I added 2 new wall sockets starting from an existing wall socket. After wiring them up and connecting the power I plugged a GRT-500 into the two sockets - I happened to have two so I plugged one into the socket closest to the starter and the other at the end of the line.

The socket closest to the starter socket read "correct" but the last one read "open ground". I shut off the power, inspected the box and receptacle but found no problem. I checked all the boxes I had opened or worked with, again finding no problem.

After failing my last attempt, I removed the socket testers, and just happened to remove the socket tester closest to the starter socket first -- when I did this, the socket tester in the other wall socket switched to "correct"!

I then verified that each socket "individually" reads correct, but only when there is no other tester ahead of it... Is this normal?

  • 1
    Have you tried plugging in some other thing in the first receptacle and then using the tester in the 2nd? Aug 26, 2017 at 5:21
  • What is the voltage between hot and ground on each socket? Aug 26, 2017 at 5:31
  • It appears the test equipment you have is not designed to work with more than one at a time. The electronics of the tester is confused when you plug in another tester. Don't do that.
    – ArchonOSX
    Aug 26, 2017 at 8:39
  • @ArchonOSX The tester the OP used seems to be a simple 3-light tester (assuming he using the GRT-500A filmtools.com/idcirtes61.html). I don't see any way one would interfere with another. More likely somehow plugging the tester into the first outlet is causing the ground wire to open. ThreePhaseEel's comment seems more on track.
    – DoxyLover
    Aug 26, 2017 at 16:36
  • A photo of the wiring in the two boxes would be helpful.
    – DoxyLover
    Aug 26, 2017 at 16:36

1 Answer 1


The way those cheap 3-lamp testers work, they can't possibly be interacting with one another. If they are acting that way, then either they are pieces of junk (Made in China?) or they have exposed a wiring problem.

There is also no benefit whatsoever to using two such testers at the same time. Test one outlet... Then test another.

Keep in mind 3-light testers are just "idiot lights" only slightly more useful than the Magic 8-Ball, and fail to detect a wide variety of faults. You've seen neon testers with two test probes; think of a 3-light tester as three of those.

  • hot-to-neutral (yellow, the one that is on for "open ground")
  • hot-to-ground (yellow, the one that is on for "open neutral")
  • neutral-to-ground (red)

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