AC Wiring

[Mike and Theresa Vaccaro]

Folks,

Have an '88, Hull 563.  Am currently replacing the primary electrical control panel and attempting to ensure a safe, baseline system.  Currently, the AC ground is not tied to the DC ground at the engine as is recommended by Calder and standard accepted practice.  Understand that new Catalinas are being delivered with the AC ground tied at the main ground bus at the engine.  In addition, a galvanic isolator is standard equipment.

Does anyone have any experience with this mod or lessons learned?

Thanks,

Mike

[Mike and Theresa Vaccaro]

Ron,

Thanks for the quick reply.  Found same thing with schematics.  Did speak with the factory and asked them the question--that's where I got the info above.  

Whole thing came about as a result of Calder's recommendations that the AC grounding (green, not "grounded" neutral) be tied to the DC ground (at the engine, not the panel).  He lists three reasons why the two need to be connected:

1.  AC leak into DC negative.  Most likely cause, defective charger or short between adjacent wiring.  Without AC grounding to DC negative, fault current has no safe path back ashore.
2.  Proper lightening protection--holds AC grounding and DC ground circuit to same potential.  
3.  Unintentional path to DC negative.

He goes on to state:  "The AC grounding to DC negative connection should never be cut.  The only correct way to galvanically isolate an AC circuit is with a galvanic isolator or an isolation transformer."

True that if the AC neutral were to come in contact with the ground (e.g., reverse polarity), the DC ground circuit would become hot.

Definitely time for more research!  With you on the caveat about "improvements"!  Will try to run down the ABYC standards.

Cheers,

Mike

[Stu Jackson]

C34 Electrical Systems

Mike

I thought about that too, having been a Calder reader since day one.

Seems to me that without the galvanic isolator, which we don't have, then it was wise to leave well enough alone, and stick with the isolated systems.

Just ANOTHER reason to never leave your boat plugged in to shorepower when you are not there. *5

Stu

[Mike and Theresa Vaccaro]

Stu,

Concur for time being.  Definitely another reason to avoid swimming around the Marina!

Also agree that a complete power-down (with exception of hot-wired bilge pump system) will always work.

You have two options if you connect the systems:  galvanic isolator or isolation transformer.  

The isolator uses diodes to stop stray DC and may also have capacitors to stop stray low-voltage AC as well.  It's best to have an isolator capable of both.  They are rated for a baseline 30 or 50 amp system.  One per shorepower recepticle required.  They also require a means to monitor--usually a remote panel, although some have built in LEDs and it might be possible to mount in a location that allows monitoring.  Overall cost is 3-5 boat units for parts depending on the model selected.  If you're handy, there are instructions on the net for building your own.

Optimal solution is an isolation transformer.  Completely disconnects the shipboard system from shore (energy is transfered magnetically between coils).  A simple unit designed for 120v/60hz runs about 5 boat units.  If you go this route, there are transformers that are capable of processing multiple voltage/hertz.  This would be the ticket if you sail off-shore to ports with various types of AC power.  Obviously, these transformers cost more.

Biggest safety issue with the systems not connected is to have an AC component fail (usually a battery charger) that allows stray AC current into the DC ground.  This will then make the DC ground circuit (i.e., engine) hot.  If a standard or non-isolating coupling is used, this current is then transfered to the water around the boat via the shaft and prop.  If your boat is bonded, and the bonding system is tied to the primary DC ground, all metal bonded metal components will also be hot (ouch!).  

Salt water mitigates the hazard, but it's still potentially life threatening--even at reduced voltage.  

Other lesson of note is that unlike a home AC system, the AC ground on the boat is NOT tied to the common--it is a separate circuit (hence the ability to tie to a DC ground).

Cheers,

Mike

[Mike and Theresa Vaccaro]

Ron,

The more I research--the less definitive the guidance.  Even the ABYC can't seem to make up it's mind just exactly what to do with the green AC wire.  Gets even more bizzare with an isolation transformer and an on-board source of AC (in our case, an engine-driven generator).  Our shaft is isolated as is yours, and pending a significant increase in the family budget--we're gonna' go ahead and keep the systems separate for the time being.

Cheers,

Mike

[Gary Wilson]

There's a confusing and conflicting statement in my owners manual.  The manual is dated 6-23-86.  In Section 6.6 on lightning protection, it states:

 "Factory installed metal tanks, 110 volt systems, and major components are grounded to the engine.  The engine is grounded via the shaft and prop to the water.  The purpose of the internal grounding is for static charge control and accidental shorts in the internal systems--not to provide lightning protection.  However, you can incorporate the ground lines present in a lightning protection system you may wish to add."

The wiring diagrams in the manual do not indicate any connection between the AC and DC systems.  What would be the best way to verify whether or not this connection exists?

[Ray & Sandy Erps]

I suppose a person could check for continuity between the A.C. Green Wire and a D.C. Black wire.  Might confirm a common ground connection, but wouldn't tell you where it is.

[Mike and Theresa Vaccaro]

You can do a continuity (resistance) check between the ground prong on the shorepower cord and the engine block.  

Disconnect the shorepower cord from the dock connection and bring it on board.  You can then set your multi-meter to mesure resistance and touch one lead to the ground pin and one lead to the engine.  If the resistance is high, there is no common connection.

Cheers,

Mike

[Gary Wilson]

Thanks, Mike and Ray.  I will give it a try.

[Joe Nalley]

Mike,
If you have not solved your electrical problem or decided on an electrical panel, see Bassproducts.com, or call 860-583-1144

Best Regards,
Joe Nalley

[Mike and Theresa Vaccaro]

Joe,

Thanks for the reply.  I did get quotes for custom made panels by Bass and Blue Sea.  Ended up building from scratch with Blue Sea components since I was able to buy them on sale--saved quite a bit.  The tradeoff was the week that was required to build the panel.  Much more convenient to build the panel at home and "prewire" it with sufficient pigtails.  I still have to install it in the boat.

Both the Bass and Blue Sea panels would make an excellent replacement for the stock panel, and there's no doubt a custom-made panel would do the trick.  The decision to build my own was purely monetary!  Saved enough to buy a Link monitor for the DC system.  

The project is a bit more extensive than simply replacing the panel, since some re-wiring is required in addition to properly fusing the house bank and adding the monitoring system.

The jury is definitely out on the AC grounding issue, and thus I'll defer that for a bit!  After the panel replacement, the next project will be a galvanic isolator or isolation transformer--the perfect time to figure out what to do about tying everything together.

Also, cudos to the folks at Bass for a very quick reply to my query.  When you request a panel, they fax you worksheets that allow you to layout the panel.  After you fax them back, they'll provide you with a quote.  I even received a call from a sales rep who was willing to come to the boat!  Hard to beat that for service.  If you're not inclined to do your own work, I'd highly recommend that you consider this route.

When we finish this project, we'll post any lessons learned.

Cheers,

Mike

[Joe Nalley]

Mike,

WHAT YOU SHOULD KNOW ABOUT GROUNDS!!

The term “grounding” is often misunderstood.  A basic understanding of the various uses is important.  The following three basic applications are associated with safety of people and protection of electrical equipment:

1.   The grounding of metal frames or housings of electrical equipment (chassis ground).
2.   The grounding of neutral current â€" current-carrying conductor of an electrical source or distribution system.
3.   The grounding of an electrical source of power in such a manner that the ground is used as a current carrying conductor (battery).

Let’s deal with one item at a time because on a boat this issue will lead into bonding, zincs, transformers and galvanic isolation.

The first application is one of the most important uses of grounding to protect people from electrical shock.  Fixed equipment is usually grounded by its method of attachment or by a grounding strap between the equipment and the vessels hull ground.  Under normal conditions the housing of the equipment is not energized; however, internal insulation breakdown or other failure can bring energized components in contact with the housing.  If the housing is not grounded, the voltage on the housing could equal the voltage of the power source and a person touching the housing would be exposed to this voltage.  Zap!! With a proper ground this voltage would go to ground through its ground wire not the person. Remember electricity is very patient and will wait for something or
Someone to come along and supply it a path to ground, you don’t want to be that path.

If you think my comments will be of help let me know and I will continue with Ground Application #2.  In the end, we will cover all the items raised on the message board.  

Joe Nalley

[Monty DeLoach]

Reference AC grounding to Joe Nally. PLease continue the forum on #2 & #3.

[Mike and Theresa Vaccaro]

Dear Joe,

Thanks so much for the reply.  Think this is the perfect place to continue the discussion!  Please do.  

Since judgment is required, information and understanding are critical to making an informed decision.  It sure would be nice if there was difinitive "tech order" guidance, but unfortunately this isn't the case.  Posts like yours go a long way to helping history majors like me!  

Cheers,

Mike

[Joe Nalley]

Mike,

Below are the other applications we consider important when discussing electrical grounds.  If this data is considered to be useful, we will be happy to provide answers to specific questions/applications.  The main considerations are of course, safety above all, and protection of valuable electronics.

Joe Nalley

GROUNDING APPLICATION #2

The second application is the intentional grounding of a single pole or terminal of the power supply of an electrical distribution system (120VAC circuit, neutral).

This is accomplished by connecting a low resistance conductor from the pole or terminal to hull ground.  The purpose of grounding one of the conductors is limit the voltage that the system can be subject to under certain fault conditions.  It is important that the neutral ground have only a single point of connection to the hull ground regardless of the number of power sources.  The neutral of each generator and or distribution system must be grounded at the switchboard.

GROUNDING APPLICATION #3

The third application is the grounding of a power supply and an electrical load such that the hull ground is used as a normal current-carrying conductor (battery).  This is a locally grounded system.