Shore Ground NOT Connected to Isolation Transformer

[Cwens]

Originally Posted by goboatingnow

If you connect the boat side protective earth on a supply generated by an isolation transformer to seawater , you are in my view undoing one of the major advantages of such a transformer. This is leaving aside the fact that such a circuit is meaningless as there is no seawater path.

The part that I have trouble reconciling, and I don't have ABYC or RCD or ISO standards at hand, is this:

1. I believe that anything remotely capable of becoming energized by the AC power supply in the case of an insulation failure or wiring fault, must be connected to the boat side protective earth. That includes, for example, the metal case of your microwave oven; and pretty much every large piece of metal on the boat, such as the mast, the standing rigging, the engine, etc.
2. Some or all of the above are connected to seawater, either deliberately via the bonding system or through incidental contact.
3. DC Negative is (usually) connected to the engine block.
4. Therefore I don't see how you can not have DC neutral, Boat side AC protective earth, and seawater all in contact with each other.

[Fishspearit]

Originally Posted by ChrisOwens

The part that I have trouble reconciling, and I don't have ABYC or RCD or ISO standards at hand, is this:

1. I believe that anything remotely capable of becoming energized by the AC power supply in the case of an insulation failure or wiring fault, must be connected to the boat side protective earth. That includes, for example, the metal case of your microwave oven; and pretty much every large piece of metal on the boat, such as the mast, the standing rigging, the engine, etc.
2. Some or all of the above are connected to seawater, either deliberately via the bonding system or through incidental contact.
3. DC Negative is (usually) connected to the engine block.
4. Therefore I don't see how you can not have DC neutral, Boat side AC protective earth, and seawater all in contact with each other.

You're right. Goboatingnow is only thinking about the boat side of the transformer. A fault to ground will go back to the transformer (its source) and not through the sea water. The problem he is forgetting about is the fault of the shore side to the boats ground (input cable chafed against transformer case), which then goes through the water back to shore.

[Lake-Effect]

Originally Posted by Fishspearit

Explain to me how a short from the primary winding of the transformer to the case will not result in an electrical shock hazard on the boat with an isolation transformer.

ABYC permits the use of pure isolation transformers where the boat ground and shorepower ground are not interconnected. They apparently consider this acceptable because the failure rate of a properly-installed ABYC-compliant isolation transformers is very low. (paraphrasing from the certification manual). They imply that shorepower issues, including galvanic or corrosion-inducing situations are more common.

There's not much difference between a proper isolation transformer and an onboard AC generator, EXCEPT that there's shore AC and ground led into the isolation transformer.

It's also understood by most pros that shorepower ground connected to boat ground through a suitable galvanic isolator is the safest possible.

So, in the case of isolation transformers, it seems the ABYC leaves the final choice of connecting the boat ground to shore ground up to the boatowner or their electrician.

[Fishspearit]

Originally Posted by Lake-Effect

ABYC permits the use of pure isolation transformers where the boat ground and shorepower ground are not interconnected. They apparently consider this acceptable because the failure rate of a properly-installed ABYC-compliant isolation transformers is very low. (paraphrasing from the certification manual). They imply that shorepower issues, including galvanic or corrosion-inducing situations are more common.

There's not much difference between a proper isolation transformer and an onboard AC generator, EXCEPT that there's shore AC and ground led into the isolation transformer.

It's also understood by most pros that shorepower ground connected to boat ground through a suitable galvanic isolator is the safest possible.

So, in the case of isolation transformers, it seems the ABYC leaves the final choice of connecting the boat ground to shore ground up to the boatowner or their electrician.

Yes, that's exactly what I'm trying to say. Both ways are acceptable, one provides better isolation and one is (arguably) safer. Just make an informed decision on which aspect is more important to you.

[lvictorlucas]

[QUOTE=s/v Jedi;3648215]It is SHOCKING that this is still presented all wrong. How many times has this been discussed?!

Make sure that shore ground is NOT connected to ships ground.
These are ISOLATION transformers, they prevent shore ground from stretching beyond the transformer.

I don't post much as some people believe some of this stuff.
The entire purpose of an ISOLATION transformer is to ISOLATE the the input from the output, hence the name! Why use an isolation transformer at the increase of size, weight and usually great cost and defeat its purpose and reduce safety? Please listen to s/v Jedi !

[Lake-Effect]

Originally Posted by lvictorlucas

The entire purpose of an ISOLATION transformer is to ISOLATE the the input from the output, hence the name!

Why use an isolation transformer at the increase of size, weight and usually great cost and defeat its purpose and reduce safety?

Isolation transformers:

• isolate boat AC from shore AC
• permit the isolation of shore ground and boat ground (if desired)
• correct any polarization issues with shorepower
• can convert shorepower voltages (120 to 240 or vice versa)

Isolating the grounds does not increase safety. But isolation transformers are considered dependable enough that the risk of shorepower AC touching the transformer case is deemed to be acceptably low by the ABYC and many users.

[goboatingnow]

Originally Posted by s/v Jedi

It is SHOCKING that this is still presented all wrong. How many times has this been discussed?!

The attached diagram. Take it as authoritative. One test that MUST be done is make sure that shore ground is NOT connected to ships ground. Simply test with multimeter in continuity mode, then check with resistance mode to see that there exists a high isolation value.

These are ISOLATION transformers, they prevent shore ground from stretching beyond the transformer.

Ships ground as shown in the diagram is good to go, no need to connect it to anything else except all the outlets and appliances connected to the breaker panel.

[goboatingnow]

Originally Posted by Lake-Effect

Isolation transformers:

• isolate boat AC from shore AC
• permit the isolation of shore ground and boat ground (if desired)
• correct any polarization issues with shorepower
• can convert shorepower voltages (120 to 240 or vice versa)

Isolating the grounds does not increase safety. But isolation transformers are considered dependable enough that the risk of shorepower AC touching the transformer case is deemed to be acceptably low by the ABYC and many users.

An isolation transformer isolates the boats electrical supply from the shore supply , it in effect a local AC generator no different to a diesel one.

Connecting the grounds together confers no safety advantage but exposes the boat to dock side stray current and any dockside earth faults. Connecting the boat side earth in such situations to sea water earth is equivalent to connecting it to shore side earth. Don’t do it.

Polarisation and voltage transformation are not primary functions and don’t in themselves need isolating transformer features.

The shore side ground can be connected to the electro static shield or sometimes to the metal case of the transformer AGAIN only if that case is not connected to anything ship side. It’s optional and I don’t do it. I don’t bother with electro static shields as such transformers are typically not designed with these shields as safety devices as ABYC intended.

[Lake-Effect]

Originally Posted by goboatingnow

Connecting the grounds together confers no safety advantage but exposes the boat to dock side stray current and any dockside earth faults. Connecting the boat side earth in such situations to sea water earth is equivalent to connecting it to shore side earth. Don’t do it.

This is an area open to discussion; even ABYC acknowledges this, which is why they consider the isolation transformer and no connection to boat ground as acceptable practice.

There IS a safety benefit to connecting the boat ground to shorepower ground (through a galvanic isolator); but we all (including the ABYC) agree that the chances of an isolation transformer having a danger-inducing failure are quite low.

So the scorecard is - we know what the ABYC and several professionals think and say, and we know what a few apparently knowledgeable yet anonymous forum posters think.

I don’t bother with electro static shields as such transformers are typically not designed with these shields as safety devices as ABYC intended.

The caveat around boat isolation transformers is that they, and the manner in which they are installed, should be ABYC compliant. Any old iso transformer with a Faraday shield is not necessarily ABYC compliant.

[s/v Jedi]

Originally Posted by Fishspearit

By all means, tell me what I wrote that is wrong and prove it. Everything I wrote is in the ABYC Electrical certification study guide and in the ABYC standards. Explain to me how a short from the primary winding of the transformer to the case will not result in an electrical shock hazard on the boat with an isolation transformer.

I'll post this again because it's clear you either didn't read it or don't understand it. http://qualitymarineservices.net/wp-...le-10-2006.pdf

And here's another article by Steve D'Antonio saying all the same things I just wrote. https://www.passagemaker.com/technic...r-transformers

Pfff… why don’t you show how a non metal, insulated toroidal transformer can create a short to the case and show me how this then puts people at risk. Unless you are able to do so, right here, not by posting links, then it is you who doesn’t understand this. But I already see, you’re one of the ABYC financial contributors let me guess, you’re gonna want to see a shield around the primary winding of the isolation transformer, right? Just like ABYC describes? Show me how to do that with toroidal transformers.

It took ABYC 25 years to finally recognize RCD protection; it’s only a matter of time before they discover toroidal transformers and, like the rest of the world, accept Victron isolation transformers.

[goboatingnow]

Originally Posted by s/v Jedi

Pfff… why don’t you show how a non metal, insulated toroidal transformer can create a short to the case and show me how this then puts people at risk. Unless you are able to do so, right here, not by posting links, then it is you who doesn’t understand this. But I already see, you’re one of the ABYC financial contributors let me guess, you’re gonna want to see a shield around the primary winding of the isolation transformer, right? Just like ABYC describes? Show me how to do that with toroidal transformers.



It took ABYC 25 years to finally recognize RCD protection; it’s only a matter of time before they discover toroidal transformers and, like the rest of the world, accept Victron isolation transformers.

Woe betide when the ABYC finally gets around to high frequency isolation systems !!!

[goboatingnow]

Originally Posted by Fishspearit

Yes, that's exactly what I'm trying to say. Both ways are acceptable, one provides better isolation and one is (arguably) safer. Just make an informed decision on which aspect is more important to you.

It’s not safer.

[s/v Jedi]

Originally Posted by goboatingnow

Woe betide when the ABYC finally gets around to high frequency isolation systems !!!

They actually do and guess what: no shielding of primary winding required, which means Mastervolt’s unit is okay with ABYC. I bet they send one of their people as “volunteer” to write the “standard”

[Horus]

Shorepower.. Installation and cable's must NOT be mounted in the engine room!!

[goboatingnow]

Originally Posted by ChrisOwens

The part that I have trouble reconciling, and I don't have ABYC or RCD or ISO standards at hand, is this:

1. I believe that anything remotely capable of becoming energized by the AC power supply in the case of an insulation failure or wiring fault, must be connected to the boat side protective earth. That includes, for example, the metal case of your microwave oven; and pretty much every large piece of metal on the boat, such as the mast, the standing rigging, the engine, etc.
2. Some or all of the above are connected to seawater, either deliberately via the bonding system or through incidental contact.
3. DC Negative is (usually) connected to the engine block.
4. Therefore I don't see how you can not have DC neutral, Boat side AC protective earth, and seawater all in contact with each other.

There is NO connection between my AC system protective earth and seawater and underwater metals are not bonded together as per ISO ( which is why European boats wired to ABYC have tru hull issues )

So with an isolation transformer it makes zero electrical sense to bond the ship side protective earth ( which is returned to one side of the transformer ) to seawater or metals not normally fed by AC like the rigging etc.

The point is there is zero shock hazard with an isolation Transformer is an unexpected metal object goes live , the ussr would have to physically insert themselves into the circuit to receive a shock.

In fact it actually adds to the danger of causing a shock by connecting in metal objects that are not normally exposed to AC to the boats protective earth.

The reason it’s done in shore power AC is the mains is earth referenced. The best thing for a boat is non earth referenced mains electrical generation.

Electricity is a science not magic.