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I am running electric to a building on my property. i have a 30 amp double breaker at the house panel and have ran roughly 110 feet of 8/2 with a bare ground and installed a ground rod at the sub panel for the building.

I know black and white are my 2 hot wires and the #6 coming from ground rod goes to my grounding bar in the sub panel, but do I hook the ground wire from the #8 to the ground bar or common bar at the house panel and the sub panel?

  • What country are you in? If USA, under NEC rules this will not fly under current code (it was eliminated many years ago - the remote structure needs a 4-wire connection - i.e. 8/3 with ground, not 8/2) maintaining hot1, hot2, neutral and ground as separate wires, and keeping the ground and neutral isolated at the remote sub-panel. – Ecnerwal Jul 19 '17 at 15:59
  • In the US, but i was under the understanding if i drove a ground rod with a #6 wire at the sub panel for grounding at the other structure it would be fine – Gareri Jul 19 '17 at 16:10
  • "Would be fine" under a version of the code more than 18 years out of date, which is probably not what your local jurisdiction uses for code. You still need the ground rod for the grounding conductor (green or bare) but it is not connected to the grounded (neutral) connector at the sub-panel. – Ecnerwal Jul 19 '17 at 16:23
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The current National Electrical Code that most jurisdictions employ will no longer allow a 3 wire sub-panel feed.

4 wire feeders are now required for sub panels. Two hot legs, a neutral, and an equipment ground.

250.32 Buildings or Structures Supplied by a Feeder(s) or Branch Circuit(s).

(B) Grounded Systems.

(1) Supplied by a Feeder or Branch Circuit. An equipment grounding conductor, as described in 250.118, 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 conductor 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 accordance with 250.122. Any installed grounded conductor shall not be connected to the equipment grounding conductor or to the grounding electrode(s).

Hopefully, you can correct this without too much hassle.

Good luck!

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You have four choices.

All of these choices require you drive local grounding rods and also have a ground wire running back to the main building, and tie both of those together. You cannot do one as a substitute for the other, they do different things.

Take that wire back and get /3

/3 cable will let you hook it up in the normal way you expect.

If the people who sold you this wire were the same ones who told you you didn't need /3 cable, they ought to take it back!

Supply 120V only

Bare goes to ground. White goes to neutral. Black goes to hot.

You can carry 40A@120V over that cable. That will happen at about 6% voltage drop (114V) which is a little concerning but I wouldn't worry too much. 20A will happen at 3% drop.

40A is not very useful for receptacles, so you'll need to bust that out into a subpanel. Get a large subpanel (for future expansion) and feed to one hot bus. Only every other row of breakers will light up.

Supply 240V only

Voltage drop is less than 3% at 240V. Here, ground is ground. Tape the last few inches of the white a color like black or red and it is hot 1. Black is hot 2. You do not have neutral and cannot power any 120V load. You will have a subpanel with no neutral bus. It will have a ground bus.

This can work if the primary load is a pump, hot tub, pool, well. etc. 240V lighting is readily available. For small amounts of 120V power, like a 15A receptacle circuit, do not use a step-down transformer, use a "mini" separately derived service, with a smaller (more affordable) transformer.

The problem with this setup is it is indistinguishable from a normal main panel where ground/neutral are the same bus. Of course people will want 120V loads out there, and less skilled electricians will blithely hook it up (and it'll work by bootlegging). A skilled electrician will go "You forgot neutral" and call the installation a botch job - no, it's a 240V only panel.

Separately derived service

Ground doesn't matter. White is taped with a color. Black and white both go to the 240V primary of a transformer. The secondary gives 120/240V split phase. Feed that into a service panel which is a main panel owing to the isolation caused by the transformer. In this main panel, bond neutral to your local ground rod.

Since electricity is transmitted at 240V, voltage drop would be less than 3%, and would remain so after being transformed down to 120V.

For the full 40A@240V, that's 9600 VA so a 10KVA transformer would be needed. Those are several hundred dollars at least, so it's probably cheaper just to use the right cable. However if most of your loads can work on 240V and you only needed 120V for a receptacle string or two, you could use a much smaller 1.5KVA or 5 KVA transformer, which are cheaper and readily available used.

Honestly, this plan works better over longer distances, where you can go even further by using 2 transformers back to back to step up transmission voltages.

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