I am going to install an inverter in my sailboat. The connections on the input side of the unit are positive, negative, and a ground connection. Should I connect the ground on the inverter to the ground wire on the keel bolt?
SailNet repsonds:
Thanks for the question. For starters, working with AC power is serious business because it can injure or kill you if you don’t know what you’re doing. I’ll leave your electrical skills assessment up to you, but AC electricity needs to be treated with the utmost respect and caution. Needless to say all electrical sources should be turned off, unplugged, disconnected or otherwise taken out of the electrical equation, including shorepower, wind generators, inverters, and solar panels.
There are several things to consider when it comes to installing an inverter/charger on the boat and grounding the chassis of the unit. On many boats the AC ground is intentionally or otherwise isolated from the DC ground, or DC negative. Done intentionally, this prevents galvanic corrosion while connected to shore power, but raises some safety issues. If the grounds are isolated and a short circuit were to develop between the AC hot and the boats’s DC system, DC ground, or bonding system, there would not be enough fault current to trip the AC breaker on the dock. In this scenario, the whole boat would become energized at a 120-volts. A person could be electrocuted by touching the boat, and the electric field created in the water could also paralyze unlucky swimmers.
To avoid this ABYC recommends grounding the inverter/charger chassis to the DC ground, and to also add a ground wire between the AC ground bus and DC ground, since this is where the primary bond between the two grounds should be established anyway. Then, add a galvanic isolator or isolation transformer at the shore power inlet to prevent galvanic corrosion.
For additional information on this topic, check out Tom Wood's feature article 110 Volts on Board.
