GFI

weinie · May 21, 2012

The neutral (white) and ground (green) are not interchangeable in AC wiring.
Neutral goes to neutral and green goes to green.
If your shore power is very old and dosn't have a ground connection, you can leave it off and the GFCI will still work as it detects current differential between the hot and the neutral wires.

Ross · May 21, 2012

I think that you have some wiring that needs tracing and inspection. A ground fault circuit interrupter compares the current in the hot leg and the neutral leg and senses any current in the ground conductor. 5 Milliamps will trip the breaker. I have seen rust crystals under romex staples sufficiently to trip a gfci in wet weather.

Bob J. · May 22, 2012

I forget the technical term but many of the new GFI's trip out on voltage drop.

Maine Sail · May 22, 2012

AC white and AC green should NEVER be grounded or tied together on-board the boat. The ONLY time this is acceptable is at a new on-board "source" of AC power such as an inverter or gen set. Once white & green leave the new "source" they are never to be tied together again.

Green goes to the ships DC ground or ground bus and white to its own isolated bus which goes directly back to shore, via the shore power cord. If your GFCI is tripping you likely have some wiring issues to work out on to of your AC green/white tie in......

weinie · May 23, 2012

Webone said:
One more thing, how does shore power get grounded if the grounds are move to the boat dc bar??

Say a hair dryer on your boat shorts out. What has happened is that a positive or neutral wire has made contact with the metal casing of the dryer. If there was no green ground wire, your body would become the path of least resistance for the current. However, if a ground wire is attached to the casing, then the ground wire would carry that current instead and no electricity would pass through your body.

Where does that green ground wire go? Well, from your AC outlet on your boat it should go to a bus where all the other AC green ground wires from all the other AC outlets and equipment go. This is not the same "ground" as the black DC negative current from your batteries nor is it the AC white neutral bus! This green ground bus must also have a green wire going to your shore power socket on the side of your boat. When you plug your yellow shore power cord into the socket, you are now connecting the ground bus on your boat to the ground prong on your dock. In essence, the case of your hair dryer now has a direct electrical path back to the shore should a short occur.
Now, the "green" AC ground bus on your boat should also, in fact, go to to the engine block. Any device like a battery charger or inverter poses the danger that an AC circuit could short into a DC circuit. Since the DC circuit is already grounded to the engine block and hence the water, any AC short into your DC wiring could electrocute anyone in the water. But with the engine connected via a wire to the ground bus and hence the shore power ground, any short will be conducted more readily by the shore power ground wire rather than the water.

Therefore, to answer your question, the shore power is NOT grounded to the DC bus bar. But they do both ground to the engine block. One thing to keep in mind: DC circuits use two wires: a positive (red) and negative (black). AC circuits use three wires: a hot (black), neutral (white), and ground (green). The two circuits should never be combined.

Maine Sail · May 24, 2012

weinie said:
Where does that green ground wire go? Well, from your AC outlet on your boat it should go to a bus where all the other AC green ground wires from all the other AC outlets and equipment go. This is not the same "ground" as the black DC negative current from your batteries.

Yes it absolutely is the same ground as your vessels DC system.The green AC wire is bonded directly to the ships DC ground.

weinie said:
nor is it the AC white neutral bus!

AC is tied to nothing on the boat but a reverse polarity indicator, AC devices, and back through the shore power cord. Green has TWO paths back to earth one is through the vessels DC ground and one is back through the shore power cord.

White and green AC should not be connected on-board unless at a "source" such as an inverter, generator or isolation transformer.

weinie said:
This green ground bus must also have a green wire going to your shore power socket on the side of your boat. When you plug your yellow shore power cord into the socket, you are now connecting the ground bus on your boat to the ground prong on your dock. In essence, the case of your hair dryer now has a direct electrical path back to the shore should a short occur.

And it is due to the massively high failure rate of dock power systems, shore power cords etc. that the AC green has TWO paths to ground. When buffy & skippy pull away from the dock in theier brand new Sea Ray and yank the dock pedestal out by the roots who do you think fixes it? Yep usually Darrell & his other brother Darrell.... Dropped dock grounds are VERY, VERY common hence the green AC ground tied to the DC ground for the shortest path to earth if the shore power ground is dropped.

weinie said:
Therefore, to answer your question, the shore power is NOT grounded to the DC bus bar. But they do both ground to the engine block. One thing to keep in mind: DC circuits use two wires: a positive (red) and negative (black). AC circuits use three wires: a hot (black), neutral (white), and ground (green). The two circuits should never be combined.

Does not matter where in the system the AC green ties in it is all earth potential. It should all be tied into the ships ground or engine anyway. What you want to avoid is the potential for AC green to carry any AC or DC current. Most builders simply jumper over to the DC neg bus behind the AC / DC panel and this meets the ABYC standards. There can be some good reasons to tie to the DC buss instead of the engine in an "unknown" system. If you have a bad engine ground it the large wire where your starter or alternator current flows the AC green wire, if it has alternate tie points, and it can be forced to pick up some of the slack. Being VERY small in comparison to the large 2GA to 4/0 wire used to start motors this wire can be vaporized if the engine ground drops. I actually got to see this in real life with a water pump wire, which never should have been grounded to block anyway... Bolt fell out of the engine for the large neg wire and the other smaller grounds attached to the motor tried to take up the slack, rather unsuccessfully.. A rare occurrence but one that has potential. This is why I am a proponent of one single engine ground connection. I generally prefer a bus close to the motor with one jumper going to the starter ear or as close to it as possible.. If the bolt falls out you'll know before lighting some smaller wires on fire..

Crazy Dave Condon · May 25, 2012

On the newer boats, you will note that the DC ground formerly black is now yellow as it was confusing when you saw the AC black hot wire. FYI

Ross · May 26, 2012

AC hot and AC neutral should be connected only to the shore power hot and neutral. The ac shore power ground should be connected to the boat's ground buss.
The power grid uses center tapped transformers to supply 120 and 240 volts to the house the center tap is taken to ground (earth). In your house the ground buss is taken to earth by a heavy solid copper wire connected to a rod driven deep into the earth. The neutral wire is brought to the house as the strand that supports the two insulated conductors. The thick cable that bring the power into the house has two insulated conductors and a spiral wrapping of stranded wire that carries the neutral. Therefore in proper land based power distribution the neutral is grounded at the transformer and at the breaker box.
Water does not make a good connection to the earth and is not a very good conductor. The result is you can't depend on a neutral ground on the water.
You should therefore have a separate neutral buss.