Running ground and other battery quesitons

[Greenhand]

According to Nigel Calder, you should never run your DC ground directly from the distribution panel to the engine block. What are the ABYC standards and what are common practices? (And because this is an internet forum, I expect to get plenty of "what do you do") Should we leave the bus to engine block cable, or reroute it back to the batteries?

Also, my husband seems to think that we do not need an isolator nor an ACR. The isolator that came with the boat was not wired correctly - the two banks were connected, but not the alternator. As such, he wants to just use the battery switch. My concern is the possibility of frying our brand new AGM batteries when we start the engine.

[GordMay]

The DC Negative (ground) is connected from Battery Negative Post to Engine & Main DC Ground Bus.
The House Distribution Negative bus is also connected to the Main DC Ground Bus, but not the Engine.


See the “DC Negative & Grounding Diagram”(Fig. 18, from ABYC E-11)
➥ Dc Negative & Grounding Diagram - ABYC Section E-11 - Figure 18 Cruisers & Sailing Photo Gallery

[Greenhand]

Your diagram suggests something that I haven't noticed - I wasn't the one to inspect the connections in the engine room. Perhaps there is another bus there: he just said they all ran to the corner.

I was tired, in case you are wondering why I didn't try to figure out he meant by that.

[djmarchand]

Most boats are wired this way:

The pos from each of the battery bansk goes to the battery switch and then goes to the starter with big 2/0 or so cable. The negative from the batteries goes to a negative bus and then to the engine block to power the starter. The main house panel is powered from the battery switch with #6 or #8 wire. The main house panel's ground is wired to the ground bus.

Nigel's advice was presumably to avoid two grounds from the house panel, but they are tied together via the engine block and the ground bus.

I don't see how you can harm AGMs or any type of battery by starting the engine with the switch set to the starting battery. Then switch to both while the engine is running and back to the house bank when you drop the anchor to keep from running down the starting battery.

David