I have a scenario where I am connecting a connex box that has a US Style single phase 120/240V Panel to a cruise ship that is in dry dock. The ship supplies a EU style weatherproof connector (basically a receptacle) with 230VAC, a neutral, and a ground. I would then obviously need to use an isolation transformer to create 2 phases of 120VAC 180 from each other with a center tap neutral. The confusing part is I know I use the ships ground to connect to the Transformer case, but I also know that according to NEC 250.30 the transformer has created a separately derived system that would then need the neutral bonded to the ground either in the transformer or at the first means of disconnect. My main question is should the ground coming from the ship also be connected to the ground used in the connex box or can this cause issues on the ship side?
Bonding Neutral to Ground after Isolation Transformer?
- Thread starter zach_2004
- Start date
TwoBlocked
Senior Member
- Location
- Bradford County, PA
- Occupation
- Industrial Electrician
You can't go wrong by bonding all metal together in order to strive for an equipotential situation. One odd thing you may see is a small DC current in the bonding due to the ship and/or drydock and/or shore facilities using impressed cathodic protection. Wouldn't hurt to have a discussion with the shipyard about that. They may need to adjust their equipment.
I am right about the neutral and ground should be bonded on the secondary side of the transformer, correct?
TwoBlocked
Senior Member
- Location
- Bradford County, PA
- Occupation
- Industrial Electrician
I bond it there in the transformer and at the service disconnect, which in your case would be the first breaker.
Others may disagree.
zbang
Senior Member
- Location
- Roughly 5346 miles from Earls Court
Think of it this way- for a hot to ground fault, the only way to trip the breaker is for current to flow over the grounding conductor, then through the bond, to the actual neutral and complete a circuit. (I put the bond at the transformer, but that's personal preference.)
Big question- does the NEC apply at all? If the conex box is on the ship, I'd be speaking with the shipboard electricians. It's possible that they might want an isolated system with ground detectors. Shipboard wiring can be quite different from land-based wiring.
Big question- does the NEC apply at all? If the conex box is on the ship, I'd be speaking with the shipboard electricians. It's possible that they might want an isolated system with ground detectors. Shipboard wiring can be quite different from land-based wiring.