RES Technical Corner by Brett Eliasz, PE

Technical Corner

For the Electrical article this month we will go over adding ground rods to a subpanel and when it is acceptable and not. This will also naturally go over isolation of the neutral bussing and equipment ground bussing.

The non-electrical piece of the puzzle lies on where the subpanel is installed physically. If it is on the same structure as the main panel or service panel then a ground rod is not required. If the subpanel is installed on a detached garage, for example, then it will require a ground rod connection.

For the scenarios above there must be a separate equipment grounding conductor (green) that runs from the main panel and lands on a separate equipment grounding bus which is directly connected to the case of the subpanel.

Additionally, the grounded conductor or Neutral conductor (white) will need to be routed from the main panel to a separate neutral bus which is isolated from the subpanel case and all other green equipment grounding conductors.

The neutral and equipment ground wiring should never be connected after (downstream) there is a connection residing in the main panel or service panel.

This photo represents a subpanel attached to the same structure as the main/service panel. This is a 120/240V single phase subpanel which is often seen at larger houses or for a hot tub installation.

Good News:

a) The neutral bus is isolated b) Both an equipment ground (green) and neutral (white) are ran from the main/service panel c) No connection to ground rod

Bad News:

a) The neutral (white) and equipment ground (green) which come from the main/service panel both land on the neutral bus. b) No separate equipment grounding bus. c) The branch circuit equipment ground (green) conductor lands on the neutral bus.

The Fix:

a) Remove both equipment grounding conductors (green) from the neutral bus. b) Provide a new equipment ground bus and connect directly to case. (Must use the screws provided with the bussing). c) Land both the equipment grounding conductors (green) to this new equipment ground bus.

Hopefully this article finds you well and can be used as a reference for your project needs. If anyone would like to contribute to the Rochester Engineer and add an article or would like to request information on a specific topic (not limited to Electrical) just email me at beliasz@bergmannpc.com. As always, any comments are appreciated…! Thank you for reading.

Brett Eliasz, P.E., LEED AP BD+C , RES Director