Old Electrical Receptacle and Ground

You're dealing with near 100 year old wiring so I wouldn't be expecting to much from the steel cable, however, try taping a 10/32 threaded hole in the box and attaching a ground wire from the box to the outlet. Also try tightening up on the cable clamp if it's accessible

I recently repaired and upgraded two old 2-prong electrical receptacles to 3-prong. Both receptacles had 2 wires and grounded boxes.

One of the receptacles is now powered and grounded properly. The other receptacle is powered correctly but has a weak ground -- when I used a voltage tester, the power light was bright but the ground light flickered.

I think that the ground fault is either between the metal cable and the box or between the screws of the receptacle and the box. The metal bars of the box where the receptacle screws in are very rusted and corroded.

Has anyone had similar problems with this type of weak ground in a old-style grounded box? Do you think trying to de-rust the box will help?

Thank you.

A weak ground is essentially no ground, as far as ground protection is concerned. Also, check your tester, as the "flickering" could be a neon lamp going bad. They do make more expensive testers though, that can simulate higher ground fault currents. Can you protect the circuit with a GFCI mounted somewhere upsteam? Might be a good idea.

Beachcomber

It'll be much easier, and probably cheaper in the long run, to just replace the box.

Good Luck! Rich

Assuming BX I'd pull the box and cable out and try to make a good clamp ground to the BX cable or the ferrule it attaches to. ADD that to your existing ground (don't rely on it alone).

That can only be done by REMOVAL and careful visual inspection of the AC outlet and its associated wiring by an experienced person.

....... Phil

In the absence of a proper ground resistance meter, a 150 Watt light bulb is a good test !

Just replace the box. Its not worth the time and effort !

See above.

Also, since this is very old wiring and the grounding is in question, I'd switch to GFCI.

Sounds to me like the reality is NEITHER is safely grounded. It doesn't take a lot of current to light that neon, the one that flickers is definitely not safe. The other one probably isn't either as it probably is using a BX armor as ground. Replace the outlets with GFCIs and mark them No Equipment Ground. You will be much safer.