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Subpanel Feedback


inspectorwill
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Inspected a home with detached, all steel (frame and siding) constructed shop about 75' from main house and main panel. All outlets are equipped with two conductor wiring (hot and neutral) and run through metal conduit back to the subpanel. The subpanel is connected via metal conduit (as far as I can tell because it is buried) back to the main panel. The neutral terminal in the subpanel is isolated from the panel and there is a bare, stranded copper wire connected to the neutral terminal and run to a ground rod at the exterior of the shop. The grounding conductor is doubled up with the neutral under a single lug. Seems to me the bare copper grounding conductor connected to the neutral creates a potential path for stray current since it is not isolated from the conduit through which it runs. Not really sure why or if the separate ground rod is necessary. See photos attached. Thanks for any feedback.

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Inspected a home with detached, all steel (frame and siding) constructed shop about 75' from main house and main panel. All outlets are equipped with two conductor wiring (hot and neutral) and run through metal conduit back to the subpanel. The subpanel is connected via metal conduit (as far as I can tell because it is buried) back to the main panel. The neutral terminal in the subpanel is isolated from the panel and there is a bare, stranded copper wire connected to the neutral terminal and run to a ground rod at the exterior of the shop. The grounding conductor is doubled up with the neutral under a single lug. Seems to me the bare copper grounding conductor connected to the neutral creates a potential path for stray current since it is not isolated from the conduit through which it runs. Not really sure why or if the separate ground rod is necessary. See photos attached. Thanks for any feedback.

You say that "the subpanel is connected via metal conduit . . . back to the main panel," yet, in the picture, I see plastic conduit???

The ground rod is required at the separate building because there's more than one circuit.

Per the NEC, up until 1996, the grounding electrode conductor and all of the equipment grounds were supposed to be connected to the feeder's neutral unless the feeder contained an equipment grounding conductor (4th wire).

From 1996 to 2008, it was still OK to connect all of the grounding wires to the feeder neutral as long as there were no "continuous metallic paths" bonded to the grounding system in both buildings. (The telephone in your picture, for instance, might be connected to wires that are bonded to each building.)

After 2008, you had to run a 4 wire feeder and keep the grounding & neutral wires separate.

It was never ok to have both the grounding and neutral wires under a single lug unless the lug was listed for that purpose. (Unlikely.)

Given that it seems to be an older installation and there's only a three-conductor feeder, I'd guess that a competent electrician would simply bond the neutral terminal bar to the cabinet and install a new lug for the grounding electrode conductor. Alternatively, he could run a new 4-wire feeder and install a separate grounding bar.

As a home inspector, I wouldn't propose a solution, I'd let the electrician choose one.

- Jim Katen, Oregon

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