Re: What's it mean to ground something?
Mark, I do not agree that we are saying the same thing. I consider grounding one pole of a battery to the chassis, block or frame simply a way for the manufacturer to save money, not as a DC electrical standard. There can be some electrolosis advantage in boats to this type of grounding, however.
In addition, commercial AC power companies use a ground return to save money on copper conductors. There are some safety advantages when you connect the neutral and ground connectors together at a residence, however.
Well, beins this is dragging on, and there is something to be gleaned from it by other interested parties, I'll ramble on.
We have 2 things to consider in wiring for our engine driven boats. One is the high current loop, which for most of us is the connection between the battery and starter since it draws 100-200 amperes when working. The other, as you said is electrolysis.
The former dictates that you minimize the length of the start circuit and maximize the wire size. Since the starter is mounted to the block of the engine (for my OB at least) the best place to put the return wire from the battery (- pole in today's US standard) is either on the starter shell, or on the block adjacent to it and there you have your "ground" reference for all the electronics associated with your engine. Mine goes to the shell with a jumper off to the block to insure adequate ground for the engine's electronics. The shell is ceramic (non conductive material), not metallic which would not need the extra jumper. My 90 hp Merc sucks about 125 amperes (rated) starting current so the wiring supplied with the engine to connect to the battery is 6AWG and is roughly 6' long.
Even though the engine is 6' from the battery , the 6AWG wire is usually adequate to insure that the engine and battery are at the same reference potential (call it ground) so external wiring like for accessories, lights and all, can come from the engine block or the battery terminal. I realize that if you have large cabin cruisers and all, you need to rethink the wiring especially since you may be running power inverters, air conditioners, and other high load circuits long distances.
My engine has Zinc sacrificial plates both on the mid-section of the lower unit and on the bottom of the clamp bracket. On the lower unit, the trim tab is also Zinc. The mid section has a grounding jumper between it and the clamp bracket. The clamp bracket is bolted onto the transom, aluminum in my case. So we have a nice tidy ground reference for all the metallic parts and if any eddy currents get going the Zinc is there to sacrifice.
Now, my hull could be my wiring ground reference, since it is a nice conductor (aluminum) and is connected to the ground reference, but it's not; I use the - terminal of the battery for all wiring other than engine and trolling motor (trolling motor/batteries is a totally separate circuit). On a bigger boat, or a plastic one, If I had too many wires to mount directly on the battery, I would mount a ground reference plate adjacent to the battery, as close as is practical, with adequately sized wiring to insure essentially a zero voltage difference between the two.
On non-related house power, but it is as I used it initially in explaining the term "ground", The NEC code that my house and power input are wired to specifies an 8' stake driven into the ground immediately adjacent to the input power/power distribution box. This is my neutral/ground reference for my house.
The transformer hanging on the utility pole has a single primary winding of 14kv and a dual, or center tapped secondary of 230v, or, using the center tap to supply 2 outputs of 115v per leg.
The transformer input utility wiring also carries a ground return (ac neutral) wire the same size as the hot lead. The return wire is also earth grounded at each utility pole to insure that voltages don't develop along the return wire that could pose a health threat.
The 3 secondary transformer wires are connected to my ac power distribution panel for usage as necessary, 230v for the high power loads, and 2 ea. 115v inputs for the light loads and everything is referenced to the earth you stand on, hence ground.
Some years ago, the third wire (safety ground) was added and was used to establish a ground reference on metallic cases of things powered by ac in the event the ac neutral accidentally developed a voltage. The ac return wire carries the same current as the hot lead (on 115v circuits) and could develop a voltage caused by the ac current used by the appliance, but the safety ground does not carry any current and hence develops no voltage as a result, remaining at the same potential as the ground reference in the power box; hence the user has no shock potential (theoretically). Course, with a lot of today's portable appliances with plastic cases, this becomes somewhat of a moot point.
Well, I guess we gleaned something from this.
Have a nice day,
Mark
Most likely would be the old 6v system as well.
