Wiring isolation transformers

[oscarvan]

Ask a few people to post up pics of the data plate on their Hatt transformers.

I second this request.

The main situation where marine electronics are special are in the engine rooms of gas powered boats. Being "spark free" is kinda handy there.

And yes, the ground/neutral story with inverters.

[rourkeh]

From your replies I am understanding that the boat side green ground on both transformers should
be attached to the boat's grounding system. This avoids a floating ground onboard. I did buy my Charles 50 amp transformers from Defender last year for a great price, I think they are International 12kva units. They are a lot of fun to move around and install, two in two out below the galley floor.

[kingsley_oasis]

Label a.jpgVoltage taps.jpg
Original equipment wired as polarizing transformers.
Ships ground is carried all the way to shore as per as built drawings.

[Doug.T]

It's my understanding that a Galvanic Isolator prevents electrocution in the event that AC current escapes from the AC wiring on board (i.e. through a short in an AC battery charger), and the AC green ground wire should be bonded to the DC ground on board. It protects the hull, anodes and aluminum parts from galvanic corrosion when plugged into shore power. It is wired into the shore power grounding wire. They are two opposing semiconductor diodes. They prevent low voltage galvanic current leaving or entering the boat but easily allow 110 volts to pass through. Some may offer a monitoring panel -KCB Technologies in Canada ... if not discontinued.
The Isolation Transformer is completely different animal which completely separates the incoming AC power from the DC power on board. The AC power is transmitted electronically through the transformer. It prevents stray galvanic current from the dockside from reaching the boat, and prevents AC power from the dockside from posing a safety hazard for the crew. The AC ground wire is still connected to the DC ground to provide protection against faulty AC circuits on the boat.
By what I read, the galvanic isolator should be on any boat that plugs into shore power. It is lighter and less expensive that the transformer.
The AC and DC electrical systems are to be connected at one common grounding point.
There is a lot of easily understood info on the web about these devices, although I read where there may not be unanimous agreement where the ground wires should go. My opinion, get a qualified expert, and verify the qualifications.

The problem that I have is that I have two isolation transformers, but then they connect the ground from the shore power to the ground for the boat side, essentially making the isolation transformers useless.

[madhatter1]

The problem that I have is that I have two isolation transformers, but then they connect the ground from the shore power to the ground for the boat side, essentially making the isolation transformers useless.

Semi educated response and I could be wrong. Business is electrical controls but self educated.

That said ground is ground is ground. Does not matter. Earth ground is bonded (this is a whole area of expertise)
to the neutral of any transformer. The isolation transformer is there just to make the vessel have it's own separately derived power source. It does this by isolating the wires from shore to the wires on the vessel through windings of the transformer. Therefore once the power is isolated it is like power from your generator. Even the genset is grounded (including neutral). But as a separately derived power source your hot legs can only seek to return to the other hot leg or the neutral of the genny or the isolation transformer. The power cannot return (cause current) to another miswired vessel or dock power.

Take for example a 24VAC transformer in your home HVAC system. It is a step down transformer that drops from 480/277/240/230/220/208 volts (doesn't matter which as long as you have correct transformer for power source) to 24 volts. When it poops out the 24 volts neither wire is now grounded even if one of the power source wires were. The 24 volts can only return from one wire to the other. Now we ground one of the conductors. The ungrounded conductor can return to the other via the circuit wiring or has a path through ground. Even though every other power source around is grounded that are isolated by transformers and have no relation to each other.

A word about grounding. Not much skill in this arena but can say grounding has to do with safety and safety circuits like GF breakers. The ground is supposed to be the non current carrying conductors and should never be used as a neutral. You get correct power between a hot and a neutral (current carrying conductor) which happens to be grounded for safety reasons.

Krush is 100% correct saying a transformer is a transformer. Special marine specs?? I'll leave that to an expert but guessing not other than for corrosion in salty environment and maybe special cabinets or specs for gas powered situations.

Did I throw gas on the fire or clear things up?

[SKYCHENEY]

Semi educated response and I could be wrong. Business is electrical controls but self educated.

That said ground is ground is ground. Does not matter. Earth ground is bonded (this is a whole area of expertise)
to the neutral of any transformer. The isolation transformer is there just to make the vessel have it's own separately derived power source. It does this by isolating the wires from shore to the wires on the vessel through windings of the transformer. Therefore once the power is isolated it is like power from your generator. Even the genset is grounded (including neutral). But as a separately derived power source your hot legs can only seek to return to the other hot leg or the neutral of the genny or the isolation transformer. The power cannot return (cause current) to another miswired vessel or dock power.

Take for example a 24VAC transformer in your home HVAC system. It is a step down transformer that drops from 480/277/240/230/220/208 volts (doesn't matter which as long as you have correct transformer for power source) to 24 volts. When it poops out the 24 volts neither wire is now grounded even if one of the power source wires were. The 24 volts can only return from one wire to the other. Now we ground one of the conductors. The ungrounded conductor can return to the other via the circuit wiring or has a path through ground. Even though every other power source around is grounded that are isolated by transformers and have no relation to each other.

A word about grounding. Not much skill in this arena but can say grounding has to do with safety and safety circuits like GF breakers. The ground is supposed to be the non current carrying conductors and should never be used as a neutral. You get correct power between a hot and a neutral (current carrying conductor) which happens to be grounded for safety reasons.

Krush is 100% correct saying a transformer is a transformer. Special marine specs?? I'll leave that to an expert but guessing not other than for corrosion in salty environment and maybe special cabinets or specs for gas powered situations.

Did I throw gas on the fire or clear things up?

Great explanation.

[Photolomy]

A word about grounding. Not much skill in this arena but can say grounding has to do with safety and safety circuits like GF breakers. The ground is supposed to be the non current carrying conductors and should never be used as a neutral. You get correct power between a hot and a neutral (current carrying conductor) which happens to be grounded for safety reasons.

Just to be clear, in an isolation transformer setup (and a generator setup), the neutral (center tap) and ground are connected on the boat side. In a shore power setup there is a separate (earth) ground and neutral. I was just clarifying to make sure someone didn't think that the ground will work if it is left unconnected or just connected to the case. In that event, the ground wouldn't do anything and if there is a wiring fault, all of the metal on the boat will become electrified, rather than throwing a circuit breaker. Everything would work normally, but all the metal would be electrified.

But your comment is correct about not using the ground wire (in a switch or outlet) as the neutral wire, even though they are connected at the transformer.

Also, if it isn't clear yet, the shore ground and boat ground cannot be connected, or you lose galvanic protection and electrocution protection. Even if you add a galvanic isolator, you still lose electrocution protection. The shore ground will be connected to the shield (NOT THE CASE) or not connected at all and the boat ground to the neutral (center tap) and the case.

[krush]

Also, if it isn't clear yet, the shore ground and boat ground cannot be connected, or you lose galvanic protection and electrocution protection. Even if you add a galvanic isolator, you still lose electrocution protection. The shore ground will be connected to the shield (NOT THE CASE) or not connected at all and the boat ground to the neutral (center tap) and the case.

^^^^^^^^
What he said is the most important information on this thread!


People confuse land wiring with boat/ship wiring. On land, everybody uses the earth as the reference point for 0volts. Devices after the isolation transformer will normally "grounded" to the earth (just like devices before the transformer), because everything is referenced to the dirt. Even though the ground wires may not be connected, they are indirectly connected because both are grounded to the earth.

In some cases the system after the transformer is not grounded to the earth, to create galvanic isolation for things like control systems (so signals don't get messed up). Keeping it simple here.

[doc g]

the whole idea of an isolation transformer is to generate the neutral onboard and leave all the nasty issues including the (green)dock ground on the dock. Basically L1 and L2 are the only 2 wires brought onboard. Neutral (white) is generated by the transformer and the green and white are tied together at the transformer case. This way you isolate yourself from the issues that are on the dock and on other boats around you. This is the way my boat is wired ...................Pat ......