I'm confused, one person sez to connect green shore ground to engine and another sez not to. Don Casey's article (Sailboat Electrics Simplified) sez that disconnecting the green wire from engine stops corrosion from other boats, but puts anyone in water at risk if the shore power remains connected. He recommends that a "galvanic isolator" be installed in green lead if the shore power must remain connected. Can anyone help me understand what to do?
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Gord May
Green is Grounded on Boat - White is not
Your AC Shore Power Ground (Green) IS Grounded to your Boat's Ground Bus AND Engine. If a Galvanic Isolator is installed, the Shore Power Ground (Green) connects to the Isolator - then to Boat's Ground Bus & Engine. However, your AC Shore Power NEUTRAL (White)is Bonded to Ground ONLY on the Shore side - NOT on your engine. HTH, Gord
Your AC Shore Power Ground (Green) IS Grounded to your Boat's Ground Bus AND Engine. If a Galvanic Isolator is installed, the Shore Power Ground (Green) connects to the Isolator - then to Boat's Ground Bus & Engine. However, your AC Shore Power NEUTRAL (White)is Bonded to Ground ONLY on the Shore side - NOT on your engine. HTH, Gord
F
Forrest
Thanks Gord, your view makes sense!
I still don't understand why some advise to NOT connect the green/ground to the engine unless they are too frugal to buy an isolator or replace a leaking AC/DC appliance.
I still don't understand why some advise to NOT connect the green/ground to the engine unless they are too frugal to buy an isolator or replace a leaking AC/DC appliance.
AC ground to Ship's ground
The ABYC requires that the AC Grounding wire(green wire) be connected to the ships ground; usually the engine. The Engine serves as the ships ground due to its contact with the water via shaft and propeller. It is possible to stop the potential for stray current corrision by placing a galvanic isolator in the green wire at the AC inlet and still providing shock protection on board. The AC ground connection to the engine is actually a way for AC current to leak into the water. Hence, I wouldn't recommend swimming near a boat that has a source fo AC power on; no shorepower, no generator and no inverter. Best, Trevor
The ABYC requires that the AC Grounding wire(green wire) be connected to the ships ground; usually the engine. The Engine serves as the ships ground due to its contact with the water via shaft and propeller. It is possible to stop the potential for stray current corrision by placing a galvanic isolator in the green wire at the AC inlet and still providing shock protection on board. The AC ground connection to the engine is actually a way for AC current to leak into the water. Hence, I wouldn't recommend swimming near a boat that has a source fo AC power on; no shorepower, no generator and no inverter. Best, Trevor
Disconnect your Shore power when....
There are two situations where I always disconnect my shore power for safety, because the AC green ground is tied to my engine: 1. When the diver comes to clean my boat bottom: I always disconnect to protect him. He cleans my prop, so is connected to the AC green ground. If there is the slightest current flowing through that ground, it will flow through him. 2. In a thunderstorm. On the Gulf Coast, we all have lightning arrestors in our electric-meter bases which shunt a power-line lightning hit to our local ground rod. But I have found that our local ground rod gets overwhelmed by the hit, and so part of the lightning surge goes down both the green and white wires to the dock (because green and white are tied together in your main breaker box), and then onto my boat. The lightning surge sees my propeller in saltwater as a better ground. This surge has fried AC appliances, the AC inverter, and all the GFI outlets on the boat. SO I ALWAYS DISCONNECT SHORE POWER DURING A THUNDERSTORM. Al Carlson C36 Wings of Dawn Orange Beach, Alabama
There are two situations where I always disconnect my shore power for safety, because the AC green ground is tied to my engine: 1. When the diver comes to clean my boat bottom: I always disconnect to protect him. He cleans my prop, so is connected to the AC green ground. If there is the slightest current flowing through that ground, it will flow through him. 2. In a thunderstorm. On the Gulf Coast, we all have lightning arrestors in our electric-meter bases which shunt a power-line lightning hit to our local ground rod. But I have found that our local ground rod gets overwhelmed by the hit, and so part of the lightning surge goes down both the green and white wires to the dock (because green and white are tied together in your main breaker box), and then onto my boat. The lightning surge sees my propeller in saltwater as a better ground. This surge has fried AC appliances, the AC inverter, and all the GFI outlets on the boat. SO I ALWAYS DISCONNECT SHORE POWER DURING A THUNDERSTORM. Al Carlson C36 Wings of Dawn Orange Beach, Alabama
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daveM
green ground
if you use a isolator transformer, on the secondary side you have to bond the neutral and ground together.
if you use a isolator transformer, on the secondary side you have to bond the neutral and ground together.
Isolation Transformers
Isolation Transformers are a great idea, but may not always be feasible. An Isolation Transformer, for a typical 30 Amp 120VAC Shore Power Service, would be rated 3.6 KVA; which would measure about 10-1/2" Square x 8" High and weigh in at 60 Lbs., and might cost in the neighbourhood of $600 USD plus shipping & installation. See:Charles Marine ~ 3.6KVA, 30 amp, 120VAC, 60Hz Isolation Transformer, part #CM-93-IXFMR3-6T-A http://store.wmjmarine.com/s93-ixfmr3-6n-a.html
Isolation Transformers are a great idea, but may not always be feasible. An Isolation Transformer, for a typical 30 Amp 120VAC Shore Power Service, would be rated 3.6 KVA; which would measure about 10-1/2" Square x 8" High and weigh in at 60 Lbs., and might cost in the neighbourhood of $600 USD plus shipping & installation. See:Charles Marine ~ 3.6KVA, 30 amp, 120VAC, 60Hz Isolation Transformer, part #CM-93-IXFMR3-6T-A http://store.wmjmarine.com/s93-ixfmr3-6n-a.html
Neutral-Ground Bonding
Any "on-board" AC power source, be that the secondary of an isolation transformer, a generator, or an inverter, should have neutral bonded to ground at that power source. However, if there's more than one source, they should be connected through a double pole transfer switch that disconnects their ground-bonded neutral from the AC bus when they aren't in use. There should be only one point of neutral-ground bonding at any time, and that's at the source of the power at that time. In the case of shorepower without an isolation transformer, that bond occurs off the boat at the power distribution box. As others have said, the AC bus ground should be connected to the boat ground and DC negative at one point, preferably the engine. Without an isolation transformer, both a galvanic isolator AND a reverse polarity indicator should be used on the shorepower connection.
Any "on-board" AC power source, be that the secondary of an isolation transformer, a generator, or an inverter, should have neutral bonded to ground at that power source. However, if there's more than one source, they should be connected through a double pole transfer switch that disconnects their ground-bonded neutral from the AC bus when they aren't in use. There should be only one point of neutral-ground bonding at any time, and that's at the source of the power at that time. In the case of shorepower without an isolation transformer, that bond occurs off the boat at the power distribution box. As others have said, the AC bus ground should be connected to the boat ground and DC negative at one point, preferably the engine. Without an isolation transformer, both a galvanic isolator AND a reverse polarity indicator should be used on the shorepower connection.
Isolation Transformers
Gord: Although not pertinant to the current thread, those contemplating the purchase of a new Hunter cruiser might be pleased to note that Hunter seems to have decided to use isolation transformers as standard equipment on new Hunter Cruising boats. Our 306 came with one as standard, and I am sure this is not a "one of".
Gord: Although not pertinant to the current thread, those contemplating the purchase of a new Hunter cruiser might be pleased to note that Hunter seems to have decided to use isolation transformers as standard equipment on new Hunter Cruising boats. Our 306 came with one as standard, and I am sure this is not a "one of".
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