Sperry Tester with unusual indicator lights

I’ve had two inspections within the last month where my simple tester showed unusual light indications. In both cases I’ve referred to a licensed electrical contractor for further evaluations/repairs. However, I would like to know what is going on.

Here’s the situation. In both cases, the homes were built in the late 40’s early 50’s with NM 2 conductor cable (ungrounded). A 3 prong receptacle was installed using 14/2 with ground although there is no grounding conductor that would terminate in the service panel. In one case, the branch wiring was encased with armored cable. In the other it was not.

All three indicator lights lit but the center light was very bright indicating an ungrounded circuit. However the left and right lights also were energized albeit much dimmer than the center light.

I’m just looking for an explanation as to the reason for this result. Any suggestions?

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240V circuit. Get a “real” circuit tester to verify.

I figured I would see response ;-). The one handed unit works just fine in most circumstances (except this one). Fits in my pouch and did I mention one handed operation? I have a VOM in the truck, but I would leave this for Sparky to evaluate.


If that is a 240 volt circuit the receptacle is the wrong type. That is a 120 volt 15 amp configuration.


I have come across this condition on many occasions. Not that the receptacle was intended to be used as a 240V circuit, but it was improperly wired somewhere within the circuit.

Possibly a potential split-wired receptacle in line somewhere or shared neutral circuit that (as Jeff mentioned) has become improper due to modifications over the years or was improper to begin with.


I did some testing using a sperry 3-light tester and another brand purchased at wal–mart, the red light would not come on with either tester when the hot and neutral or hot and ground was reversed if the ground or neutral was also missing or had high resistance. What this means is that when you find an outlet with a missing ground or missing neutral you should not report that as the whole story, it may just have the hot wire on the neutral or ground lug also. There are other faults with these testers also but the above is the only one I have not seen discussed on here in detail.

Here is an article that explains other incorrect readings based on issues other than simple wiring errors as shown above.

I originally thought it might have been wired with a “False Ground”. Then I thought it might have been a “False Ground” wired on the hot side rather than the neutral side. That’s why I took the time to partially remove the receptacle. I did not have time to do that on the other inspection. It was not 240 volts because I did check across the typical hot/neutral receptacles. That’s why this is so odd.

Was the house occupied? Something plugged in on that circuit that has a problem? Looks like some stray voltage on the neutral that made a path through your tester to make a weird combination of lights and brightness. I find many with dim flickering lights on older homes with lots of mods.

Yes it was occupied. I thought the same thing. It was, by rights, an ungrounded 3-prong receptacle. With this type of reading, I would doubt that a GFCI would have worked as a replacement. I wish I had more time to investigate. I will be contacting my client in a week or two. Hopefully he asked for this to be looked at as recommended in the inspection report.

I don’t understand what you mean here.

Where does the ground wire in #3 picture terminate? Is it possibly connected to the neutral?

I have found rare occasions where someone wired a 240 volt circuit using a 15 amp receptacle. In that case, they hand wrote 220 Volt Only on the faceplate. It was in a garage for a very old air compressor which was also jury-rigged with a 15 amp plug with a 14-1 cord with ground.

I had a volt meter with me and I probed across the neutral and hot side of the receptacle and it registered 120 VAC not 240 VAC. I also probed from each side to the equipment ground and did not get any reading which indicates this was an ungrounded receptacle. I wish I had my VOM with me to determine if there was any stray voltage below 120/240. I hope that adds clarity.

Someplace in the attic. That was my original thought that there was a fake ground from the neutral side to the equipment ground. It was not wired that way at the receptacle.

Here is the answer I received from Sperry:

When this comes up, it normally means that either there is another appliance plugged in on the circuit somewhere that is causing interference or there is a problem with the circuitry that should be evaluated by a professional electrician. This is a problem we have been unable to recreate at our labs to get a definitive answer. If you have any other questions, please let me know.


Eric Key
Gardner Bender/Sperry Instruments