Is my metal building enough to bond subpanel to for a earth ground with neutral bar isolated? [closed]

Question

I want to follow up my prior subpanel inquiry with another question for my understanding and overall grasp of neutral-ground-main supply-subpanel and building’s relationship.

I have an all metal framed structure covered with tin, built on a steel reinforced monolithic pad. The frame is anchored to the concrete pad every 2 ft with 1/2” 12-14” long, redhead hammer drill anchors so there must be close to 16 or so of these.

My breaker box is a big one with like 15 total breaker contacts split between the two 120v supplies. I have my box directly mounted to a vertical metal support stud with stainless lags.

My neutral/ground connection bars on each side of the bus bars in my box both rest on plastic insulated barrier between box and are connected via top horizontal bar.

To achieve neutral-ground separation I must remove horizontal bar, correct?

Then I must install the green, circuit box bonding screw connecting/bonding the isolated ground bar and the box itself, and due to the nature of the building being metal and well anchored to the concrete, would this not suffice in being a safe earth ground for my system?
Or do I not bond the box to the isolated ground bar and I HAVE to drive two copper rods and bond only to the ground?

Would I not being bonding the ground to the building via copper wire connecting ground bar and ground rods as soon as the copper wire touched the box or my frame?

Answer 1

No, You leave the bar joining the neutral bars alone.

You don't have any ground bars in this panel. Yet. You only have the neutral bars, and you leave them assembled just as they are. The only thing you take out, or don't put in, is a bonding screw that ties the insulated Neutral bars to the case, when it is installed.

Then you buy one or more ground bar kits for your panel and install them for your grounds. They do not have any insulation between the bar and the case. That's one way you can tell they are ground bars, not neutral bars.

When, and only when, a panel is a main panel, grounds can be guests on the neutral bars, and the bonding screw is installed. In a sub panel, you need to add ground bars (if not provided with the panel - typical if it was sold as a potential main panel) as the functions are not shared.

Answer 2

Ecnerwal's answer clearly explained the neutral bars vs. ground bars and bonding screw issues.

The second part is ground rods. The usual requirement for an outbuilding is that it have a ground wire going from the subpanel to either one ufer ground or to two ground rods. An ufer ground is installed when the concrete is poured, so that is not normally an option if you add a subpanel to an existing structure. The ufer ground/ground rods has a different purpose from sending ground back to the neutral-ground bond in the main panel, so you still have to have a 4-wire connection between the panels (hot, hot, neutral, ground).

Is it possible that anchors for a metal building into concrete or the ground will effectively ground the building? Yes. But that is not an easy thing to actually test. In fact, it is possible to do a test after installing one ground rod and based on a good result avoid installing a second ground rod. Nobody does that because the test costs more than just installing a second ground rod.

It is remotely possible, but exceeding unlikely, that your local inspector will allow anything other than a standard configuration (ufer ground, one ground rod with test or two ground rods), particularly since the cost of installing ground rods is very low. About the only time it would be expensive is if there was no accessible patch of dirt within several feet of the building - which is a bit unlikely for your shop building.