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?
Best Answer
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.