Electrical Grounding on Boats and RVs

One of the least understood aspects of boats' and RVs' electrical system, and the most troublesome, is the proper method of grounding. This article is intended to clarify the questions on electrical grounding on boats and RVs.

We often get questions on whether AC or DC electrical equipment should be grounded to the boat's or RV's bonding system. There are four separate ground systems: (i) DC ground, (ii) AC ground (neutral), (iii) AC grounding (or bond), and (iv) the boat's or RV's bonding system. 

typical boat installation with battery and inverter

The Boat

The AC ground and grounding systems are "free floating," meaning that they do not ground on the vessel, but only to shore. The (ii) AC ground, or neutral, is a current carrying conductor, and could be the source of many troubles because it's not actually the grounding. The (iii) AC grounding, bond or green wire is the "safety" intended to channel current safely to ground in the event of a short circuit. Both of these circuits are capable of conducting current and can result in electrolysis on a boat when there are system faults with the dock or marina wiring.

The battery is the only point where the (i) DC side is grounded. It is also a "free floating" system in which nothing is ever grounded to any metallic part of the vessel, especially not the bonding system. Just like a car sitting on rubber tires, completely insulated from earth potential, the battery itself provides the negative potential.

The (iv) bonding system, also green wire, has nothing to do with electrical systems. Underwater metals are simply wired together to equalize differences in potential of different kinds of metal. Nothing should ever be grounded to the bonding system. The (iii) bonding system -or the common grounding system- may be a bus bar with a strip with screws or clamps. It may be a grounding wire running from the bow or the stern, hidden somewhere behind a panel and it will connect to (iv) the vessel's bonding system which could be the keel or a metal strip on the hull. Your boat's manual will provide the location.

charge controller installation on a boat

The RV

Grounding of an RV and a boat are almost the same. The only difference is on the (i) DC ground where the negative DC wires could be directly connected to the chasis of the vehicle rather than connecting via a wire. In this case, the common grounding wire is the chassis.

charge controller installation on an RV

I hope this was a helpful overview. Please remind yourself that the grounding could be very hazardous both on AC and DC side. Unless you are absolutely certain of what you are doing, consult to an electrician when wiring your electrical system.

Here are some resources I've used for putting this article together: