Shore Ground NOT Connected to Isolation Transformer

[s/v Jedi]

Originally Posted by Pelagic

So I switched over to a new 100ft Shore cable yesterday from my somewhat frayed old one..... this cable was spliced on to a 50ft extension by the Shipyard before plugging into the shore pedestal
AT THE SPLICE THE ELECTRICIAN HAD NOT CONNECTED THE GROUND WIRE ...Just L & N
Part of my querie on first post .

So I was planning on installing the new RCBO before the onboard Junction box and Isolation Transformer today.....

But does that do anything given the way the yard wired the splice??

The splice is bad. Just follow the diagram I posted and all will be okay. If you put an ELCI on the primary side of the transformer then you waste money but it doesn’t hurt the safety either… it’s a feature not used, that’s all.

My diagram has actual conductors and where they go. After install, test with a multimeter that there is no connection between PE terminals (ground conductors) of input and output of the transformer. If there is, remove the jumper causing that connection.

Also, note that the ships ground in my diagram is not connected to DC negative, not to engine blocks etc.

[Pelagic]

Originally Posted by s/v Jedi

The splice is bad. Just follow the diagram I posted and all will be okay.

NOTED


Also, note that the ships ground in my diagram is not connected to DC negative, not to engine blocks etc.

Is that because you have an Aloy hull and everything is "above ground"?

[goboatingnow]

Originally Posted by Pelagic

So I switched over to a new 100ft Shore cable yesterday from my somewhat frayed old one..... this cable was spliced on to a 50ft extension by the Shipyard before plugging into the shore pedestal
AT THE SPLICE THE ELECTRICIAN HAD NOT CONNECTED THE GROUND WIRE ...Just L & N
Part of my querie on first post .

So I was planning on installing the new RCBO before the onboard Junction box and Isolation Transformer today.....

But does that do anything given the way the yard wired the splice??

Rcbo does not need an earth wire to work

[s/v Jedi]

Originally Posted by Pelagic

Is that because you have an Aloy hull and everything is "above ground"?

We are fiberglass. Most of the world do not connect AC to DC systems and keep them separated. For alloy hulls it becomes crucial that their hull is completely isolated from all electrical systems. Many have an alarm system with a silver chloride electrode to ensure the hull is safe.

GoBoating writes that rcbo doesn’t need the ground wire and this is true. All these systems, incl simple gfci outlets, compare the current in the L and N conductors and trigger when the difference is more than the rated value, like 30mA or 10mA etc.

You need the ground conductor in the shore power cable to help protect the circuit all the way to the isolation transformer input.

[Fishspearit]

Everybody can make their own choice on what standard they want their boat wired to. ABYC says to connect the AC and DC ground even with an isolation transformer.

There is a reason why ABYC recommends it. Think about what happened with your shore power cord that was put together without a ground connection. Think about all the boats out there without isolation transformers. Any short to ground on any AC equipment has no path back to its source in this case if the AC and DC grounds aren't connected. The water is the only path back without causing an electrical shock hazard, tripping your ELCI or RCB. This is the same reason there is greater risk involving AC systems when boats are on the hard, yards are notorious for lacking good safety grounds on their yard power supplies.

Even with the isolation transformer, wiring faults happen in the real world. Someone can see that loose black wire and assume it's a dc ground, connects it back to a ground bus. A screw accidently put into a wire bundle, heat melting insulation and the wire touches something on the DC side, chafe, etc.

ABYC errs on the side of safety in this case, which is probably what a standards setting organization should do. Like it or not, that's the standard that US boats will be surveyed to, and that's the standard that insurance companies and civil lawsuits in the US will be decided against.

[bdgWesternMass]

Originally Posted by goboatingnow

It’s not safer.

I certainly don't have any authority to say which is safer.


I think to believe connecting shore ground to boat ground is safer. One would have to have more faith in shore power than the breakers on the boat system.

(and add no safety value to minimizing galvanic corrosion exposure)

Is that the "trade off" between the two installations ?

[Fishspearit]

Originally Posted by bdgWesternMass

I certainly don't have any authority to say which is safer.


I think to believe connecting shore ground to boat ground is safer. One would have to have more faith in shore power than the breakers on the boat system.

(and add no safety value to minimizing galvanic corrosion exposure)

Is that the "trade off" between the two installations ?

It has nothing to do with galvanic corrosion, the advantage of wiring as an isolation transformer versus a polarization transformer is to prevent stray current corrosion without needing a galvanic isolator. In the case of a steel boat like Pelagic the isolation transformer is the better choice because the safety advantage of the polarization transformer is small, and the risk of stray current corrosion on a metal hull is always great.

[goboatingnow]

Ten primary safety of an isolating transformer is that it removes earth ( sea water ) as a return path , it’s therefore quite nonsensical to then reintroduce that relationship deliberately again

[bdgWesternMass]

I see the added exposure to galvanic as another downside to safety of the system you seem to favor.

I'm sure the process works I just don't understand why someone would choose it over an isolation transformer.

I don't understand the safety argument because a breaker would trip as the transformer's case becomes electrified.

Providing one has an isolation transformer the simpler system would seem to be not connecting shore ground to boat ground.

[Lake-Effect]

So we're doing this again.

Originally Posted by s/v Jedi

Most of the world do not connect AC to DC systems and keep them separated.

That's not really the case, especially when you consider the situations closest to shorepower - eg RVs (caravans)

Originally Posted by goboatingnow

[The] primary safety of an isolating transformer is that it removes earth ( sea water ) as a return path , it’s therefore quite nonsensical to then reintroduce that relationship deliberately again

Explain please how removing this seawater return is a safety issue (and not just a measure to prevent galvanic corrosion). This "removing a seawater return path" stuff is all moot anyway if the boat next to you IS grounded. Why do you not acknowledge that having a low-resistance return path to shore ground is safer (however marginal)?

Guys - the IEC and ABYC acknowledge that an isolation transformer without connecting up the ground systems is safe enough for them to accept it. They have left it up to the boatowner and their electrician to choose. You've made the valid technical argument for your preference - prevention of galvanic corrosion - why not leave it there? Making strained or outrageous arguments for your preferred option isn't helping.

[Fishspearit]

Originally Posted by bdgWesternMass

I see the added exposure to galvanic as another downside to safety of the system you seem to favor.

I'm sure the process works I just don't understand why someone would choose it over an isolation transformer.

I don't understand the safety argument because a breaker would trip as the transformer's case becomes electrified.

Providing one has an isolation transformer the simpler system would seem to be not connecting shore ground to boat ground.

Not sure why you think I am favoring the polarization transformer, I've never said that and I specifically wrote above that I favor the isolation transformer in Pelagic's case because it's a steel vessel. It was simply presented early on that there are two options, some skilled electricians prefer the polarization, the ABYC says both are acceptable. And no, the breaker won't trip if the transformer case is energized by the incoming shore power. It would be 'hot', but no current would be flowing to trip the breaker until it makes a connection to ground.

[goboatingnow]

Originally Posted by Fishspearit

Not sure why you think I am favoring the polarization transformer, I've never said that and I specifically wrote above that I favor the isolation transformer in Pelagic's case because it's a steel vessel. It was simply presented early on that there are two options, some skilled electricians prefer the polarization, the ABYC says both are acceptable. And no, the breaker won't trip if the transformer case is energized by the incoming shore power. It would be 'hot', but no current would be flowing to trip the breaker until it makes a connection to ground.

Why don’t you stop posting then !!

[s/v Jedi]

I think many reading this thread have non USA electrical installations and they are larger installations than my posted diagram shows. So here is my advanced diagram for EU power.

Here are the specifics:

- a fixed install genset is added. Portable generators are connected to the shore power inlet but with a fixed install, a selector switch is used.

- the diagram shows two Victron Multiplus units to double power. There are multiple ways to do this and different applications incl. shore power frequency conversion. To enable these, every input and output of the units have a breaker (is mandatory anyway) and a total of 4 busses are used: 1 input bus and 3 output busses. Each buss is a dual busbar.

- there is a bypass breaker, feeding output bus 3. This allows continued operation during maintenance, configuration or even failure of invert/charger units.

- a method of multiple distribution groups is implemented. Each group has a selector switch to chose which output bus is used.

- this diagram can be simplified or extended: the genset can be left out, a single inverter/charger or three can be used; same for distribution groups where you can have just one and replacing the rotary switch with a wire jumper.

Example of possibilities, frequency conversion: assume 50Hz boat connecting to US 120V 30A 60Hz power. The inverters must be configured as separate units, not for parallel service. First step is to set the isolation transformer to double the output voltage to 240V. This halves the current to 15A and the frequency is still 60Hz. Now on inverter/charger unit 1, set output breakers open and input breaker closed. This unit will start charging the battery bank.
Now for the second unit set input breaker open and output breakers closed. This unit will start inverting and supply 50Hz power to the boat.
As soon as shore power is connected, the charge current from the first unit will go straight to the second unit, skipping the battery charge-discharge cycle, effectively creating frequency conversion.
Edit: output bus 3 will be a 60Hz bus straight from shore power, which could be just for things like an electric water heater that doesn’t care about frequency, reducing inverter load.