3-light tester and reversed polarity

I’ve been inspecting for several years, and recently learned something. (I learn new things every day, but this is something that I am surprised that I did not realize until now.) A three-light tester will NOT show a hot/neutral reverse if the receptacle being tested is not grounded. I inspect a lot of older homes that have a lot of ungrounded outlets, so I am sure that I have missed many hot/neutral reverses over the years by relying too much on my three-light tester. Fortunately, I am now using the SureTest which can find a hot/neutral reverse on an ungrounded receptacle. Just thought I would share this info.
I wrote a blog post about this with a little more detail about some “experiments” that I did with several of these three-light testers.


Good info, Mike. Thanks for posting. If i get any error code on a three-light tester, I recommend that an electrician make repairs.

The problem with the three light tester has always been that it can only identify ONE problem. In the case of older homes with out circuit grounds it simply can’t light the indicators that require a ground connection. As a result only the center light is lit but can’t identify correct polarity because that requires a ground connection on the outside two lights.

Sure test is the way to go with two slot outlets.

Morning, Mike. Hope this post finds you well.

Glade to hear you learned something new. Always invigorated me. More so when the something new is one of your strong suites or your are evolving in a particular field. Electrical being one of my enjoyments.

That being said. There have been several articles and post through the years referring to 3 Bulb Outlet Testers and Interpreting 3-Prong Receptacle Testers Readings. Here’s one by The Circuit Detective.

Having discovered the lack of accuracy and frailties of 3 Bulb Circuit Testers, the grounding prong for one and cheep wiring terminations, I upgraded to analysing circuits with a Circuit Analyser or Circuit Load Tester. First stating with General Equipment then moving forward to the Extech CT70 AC Circuit Load Tester. Quickly checks for AC ‘outlet load handling capabilities’ plus outlet tester functions. GFCI and AFCI for the CT80 series although the later model was recalled although mine never exhibited false positives. When a negative reading is exhibited I use other complementary tools/equipment to back up the findings.

A Wiggly for continuity + Voltage and A Category IV Fluke 1AC-II non-contact voltage detector as backups.

Keep up the great work because you know what they say. When you think you know everything its time to close shop.

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When I run into ungrounded receptacles, I use a tester screwdriver to find which side is “hot”. It usually tells me if the receptacle was wired in reverse


And, I used one of these. I would insert one probe into the narrow slot and pinch the other probe between my thumb and index finger and again on the longer slot, as needed.