Separating AC and DC grounds.......

[ericinga]

As part of installing AC, I added a breaker panel. Honestly, I was surprised the shore power was wired directly into power distribution strips. I noticed the AC power ground shared the DC power grounding strip. This doesn't seem correct since the DC power grounds to the hull . Seems like the AC ground to the hull would cause electrolysis problems.

I separated the two grounds with the panel installation. For $200, the breaker panel seemed like a simple upgrade. It certainly gives me some peace of mind.

Has anyone else found this problem? Do the grounds require separate paths?

Eric

[jtalberts]

I just recently tied my two systems together. In all the books I have been reading always show the grounds tied together.

[barkleydave]

Original wiring is correct.

safe boating ,
dave

[newendeavor]

If that is true, then you are taking the AC Ground to Hull as well. Should be isolated.

[Roger2]

Ground, is Ground. If you connect to the hull,(ground) in separate places, then there is the possibility of current flow between those places. ALL should be connected to the hull in or very near the same place.
Roger

[Dougrose]

When it comes to AC grounds, there are two things to remember:

One, the ac coming from the dock must be grounded to the hull, and

Two, the ground connection to the hull must be blocked for DC so that electrolysis does not eat the hull.

The ac from the dock must be grounded to the hull because, if there is a short from the hot side of the ac to the hull, then the entire hull is hot and anyone touching it while grounded outside the boat will be zapped. This would include someone stepping off the boat to an aluminum dock or a hapless swimmer. If the ac ground is connected to the hull, then a short to the hull will not make the hull hot, but will instead trip the breaker and open the circuit.

There should be no dc connection from the ac ground to the hull because the marina's ac ground is a grounding rod back at the utility company's transformer, and there is likely some small voltage between that ground up on land and the water around your boat. This small voltage must be blocked to prevent a flow of current from the marina ac ground into the water around the boat. This small current will likely take aluminum ions with it, and we do not want that.

There are two solutions to this problem:

The best is to use an isolation transformer to isolate the wiring within the boat from the marina ac wiring. The marina's hot and neutral are wired to the isolation transformer's primary coil, and the marina ground is wired to nothing. The isolation transformer's secondary coil is wired to the boat's hot and neutral, and the neutral itself is wired to the boat's ac ground and hull. Excellent, the only problem being the cost, around $500 or more.

The second method is to use a galvanic isolator, a device which will not pass small dc voltages but will pass large ac voltages. The marina's hot and neutral are wired to the boat's hot and neutral, and the marina's ground (green) is wired to the boat's ac ground (and hull) through the galvanic isolator. This is the method that Marinette used. It works quite well, except that the galvanic isolators are getting old.

I replaced my galvanic isolator with an isolation transformer, and it is nice to not worry about ac grounding problems. My transformer has 110VAC and 220VAC inputs and outputs, so I could use 220 in and convert it down, or run a 220 appliance, if needed. This sounds strange, but at one time I had hoped to retire to places where 110 was not available, but those dreams are long gone....

[jtalberts]

Doug,

As I understand it the isolation transformer allows will protect you from corrosion even with a DC ground to the hull?

[Roger2]

An isolation transformer DOES NOT protect from corrosion!!

Roger

[jtalberts]

Why is there always the option between the Isolation transformer and a galvonic isolater? Everything I have read up on is that the isolation transformer and galvonic isolater both prevent galvanic corrosion.

http://www.charlesindustries.com/main/iso_guard.html
http://www.airlinktransformers.com/boating_transformers

Also per another source http://www.passagemaker.com

http://www.passagemaker.com/articles/te ... ansformers

The ultimate solution for most of these problems is the isolation transformer. Once installed, the isolation transformer acts much like its own power supply, similar to a generator or an inverter, or a utility company, for that matter. All voltage produced by the isolation transformer seeks a return to its origin, not just any ground. The importance of this feature cannot be overemphasized. Shorepower voltage, once it passes through the isolation transformer, will return only to that isolation transformer, through either the white neutral conductor or the green safety grounding conductor, whether by design or fault. Voltage that now emanates from the isolation transformer will never travel through sea water to seek a path to ground. This protects swimmers. Damaging galvanic voltages that normally would be allowed to come aboard via the green safety grounding conductor in the shorepower cable are also thwarted, because there is no longer any direct connection to shoreside grounds. This is where the isolation transformer and the galvanic isolator diverge. Where the galvanic isolator attempts to block DC current from coming aboard, like the walls around a medieval fortress, the isolation transformer severs this connection altogether, much like digging a moat around the same fort, filling it with water and crocodiles, and pulling up the drawbridge.

The isolation transformer achieves all of this through the principle of magnetic inductance. Here’s how it works. Shorepower voltage travels from the dock, through the shorepower cable or cables, and onto the boat’s shorepower inlet. As is the case for the galvanic isolator, one transformer is required for each shorepower inlet. But instead of allowing current to go from there to the shorepower circuit breaker panel, the isolation transformer interrupts the current before it can reach the circuit breaker. The incoming AC power travels through the primary or input winding of the transformer and back to shore. That’s as close as the dockside shorepower ever gets to the boat’s electrical system. Electricity is induced on the transformer’s secondary or boat side winding magnetically. There is no direct connection. This arrangement eliminates the possibility of reverse polarity and of unintentionally creating the potential for a swimmer either drowning—because the electricity paralyzes his or her voluntary muscle reflexes—or, if the current is strong, being electrocuted. (It’s telling that vessels equipped with isolation transformers are exempt from ABYC’s reverse-polarity indicator requirement.)

[jralbert]

I found the following text in the 1988 owners manual and hope it will add to the discussion:

IX. GALVANIC (OR VOLTAGE) ISOLATOR
t. General Function
In an attempt to isolate their vessels from nearby boats to lessen galvanic corrosion problems, many mariners are wrongly clipping the green ground leads at their dockside 110V AC connections, but the ground connection is there for safety reasons; it prevents the boat from becoming an electrical shock hazard in the event of an on-board wiring fault. Although clipping the ground wire may lessen the possibility of galvanic corrosion between two side-by-side vessels, it could also lead to a fatal shock.
There is available, however, a piece of equipment that will have the same effect as clipping the green wire, but still provide electric shock safety. It is called Voltage or Galvanic Isolator.
Galvanic Isolators will combat the effect of vessels acting like giant batteries. A "battery" is created when two dissimilar metals are connected via the common green ground wire. The voltage isolator is an alternative means of grounding the boat to keep it free from hazardous AC voltages, while at the same time blocking the flow of destructive low voltage galvanic DC current that is potentially destructive to active metals such as aluminum hull vessels.
Galvanic Isolators do not necessarily contribute to the complete elimination of all your corrosion problems. Galvanic corrosion occurs from dissimilar metals submerged in sea water. Voltage isolators won't help here. Electrolysis is stray current corrosion from your improperly wired ship's electrical system. Voltage isolators won't help here either. These two common corrosion problems must be tackled individually.
Voltage isolators do work to break up common wire circuits that bond your vessel to all of the other vessels in nearby slips.
The voltage isolator consists of solid state electronics, made up of large capacitors and several silicon diodes. The isolator is a special "filter" inserted only in the shore green ground wire lead. It imposes no resistance to the passage of alternating current (electrical shocking voltage) while it has an almost infinite opposition to the flow of low voltage DC galvanic current. This prevents corrosion to the boat caused by stray current flow, yet provides safety by preventing the boat from becoming a dangerous source of electrical shock.
Voltage isolators do work to break up common wire circuits that bond your vessel to all of the other vessels in nearby slips.
The voltage isolator consists of solid state electronics, made up of large capacitors and several silicon diodes. The isolator is a special "filter" inserted only in the shore green ground wire lead. It imposes no resistance to the passage of alternating current (electrical shocking voltage) while it has an almost infinite opposition to the flow of low voltage DC galvanic current. This prevents corrosion to the boat caused by stray current flow, yet provides safety by preventing the boat from becoming a dangerous source of electrical shock.

I interpret this to mean the device does offer protection against some causes of galvanic corrosion while, most importantly, guarding against electrocution. I recall the isolator brand name was "Quicksilver"