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A contractor replaced my subpanel with a new one, and will come back for other work and inspection. (Old subpanel is Federal Pacific.) My home is in California, built in early 1980s. The subpanel is in the attached garage, feeding everything in my home except AC.

I noticed that my subpanel is fed with 3 wires (hot, hot, neutral).

  • Does this mean my home is not properly grounded?
  • Is it a code violation to replace the subpanel without fixing grounding?
  • The contractor recommended connecting subpanel to a new ground rod without adding a 4th wire. That appears like a bad idea based on another question on this site. What's the right way to fix this?
  • When I put a voltage meter between hot and ground bar of the new subpanel, it shows approximately 120V. Is that expected when the panel is not connected to ground feed? How do I verify that ground and neutral are not accidentally bonded in the subpanel?

Photos of the inside after replacement: (In the photo, breaker is not properly set up for MWBC. That will be fixed. Please ignore.)

inside of subpanel, where feeder enters inside of subpanel

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    Can you post photos of the inside of the subpanel please, especially where the feeder enters it at?
    – ThreePhaseEel
    Commented Aug 20, 2020 at 3:15
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    Do you have metal conduit for the feed from the main panel to the subpanel? If you do, that is likely the ground.
    – manassehkatz-Moving 2 Codidact
    Commented Aug 20, 2020 at 3:17
  • @ThreePhaseEel, I just added photos
    – Haozhun
    Commented Aug 20, 2020 at 3:49
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    @manassehkatz-Moving2Codidact, the feed from main panel to the subpanel is a metal conduit. I don't have a photo of the inside of the subpanel prior to replacement. However, now that you bring it up, I did see a special hook screwed to the conduit on the inside of the subpanel before replacement. And I remember that the hook was connected to the ground bar. Is that a legitimate/meaningful way to feed ground to subpanel?
    – Haozhun
    Commented Aug 20, 2020 at 3:51

2 Answers 2

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Your feeder appears to be in metal conduit, which is the grounding conductor

Since your feeder appears to have been run as wires in a metal conduit, that conduit would serve as your grounding conductor provided it is continuous back to the main panel. I would turn off the feeder at the main panel and do a continuity check from the neutral lug on the panel to the panel cabinet, though, to make sure of this.

... and that "hook" wasn't ever needed in your situation

Note that the "hook" you describe, which is more properly called a lug on a bonding bushing that was present in the old installation, wasn't actually ever needed in this case, since the conduit does not have service entrance wires in it, just feeder wires, and your circuits are running at less than 250V to ground. (Bonding around concentric/eccentric/impaired KOs in the fashion you describe is only required for service entrances and circuits upwards of 250V to ground, as per 250.92(B) and 250.97 respectively.)

You will need to have those open knockout holes plugged though

Unless the contractor is planning on using those open holes in the top of the panel for a cable run when they come back, they'll need to put knockout plugs in the open KOs in the top of the subpanel in order to keep junk from getting into the panel and causing trouble there. (They're a Code violation for that reason.)

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  • Regarding "do a continuity check from the neutral lug on the panel to the panel cabinet". I turned off breaker at the main panel, and used a multimeter to measure the resistance between the neutral lug and ground bar. It reads 0 ohm. (I made sure it's 0, not 0L.) Is that the right way to do the check you recommended?
    – Haozhun
    Commented Aug 20, 2020 at 4:47
  • @nobody, it seems that you deleted your comment. I don't know why, but I did follow your instruction to disconnect neutral feed in subpanel. That allowed me to find out that my electric oven is incorrectly wired. After disconnecting the oven's neutral in the subpanel, I confirmed that ground and neutral in the subpanel (with neutral feed removed) are not connected, and also confirmed that ground and neutral feed are connected. Thank you!
    – Haozhun
    Commented Aug 20, 2020 at 7:38
  • You have answered my questions so helpfully so many times that I'd be more than happy to pay you for your service if you happen to be an electrician in my area. By any chance, are you an electrician doing residential work?
    – Haozhun
    Commented Aug 20, 2020 at 7:41
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Your feed is in conduit. Continuous metal conduit is a legal grounding conductor.

If you didn’t measure 120V from hot to the panel box, that would be bad (though the reading itself doesn’t prove whether the box is connected to ground or neutral).

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  • Q1. Why it is bad if I didn’t measure 120V from hot to ground? Isn't ground not connected to anything in my photo?
    – Haozhun
    Commented Aug 20, 2020 at 3:59
  • Q2. Is my ground connection now broken? The hook that was present in my old subpanel isn't present any more. Please see photo.
    – Haozhun
    Commented Aug 20, 2020 at 4:00
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    @Haozhun Ground and neutral are connected in the main panel. All neutrals in the building are connected. All grounds in the building are connected. Therefore all grounds are at the same level (120 to each hot) as neutral. This is normal. The only concern then is to make sure that the only ground to neutral connection is in the main panel.
    – manassehkatz-Moving 2 Codidact
    Commented Aug 20, 2020 at 4:40

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