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-   -   Bonded Ground and Neutal in Outbuilding Panel (http://www.houserepairtalk.com/f9/bonded-ground-neutal-outbuilding-panel-17543/)

VikingsFan 04-10-2014 01:18 PM

Bonded Ground and Neutal in Outbuilding Panel
 
I have a bit of a unique situation. My outbuilding has two hots and a Neutral coming into it's panel, but a dedicated / separate grounding rod. In this situation, should I bond the Neutral and Ground bus bars in the outbuilding sub panel? See the attached image for a better understanding.

http://iehardcore.com/pics/Electrical.JPG

JoeD 04-10-2014 01:32 PM

Yes you should. That setup was permitted in the past. New installations require a separate ground in the feeder.

Wuzzat? 04-10-2014 02:57 PM

Quote:

Originally Posted by JoeD (Post 103220)
That setup was permitted in the past.

Meaning there was no jumper?

Quote:

Originally Posted by JoeD (Post 103220)
New installations require a separate ground in the feeder.

Meaning a cable with four conductors from main to outbuilding?


It's not my place to come up with a rationale for the electrical code, but:

Option 1, with outbuilding N & G unconnected, a person who is grounded at the outbuilding (let's say standing barefoot on wet ground) would see zero volts on outbuilding metal enclosures.

Option 2, with outbuilding N & G connected, a person who is grounded at the outbuilding would see 2-3 v on outbuilding metal enclosures assuming current was being drawn by the outbuilding.

Option 3, with outbuilding N & G connected through a four wire cable from the main building and with outbuilding N & G unconnected, a person who is grounded at the outbuilding would see the voltage difference between the ground at the outbuilding and the ground at the main building.
This voltage is probably indeterminate and small unless the current density in the ground happens to be very high, like in a metropolitan area.

I'd say go with option 1 but the electrical code people must have some good reason for picking option 3.

These various option voltages can be tested with a multimeter and a heavy 120v load turned on in the outbuilding.

VikingsFan 04-10-2014 08:01 PM

Thanks for the replies! I haven't encountered this situation before and wanted a second set of eyes. I also am of the opinion that they bus bars should be separated, but that's just because it's been drilled into me that you always keep them separate in sub. panels. If anyone else has other experience, or opinions, I would be glad to hear them!

Wuzzat? 04-10-2014 08:11 PM

Quote:

Originally Posted by VikingsFan (Post 103253)
that you always keep them separate in sub. panels.

Which means you get a Single Point Ground. It's necessary in some electronics gear but the ins and outs for resi wiring are not obvious.
http://www.google.com/search?client=...+ground&rls=en

VikingsFan 04-10-2014 09:06 PM

OK, so it seems like it's a Single Point Ground vs. Distributed Single Point Ground, but I'm not sure that's applicable. It implies that I have an option of either using the common ground from the Service Panel, or tying the Service Panel Ground to the Neutral at multiple points with multiple earthing locations. I have neither choice. My choice is to either not tie the Neutral to a ground at all, or tie it into a separate ground altogether. The challenge is that there is no continuous ground connection from the Service Panel to the outbuilding Sub-Panel, and running one would be a challenge. The last bit of confusion comes in that I would like to add a 30A GFCI / Arc Fault Detection breaker to the outbuilding, but I'm not certain that it would work considering the issues with the ground.

JoeD 04-11-2014 06:40 AM

Under current code you do not have that option. Past codes allowed for a three feed to out buildings and a ground rod except under certain conditions. Current code requires a four wire feed to out buildings and a ground for all circumstances.

Wuzzat? 04-11-2014 09:23 AM

Quote:

Originally Posted by VikingsFan (Post 103257)
I would like to add a 30A GFCI / Arc Fault Detection breaker to the outbuilding, but I'm not certain that it would work considering the issues with the ground.

And I don't know of any way you can find out ahead of time.

You'd have to gamble the price of this device on the likelihood that you don't get nuisance tripping once per day/week/month/year, balanced with whatever marginal additional safety you'd get.
GFCIs give you some safety but I can't get credible numbers on this and I have my doubts about AFCIs.

BTW, GFCIs don't need a ground to work and maybe the same is true for AFCIs.

Putting this in perspective, people dying from electricity each year is about 15x less than from driving a car. Your odds are much better than this because you look before you leap.

nealtw 04-11-2014 10:40 AM

I don't understand what the problem is?

speedy petey 04-12-2014 10:07 AM

OK, if this is an existing installation it is FINE. The neutral IS bonded to the panel enclosure. It is treated just like a main panel.

You have to remember, the ground rod and associated wire have NOTHING to do with the incoming feeder wire(s). A ground rod "ground" serves a completely different purpose.

Not sure why you would even want to, but you CANNOT use a GFI or AFCI feeder breaker in cases like this. You'll have to protect everything from the sub-panel location or local devices.


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