Rack grounding/bonding to primary earth

[MJSullivan]

1800s barn which has been converted back in the 1920s and 1960s to be a residence.

I wish to bond my PV racks to the primary ground used at the 200A primary service panel. Given that this is an older home (where Harry Homeowner previously went wild), I'm not seeing a "traditional" place to bond my racking ground wire. I note that previous electricians chose to bond their equipment as shown in the attached photo. Would doing something similar be adequate for a 6 AWG ground wire from my racks? I'm thinking of removing the unused bond at the top of the panel and hooking up my racking ground there. Thoughts?

Michael

 

[MarkSolar]

You've got the right idea, since it's an old house I think I'd follow that ground conductor into the ground and make sure it's properly attached to the top of one or more ground rods. You could also do a resistance measurement of the ground to make sure it's adequate but you'd probably have to hire someone to do that unless you have the right meter. I think I'd just pound a few new ground rods and reconnect that existing ground wire to the new ground rods. Then you can connect the ground conductor from your solar array to the neutral bar in the service panel.

 

[MJSullivan]

The ground wire appears to be inside a conduit. And of course, the service box is locked. I assume one cannot measure resistance through a conduit? Seems I must get out a shovel and dig until I find either the wire or the rod — right?

 

[MarkSolar]

I think the best thing to do would be ask the electric company to come out and confirm what's in the meter box. It's possible they bonded the ground to neutral there. If not it needs to be bonded in your service panel. I think it's acceptable to use the meter to panel conduit connection as a ground conductor, but I'm not sure about code requirement.

If you want to explore I'd start in your service panel, I assume it's behind the meter. Normally the wires coming from the meter there should be two hots and a neutral. The neutral bar in your service panel needs to have one heavy gauge ground wire, probably 6ga, that goes directly to a ground rod. It's possible that conduit you see that disappears into the meter is carrying a ground wire that's attached to your neutral bar. If it is, you will see it come from the meter conduit along with the two hots and neutral. Assuming that wire is connected to your neutral bar, then I'd follow the other end into the ground to make sure it's connected to at least one ground rod. If you don't have a ground wire connecting your neutral bus to a ground rod, I'd install one. Code requires a ground resistance of <25 ohm. If you can achieve that with one ground rod great, if not you may have to add a few. If you've got a wet spot, like by a gutter drain, put the rod there, you'll get better contact to earth.

 

[MJSullivan]

So how do I legally open the box? It has a lock on it. Do I call my electric company to ask them to open the box for me? Or would they be down with me opening it up?

 

[MarkSolar]

Not sure how your utility handles tamper tags. Around here we mostly have smart meters, so the utility can tell immediately if you pull the meter, so they don't seem to care too much. When I had a transfer switch put in, the electrician cut them off, added the stuff, then just hung the tags back on there still cut. That was 10 years ago and the utility company hasn't said anything yet.

If you cut the tag, you could call the electric company and tell them you had to have an electrician out and he tightened the lugs in your panel so he cut the tag and pulled the meter. Then they'd send someone out to put another tag on it and you could ask them some questions when they show up.

Have you looked to see if you have a ground wire connected to the neutral bar in your service panel?

 

[MJSullivan]

Have you looked to see if you have a ground wire connected to the neutral bar in your service panel?

Just took a look. Boy what a mess. But yes, the grounds and neutrals are definitely "bonded" (such as it is).

 

[MarkSolar]

That meter conduit is plastic. I can only see 3 wires in that conduit. So you have to assume they bonded the ground and neutral in the meter enclosure. It would be nice to confirm that. I'd still follow that ground wire/conduit coming out of the meter enclosure and make sure it's attached to a ground rod.

 

[DerpsyDoodler]

That meter conduit is plastic. I can only see 3 wires in that conduit. So you have to assume they bonded the ground and neutral in the meter enclosure. It would be nice to confirm that. I'd still follow that ground wire/conduit coming out of the meter enclosure and make sure it's attached to a ground rod.

I thought neutral and ground are only supposed to be bonded in one place. bonded in the panel and at the meter is a bad thing, isnt it?

 

[MarkSolar]

I thought neutral and ground are only supposed to be bonded in one place. bonded in the panel and at the meter is a bad thing, isnt it?

There should only be one bond on the residence side, that's the neutral bus in the service panel. The bond in the meter belongs to the utility company. They also bond neutral to ground on some/most/all poles depending on soil type, rainfall, and other things. And they bond at substations, at the generating plant and who knows how many other places.