Pos and Neg Battery switching

Discussion in 'Electrical Systems' started by Frosty, Jul 9, 2011.

  1. Frosty

    Frosty Previous Member

    I've always used Pos and Neg battery switches. Im not sure now if thats a good Idea.

    What do you think? any advantages of a Neg battery switch.

    Ive done this on a steel boat and a fibre glass boat, I have had no trouble with either but do get a tingling feeling off the engines of the fibre glass boat but no big readings on the multi meter.

    It makes no difference if neg is on or off.
  2. Ike
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    Ike Senior Member

    The typical arrangement for DC systems is, the switch is in the positive side. However, if you want to be absolutely sure the system is dead a switch in the negative side will accomplish that, but they should be ganged so that both are switched at the same time like Circuit breakers in and AC system. But having a switch in the negative is really not necessary. It's overkill.
    1 person likes this.
  3. yipster
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    yipster designer

    Could be handy checking the amps tho
    dont know why but all inet sources mention checking amps on the ngative side
  4. DianneB
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    DianneB Junior Member

    I've been in the electrical/electronics field for nearly 50 years and I can't explain the "tingling feeling" from the engine of a fibreglass boat.

    Switching the negative battery lead is unnecessary - it accomplishes nothing and only provides something else to fail (the negative switch). The only case where it would make sense is with shore power if you were having trouble with the charger, stray currents, etc.

    Normally, in other electrical areas, we want all the neutrals/return lines permanently tied together and always connected.
  5. bntii
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    bntii Senior Member

    Just mind that the high voltage service has a two pole breaker & some sort of indicator for reverse polarity.

    Tingling from the engine??
    That sounds more like some stray ac current wandering around in the boat.. Is it always present- that is if shore power is off/disconnected and all battery switches killed?
    What voltage are you running for ships dc power?
  6. Frosty

    Frosty Previous Member

    No all Dc is 12V I have an automatic batt charger and a 2 wire Ac,-- that is no earth what so ever,-- all 240 V appliances are two pin plugs as bought from the shop and is plugged into a 240 v ring main.
  7. sdowney717
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    sdowney717 Senior Member

    so if the appliance wiring fails and somehow shorts to some metal that you could touch, you might become part of a return circuit.

    ABYC new boat standards now calling for ELCI 30 milliamp on the shore power coming into the boat. so if someone goes swimming and you have an electric fault, they wont die?

    They keep taking all the fun out of boating.
  8. thudpucker
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    thudpucker Senior Member

    I'm guessing a 'tingling' is some device in the boat is not well grounded. The AC of that device is grounding through any path it can find. Through some wires, to a crusty old fart leaning on his engine. :)

    An example would be like this:
    As in two appliances sitting on a Stainless counter. One has a 3-wire plug (with ground) and the other has a 2-wire plug supposedly grounded through the Neutral wire to the Entrance panel.
    So the errant ground path from the 2-wire device runs along the stainless counter to the 3-wire device and through it to the grounded wire.

    If you lean against the counter and touch the grounded device you'll get a 'tingle'. That's a parallel path to ground.

    Yes the 2-Wire plug is supposed to be tied to ground through the Neutral. But it dont work out that way all the time and sometimes the resistance is so much that a person leaning on a grounded surface is an easier path to ground.

    If I remember I found an AC Signal on the Smallest AC Scale.
    If you set the 2-wire device up on an insulated surface, and then lean against the Stainless counter you'll likely get the full 110 in half cycles feeling like your in the electric chair.

    I would try this to locate the problem child.
    Put your meter on the low AC scale, ground one end to the Engine or other good ground, and go about touching each device till the meter gives you a reading.

    PS: If your gonna test for AC by touch, ground your Elboe and touch with the back of your hand. That way you dont destroy so much flesh and bone! :)
  9. bntii
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    bntii Senior Member

    I have never felt DC at 12 volt.
    24 can tingle.. so if you are feeling current on something & don't have 24 DC, I am betting you have some AC on the loose.

    Take care- what feels like tingling can become a fatal electrocution if your body is grounded well enough.
  10. thudpucker
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    thudpucker Senior Member

    Yes, only something alternating will give you that Tingle.
  11. Frosty

    Frosty Previous Member

    There is no stainless steel counter, there is nothing standing on steel including me, there is 2 AC wires one comes in and the other out, there is no ac in the engine room at all apart from the power cord that runs up high clipped to the wall.

    Sometimes the tingling feels pshycological and I cant make it do it twice.

    I think it is electrolytic currents I have 2x 24 inch 4 bladers on 2 inch stainless shafts and they are bonded to the stern tube with a shaft brush and attached to the steel rudder that has 2 anodes and 1 on the shaft plus one hanging externally when in dock.

    But would that stray elecrolytic current go the the battery if I left the neg sw on.

    It is very unlikely you will not get a tingle if you try to jump start a ski boat battery in sea water and you are wet through.
  12. Poida
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    Poida Senior Member

    AC current has a magnetic field around it. That's how transformers work. The wirings on a transformer do not touch they pick up the electromagnetic field from one set of wirings to the other.

    Without an earth your metal parts could be picking up the electro magnetic field. Obviously when you touch it you get a tingling feeling, but after grounding it with your body it may take a while for the charge to be enough for your second discharge.
  13. bntii
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    bntii Senior Member

    OK- a wild card: perhaps you are feeling stray current which is in the water from another source.
    If there is current in the water- it will travel up the shafts..

    You in a crowded marina?
  14. Mark Cat
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    Mark Cat Senior Member


    My soon to be toasted friend.

    Where are you (so I can send flowers) and how do they connect AC earth grounding at your marina?

    If AC leakage can find its way through the water back to the AC source without ground fault detection, then your AC installation is not safe.

    Your already feeling AC leakage, an improperly grounded leaky battery charger, and it is most likely finding its way to the water through BAT-. AC appliances electrical insulation can breakdown over time placing AC leakage on the case and output. Especially ones that are not Marine rated and have no AC grounding conductor.

    I can only speak on US/UK and Europe Marine practices.

    In the US your AC installation in unsafe. No Marina would allow this (if they knew), and your AC installation should be repaired by an ABYC electrician.

    In UK/Europe an RCD has been used for many years for pleasure craft, I would have to look up ISO for the adoption date, but I think the RCD is now manditory, although at one point it was voluntary but builders still used it.

    For the US ABYC requires an ELCI which is set to the standard 30mA RCD trip for whole boat AC leakage protection.


  15. thudpucker
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    thudpucker Senior Member

    I bet Poida has the right answer. You wont feel electrolysis from other harbor sources. Only something alternating. Induction is a good bet if everthing is grounded.

    Marks gonna send flowers. Probably Dandylions!
    He reiterates what we've all said. You gotta potentially deadly tickler in there somewhere.
    Remember this: An old Tech's warning. Dont touch anything where the Tickle can go in one arm and out the other!
    It can go across your chest and stop your pacemaker! Even a small AC voltage.
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