bigal.nz 59 Posted February 23, 2019 Share Posted February 23, 2019 I went to find earth on my boat the other day. It looks like its on the engine in the attached picture. There is a very thick black wire which goes to the battery compartment. Also to the same mounting point on the engine is several smaller white wires which join in the photo just below the coolant hose and go to the same spot on the engine. If this is earth, shouldn't the wires be green? In the second photo, one of the same white wires seems to go to a bolt which I think connects to the prop shaft mount. What would this be fore? Cheers AG Quote Link to post Share on other sites
bigal.nz 59 Posted February 23, 2019 Author Share Posted February 23, 2019 Well in addition to the white wires there is a few green ones, but I haven't established where they terminate. More time tracing I guess. Quote Link to post Share on other sites
bigal.nz 59 Posted February 24, 2019 Author Share Posted February 24, 2019 Got one of those. What in particular do you suggest checking? Quote Link to post Share on other sites
Crazyhorse 47 Posted February 24, 2019 Share Posted February 24, 2019 As above, hate the term earth, much prefer "common" as in zero volts potential in relation to all other equipment and power supplies. Unless your starter motor and alternator is designed to run on a common plus volts (positive earth) then any cable connected directly to the engine body is going to be a common so zero volts. Unless you are wired for 240v AC you will find any and all wires attached to the same common point on the engine are simply supplying a direct return path from other equipment like your DC switch board etc. Quote Link to post Share on other sites
bigal.nz 59 Posted February 24, 2019 Author Share Posted February 24, 2019 I am still curious about the colors of the wires. ABYC details colors for the DC system (green for DC grounding conductor). No mention I could see in the standards for any AC system. Still leaves me wondering what the difference is between the white and green circuits on the boat......be there tomorrow..... Quote Link to post Share on other sites
Crazyhorse 47 Posted February 24, 2019 Share Posted February 24, 2019 I am still curious about the colors of the wires. ABYC details colors for the DC system (green for DC grounding conductor). No mention I could see in the standards for any AC system. Still leaves me wondering what the difference is between the white and green circuits on the boat......be there tomorrow..... With out actually seeing the wiring, as its DV (12v?) I am guessing the white and green wires were put in by a previous owner and to no accepted standard other than their own. Running multiple commons back to one point is nothing to be worried about and is advisable to prevent voltage drop between various components which could acellerate electrolysis. You haven't said if you also have a parallel AC system? Quote Link to post Share on other sites
bigal.nz 59 Posted February 25, 2019 Author Share Posted February 25, 2019 I checked tonight. The white wires which run all over the boat connect to all the thro hulls, like sea cocks, dynaplate etc. Quote Link to post Share on other sites
Island Time 1,211 Posted February 25, 2019 Share Posted February 25, 2019 Bonding system. Quote Link to post Share on other sites
idlerboat 116 Posted February 25, 2019 Share Posted February 25, 2019 As IT said. White wires are the bonding system that connects bronze through hull to the anodes. Sometimes this is connected to the boats overal earth / Negative / ground ... Lots of variations exist depending on what is bonded and why..... To be blunt, often there is a lack of coherent reason ! Colour coding is a great idea but the reality is that very few boats are fully wired to spec (and there are different specifications as well. ) Retro fit wiring makes it even more complicated as this is almost never done to any specific colour code. American specifications can also cause problems, particularly if there is 110 volts in an older vessel. Be VERY careful of this... They can be wired with a black and a white wire that are not in two wire shielding (ie individual lose conductors.) What makes this even more dangerous is that sometimes this setup is converted to take 240/220 volts... To make life really interesting...some production boats have nearly all of the 12 volt + wires as red...with little numbered tags that are great....if you have the original boats manual....and....before they all fall off : ) The large black wire is the essential return for the engine alternator and starter motor. (although some "marine spec alternators will have a dedicated earth wire.) The starter motor will be earthed through the motor. Good luck with your mission... Quote Link to post Share on other sites
Crazyhorse 47 Posted February 26, 2019 Share Posted February 26, 2019 I checked tonight. The white wires which run all over the boat connect to all the thro hulls, like sea cocks, dynaplate etc. If your hull is constructed in ply or timber, be careful running a common to all through hull fittings. Earthing straps are heavy duty fine mesh copper to minimize voltage drop and anything else can cause a voltage potential to occur between components in sea water which will slowly weaken the timber around them. My understanding is earthing skin fittings is actually counter productive and not necessary as a circuit can not be set up unless the hull is made of a conducting material, aluminium or steel. Quote Link to post Share on other sites
Dagwood 57 Posted February 26, 2019 Share Posted February 26, 2019 If you have a traditional wooden vessel - some interesting info re bonding here: https://waitematawoodys.com/2015/05/15/electrochemical-damage-to-wood-the-marine-version-of-leaky-homes/ Quote Link to post Share on other sites
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