AskCodeMan

I live in La Canada, California.

I bought a circuit tester of the $8.00 variety that tests receptacles for ground, faulty wiring, and GFCI. I have a house built in 1955. The tester indicates OK and does not indicate a weak ground, on a certain 3-pin receptacle that I determined to have no green grounding wire except to the outlet box, and moreover, the resistance measured between the neutral socket and the ground socket is 5 ohms (seems much too high). By inspecting the wiring I find that the only ground connection from the outlet box to the service panel goes through flexible steel conduit that has no straight-through solid wire. The conduit contains only one white and one black wire.

If the 3-pin receptacle had been installed in 1960, shouldn't it have been grounded better than that?

What kind of tester should I be using to determine this kind of fault, if it is a fault?

carterjs wrote:If the 3-pin receptacle had been installed in 1960, shouldn't it have been grounded better than that?

Not even required to be grounded then, however, when a grounding-type receptacle was installed, it should have been grounded properly ... except that "grounded properly" back then was not as clear cut as what it means today.

Back then, any attempt at grounding was better than no attempt at all.

What kind of tester should I be using to determine this kind of fault, if it is a fault?

SureTest makes some really nice circuit testers, and it will show you all kinds of problems/faults/etc with the circuits, however, as to whether that is a fault or not would depend on what edition of the NEC the AHJ (local building department) had adopted and was using at that time, and, their local practices with grounding.

Your description of the wiring type sounds like what was called "BX" cable at the time, and you are correct, there was no bonding strip or conductor inside, which means the spiral wound outer covering would have served as the ground, and that was not intended to be used as the ground.

If the spiral wound outer covering is used as the ground and there is a ground fault, then that fault current will flow spirally (like a coil) around the conductors within the outer covering, and that coil-like current flow could effectively generate a magnetic field making that into a choke coil, which would resist the flow of current, thus the current may stop flowing, even though there is a fault.

That could lead to a serious problem in trying to clear the fault.