Equipment Ground 2

[mikeengurs]

I have a switchgear cubical with a ground bus. The case is all grounded through the ground bar. The bar is connected to a local ground, and the 4160v feeder ground. We have multiple power circuits terminating in the switchgear, 120VAC, and 125DC. Do I have to pull a ground cable and terminate it for every circuit? The vendor only provided terminations for local and feeder ground.

 

[7anoter4]

You don't have to use a grounding wire if the cables are in cable trays, conduit or other permitted grounding means.
The cable tray system has to be continuous and the grounding connections through approved [for grounding] appurtenances.
The cable tray system has to be connected to the Grounding Bus.
The cable tray has to be suitable to convey the grounding current-for instance steel cable tray current is limited to 600 A and aluminum
up to 2000 A.
Usually starting from the cable tray the cable rigid steel conduit should be connected by a jumper to the cable tray and at the receiver end another
jumper will connect the conduit to the receiver grounding point. Sometime the flexible conduit could be an approved grounding mean.

 

[waross]

Many installations now install a large grounding conductor in the tray and bonded to the tray every 50 Ft. (15 M)

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[mikeengurs]

All Panels, Tray, and Switchgear are in the same room, and connected to the same ground ring. The switchgear bus is connected to the ground ring by a large 500 MCM cable, so the ground ring will be the effective ground path back to the source panel. Would that be sufficient?

 

[7anoter4]

The equipment grounding conductor has to be connected to the Grounding Bus directly. The connection directly to the grounding ring
is not sufficient. All structural metallic parts, including cable trays, metallic ladders or pipes could be connected directly to the grounding ring in order
to mitigate the touch potential but this way does not present a low impedance in order to put the protection in operation.

 

[dpc]

The switchgear bus is connected to the ground ring by a large 500 MCM cable, so the ground ring will be the effective ground path back to the source panel. Would that be sufficient?

No. For an equipment grounding conductor to be an effective fault return path, it needs to be physically close to the phase conductors. When the grounding conductor is outside the conduit and physically distant from the phase conductors, the inductive reactance is much higher resulting in higher circuit impedance.

If this installation is in the US and under the NEC, you have to have an equipment grounding conductor run in each feeder conduit. As 7anoter4 indicated, steel conduit, cable tray and other raceways are allowed to be used as equipment grounding conductors in some situations. But regardless of this, we always run a ground wire in every conduit. No exceptions.