N/G bond in distro box

[zbang]

I recently did an outdoor event and we rented six spider-box distro panels (camlock in, 14 CS connectors out) from a local company. They were built by Trystar and looked like they'd never been used. They also came with a N/G bonding jumper inside and a sticker on the back about it. Why? I can't think of a place where you would use one of these boxes and would want a bonding jumper in the box itself. The generators are all bonded properly at the genny, and the any other tie-in should have it's own jumper. Best I can come up with is maybe some case of a SDS from a transformer, but usually the bond will be in the transformer case or output OCP/disconnect. I certainly don't want it down 300' of 5-wire feeder from the source.

We removed the bond and added a "bond removed" label next to the "it's bonded" one.

 

[bphgravity]

As you indicated, there are several sections of the NEC that mandate the installation of a main bonding jumper / system bondin jumper. And there are several sections that prohibnt this connection. The installer is charged with ensuring a compliant installation based on how the equipment is being used and connected...

 

[Rick Christopherson]

You have to understand that those are universal panels, and there is no specific setup for where/how they may be used. In the field, it is easier to remove a jumper than it is to create one that never existed. That's why they are put in by default. What's good here is that the panel was labeled. For the past 3 or 4 decades, none of the manufacturers of portable distribution panels labeled the panel as being bonded, even though they were.

It's not an oversight to put the jumper in--it's deliberate. I haven't dealt with Trystar in several years, but this is a picture of the electronic tester they have for testing panels and cables. (I built it for them about 5 years ago). The tester will actually fail the panel test when it sees the G-N bond (unless they suppress the warning message). So for every panel they build, they get a failure warning and have to override it. I suspect that it becomes a reminder to put that sticker on the outside of the box.

 

[zbang]

I understand that the jumper may serve a legitimate purpose, but I can't think of what that is, That's my question- when would it be used? Since these aren't service-rated (and have 14 breakers with no main), there will/should always be a disconnect closer to the power source, so the bond would go there. As for removing the jumpers, "easy" is relative .

At least Trystar did label the box (and my crew added their label when the jumper was removed). Generally, I've been quite happy with Trystar's products, except for getting cables in super-tight coils, but the carpenter built an unwinder for me.

 

[Rick Christopherson]

I don't disagree with you. The bond really shouldn't be there, but it typically is by default.

I haven't been associated with that industry for quite a while now, so my memory of the following events may be wrong. My father used to be the manager of one of the largest power distribution rental groups in the country, and I did some consulting work for him. He and I were on an out-of-state project, and the local State Inspector wanted the bonding straps removed from all of the generators on the site. That was the first time I learned that all of the generators in the fleet were bonded. This got me thinking, and I suddenly realized that the entire fleet of rental equipment was set up with ground loops. Even though the inspector was wrong about removing the generator bond, it did make me realize that none of the distribution panels in their fleet should be bonded. After my father confirmed my conclusion with our own State Electrical board, the company had all of the bonds removed from their distribution equipment. (I had nothing to do with equipment design. I was consulting for on-site project management.)

I did some design work for Trystar a few years ago, and I may have mentioned to them that the bond should not be present, but I can't recall if I did or didn't, because it was beyond my scope of work. It's been an industry norm for over 40 years, and that may be the sole reason behind it. Another possibility is that it is done as "the lesser of two evils". Ground loops would typically be the lesser evil than an unbonded system. Even though that particular panel shouldn't be used as a main panel, it doesn't mean that it never will. It's rental equipment, so you never know how it will be configured by the end-user. Because it is cord-and-plug, you don't need to be an electrician to connect it (at least not here).

 

[zbang]

Thanks Rick. This pretty much confirms the reason is along the lines of "we've always done it that way". I was fishing for some obscure code section that I'd missed.