Please advise as to why R2 would show open ground using a receptacle tester.
All three connections on R2 seem secure.


R1 shows correct wiring.


S1 is old time switch with no ground.
The ground wires are bound together in old plastic box.

There are several possible reasons.

1) While the ground wires are connected in the plastic box, the ground wire may be open between the panel box and the junction box.
2) The main panelboard may not be properly grounded.
3) Improper "Bonding" could cause a problem if the metal ground you are using is not bonded with all the other pipes and then to the electrical ground.
4) Defective circuit tester.

If 1)
Would not R1 also show open ground ?


If 2)
Would not all receps show open ground ?

Went around the house checking all easy accesible receps and R2 is the only one
showing the open ground.


R2 has a lamp and adding machine plugged in and used almost daily.


Is this a dangerous situation ?

Thanks very much for your reply.

No so dangerous with what you have plugged in. A Lamp will likely not have a Ground terminal, 3rd prong of a Drill for example will connect to the Housing of the drill, if you drilled into a live wire, or a hot wire breaks loose inside and touches case, it will trip breaker, Not become Live.
If a Plastic Box, it may just need a small pigtail(jumper) to restore the ground.
A meter with 1 wire on hot, and the other on ground wire should show 120 volts.
Ground and Neutral are Physically connected at Panel. Difference is, Neutral carries current, Ground is to keep things from becoming live.

Does R2 come from R1 or the J Box? Could be a loose ground in either one.
I just found an ungrounded outlet in a house with ground connected and the ground came from a switch box. Opened box and found loose wire, looked like it was never connected. Wire nutted to box ground and solved the problem. This was the only outlet showing no ground.

@ Stratmando
R2 hot wire and ground shows approx 25v.


@ ma0641
I believe R2 comes from junction box.
Opened R1 and it has only one wire.


I cannot get to the junction box, which I guess is the main problem now.


It was put in place when part of a brick wall was torn down
to enlarge a exterior door and to setup a recep for a generator.


I checked that all worked before closing up the brick wall,
but did not test it correctly to catch the open ground.

As mentioned, R2 is pretty much used daily.
Lamp. adding machine, laptop (3prong) for about 3 years now.

Sw1 and R1 are on the outside brick wall.
R2 is on an inside wall.

Pretty sure I could get a new line to R2.
But what would I do with the screwed up line there now ?


Thanks for the replies.

If you get a new wire, wire nut and tape the old hot and neutral out of the way, connect old ground to new ground.

Thanks ma0641.