Bonding Systems and Grounding Systems - isolate?

[the_alpine]

Maine Sail - whats your take on this? Should a boats bonding system be completely seperate from any DC ground? The only way to do this is to not connect DC negative to the engine block, no?

If lightning suppression is taken out of it (mast, stays, etc to keel), and bronze thru-hulls are bonded together, the system would need to be bonded to the prop. The rub is if ya do that, you're now bonded to DC negative via the engine block.

 

[Stu Jackson]

This is an oft-quoted article:

http://www.westmarine.com/WestAdvisor/Marine-Grounding-Systems

 

[Charles Erwin]

Think about it this way:

DC negative conductors and (underwater) metals bonding conductors are actually separate even though they are fastened together at one place - the motor block. The common fastening point at the motor block is the end of a bonding series whereas the battery is the end of a DC circuit.

The idea is to assure bonding conductors never conduct DC battery current. So the rule is never use a bonding conductor (traditionally green) as a DC negative conductor (black.) Actually in many boats a bonding conductor does not end at the motor block and instead ends at a separate submerged zinc fastened through the hull to the bonding conductor. But it is easier to end bonding at the motor block which means the shaft zincs protect the underwater metals connected together in the bonding conductor chain.

So you are right. The bonding series is fastened to DC negative because the battery negative cable is fastened to the motor at the same place. But - the bonding system is considered 'separate' because it does not carry any DC battery current.

Charles

 

[centerline]

Maine Sail - whats your take on this? Should a boats bonding system be completely seperate from any DC ground? The only way to do this is to not connect DC negative to the engine block, no?

If lightning suppression is taken out of it (mast, stays, etc to keel), and bronze thru-hulls are bonded together, the system would need to be bonded to the prop. The rub is if ya do that, you're now bonded to DC negative via the engine block.

the word "bonding" as applied to boats can be a confusing, yet relative term.

there can be bonding between the AC and DC grounds..
there can be bonding between all underwater fittings, prop shaft and other protuberances...
and then there can be bonding for lightening protection.

and the "how and why" of bonding any system, or systems together can be more than a bit confusing too, as you seem to be well aware of

but no matter what type of bonding you are working with, how you do it or what you believe to be safe, there will always be a DC ground to your engine block as long as it requires a battery to start, run or monitor gauges.... you cannot do away with the DC ground to the motor.

 

[Bill Roosa]

there are several grounds in a sailboat
DC
AC
corrosion
Radio
lightning
shore power (only when on sp of course)

The trick is to get them all to work at the same time.
FWIW I would ground the radio to sea water directly and not screw around with lining the inside of the boat with foil. It is much better to use the sea directly than to try and "connect to it in a capacitive fashion"
AC to DC (that is pretty much a law) at the common ground point.
corrosion.........kinda depends on your corrosion prevention plan, you do have a plan right?
Lightning, this stuff has NO business inside a boat, direct it overboard with battery jumper cables off the forestay, shrouds port and starboard and back stay(s). I used a set of old jumper cables cut in half so there is a battery clamp on one end and bear wire on the other. Size for you boat as the bow one will be longer then the stern.
Shore power, best is an isolator, which you can make pretty easy BTW