Good one. Happy Monday!

Jun 20, 2016 03:44 AM #4
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Charles Buell

Seattle Home Inspector
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