grounding a panel

JimCarlisleJuly 21, 2014

I have a service pole with a meter and external panel that is 250' from my house and 100' from both my garage and a small cabin. The service panel feeds 100 amps to the house and 100 amps each to the sub panel in the garage and to the new subpanel in the cabin.

The phone company tells me that I need a ground (two 6' copper rods with copper wire) at the cabin to ground the subpanel there and to ground their NIB. The service panel is grounded and is about 10' from their phone pole. Can they ground the phone line to the service pole ground and not at the cabin?

The subpanel in the garage is not grounded. I am not sure about the house, as it is 70 years old and I cannot see any copper poles into the ground.

I am ready to close and tape the sheetrock around the panel in the cabin so I need to know if it has to be grounded there. No appliances int he cabin, just phone, computers, lights, fan...

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Yep, subpanels in detached buildings need their own ground rods (and they need to be fed with 4 wires).

    Bookmark   July 21, 2014 at 2:26PM
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Yep, you do need some additional grounding at the cabin. For new construction here is what you are supposed to do. There are some exceptions for existing premises.

Building 1 feeds Building 2 with four wires (ground, neutral, hot (red) and hot (black)), then:
- Bond Neutral to Ground in the Building 1 service panel
- Do NOT Bond Neutral to Ground in the Building 2 panel (may have to remove a bonding screw or strap)
- Connect green to green and white to white in both panels
- Connect the ground bar in Building 2 to a grounding electrode at that building (ground rods, concrete encased electrode, ground ring, etc.)

A single ground rod can be used to ground a panel, but if the resistivity is more than 25 ohms, then you need to add a second rod. However, since it is usually cheaper to just drive two rods 6' apart than it is to get someone out to test ground resistivity, most people skip the test and just put in two rods.

Bonding conductor from the rods to your panel should be #6 bare copper.

Also, keep in mind that even if your local inspector missed this or doesn't care, the phone company can ask for additional facilities to be added above and beyond the building department - telecom grounding is a bit of a black art and sometimes has additional requirements.

    Bookmark   July 21, 2014 at 3:16PM
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Ron Natalie

Fido has it right with one exception. The ground and neutral is connected at the (Building 1) service disconnect, which may be the main panel there or it may not be.

There's no requirement that the grounding electrode conductor be bare.

    Bookmark   July 22, 2014 at 8:45AM
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Grounding is one of the most important thing for electrical service panel. Yes subpanel in the garage grounding is necessary to put in panel, grounding is providing a path back to an earth ground whereas bonding is connective. You find underground of building to search the sub panel of grounding there.

Here is a link that might be useful: Find electrical contractors

    Bookmark   July 24, 2014 at 7:10AM
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