Green Wire Confusion

[YourBOATDoctor]

The grounding is attached at the inverter, and to the gen set, and then to the dockbox if I read that correctly. Sounds correctly connected to the power sources but hard to tell.

The green wire could play many roles, including bonding, lightening protection and SSB interference prevention, but its most important role is to prevent lethal shocks. This gets a bit confusing on boats with multiple AC power supplies (a genset, an inverter, and shore power) when it comes to switching from one source to another. The system must be configured so that both the hot (black) wire and the neutral (white) wire get switched from one source to the next,--- but the green wire doesn’t. The grounding connection must always be continuous to the ground point at the power source. The green wire, when the system’s operating normally, shouldn’t carry any current at all. But if there is a short circuit, the current is delivered to the metallic case of an appliance. Without an alternate route for the fault current to travel back to the source of power, the case of the equipment becomes live. If a person touches the case, her body becomes the alternate route to ground, bypassing the neutral (white) conductor and exposing him to full AC voltage potential—likely a lethal encounter or a very bad day at the least Here’s where the grounding wire comes in.

This third wire, attached to the case of the appliance, carries the fault current back to the power source and trips the circuit breaker, shutting off current flow. Marine-grade circuit breakers are designed to be “trip-free,” which means the circuit can’t be turned back on until the problem is solved. In the grounding system in AC circuitry, the green wire must take a direct path back to the source of power and at that point be connected to the neutral conductor for the scenario above to play itself out. Neutral and grounding are only connected at any AC power source --including Gen set /inverter. So while the green wire may also being double duty for bonding, best to have a second opinion be sure if there is any doubt on the wiring. Cheers,.

Cpt Lori

[smac999]

Originally Posted by btrayfors

Authorities differ over whether or not to tie AC ground to DC ground on the boat. Both are in common use.

Bill

If you don't. And an ac wire shorts against a DC neg cable, bonding system, throughhull, mast rigging plates, engine block etc. then you just put ac into the water through your though hulls and will kill swimmers and divers at the marina. Though most Likly only in fresh water not salt due to conductivity.

With them bonded you would trip the ac breaker.

An rcd, gfci, or Elci would prevent it, but they are not used in North America, yet anyways.

[hellosailor]

"the ac ground, dc ground, and ships bonding all get joined in north America."
Joined by whom? The wiring fairy?


Grounding and bonding and whether or not to join the two systems have been a running debate for decades. There's no right or wrong on that, there are good reasons to join them, and to keep them separate.


Stick to a mooring, keep AC mains power off the boat, and the choices become much simpler.

[Maine Sail]

In the US I don't know of any "debate" about whether AC Green/grounding is tied to ships ground, which is also DC ground..

If someone can point me to a credible expert who disagrees with this please let me know... It is a safety issue, human safety..


Quote Nigel Calder:

"The AC grounding to DC negative connection should never be cut. The only correct ways to galvanically isolate an AC circuit are with a galvanic isolator or an isolation transformer."

Here is a good article that explains the reasons for bonding AC to DC on-board the vessel..

Earthing On Boats

[hellosailor]

"In the US I don't know of any "debate" about whether AC Green/grounding is tied to ships ground,"


I didn't suggest there was. I referred to joining the GROUND and the BONDING systems.


Bonding has nothing to do with joining the AC and DC systems. I'm talking only about keeping all the metal bits at the same galvanic level by BONDING them to each other.


I've read the arguments, by all the professional long-term authors, often enough over the years. Should we have meat of fish tonight? Some arguments will never be resolved objectively.

[smac999]

keeping every through hull not connected to anything is best for corrosion.




unfortunately the codes are written for safety, not for performance. and sadly the codes are written and changed throughout time because people died and they investagated why.


the progression from unbounded, to bonded together, to connected to dc neg happened over many years due to safty issues.

[rwidman]

Originally Posted by smac999

keeping every through hull not connected to anything is best for corrosion................

Some folks believe that. Most experts do not.