AC DC common ground

[goboatingnow]

Originally Posted by s/v Jedi

Sorry, but this is wrong. First, ESD should be called Electric Shock Drowning, because ESD is something entirely different. Second, getting electrocuted in water was discovered very shortly after the discovery of electricity. Kevin Ritz became known as an advocate to prevent these deaths after his son died during swimming in their marina.



According to Wikipedia:







and this is for the simple reason that the USA is about the only place that allows electrical installations near the water without the use of RCD safeties. This is what kills Americans, not a missing bonding jumper between AC and DC systems aboard boats.



All this anecdotal evidence and name dropping has no merit when science simply points to the reason for the danger and that is a return path via ground. Even all of the ABYC, Kevin Ritz and Dave Rifkin feature drawings showing this return path via ground as the killer.



I believe they also call for an RCD (they ramble on about inventing ELCI because they didn’t get that RCD was invented 30 years prior and in use worldwide for decennia) as being the final solution, yet the US still does not have this.



Instead, they keep piling onto a heap of BS with methods to fight symptoms instead of fixing the cause. A very silly and debatable path…



Luckily boats can just be done with all that BS and install an isolation transformer, WHICH BREAKS THE RETURN PATH VIA GROUND and thus eliminates all risks.



I will attach my diagram once again: do this and your boat is safe, your crew is safe and anyone in the water around you is safe. All other options are inferior and will cost you dearly in repairs as described in previous posts.

This diagram is good

[goboatingnow]

Originally Posted by s/v Jedi

Indeed, and after all that fighting and all the deaths, still no RCD safety required near the water. Well, for boats they now do, but it must be done shore side just like in the rest of the 1st world.



Isn’t that the NEC who is at fault?

Yes the nec is clearly out of step with the rest of the world in this regard.

[team karst]

NEC 2020 addresses improvements in dock safety.

https://www.tradeonlytoday.com/indus...n-requirements

i am not so sure about rework of existing installs, though. And then you have the issue of the AHJ actually adopting the latest NEC standard.

[s/v Jedi]

Originally Posted by pdqsailor

The Hammond isolation transformer I have has no input for ground - just line and neutral.. The question now is do I maintain the ground connection to the shore power ground from the ships wiring or go with a floating ground and GFCI protection only on the boat - which I am fine with BTW...

Look for ground terminals on the housing etc. The outer housing should be connected to ships ground only. Often there is a terminal for a ground conductor from shore ground; if your transformer doesn’t have that, then leave the shore ground wire disconnected in the transformer. I crimp an isolated butt connector to it so it can’t make accidental contact with something.

You want this ground wire in the cable to protect that cable.

I don’t understand the other things you write? An isolation transformer means you isolate all conductors from shore, especially the ground. When you connect shore ground to your boat, you defeat the whole purpose.

Follow my diagram precisely. Any deviation can have catastrophic consequences. The pictured Victron transformer has a ground input terminal that normally connects to nothing. Simulate that like I explained above.

For this with a Victron transformer: it comes with a ground jumper which must be installed when you haul out and connect to power while on the hard. Make sure this is not installed.

After installation, use a multimeter in resistance mode and test the shore ground to ships ground. It should show infinite resistance, meaning there should be no connection whatsoever.

[goboatingnow]

Agreed no connections to ground unless absolutely necessary on water that’s not ground connections it defeats the whole point.

[goboatingnow]

Don’t see your issue with wiring isolating Seems very straightforward a few RCBOs and no grounds

[team karst]

Just the transformer is likely to have some leakage current into the core/shield/housing. Not much, but certainly measure able. Mostly capacitive I suspect.

[Bowdrie]

Originally Posted by team karst

Mostly capacitive I suspect.

I'm not sure, but might that not be similar to the "Phantom power" in recording studio boards that is used to power low-impedance capacitor microphones that are transformer coupled?
I've observed a "transformer effect" in wiring bundles that had both AC and DC wiring in them.
With the AC conductors active and the DC conductors in-active it was possible to measure a small AC component on the DC conductors.
The AC wires acting as a primary winding surrounded by DC wires that were acting as a secondary.
Of course, without a real core, (air core?) and no real "winding" to speak of, the potential was quite low, and no currant flow could be detected, (no place to go/no path).
However, on an old-fashioned battery charger if the filter caps get leaky an AC ripple can be superimposed over the DC output and it will kill a battery in short order.

[team karst]

Yeah; electricians mention "phantom" power a lot, when probing V in unknown wiring runs, where a wire is an open circuit on both ends. Just simple capacitive coupling from usually a low impedance circuit into a hi-Z circuit will make measurable voltage.
Saying that, it has killed linemen. Failing to earth one phase on a transmission line has produced plenty of voltage and Amps to kill if touched. Even though both ends are open.

[Bowdrie]

Originally Posted by team karst

Yeah; electricians mention "phantom" power a lot, when probing V in unknown wiring runs, where a wire is an open circuit on both ends. Just simple capacitive coupling from usually a low impedance circuit into a hi-Z circuit will make measurable voltage.
Saying that, it has killed linemen. Failing to earth one phase on a transmission line has produced plenty of voltage and Amps to kill if touched. Even though both ends are open.

Interesting.
I watched the linemen as they were replacing the main transformer that powers our whole marina.
The transformer was ~the size of a commercial washing machine, the input was 7,200V from the main 14,400V lines nearby.
They were VERY careful, using long non-metallic "arms" to make the connections.

[Pete7]

Interesting if a little confusing thread for non electrical experts and differing standards across continents.

So we have a UK yacht with the AC earth (ground) connected to the DC negative (neutral) going to a large zinc anode. The only bonded items are the rudder shaft, p bracket and engine. No bonding to any seacocks.

The AC circuit is; shore power pedestal with RCD socket, to on board box with RCD, to mains 230v distribution panel with double pole circuit breaker like Jedi's picture. This is the original high quality fitout by Moody. Ring main around the yacht with 4 AC sockets. UK plugs all have fuses.

Only changes I have made are adding an inverter to the 12v circuit and earthed the case to the 12v DC negative (neutral) in accordance with Sterling Power's recommendation. Inverter has single outlet with active RCD breaker powering 230v kettle or toaster etc via red socket, to clearly identify it as "inverter". No connection of this circuit to the original Moody installation or likely to be, just not needed.

We use very little shore power since installing lots of solar and have noticed zincs last 18 - 24 months rather than previous 12 months.

Is there anything else I should consider? Galvanic isolator for occasional shore power use? Don't want to go down the transformer route.

Thanks Pete

[s/v Jedi]

Originally Posted by Pete7

Interesting if a little confusing thread for non electrical experts and differing standards across continents.

So we have a UK yacht with the AC earth (ground) connected to the DC negative (neutral) going to a large zinc anode. The only bonded items are the rudder shaft, p bracket and engine. No bonding to any seacocks.

The AC circuit is; shore power pedestal with RCD socket, to on board box with RCD, to mains 230v distribution panel with double pole circuit breaker like Jedi's picture. This is the original high quality fitout by Moody. Ring main around the yacht with 4 AC sockets. UK plugs all have fuses.

Only changes I have made are adding an inverter to the 12v circuit and earthed the case to the 12v DC negative (neutral) in accordance with Sterling Power's recommendation. Inverter has single outlet with active RCD breaker powering 230v kettle or toaster etc via red socket, to clearly identify it as "inverter". No connection of this circuit to the original Moody installation or likely to be, just not needed.

We use very little shore power since installing lots of solar and have noticed zincs last 18 - 24 months rather than previous 12 months.

Is there anything else I should consider? Galvanic isolator for occasional shore power use? Don't want to go down the transformer route.

Thanks Pete

Difficult… I only recommend what is in my diagram and don’t fancy what you describe at all. A Galvanic isolator is one little step in the right direction but for the distance to go and you hardly using shore power, I am not sure it matters.

You do have a RCD breaker on the shore power inlet, right?

[goboatingnow]

Originally Posted by Pete7

Interesting if a little confusing thread for non electrical experts and differing standards across continents.



So we have a UK yacht with the AC earth (ground) connected to the DC negative (neutral) going to a large zinc anode. The only bonded items are the rudder shaft, p bracket and engine. No bonding to any seacocks.



The AC circuit is; shore power pedestal with RCD socket, to on board box with RCD, to mains 230v distribution panel with double pole circuit breaker like Jedi's picture. This is the original high quality fitout by Moody. Ring main around the yacht with 4 AC sockets. UK plugs all have fuses.



Only changes I have made are adding an inverter to the 12v circuit and earthed the case to the 12v DC negative (neutral) in accordance with Sterling Power's recommendation. Inverter has single outlet with active RCD breaker powering 230v kettle or toaster etc via red socket, to clearly identify it as "inverter". No connection of this circuit to the original Moody installation or likely to be, just not needed.



We use very little shore power since installing lots of solar and have noticed zincs last 18 - 24 months rather than previous 12 months.



Is there anything else I should consider? Galvanic isolator for occasional shore power use? Don't want to go down the transformer route.



Thanks Pete

Your setup is as perfect typically euro boat

Yes add a GI, make sure incoming earth is not Dc bonded or the engine isn’t bonded etc.

[Pete7]

Originally Posted by s/v Jedi

Difficult… I only recommend what is in my diagram and don’t fancy what you describe at all. A Galvanic isolator is one little step in the right direction but for the distance to go and you hardly using shore power, I am not sure it matters.

You do have a RCD breaker on the shore power inlet, right?

Jedi, Yes now pretty standard across most of Europe including inland rivers and canals. Older pedestals sometimes have a mix of 1 x 13A and 3 x 6A rather than 4 x 13A, so its first mouse to the cheese that wins. Though we can survive on 6A at 230v. 32A supply becoming popular in marinas for AC and cooking on gin palaces.

Originally Posted by goboatingnow

Your setup is as perfect typically euro boat. Yes add a GI, make sure incoming earth is not Dc bonded or the engine isn’t bonded etc.

Thank you, we will add a GI and check the earth path. Both AC earth and engine are bonded to the anode via the 12v negative DC circuit at present. This is after the RCD and the 230v AC panel circuit breaker. GI will be installed as the first item after the yachts AC input socket.

Pete

[s/v Jedi]

Originally Posted by Pete7

Jedi, Yes now pretty standard across most of Europe including inland rivers and canals. Older pedestals sometimes have a mix of 1 x 13A and 3 x 6A rather than 4 x 13A, so its first mouse to the cheese that wins. Though we can survive on 6A at 230v. 32A supply becoming popular in marinas for AC and cooking on gin palaces.



Thank you, we will add a GI and check the earth path. Both AC earth and engine are bonded to the anode via the 12v negative DC circuit at present. This is after the RCD and the 230v AC panel circuit breaker. GI will be installed as the first item after the yachts AC input socket.

Pete

I was wondering if you have an RCD at your shore power inlet.

The bonding you have makes me shudder… AC ground to engine and anode… brrrrr

I recommend, after installation of the GI, to isolate ships ground from both the engine and the anodes. Use it for the AC outlets, metal housings of inverter/charger etc. but no link to DC or any other metals on board at all.