Common Ground - do I need it

craigswardmtb

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?

craigswardmtb

Boat is a 2005 360.

212rowboat

fuse on ground?

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..

212rowboat

exert:

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.

Capt Ron

If you are tying your battery charger to the shore power then it's not separate from the existing system. I would recommend you tie the grounds to the panel bus bar as recommended in the previous post by Drewactual.

craigswardmtb

Thanks for the info guys.  Sounds like i'll be running a ground wire.  So would the panel bus bar be behind circuit breaker panel in the cabin?  My panel is located towards the bow starboard side in a cabinet.

Black_Diamond

I bet your ground bar is in the engine room.

TikiHut2

Here's another thought. Galvanic corrosion is quirky stuff with two seperate systems containing dissimilar metals on the same boat that aren't bonded together. The interconnected ground wire connection seems obvious to me but It may be that they are referring to an additional bond wire and not necessarily a ground so that everything is tied together to act on your main anodes for protection against galvanic corrosion rather than each other/themselves (like all the through hulls should be).... Just a thought, but I don't have the manual in front of me either.

craigswardmtb

TikiHut2 said:

Here's another thought. Galvanic corrosion is quirky stuff with two seperate systems containing dissimilar metals on the same boat that aren't bonded together. The interconnected ground wire connection seems obvious to me but It may be that they are referring to an additional bond wire and not necessarily a ground so that everything is tied together to act on your main anodes for protection against galvanic corrosion rather than each other/themselves (like all the through hulls should be).... Just a thought, but I don't have the manual in front of me either.

Here is the wiring schematic and installation instructions..  It shows going back to the ground on my starting battery.  If I can find somewhere to ground everything closer to the panel in the cabin that would be ideal.  Either way i'll be fishing wires from the joystick back to the motor controller.  So I'm hopeful I can make heads or tails of how Rinker wired this beast, and hopefully the wire chases are somewhat accessible.  I'll be sure to take lots of pictures and a how to for anyone else that decides to embark on this.

frenchship

craigswardmtb You should contact Randy Rinker to get the wiring diagram for your boat it will surely help find where things are for your need: rrinker@nauticglobalgroup.com

craigswardmtb

I actually did get the wiring diagram from Randy.  Pretty impressive 70 pages of wiring.  I couldn't locate the grounding bar in the diagrams.  However to my surprise I got a call from Randy this morning.  That's some great customer service.  He informed me that I do not need to ground to a grounding bar because the bow thrusters are operating on their own system.  He said so long as I ground the joystick to the bow thruster batteries rather than a ground in the engine bay I would be fine.  I asked about the charger being tied into the AC system and he wasn't concerned.  I have a call into the bow thruster manufacturer to vet this info, however their lead tech and owner of the company is on vacation this week.  I want to believe Randy.  We also talked about fishing wires from up at the helm.  This does not sound fun.  He said the wires do not have a chase tube but rather fish along the deck joint on the starboard side.  He said I would likely have to remove cabinetry and panels to get at the wires.  Not fun.  I'm going down to the boat today to look around to see if there is another option to safely hide the joystick wire.

212rowboat

I'd reckon Randy would know best... and this sure makes it easier, huh? :-)

Michael T

Just my 2 cents but I don't like the sound of anything not grounded in a marine application (or anywhere else for that matter). Can you ground it to one of the shorepower sets on either side of your hull. Do you have access ports in the backs of your cabinet lockers in the cabin. Can you use those and other openings to fish a ground wire along? I know this is "easy" for me to say because I'm not the one facing the task but easy or safe pick one. If it were me I'd run a wire two AGMs produce a LOT of amps.:-) MT

raybo3

Let me chime in here. Batteries do not have "grounds" they have a positive and a negative. A negative is a big difference than a ground. So how do you ground a battery? A true ground is only for fault current and fault current only. Now the charger should be grounded for sure. Also never EVER put a battery negative with a shore power ground.