power shed grounding, etc

jtdiesel65

I'm moving (and upgrading) my current system into an outbuilding. My current scenario is one ground bar outside my house that is tied to DC disconnect, SW inverter box, and main AC panel. Bat neg and AC neg are bonded to ground. The outbuilding scenario is basically the same component setup including a main AC panel. I'm running a line from the outbuilding AC panel to the AC panel in the house. This includes a ground wire, but it's shielded. (Although I have to wonder if that's even necessary since neg is bonded to ground in the outbuilding) I would think I need a ground rod for the outbuilding that duplicates what I have in the house. But should I keep the house AC panel to ground rod tie?

I'm wondering if having a ground rod at the outbuilding and a ground rod at the house is cause for a ground loop.

Also, for GFP on charge controllers. From what I read GFP won't work with my current setup due to bat neg/ground bond. I was planning to change from outback charge controllers to Classic charge controllers. I think GFP can be disabled, but is there any change I should make to keep GFP?

Cariboocoot

Re: power shed grounding, etc

If you're going to use Midnite's GFDI you need to read through this: http://www.midnitesolar.com/pdfs/DC%20Ground%20Fault%20Protectors%20explained.pdf
Note the bit at the end: "You do not ground the battery negative when using the DC-GFP since the DC-GFP is now the
battery negative to earth ground bond."
Yes; wiring changes are required.

As for the other grounding issues, it's best to have one AC neutral to ground bond and one Earth ground rod. Other configurations have the potential to form ground loops. That said, it is sometimes necessary or preferable to have a separate ground rod elsewhere if the distance between them is great enough (soil resistance between the two points reducing the ground loop potential).

Stand by for further and no doubt conflicting opinions on this; proper grounding is one of the most argued-about aspects of electrical theory.

Personally I would not use the DC GFDI as I remain unconvinced as to its efficacy. I'm not keen on AC GFCI either, except in certain applications.

vtmaps

Re: power shed grounding, etc

jtdiesel65 wrote:

I would think I need a ground rod for the outbuilding that duplicates what I have in the house. But should I keep the house AC panel to ground rod tie? I'm wondering if having a ground rod at the outbuilding and a ground rod at the house is cause for a ground loop.

My equipment is also in an outbuilding. You certainly need a ground rod and bonding out at the shed.

As for the house, you may or may not need a ground rod and bonding. The best way for you to research this is to figure out the rules in your jurisdiction for subpanels. This comes up a lot with garages. If the power enters an attached garage, the house panel may be a subpanel (unbonded) of the main garage panel. If the power enters a detached garage, well, I never did figure out what is the right thing to do. It may be a gray area of the code. Inquire of your building inspector.
--vtMaps

mike95490

Re: power shed grounding, etc

Whats' the distance from house, to outbuilding ?

jtdiesel65

Re: power shed grounding, etc

Thanks Its 100ft. From the house it goes to a detached garage to another panel.

mike95490

Re: power shed grounding, etc

for 100', they want me to use a separate ground after 50', so I think you are going to have to do that too, at the house service entry.
I'm 300' from the battery shed, and 120' from the sub panel at the pump house. 3 ground rods, and a creek & 20' deep ravine in between.

Cariboocoot

Re: power shed grounding, etc

Agreed. With 100' distance between them, I see no problem with a second Earth grounding rod at the shed.
Although you may need to unbond the neutral in the house if it is bonded in the shed; the neutral & ground wires running between locations could cause a potential loop on them.