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Thread: Wiring isolation transformers
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01-23-2021 12:00 PM #21
Re: Wiring isolation transformers
1978 53' Motor Yacht "LADY KAY V"
Hull number 524
Chesapeake Bay
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01-24-2021 09:22 AM #22Senior Member
- Join Date
- Sep 2013
- Posts
- 165
Re: Wiring isolation transformers
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.
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Re: Wiring isolation transformers
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.Ray
1983 61CY 319
AnnaVal
Jacksonville FL.
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Re: Wiring isolation transformers
Doug Troughton
1986 Hatteras 53 MY
Hull# HATAM635H586
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Re: Wiring isolation transformers
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?1966 34c
1982 46 HP
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01-26-2021 12:55 AM #27Senior Member
- Join Date
- Jun 2018
- Posts
- 1,069
Re: Wiring isolation transformers
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.Last edited by Photolomy; 01-26-2021 at 01:05 AM.
Prometheus
1978 53' MY Hull #529
Viera, FL
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01-26-2021 07:23 AM #28Senior Member
- Join Date
- Jun 2007
- Posts
- 4,974
Re: Wiring isolation transformers
^^^^^^^^
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.FTFD... i drive a slow 1968 41c381
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01-26-2021 07:53 AM #29
Re: Wiring isolation transformers
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 ......