# Sub panel and ground rod installation: “high differential potential between the ground locations”

We have a dock (fixed-pier) that is about 40 feet from the house, and +100 feet from the main panel. 4-wire (2 hots, 1 grounded neutral, and 1 ground) run to a large junction box at the start of the dock. I was thinking about replacing this with a sub-panel as I don't feel like this current implementation (done by someone prior) is to code (Generally speaking, when is it necessary to install a sub-panel for providing electricity to an outside shed/office?) and I feel like due to the distance it would be nice to have a disconnect at the dock.

My main question is sort of based on some conflicting information. I was under the impression that I would have to install 2 grounding rods 6ft apart near the dock and connect that with the ground coming from the feeder (main panel) and have the neutral from the feeder in the sub panel un-bonded from the ground. Thus, the sub panel would follow the diagram presented in the accepted answer here: How to properly ground a subpanel in detached building?

However, I was watching a YouTube video and read the following comment:

Greg Elkins: "There is one thing that bothers me, all grounds should be single point bonded, here have a separate ground run to the remote panel and yet installed a separate ground, this is bad. grounds should only be tied back to a single point bond to ground, have a separate ground run to the new panel, no additional ground rod should be located there. this allows for a dangerous situation that can have a high differential potential between the ground locations."

Is this user correct? Doesn't his comment go against: https://www.ecmweb.com/qampa/code-qa-grounding-and-bonding-remote-building

• Well he's wrong. You need additional grounding rods at any outbuilding. A voltage differential between the ground locations is why you want it. In a situation where the earth at your dock is 60V hotter than the earth at your house, you need to suppress that or else you're going to get bit. And getting bit at dockside can cause electrical drownings so this is a showstopper. the youtube guy is worried it will cause spurious current flow on your ground wires, who cares? – Harper Jan 2 at 5:55
• I figured as much given that there is a code for this circumstance. But was wondering if I was missing something. – Alex Jan 2 at 6:00
• I think the Youtuber is confusing some related but separate ideas - although it''s important that the service neutral / grounded conductor be bonded to the grounding electrode system at a single point, this doesn't mean there should be only one grounding electrode. – batsplatsterson Jan 2 at 12:21