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I have a sub panel on back of house. From main in garage is three wire. 2 hot one neutral. NO GROUND WIRE. Sub has a single bar used as neutral and grounds. Its bonded to case (Screw in). I will add a ground only bar, a ground to earth rod and wire them together. I cannot get the snake all the way through the conduit to pull a ground wire.

Can I run a separate ground wire alongside the conduit to the sub?

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Update/clarifications:

Thank you Speters. ArchonOSX, I understand there should be a common ground back to the main, I do not have that. Currently (pre-existing), I have a 3wire 50 amp gfci breaker for a spa in this SUB. Its the only circuit. I was advised to Isolate the neutral bar and add a ground bar, bonding it to earth; Where new circuits utilize the ground bar. In this config would I be protected and no SUB/main panel metal become energized if a short occurred?

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  • 1
    Possible duplicate of Separate ground/neutral bars in sub
    – ThreePhaseEel
    Oct 2, 2017 at 23:14
  • 2
    Is this run in metal or plastic (PVC) conduit btw?
    – ThreePhaseEel
    Oct 3, 2017 at 0:07
  • ThreePhaseEel's question is very important, if this is metal conduit, it may be a valid ground path.
    – Harper - Reinstate Monica
    Oct 4, 2017 at 1:51
  • NO absolutely do NOT separate the ground and neutral if you only have three wires from the sub to the main panel. A separate ground rod isolated from the system will not function properly.
    – ArchonOSX
    Oct 6, 2017 at 22:22
  • Can you tell what the conduit is made from?
    – ThreePhaseEel
    Oct 6, 2017 at 22:23

4 Answers 4

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Absolutely, you can run a separate ground - they have allowed this for a long time and have recently liberalized the rules on retrofitting grounds to practically everything else. So if you have other outlets that could also use a ground, food for thought.

The grounds do not need to follow the same route as the original wiring. They do need to be thick enough for their purpose. Also, other circuits can share a ground wire, as long as they originate from the same panel.

Should you do it? Absolutely! The problem is, right now you have the NEMA 10 problem. Normally if a neutral wire breaks, the neutral wire is pulled up toward 120V because power has nowhere to return, but we don't care because the grounding system still protects us. Now, if ground is also the same wire (like in NEMA 10), it too will be pulled up toward 120V - and now things which are supposed to be grounded will instead shock you! Including switch plate screws, metal chassis of equipment, and of course, the metal chassis of your subpanel, which you will be opening directly when you realize there's a problem. Touch that and a water pipe, and blammo!

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  1. Ground rods do NOT effectively protect people from shock and are NOT installed for that purpose - they effectively ground the distribution system to protect from transients etc.
  2. BONDING is for connecting ALL metal parts together to form a return path in case any fault takes place and allows the fault to clear by tripping the breaker. Bonding protects people from shock by not allowing metal parts to become energized and above ground potential for long after a fault takes place.
  3. Yes, you can add an external bonding wire back to the panel.
  4. Connection if bonding ground to the distribution system neutral should take place in ONLY one place - the main disconnect location. Everywhere else neutral and ground should be separated.
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Yes, you can run an external equipment ground wire.

But my question is....why do you want to?

If the sub-panel was installed years ago under a previous Code then it is grandfathered and does not need to be updated.

If it ain't broke don't fix it.

Good luck!

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  • But that doesn't make it safe regarding today's code. Sounds like OP wants to make sure it's correct as possible by today's code. I applaud that.
    – Josh M.
    Apr 26, 2019 at 13:31
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That should not be a problem. As long as they are bonded to one common ground and have 10kOhm resistance or more it will meet code. And realistically the only real reason to have a common bond is to protect electronics. As far as protecting yourself you could run a separate ground rod and not run the other conductor to bond them all together and not be in personnel danger of a ground fault.

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  • Actually resistance to ground is supposed to be 25 ohms or LESS. And the reason to bond them together has nothing to do with electronics.
    – ArchonOSX
    Oct 3, 2017 at 0:04
  • Thank you Speters. ArchonOSX, I understand there should be a common ground back to the main At the moment I do not have that. I have been advised that at the SUB, I should add a separate ground bar bonding it to earth. Isolate the neutral bar and move actual ground wires to the ground bar. I have a 50 amp gfci breaker for a spa in this SUB. Will a separate ground allow the gfci to work properly if there was a fault? Basically if anything happened to ether ground or neutral circuits. I would still be protected and no SUB box metal be energized? Or at the main for that matter...
    – Sub-Brad
    Oct 6, 2017 at 20:20
  • REDO of my previous comment!!!Thank you Speters. ArchonOSX, I understand there should be a common ground back to the main, I do not have that. Currently (pre-existing), I have a 3wire 50 amp gfci breaker for a spa in this SUB. Its the only circuit. I was advised to Isolate the neutral bar and add a ground bar, bonding it to earth; Where new circuits utilize the ground bar. In this config would I be protected and no SUB/main panel metal become energized if a short occurred?
    – Sub-Brad
    Oct 6, 2017 at 20:48

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