Outlet tester shows “bad ground”

groundingsubpanel

I have a brand new Square D sub-panel installed in my barn that replaced an old panel that had been there for many years and was deemed a fire hazard by the inspector. The new panel has a grounding wire that runs from the panel grounding bar to outside and is connected to a copper rod sunk 6 ft into the ground. For the receptacles on the ground floor I have a 20 AMP GFCI breaker installed in the panel that feeds a single line that they are daisy chained to. The breaker is wired correctly (hot wire to breaker as normal, neutral wire to the breaker neutral and then neutral pig tail from breaker to the neutral bar on the panel. Ground as normal goes to the ground bar on the panel).

When I plug in my outlet tester it reads "Bad Ground" on any receptacle I plug it into in the barn. I tested the same unit in my house and it reads green (all correct). Here's what I've tested so far with my multimeter:

  • continuity between receptacle ground pin and ground screw – good
  • continuity between receptacle ground pin and ground wire that comes from panel – good
  • continuity between ground bar on panel and the other end of the ground wire that connects to the grounding rod – good

What could be going on giving me this reading?

Best Answer

If you only have a three wire feed to the barn then the panel should have the neutral and ground connected together.

The old method of wiring a sub-panel in a separate building was the 3-wire method like you have. The wires should be Hot, Hot, Neutral not Hot, Neutral, Ground.

Consequently the sub-panel would have been bonded (neutral and ground connected together). So, the replacement panel should be bonded.

If you have not bonded the neutral to the ground in your barn that is why your tester is saying it has an open ground.

Here is the pertinant NEC section:

(B) Grounded Systems.

(1) Supplied by a Feeder or Branch Circuit. An equipment grounding conductor, as described in 2S0.118, shall be run with the supply conductors and be connected to the building or structure disconnecting means and to the grounding electrode(s). The equipment grounding conduc- tor shall be used for grounding or bonding of equipment, structures, or frames required to be grounded or bonded. The equipment grounding conductor shall be sized in ac- cordance with 2S0.122. Any installed grounded conductor shall not be connected to the equipment grounding conduc- tor or to the grounding electrode(s).

Exception No.1: For installations made in compliance with previous editions of this Code that permitted such connection, the grounded conductor run with the supply to the building or structure shall be permitted to serve as the ground-fault return path if all of the following requirements continue to be met:

(1) An equipment grounding conductor is not run with the supply to the building or structure.

(2) There are no continuous metallic paths bonded to the grounding system in each building or structure involved.

(3) Ground-fault protection of equiprnent has not been in- stalled on the supply side ofthefeeder(s).*

Good luck and stay safe!

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