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To Bond or Not to Bond (electrical)

2807 Views 11 Replies 9 Participants Last post by  jakenbake, 
BigD
Hi all
I am finishing my JD Shed/barn and I am in the electrical wiring phase of the project. I have an existing underground in conduit 8 gage wire that runs from the main service panel to a sub panel located in the JD Shed/barn. This wire is about 150 feet long and is fused at 30 amps. It supplies 120 volts only.

Question. I've been told the sub panel should have the neutral and ground wires held separate, and there should be a grounding rod close to the metal building. Is only the building grounded to this grounding rod, or is the bare ground electrical wire also attached to the grounding rod? Reason I ask, is the original electrician who wired this existing service supply hooked the neutral and ground wires together at the outlet post, and also connected them to the grounding rod. (existing supply was for a 30 amp service to my motor coach)

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marlboro180
BigD,

I am no electrician, but will tell you what my electrician just did at my place.

I have a 100A 220 subpanel in the garage that I put in, buried EMT and then I pounded a grounding rod for the sub panel, thinking more is better, in addition to the house grounding rod.

Mr. Sparky noticed it , and was very kind to not rip me down at my knees for adding the additional rod at the garage panel .:banghead3 We yanked it out, and disconnected the grounding wire in the panel as well.

I've been told the sub panel should have the neutral and ground wires held separate
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This is what I was told as well.^^^^

I would check with the electrician who wired yours, as to what to do.
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D
The neutral is only to be bonded at one place, thats the main panel. Remove the bonding screw or jumper from the sub panel. If you have to you can add a ground bar to the panel to accommodate whatever you have running to that panel.
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W
I was told by my electrician dad that the building sub-panel needs a isolated ground rod @ the panel.. The neutral is the 3rd wire (220V--> or, in your 120V case- the 2nd) which is supplied from your main panel. I do believe this is 'code' in my state.. Another change lately is separate ground and neutral rods @ the main panel.. As ever, you should check with an electrician who is up on the local codes to be safe.. :goodl:
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T
It's been my experience that local knowledge of what the local inspectors interpretation, and opinions/biases, of the code are is what counts. I'd ask your electrician, as has been suggested, that way the inspection will most likely pass with no problems.

Mike
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73 wheelhorse
I have found out that you can actually call your local inspector and ask him or her what they want done I have been an Electrician since 1999 and yes you need a ground rod and the ground and neutral MUST be separate at your sub panel (shed/barn)
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B
I have a separate 100 Amp panel in my Morton building that I put in in '96.
I ran 3 2/0 aluminum wire burried in conduit.
I never had a problem with that.
However, after seeing all the discussion on different sites regarding the need to separate the neutral and ground in sub-panels, I chose to run a separate ground back to the main panel and remove the bonding screw from the panel in the barn.
I ran #4 bare copper as the ground wire back to the panel so in a sense, the whole line becomes a ground. Back when I built the barn I had buried about 30 ft. of heavy copper lightning protection cable 8 ft. deep when I was digging the dry well which I used as a ground for the barn system at that time.
Later, I drove a 10' ground rod straight into the ground and connected all the grounding wires to it before they enter the sub-panel. The more recent ground cable back to the main panel is also "bugged" onto these ground wires.
The simple explanation, as I understand it, of why the ground (in addition to the neutral) is needed is that the neutral becomes live whenever any 110 volt circuit switch is turned on and power is being utilized in that circuit. The ground prong on the 3 prong outlet provides a path directly to ground, for example, should either the black(hot) or white (neutral) wire short directly to the case of whatever tool you might be using.
It took me a while to get this all thru my head and I hope I really do understand the concept correctly. LOL
BTW, I installed the approx. 220 ft. of #4 copper ground wire back to the main panel just a year or so before the price of copper skyrocketed. That was pure luck!
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C
I understand the lack of bonding the ground in two places is to prevent a ground loop. You don't want your ground circuit to have two different paths to the same point. When this is present it can create a "buzz" in audio equipment or such.
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BigD
Thanks Guys.
I disconnected the neutral and ground wires and separated them. Then connected the ground wires to an additional ground rod close by. I plan to drive another ground rod close to the building and ground the metal building to that ground.
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jakenbake
i'm not sure you have to do a ground rod. any current flowing through the ground wire (which there shouldn't be ANY normally) will flow back to the main panel through the ground wire. as long as you have 3 wires for 110 or 4 wires for 220, i don't think you need a ground rod. and yes, keep ground and neutral seperated at the subpanel.

adding a second ground rod could get you in trouble. if its close at all to your water main, current could find its way from hot, to your ground rod, to your water pipe, which is grounded at the main panel. this again creates a ground loop.

if you ever wanted to do 220 out there, then you would need a ground rod since you have only 3 wires. i don't think this is to code anymore, but i am pretty sure it was at one time. so you could always claim it was done after the code changed.

i'm not an electrician, but i am an electrical engineer. so i do have an understanding of current, voltage, etc.

some quick googling "sub panel shed" confirms that you don't need a ground rod if you have 3 wires.
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C
jakenbake said:
i'm not sure you have to do a ground rod. any current flowing through the ground wire (which there shouldn't be ANY normally) will flow back to the main panel through the ground wire. as long as you have 3 wires for 110 or 4 wires for 220, i don't think you need a ground rod. and yes, keep ground and neutral seperated at the subpanel.
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The grounding rod would be required; I understand it's always required when the subpanel is in a second building. I suspect the primary reason is to eliminate the extra resistance for your ground at the remote building (you can try your own luck and see if your body has a higher resistance than the ground wire leading back to the main panel). Also, if a lightning strike were to occur you could get current flowing through the ground back to your subpanel.

Basically you just don't want the difference in potential between the two panels.
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jakenbake
as long as you don't have another conductive material between the two, i guess its not a problem. it would help with lightning.
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