I have an old style service panel - the ground wire (from a rod in the ground) and the neutral wire (leading in from the pole) are both bonded to the box. I want to install a sub-panel where I will be using a 120v and a 240v circuit. I am planning on running a 10/3 line with a ground wire to the sub-panel from the service panel.

I will be attaching the neutral wire to the neutral bar which is not bonded to the box and will be sinking an additional ground rod then attaching the ground wire to a ground bar which is bonded to the box. Where should I place the ground wire coming from the service panel, to the neutral bar or to the "new" ground bar?

Here's a shot of the subpanel (work in progress). 20 amp breaker on the left powers the A/C, 30 amp breaker on the right to power sauna and light. Main lines from service panel not installed yet. #6 ground wire connects to newly installed ground rod below the subpanel.


  • Note that I've updated your voltage references. These have been standard for more than half a century.
    – isherwood
    Commented Dec 16, 2019 at 20:54
  • quick answer: creia.org/subpanel-grounding--answers-to-common-questions
    – ron
    Commented Dec 24, 2019 at 3:45
  • it's nicely worded to explain the why's, and read page 4.
    – ron
    Commented Dec 24, 2019 at 3:53

2 Answers 2


You don’t say if the sub is in the same building or not. If it is in the same building, use the existing ground as separate grounding systems can create a problem in the same building. Since you are going to all the trouble to put a sub in I would bump the size a bit--10 awg only provides for 30 amps for the sub. Bump up the wire size and have some space for additional circuits later. I don’t waste time on anything less than 50 amp subs for the most part.

Bring the hot, hot, neutral and ground from your main panel to your sub and make sure the sub ground is isolated as you mentioned.


Main service panels all require the neutral and ground to be bonded on the same bar and to be bonded to the enclosure. All sub panels have isolated neutral bars that separate the ground from neutral. Use the separate ground bar in the sub panel that is attached to the enclosure. If one doesn't exist, buy it separate and add it.

The ground and neutral go from the same bonding bar in the main service to separate bonding bars in the sub panels.

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