Common Ground - do I need it
craigswardmtb
Member Posts: 1,015 ✭✭✭
Im getting ready to install my thruster. The instructions are pretty poor and I'm sure I'll be calling sideshift as I work through the install. I'm putting two agm batteries and an independent 20 amp charger up in the bow. The charger will be tied to my shore power. The thruster instructions call to connect the batteries to a common ground on the boat. Do I really need to do this seeing the thruster is independent of any other systems on the boat? I have read conflicting reports as to whether I really need to fish a wire back to a common ground, which I assume is in the engine room, or a grounding bar somewhere around the dash. Do you guys have any insight around this?
Comments
If you do run it to a common ground, you're gonna want to isolate the negative lead between the post and common ground.. the easiest thing to do is to is implement a stout diode or even a fuse (yes, on the negative lead) to protect both the remainder of the boat from those batteries but also those batteries from the rest of the boat.. especially while charging from shore power that isn't well known.
As far as using a common ground, I think I would, as if its truly ground its going to be common anyway... If you simply fuse between the common ground and the post with an appropriately rated fuse, you get the best of both and no draw backs.
I'm interested in seeing what the smarter folks here have to say about it, though. :-)
Edited to add: this is NOT to suggest not fusing/relaying the positive lead as well.. it won't hurt a thing to fuse both.. alterations in current are felt on the ground first, though its lightning fast.. protecting the hot line is obvious: broken lead, current stops.. in this scenario, a broken circuit on the common ground downwind of the thruster would place your thruster on its own individual circuit, still protected.. I would want as little networks/circuits as possible, so, I would common the guys on ground..
Every light or appliance should be wired with its own DC return wire. Never use the mast, engine, or other metal object as part of the return circuit. The DC load returns of all branch circuits should be tied to the negative bus of the DC distribution panel. In turn, the negative bus of the DC distribution panel should be connected to the engine negative terminal or its bus. The battery negative is also connected to the engine negative terminal or its bus. The key factor here is that the yacht's electrical system is connected to seawater ground at one point only, via the engine negative terminal or its bus.
pretty good read here: grounding
you're in a little bit of a different situation with those thrusters having their own specific batteries... I'd still limit the earth to one point on the boat, though... it makes sense.
PC BYC, Holland, MI