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dual circuit breaker

Discussion in 'Technical Discussion' started by shipman80, Dec 9, 2009.

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  1. shipman80

    shipman80 New Member

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    Why does normal yacht electrical system use dual brakers on AC?
    Please for technical explanation - I don't want explanations like...
    as safety part, because they do, etc.

    I know no house wiring system where neutral would cross fuse/braker. Why is yacht any different?
  2. Marmot

    Marmot Senior Member

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    Well, that doesn't leave much to answer then ...



    You already told us you don't want the answer. Would you like to ask another question that has an answer you might accept?
  3. Capt Bill11

    Capt Bill11 Senior Member

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    Depending on the type of set up you are talking about, they may be breaking two hot wires. Not a hot and a neutral.
  4. Loren Schweizer

    Loren Schweizer YF Associate Writer

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    On a '70s-'90s vintage Bertram main distribution panel, single pole breakers were used on 110VAC items and double pole breakers were used on 220VAC equipment such as stove, A/C compressors, A/C raw water pump.
  5. pbekker

    pbekker New Member

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    like marmot is saying

    you dont want to hear a answer
    because 1 of the most important answers is an will be .!.safety.!. (sorry to say )

    and i you dont believe in safety then i will say leave all the breakers in the store it will save you a lot off money !!

    but i can tell you this in holland we always use dubbel pole breakers on land installations 230V-400V AC singel and trippel phase
  6. Capt Fred

    Capt Fred Senior Member

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    In the marine environment there may be a voltage potential on the neutral wire due to adjacent boat or dock voltage distribution faults that could be enough to cause shock. These concerns are more real due to the conductive nature of water. I'm not an expert but pretty sure this is the somewhat technical explaination of the double breakers on boats.
  7. NYCAP123

    NYCAP123 Senior Member

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    I've been following this for a while and wonder if I'm missing something. I'm no electrician. That said, you have a main breaker where the power enters the boat, then you have the 1st breaker box, then you have the secondary box where it's borken down to some specific destinations and some general. Further up the line is the panel which splits some of the general service to the individual lines. You also have secondary breakers on high amp items like the windless, a/c, spotlight, etc. Nobody on a small yacht is going to be climbing into the engineroom every time they plan to fire up, switch to gen power, use a windless or spotlight, etc. so local breakers are needed.You don't want live lines running through a boat from what may be a less than reliable source, plus the charge has to be able to be cut from a main if you're going to work on the lines. So other than to say redundancy is the rule on boats I have to go with Marmot, but add that it's also for convenience and reliability. Theoretically you could just have one breaker box for the ac voltage and do on some commercial and home made boats. It works, but it's just not as good or as safe.
  8. Henning

    Henning Senior Member

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    You're not providing enough information. Are you sure one of the legs is neutral? I've worked on a lot of boats electrical panels and have yet to come across one where they had double pole breakers for hot and neutral single phase 110. I do see it in double phase 220 where both legs provide alternating 110 or two legs from a three phase 220 input. Can't say as I've ever seen neutral from distribution circuits run through a breaker. Mains neutral I've seen run through a breaker but that is for isolation convenience. There are GFCI breakers that take a second feed, could that be what you're referring to?
  9. Marmot

    Marmot Senior Member

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    Go back to sleep Henning.
  10. shipman80

    shipman80 New Member

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    to pbekker: I didn't say I don't want to hear the answer (what is the meaning of qustion if you don't want an answer), but I said I don't wan't untechnical anwers in terms like: "for safety reason". I remembered that sailors used to believe that garlic can mass up the commpass. Now it might be something on that but withought the sientific explanation and research I won't take such an aswer lightly.

    And I am not building any ship and also the statement about price is inappropriate, since circuit braker dual or single is just few €, compare to a yacht overall price this is like a spit into the sea.


    And since I am beginig to believe I have more electrical engineering knowledge than most here, let me just explain that fuses/circuit brakers are for wiring protection - they don't protect you against electric shock - that's RCD's job. This goes to Capt Fred statement.

    I aslo checked Mastervolt's catalogue, where you also have some great basic electrical configurations. There are also a lot of tips and warnings and one of them say that you must use dual circuit braker (and since we are not stupid I reffer to N and L both cross the breaker not L1, L2 or L3 if we have 3 phase config and I certainly don't mean multiple breakers for multiple consumers).

    However all electrical schemes suggested by Mastervolt or others include isolation transformer - meaning you have electricaly isolated yacht from shore. Also you don't bring GND from shore to the yacht since GND and DC- are both connected to immersed ground plate. Isolation transformer protect yacht from galvanic corrosion and also from shore electrical errors. It aslo provide corrected sine wave withought peaks. So why will you then need N cross braker?


    If anyone can technicaly explain why dual circuit braker I'll be most glad since I can't get answer not even from qualify electrical engineer!
  11. Marmot

    Marmot Senior Member

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    Then you should be able to research the history of marine electrical design and installations and understand why boats are not wired like houses. You should also be able to read and understand class and flag requirements for electrical installations and the reasons why they are what they are.


    I think there might be a forest between you and the trees.


    You can't get an answer or you don't like the answer you get? This isn't rocket science but if you can't accept our answers or use them to base further enquiries, perhaps you need to look elsewhere. I suggest you call a few of the class societies, your national maritime authority, the electrical engineering department of a major shipyard ... there are lots of research avenues.

    I don't mean to sound like I am completely isolating you but it might be safer to do that than start a flamefest or some other shocking behavior online.
  12. C4ENG

    C4ENG Senior Member

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    I have seen double pole breakers on a 24 V DC breaker panel before. A positive and a negative coming out of the same breaker. I wondered as well why they would had brought the negative back to the breaker.
    I can not see how that could be much of a safety feature.
    Some how the grounding get's electrified and then the breaker will pop as the power runs back through the breakers to the equipment making a new ground?
    I really do not feel any one answered the question as well.
  13. Marmot

    Marmot Senior Member

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    It all depends on if it is a grounded neutral system or not. Generally 120VAC single phase branch circuits are switched or fed through a single pole breaker or switch. If the system is 220VAC single phase it will be controlled through a double pole device and 3 phase with a 3 pole breaker or contactor.

    The reason a piece of equipment will have a double pole breaker or switch is to completely isolate it. This is not much of a big deal on plastic boats but on metal hulls it is. The equipment will have a safety ground which is never broken or switched and the line and neutral are broken to isolate the load from all possibility of becoming energized. This is a safety issue.
  14. CharlieJ

    CharlieJ New Member

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    For 110 VAC systems:
    The current carrying conductors (L and N) from any source (shore power, genset, inverter, cold fusion thermoelectric, etc.) are to be protected at the source by a double pole circuit breaker to open both poles if there is a fault to ground. Technical reason is that N and G are bonded at each of the aforementioned sources so the fault to ground would most likely affect the N.

    If there is a reverse polarity light or alarm installed on the main panelboard, then branch circuits can be a single pole circuit breaker in the L supply to each consumer. (See ABYC E-11,17.1)

    For 240 VAC systems:
    The current carrying conductors (L1 and L2) from any source (shore power, genset, inverter, cold fusion thermoelectric, etc.) are to be protected at the source by a double pole circuit breaker to open both poles if there is a fault to ground. A three pole circuit breaker may be used if it opens all three poles (L1, L2 and N in an overload event.) Technical reason is that both L1 and L2 are hot and are use to power 240 VAC consumers (L1-L2) as well as 120 VAC consumers (L1-N and L2-N). A fault to ground may occur in either leg so both legs must be protected. (See ABYC E-11.17.2)

    If there is a reverse polarity light or alarm installed on the main panelboard, then branch circuits can be a single pole circuit breaker in the L supply to each consumer. (See ABYC E-11,17.1)