Neutral to Ground, with shore power?

[Jdege]

I'm currently reading Don Casey's "Sailboat Electrics Simplified", and I ran into some advice that seems not quite right:

A look inside your breaker panel at home will reveal that neutral wires and grounding wires are all connected to the same bus bar. Connecting the neutral wire to the grounding wire on a boat makes the underwater hardware a current-carrying path to ground, an unhealthy circumstance for nearby swimmers. The potential for reversing polarity means appliance cases and wiring boxes might also become energized. On a boat plugged in to shore, the neutral (white) conductor and the grounding (green) conductor MUST NEVER BE DIRECTLY CONNECTED.

Unless I'm reading this wrong, this is exactly wrong. Yes, there are issues that must be dealt with to prevent leaking current when plugged into a miswired shore power circuit, but my understanding was that you needed to identify these, and deal with them, rather than to simply not tie grounded to grounding. And that unless you'd installed an isolation transformer, you did want to tie neutral to Ground.

Casey's book dates to 1999. Is this an instance of code and usual practice having changed? Or is he simply wrong?

[PippaB]

Originally Posted by Jdege

...Casey's book dates to 1999. Is this an instance of code and usual practice having changed? Or is he simply wrong?

He’s still right and that’s still best practice and code. Neutral and ground should only ever be tied together at the source, in the case of shorepower that is somewhere at the panelboard in the marina that serves your shorepower connection (if shorepower and ship-derived power share circuits).

Note that it becomes different if you have a generator or inverter aboard, those are then power sources and neutral may get tied to ground at the generator/inverter, but most best practice says you break that connection when connected to shore power.

Another exception is with an isolation transformer, the transformer can become the power source, and then connection may be warranted.

A couple of more recent articles (if you can’t access ABYC standards):

https://stevedmarineconsulting.com/n...d-demystified/

https://stevedmarineconsulting.com/w...mers181-04.pdf

https://abycinc.org/blogpost/1678504...Shock+Drowning

[rslifkin]

For shore power, the neutral to ground bond should be in the pedestal or distribution box before it and not on the boat. You do bond neutral and ground on the boat for generator or inverter power. Isolation transformers will also want a neutral ground bond on the boat.

It's normal to tie AC and DC grounds together on the boat. And if you're not using an isolation transformer, it's a good idea to have a galvanic isolator in the shore power ground.

[Jdege]

Originally Posted by PippaB

He’s still right and that’s still best practice and code. Neutral and ground should only ever be tied together at the source, in the case of shorepower that is somewhere at the panelboard in the marina that serves your shorepower connection (if shorepower and ship-derived power share circuits).

Note that it becomes different if you have a generator or inverter aboard, those are then power sources and neutral may get tied to ground at the generator/inverter, but most best practice says you break that connection when connected to shore power.

So, if I install something like a Victron inverter/charger, will it unbind neutral to ground, when shore power is connected, and bind it otherwise?

[smac999]

Originally Posted by Jdege

So, if I install something like a Victron inverter/charger, will it unbind neutral to ground, when shore power is connected, and bind it otherwise?

yes it will

so will an onboard gen if wired and switched correctly. only when the gen is used it will bond the g-n on the boat

[Jdege]

I'll answer my own question.

Looking around, I found this:

https://www.victronenergy.com/upload...limited-EN.pdf

And in it:

An AC power source needs to have a Neutral to Earth (MEN link) so that and RCD can operate. This is the case for the grid, but also if the AC source is a generator or an inverter.

• If the AC power source is the grid, the MEN link will have been hard wired in the switchboard where the grid enters the installation.
• If the AC power source is a generator, the MEN link will have been hard wired in AC connection terminals of the generator.
• If the AC power source is an inverter, the MEN link will have been hard wired either at the inverter’s AC connection or in the installation switchboard.

But when combination inverter/charger units are used, the MEN link is less straight forward.
The inverter/charger unit has two different modes of operation:

• In inverter mode it is operating as a standalone inverter and is the main power supply in the system.
• In charger mode it will feed through grid or generator power into the system.

When the inverter/charger is inverting and acting as a power supply, it will have to make an independent MEN link. But when it is feeding through a generator or grid supply, the incoming supply has to have the MEN link instead of the inverter/charger.

Victron inverter/chargers contain an internal ground relay. This relay automatically makes or breaks the connection between earth and neutral.

[rslifkin]

Originally Posted by Jdege

So, if I install something like a Victron inverter/charger, will it unbind neutral to ground, when shore power is connected, and bind it otherwise?

Yup, my Victron inverter has a relay to accomplish that when it transfers between shore and inverter power.

[Mike Banks]

NEVER connect the shore power earth to your vessel--always use an isolating device or an isolating transformer--The cheapest option is to buy a heavy duty battery charger, use it to charge up your batteries and then set it to float charge, then use all DC appliances or use an inverter to power small-draw items such as electric fans.

But by far the best option is an isolating transformer so you can wire your vessel for shore power, and run 12 volts DC for everything else..

[Jdege]

Originally Posted by Mike Banks

NEVER connect the shore power earth to your vessel--always use an isolating device or an isolating transformer--The cheapest option is to buy a heavy duty battery charger, use it to charge up your batteries and then set it to float charge, then use all DC appliances or use an inverter to power small-draw items such as electric fans.

But by far the best option is an isolating transformer so you can wire your vessel for shore power, and run 12 volts DC for everything else..

The choices seem to be four:

• Never use shore power, or
• Use an isolation transformer, or
• Use a galvanic isolator, or
• Be stupid and watch your prop corrode and fall off.

My intent is to eventually install sufficient solar as to not have to rely upon shore power, but I can't do everything at once.

Isolation transformers take up a lot of space, and cost too much for something whose need I hope to eliminate next year, so I was planning on installing a galvanic isolator.

[goboatingnow]

Originally Posted by rslifkin

For shore power, the neutral to ground bond should be in the pedestal or distribution box before it and not on the boat. You do bond neutral and ground on the boat for generator or inverter power. Isolation transformers will also want a neutral ground bond on the boat.

It's normal to tie AC and DC grounds together on the boat. And if you're not using an isolation transformer, it's a good idea to have a galvanic isolator in the shore power ground.

No it’s not normal anywhere except in the US to tie AC and DC grounds together and in general it’s a really bad idea. Use a RCBO and don’t tie grounds together. That’s current EU RCD procedure.

[sailcrazy]

following. FWIW....we installed a Victron Auto-Sensing Isolation Transformer, to convert incoming 110v Shore power to the 230v our (Asia-Built) boat requires. We still had considerable galvanic action, as the anti-foul paint was being "blown off" around some of the Bronze thru-hulls. I could not find any mis-wiring, so I ended up installing a Galvanic Isolator as well, just ahead of the Isolation Transofrmer. We have not had an issue since!
(

[smac999]

Originally Posted by sailcrazy

following. FWIW....we installed a Victron Auto-Sensing Isolation Transformer, to convert incoming 110v Shore power to the 230v our (Asia-Built) boat requires. We still had considerable galvanic action, as the anti-foul paint was being "blown off" around some of the Bronze thru-hulls. I could not find any mis-wiring, so I ended up installing a Galvanic Isolator as well, just ahead of the Isolation Transofrmer. We have not had an issue since!
(

That galvanic isolator is not doing anything unless you wired the transformer wrong. Like putting the ground jumper on intended for on the hard use. Or the unit is bad.


I would have figured out what was really happening.

The green wire from the shore inlet literary does not go anywhere or connect to anything once inside the transformer. It’s only there incase the transformer fails.

With an iso transformer (or no shore power at all). You still have issues on the boat that will blow the paint off. Like battery voltage getting into the bonding system.