Disconnected Barn Sub Panel missing Ground?

[Bobby Cannon]

Our barn is 500' line of sight and 700' by road away from our house. The barn has power but I noticed the ground is not connected. Now I think this panel, by today's standards, should have been connected with a 4 wire system that should have included L1, L2, N, and a ground. However this is an older system that only use a 3 wire system of L1, L2, and N.

Now I think all I have to do is just connect a wire from my ground bus bar to 2 ground rods that are 6' away from each other. Now I'm also thinking that I should "bond" the Neutral and Ground here because it's a detached subpanel that is so far away.

What do you think? Any suggestions or ideas?

My question is very similar to (1) Bonded Ground and Neutal in Outbuilding Panel | HouseRepairTalk

 

[Eddie_T]

I haven't read the code but I would bond and ground. Grounds are usually higher impedance than advertised but are useful I suppose to keep neutrals referenced to ground.

 

[afjes_2016]

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You don't have the answer in your poll.

Detached structure:

Sub panel - do not bond neutral and ground together. Neutral must be isolated from ground. This goes for any sub panel no matter where it is located (attached or detached structure).

Ground Rod - no, not just one. There are two driven eight feet into the ground at least 6 feet apart from each other - preferrably more distance if possible.

And of course this is all predicated on the fact that there are 4 conductors running from the main/sub panel feeding it - 2 hots, 1 neutral and 1 ground.

A "Poll" is more of a matter of opinion to the person answering it - this is more code and safety than opinion.

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[Bobby Cannon]

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You don't have the answer in your poll.

Detached structure:

Sub panel - do not bond neutral and ground together. Neutral must be isolated from ground. This goes for any sub panel no matter where it is located (attached or detached structure).

Ground Rod - no, not just one. There are two driven eight feet into the ground at least 6 feet apart from each other - preferrably more distance if possible.

And of course this is all predicated on the fact that there are 4 conductors running from the main/sub panel feeding it - 2 hots, 1 neutral and 1 ground.

A "Poll" is more of a matter of opinion to the person answering it - this is more code and safety than opinion.

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I'm just not sure about bonding because I've read content where one says to bond and others that says to not bond. All the articles and such that do say to bond is only for cases like mine where the building is so far away AND is *only* using 3 conductors between buildings. I have never seen anyone suggest bonding where there was 4 wire. I think this is a very important distinction.

I did state in the original post that it's only using 3 wire between the buildings. This means I think bonding will be desired.

I also stated that if connecting the ground I would use two ground rods at least 6 feet apart. My plan is to use two 8 feet ground rods that are 8-10 feet apart.

My only issue that I still need to decide on is if I should bond the ground and neutral.

 

[Bobby Cannon]

Oh and about the poll, the labels are intended to be small. I know that "a ground rod" really means two because that is what is in the original post.

 

[Eddie_T]

To be of any use a ground bar in a sub-panel must somewhere connect to the source neutral. In a three wire feed that could only be via the third wire back to the main panel. So the ground bar must either be unused or bonded. Grounding via a ground rod(s) of itself will not solve this problem.

 

[Bobby Cannon]

To be of any use a ground bar in a sub-panel must somewhere connect to the source neutral. In a three wire feed that could only be via the third wire back to the main panel. So the ground bar must either be unused or bonded. Grounding via a ground rod(s) of itself will not solve this problem.

I see. Which is why even if there was a 4th "ground" wire it would still run back to the source "neutral", right?

BTW, I like how you wrote this response, it seems to make more sense to me.

 

[Bobby Cannon]

And thinking in this way, I guess there is more more option, I could run a new single ground wire all the way back to the main panel?

Even, If I did this, I think it would still be a good idea to have a local set of ground rods at the remote building?

 

[Eddie_T]

And thinking in this way, I guess there is more more option, I could run a new single ground wire all the way back to the main panel?

Even, If I did this, I think it would still be a good idea to have a local set of ground rods at the remote building?

I think ground rods might be good if bonded or with an added ground wire back to the main panel. However ground loops are a whole 'nother thing and some insist that it can cause lightning overvoltages or arcs. It's not my field so I best say I don't know. The utility company grounds every pole but that doesn't involve your house or the code as your neutral stops at the center tap of the transformer secondary.

If your current feed is grandfathered in making a change to a four wire feed may subject you to the current code. I hired an electrician to replace my main panel, he wired it hot so I would not have to undergo inspection and possibly be held to current code. My dryer, double oven and cooktop are wired with three wire SE type cable.

edit: Further thinking, you might ask the question on Mike Holt Forums, he is a code expert.

 

[Bobby Cannon]

This picture clears up the "why you do not bond ground + neutral in a sub panel that is "connected" to the main panel in a 4 wire connection. L1, L2, N, G.


If your neutral gets disconnected on the sub panel the existing metal infrastructure could be carrying the current. This would not be good. However in a disconnected state where there is literally 0 chance the two building could ever conduct between the two then a bond would be necessary or your ground is useless.

I also see how bonding a sub panel with 4 wire would also lead the an issue like the following image shows.



Yet again would not be an issue if the 4 wire was only a 3 wire missing the ground.

I think the answer I don't want to hear but is correct is to...

1. Add 2 ground rods with a min of 6" apart to panel. I expected this.
2. I really need to run an ground from the sub panel back to the main panel to bring it to code. This will be tough as it a direct 500+ feet back to the main panel through a forest... or 700 feet if I follow the service road, ugh.

 

[Bobby Cannon]

I also found this. NEC 250.30(A)(1) Exception No. 2 | Mike Holt's Forum

2017 NEC 250.30(A)(1) Exception No. 2 includes the words "If a building or structure is supplied by a feeder from an outdoor separately derived system, a system bonding jumper at both the source and the first disconnecting means shall be permitted if doing so does not establish a parallel path for the grounded conductor".

So with this I think I can just ground + bond. However, in the future, if I run a ground between my barn and house I will need to remove the bond to protect from a parallel neutral path.

 

[Eddie_T]

I think you now have a good understanding. I notice that many code comments suggest rather improbable failure modes.