Common ground

[Bycrick]

Lead is used for battery terminals because the plates are made of lead. One wouldn’t want a copper/lead connection inside the battery.

In a high current circuit, the resistance of the block is most definitely important, which is why most high-current alternators have a separate, isolated ground, rather than using a case ground. Just because steel, or brass, conducts better than air is no justification for using it as a conductor in any circuit carrying more than a few amps over a short distance, as on a motor.

If one is going to spend hundreds/thousands of dollars on batteries, alternators/controllers, solar charging systems, etc., it doesn’t seem to make a lot of sense saving $50 on a bus bar to lose 5-10% of your energy in waste heat.

Small fractions of an ohm make a big difference overall in a high-current circuit. If the total resistance of your battery-to-alternator circuit is only 5/1000 of an ohm, that’s half a volt drop at 100 amps. That’s about 4%. And achieving that number requires that every terminal, connection and component is perfect.

[CharlieJ]

Using the engine block as a B- "bus" is not a good idea. Slight differences in potential from one part of the block to another negative connection will have slight current flow through the block. As I recall, there have been instances where the current flow was high enough that main bearings were damaged from micro-arcing.

[er9]

Originally Posted by CharlieJ

Using the engine block as a B- "bus" is not a good idea. Slight differences in potential from one part of the block to another negative connection will have slight current flow through the block. As I recall, there have been instances where the current flow was high enough that main bearings were damaged from micro-arcing.

i know this post is a bit dated but would really like to hear what IS the best place to connect a Neg bus bar? its clear using a bus bar is a better option than ten terminals on a single spot on the engine but, the other end of that negative wire has to go somewhere? iv'e heard the starter post is a favorite location but on my boat i cannot reach my starter without taking my entire exhaust manifold and expansion tank off.

[boatpoker]

Originally Posted by er9

i know this post is a bit dated but would really like to hear what IS the best place to connect a Neg bus bar? its clear using a bus bar is a better option than ten terminals on a single spot on the engine but, the other end of that negative wire has to go somewhere? iv'e heard the starter post is a favorite location but on my boat i cannot reach my starter without taking my entire exhaust manifold and expansion tank off.

Read Charlies post again. What he is saying is, don't use the engine as a bus. i.e. multiple points of grounds. Have the bus before the engine with only one point of ground on the engine.

[GordMay]

Originally Posted by boatpoker

Read Charlies post again. What he is saying is, don't use the engine as a bus. i.e. multiple points of grounds. Have the bus before the engine with only one point of ground on the engine.

Indeed.

[er9]

Originally Posted by boatpoker

Read Charlies post again. What he is saying is, don't use the engine as a bus. i.e. multiple points of grounds. Have the bus before the engine with only one point of ground on the engine.

as a novice in electrical you could also read the second half of his post another way which makes it confusing. to a novice it appears he says a (any?) negative connection to the 'block' can cause arcing damage internally.

i notice on my engine i have a second ground on the back of the engine (looks original) through one of the bolts connecting the flywheel housing cover. i have another on the front, lower engine 'block' plus alternator and starter. To add the OP asks about grounding to the transmission. so im left wondering what is actually an 'engine block' when discussed as an electrical grounding reference by those with a lot of knowledge. are they referring to the bottom half of the engine that houses the pistons or generally as the entire engine?

If they are referring to the lower half of the engine housing i would guess then that there would be another/preferred connection point? Is that why the starter lug gets referenced as a preferred ground by Mainesail and why i have another ground on my flywheel? did a P.O. add the ground i have on my lower block and i should relocate it?

sorry dont mean to make a mountain out of a molehill but i know enough about electrical now to know its not something i want to get wrong and, i just added all new heavy ground wires to my engine block (piston housing) that feeds my negative bus bar so just want to be sure.

Thank you CharlieJ. dont mean to pick on your reply in particular, it was just a good reply to use to extract a better overall understanding of proper 'grounding'. it will certainly benefit me and i hope all the future electrical novices like me that really need to understand this.

[CharlieJ]

@er9 #21
The figure from ABYC E-11; AC and DC Electrical Systems on Boats posted as #20 by GordMay is very informative and should be used as a guide.

as a novice in electrical you could also read the second half of his post another way which makes it confusing. to a novice it appears he says a (any?) negative connection to the 'block' can cause arcing damage internally.

The damage may come if there is a voltage differential from one connection point on the block to another. Best to follow the figure above and install a bus bar with a single connection to each engine block. Note that some modern engines with electronic controls have special conditions when dealing with the B-.

[boatpoker]

Originally Posted by er9

as a novice in electrical you could also read the second half of his post another way which makes it confusing. to a novice it appears he says a (any?) negative connection to the 'block' can cause arcing damage internally.

i notice on my engine i have a second ground on the back of the engine (looks original) through one of the bolts connecting the flywheel housing cover. i have another on the front, lower engine 'block' plus alternator and starter. To add the OP asks about grounding to the transmission. so im left wondering what is actually an 'engine block' when discussed as an electrical grounding reference by those with a lot of knowledge. are they referring to the bottom half of the engine that houses the pistons or generally as the entire engine?

If they are referring to the lower half of the engine housing i would guess then that there would be another/preferred connection point? Is that why the starter lug gets referenced as a preferred ground by Mainesail and why i have another ground on my flywheel? did a P.O. add the ground i have on my lower block and i should relocate it?

sorry dont mean to make a mountain out of a molehill but i know enough about electrical now to know its not something i want to get wrong and, i just added all new heavy ground wires to my engine block (piston housing) that feeds my negative bus bar so just want to be sure.

Thank you CharlieJ. dont mean to pick on your reply in particular, it was just a good reply to use to extract a better overall understanding of proper 'grounding'. it will certainly benefit me and i hope all the future electrical novices like me that really need to understand this.

Sent you a PM regarding ABYC Standards