Size of bonding jumper to equipment rack

[Matt Donovan]

I have an equipment rack on a rooftop which holds an 800A panelboard and a few pieces of equipment fed from that panelboard. The rack is made of unistrut, and is bolted to the roof with OMG anchors, but not bolted to the building steel (so, not electrically connected to the building structure). Do I need a bonding jumper from the panelboard to the equipment rack? If so, what size does that jumper need to be?

What everyone tells me is that I need the jumper if the rack is "likely to become energized". I can't imagine it becoming energized, since there's no exposed wiring on it - wiring is all in conduit. How do most AHJs interpret this?

In terms of sizing, it seems "obvious" to size the jumper for the size of the feeder equipment ground. I have a #3/0 feeder EGC. Do I really need a #3/0 bonding jumper landing on the unistrut rack? Usually I see #6 for this stuff, but don't know what the justification is for that sizing.

 

[infinity]

The panelboard is metal and attached to the rack with metal to metal contact? If so no bonding jumper is required.

 

[suemarkp]

And each conduit clamp to the strut should also bond the rack.

 

[Matt Donovan]

The panel board is metal and attached to the rack with metal to metal contact? If so no bonding jumper is required.

That seems logical, but the panelboard is painted steel, so may not make a good bonding connection, right? There’s no threaded connection to the panelboard, just surface to surface.

 

[infinity]

That seems logical, but the panelboard is painted steel, so may not make a good bonding connection, right? There’s no threaded connection to the panelboard, just surface to surface.

If there is no good connection between the panel enclosure and the rack then the rack is not likely to become energized. I would be confident that the combination of washers, bolts, and strut nuts are actually connecting the two metal part together. Either way no bonding jumper is required.