Grounding

Discussion in 'Electrical Systems' started by chuckms, Mar 27, 2011.

  1. chuckms
    Joined: Mar 2011
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    chuckms Junior Member

    I live on a saltwater/brackish water canal where i keep my 40’ boat. I have been getting some corrosion on my engines and signs of electrolysis on most of the copper fittings onboard. I have Shore power that connects to my house which is grounded at the house about 100’ from the boat. I am contemplating adding a 12’ Ground Rod next to my sea wall (not on the water side). I was planning on grounding the shore power box to the ground and after reading for several hours on the internet I have several questions.
    1. How far from the seawall or water should the ground rod be or does it matter.
    2. IN addition to the Ground, Should I connect the neutral from the shore power to the new Earth Ground rod as I have in my house?
    3. I was also planning to attach a wire directly to my engines and connecting it to the new earth ground rod with a disconnect for when I leave the dock.
    4. I have all metal parts, through hulls, railings, engines, engines and battery grounds connected to a common ground bar on the boat, should I connect the new earth ground rod to the common ground bar on the boat (also with a disconnect for when I leave the dock)?
    5. Currently I have the Ground bar, AC and DC grounds grounded to the engines. Should I separate this and if so how do I properly ground the AC and DC both at the dock and underway?
    6. I have an aluminum roof on my dock I was considering grounding it the new Ground rod will this increase my protection or add to the electrolysis problem?
     
  2. chuckms
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    chuckms Junior Member

    Five years ago I had two electrical fires onboard. The first fire originated at the wire harness for my fresh water and saltwater wash-down pumps. the second was a bad fire We later discovered that both fires resulted from the same faulty wire that fed the windless. The Windless had a separate 100 amp residential breaker at the battery and the previous owner striped the insulation from the large wire and spliced the wire for the head, then tucked the spliced wire between the holding tank and a stringer hiding the connection from view. My Bilge anti-syphon valves became clogged two months after the first fire from debris from the fire. I shut off the bilge pumps planning to clean the lines on the weekend (my boat is generally has a very dry bilge). My wife turned on the AC that had the condensation dumping in the bilge. The water in the bilge rose from the AC condensation to the point where the afore mentioned splice connection came in contact with the bilge water and sent the 4,000 cranking AMPs from my new batteries directly to ground. The insulation melted off all the DC grounds first and then the bundle of wire grouped together to go from the bilge to the electric panel in the Salon next. The hottest part of the fire was adjacent to one of the stainless gas tank and set the wood supports on fire and nearly burnt through the 3/4 “ plywood floor between the bilge and the salon (after the fire I pushed my finger through the plywood floor).
    My wife was awakened by the smoke and woke me; I grabbed her and my new 10# Halotron fire extinguisher and escaped from the boat. The smoke was so thick you could not see. My wife had just completed school to acquire her Master license knew to quickly shut down the shore power. I battled the fire and spent the portable extinguisher in the bilge vents that had flames shooting 4’ from them and the flames coming from the vent in the cockpit above the shore power connection. Standing their naked with nothing but an empty fire extinguisher to cover myself with my prayers were answered and the automatic HALON system in the bilge went off. I then used the fresh water hose to spray water in the vents until the smoke dissipated. Then we started the clean-up.
    I know that was a lengthy story but you now understand I am very concerned with proper grounding and have a new found respect for fire and electric.
    We have replaced the entire wiring system on the boat with all the wire run in carflex so no two harnesses are touching, preventing the failure of one wire melting the insulation of another. I also have added redundant automatic Halatron systems two in each of the three bilge compartments and one in the space between the bilge and the Electric panel. I found one common place from both fires where I felt safe fighting the fires was in the cockpit at the entrance to the salon. I have now added at that location a new 10# Halatron and a 10# Purple K portable extinguishers. I also have an assortment of ABC, Halotron and purple K portables throughout the boat. Each extinguisher has a flashlight and whistle attached to the locking pin so when you remove the pin you have a flashlight and whistle in your hand, you will appreciate this if the need ever arises in the middle of the night. On the dock I have a 100” red hose with a fire nozzle and two portable extinguishers should the need arise.
     
  3. michael pierzga
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    michael pierzga Senior Member

    What makes you think that you have an AC problem ? typical stray electricity comes from the DC side.

    Is your DC electrical system isolated from the hull ? Check with a voltmeter positive to earth...negative to earth. Earth will be the hull or engine block.

    Are you using an Isolation transformer for the AC input ?
     
  4. chuckms
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    chuckms Junior Member

    I am getting electrolysis; the copper fittings have patina my zincs are not lasting very long. Over the last year I have had to replace my heat exchangers, exhaust risers and elbows from corrosion. I did not have these problems in the past.
    I do not show an voltage on the ground ad no I do not have an isolation transformer
     
  5. michael pierzga
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    michael pierzga Senior Member

    If you have no DC on the hull, how are you generating the energy needed to erode heavy heat exchangers ? I doesn't make sense.

    Earth faults...stray electricity from the DC side, are almost always the cause.

    If I went to every boat in this marina, I would probably find stray DC on each one...typical leakers are brush filings in dc motors or aftermarket , none isolated equipment DC equipment..... Installing a normal automobile alternator, or an automobile single pole oil pressure sensor on a marine engine ..... trouble.

    Energize all DC equipment, then measure between earth and positive then earth and negative.

    Is your dock made of steel or wood poles ?

    Isolation transformer...

    http://www.smartgauge.co.uk/galv_tran.html
     
  6. chuckms
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    chuckms Junior Member

    wood poles
     
  7. Ike
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    Ike Senior Member

    First what you think is occurring is not electrolysis. The correct term is galvanic corrosion. And Galvanic corrosion is not caused by stray currents. Galvanic corrosion is caused by dissimilar metals in an electrolyte, in this case water. Michael has hit the nail right on the head. You are having a case of stray current corrosion. It is just what it's name implies. Stray currents in the water, usually from poorly wired DC systems. But, it can also happen from badly wired AC systems as well. See Corrosion on Boats http://newboatbuilders.com/docs/CorrosionOnBoats.pdf

    You need to find a Certified Marine Electrician to check your system. If the electrician eliminates problems with the system on your boat then it is coming from some one else's system, or from the shore power, as you suspect. The quickest way to determine if it is coming from the shore power is to measure the current in the water around your boat. The levels should be zero. But if there is current in the water the levels will tell you if it is DC or AC. If it's AC it will probably be a severe shock hazard. The electrician should have the right type of electrode to measure currents in the water.

    You are right to worry about fire. Most boat fires are electrical in origin and are due to either badly wired systems, or neglected systems with high resistance connections, usually from corrosion, or loose connections. Electrical systems need routine maintenance too. And contrary to popular belief amongst most boat owners, who love to DIY everything (me too), an AC electrical system on your boat is not something for amateurs to be fooling around with. AC kills, as well as other things like burning up your boat.
     
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  8. CDK
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    CDK retired engineer

  9. chuckms
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    chuckms Junior Member

    I still am unclear if it is a good idea or bad idea to ground my boat at dock to a ground rod in the ground on shore?
     
  10. michael pierzga
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    michael pierzga Senior Member

    You must follow regulations. You must use the ground wire on your boats AC system and it must be securely connected to the shore power ground earth. This is the only way to avoid electrocution. As far as driving an extra ground spike into the earth . I dont know. I assume the ac electical instalation in your house has the correct earth ?


    In big marinas this Earth connection can be an issue because your boat will be connected to the earth , copper conductor, of every boat in the marina. At your house you are the only boat.

    On all marine AC systems its very wise to install an ...isolation transformer.... on your boat. This transformer allows you to have no copper to copper ,physical, connection to the AC dock shorepower and thus avoid inheriting neighboring boats electrical leaks.
     
  11. gonzo
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    gonzo Senior Member

    Check the NEC and local regulations first. Counties and cities have different ways of grounding a power supply. In Florida, because of the high water table, they usually require less rods. However, grounding the system close to the boat may cause an electrocution danger in the water.
     
  12. Ike
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    Ike Senior Member

    Good Advice Gonzo. Ask an electrician. Call a local marina and find out who checks their shore power system and then ask that person. Most shore side systems (like your house and the local power substation) have a ground rod. But whatever you do it has to comply with NEC and National Fire Protection Assoc (NFPA 303) standards.
     
  13. CDK
    Joined: Aug 2007
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    CDK retired engineer

    It is never a bad idea to have an extra ground rod and it might even reduce the corrosion rate a tiny little bit.
    But the real cause of your problem is in the engine room:

    "5. Currently I have the Ground bar, AC and DC grounds grounded to the engines. Should I separate this and if so how do I properly ground the AC and DC both at the dock and underway?"

    With the shore ground tied to the DC wiring you introduce a voltage differential between all connected metal parts and the water, because what you expect to be "shore ground" isn't really at the same potential as your boat's ground. Even if the difference is just 1 volt, it already causes the zinc electrodes to work overtime and lose the battle.

    From a technical point of view, the shore ground must end where it enters your boat. It only has a protective function, so you do not need that in a boat already equipped with an effective ground system.
    All you need is a sensitive ground fault device (GFI) that cuts the shore power if a current leak occurs (wet junction box or insulation breakdown).

    Local regulations may make cutting the shore ground illegal, in that case install a ground isolator at that point. Such a device contains a number of diodes that allow a voltage differential between ship's ground and shore ground without any current flowing.

    Should you decide to install the extra ground pole, take a few minutes and a good multimeter and measure voltage and current between the so called shore ground and your new pole. You will be surprises!
    I've done that many times already and have found values up to 30 volts in locations with rocky soil, where the power grid has very inefficient earthing.
     
  14. michael pierzga
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    michael pierzga Senior Member

    "From a technical point of view, the shore ground must end where it enters your boat. It only has a protective function, so you do not need that in a boat already equipped with an effective ground system."


    If you're implying that the vessel can stay off the copper ground wire ..this is a dangerous practice. Its true that sea water is a ground. But I can introduce you to a shipyard worker with one arm. The vessel was hauled, blocked up... then plugged into shorepower. The worker erected an aluminum ladder against the SS stern rail to climb aboard and was electrocuted. The vessel had disconnected the earth wire in the ship.....the ladder and the workers body transferred the charge to earth. Be careful
     

  15. Frosty

    Frosty Previous Member

    Does your house have an earth wire or earth rod. Could be your neighbours house that has a problem and feeding down the earth wire which is your earth wire too.

    I dont use Ac earth,-- just 2 wires on my boat seeing as though everything I buy has only 2 wires on it.

    And I dont want to be the earth for the boat next to me if the marina wire is broken.

    By the way no one has asked him what his boat is made of yet.
     
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