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ContinuousWave: Small Boat Electrical
DC Power Wiring With Separate Ground Conductor
|Author||Topic: DC Power Wiring With Separate Ground Conductor|
posted 07-25-2007 02:48 PM ET (US)
I notice that most electronic equipmenet has three wires for power connection:
positive, negative, ground. Do I have to connect the ground wire to the main ground bus on the boat (which is wired directly to the battery negative)? Or can I just connect it to the negative wire (right at the equipment) and thus only have to run one wire on the negative side? Hope the question makes sense. It just seems odd to have two seperate wires run to the same place- negative bus. What's up with that?
posted 07-25-2007 08:16 PM ET (US)
I disagree with your characterization. In DC systems I do not find that most devices have three power connections. Most devices I encounter have just two:
posted 07-25-2007 09:17 PM ET (US)
I agree with JimH: Most 12V marine electronics does not have
a separate ground. There may be some exceptions (I suspect
they are radios), but most only have two wires.
How about an example (make and model)?
posted 07-25-2007 11:27 PM ET (US)
I suspect that in the case of a RADAR ( and I am making this assumption based on other articles posted by the author on this topic) that the power conductors are provided in a shielded cable in order to help prevent any radio frequency feedback which might tend to occur due to the high power radio emission from the antenna inducing some voltage into the power supply line.
posted 07-27-2007 07:10 AM ET (US)
OK, got it figured out! Thanks for the input all. A quick rundown for all those who may have similar questions in the future-
Normally (not always), most 12/24v systems on outboard boats DO NOT have a bonding/grounding system connected to the H2O. Some Mfgs. call it a "floating" ground because it is never truly "grounded" by the water/earth. In this case, most electronics mfg. either tell you to cut and insulate the ground wire (i.e. don't even use it), or like in the case of Raymarine, they say connect it to the negative side of the battery. Some, like Garmin, just give you a red and black wire period- no choice in the matter 'cuz there is no ground wire to worry about.
I don't know how other boat builders do there systems, but BW has what they call a "main ground bus". This is NOT a ground at all, it is the negative side of the connection, and is wired directly to the negative battery post. This is where I got really confused!
As for the radar and converter: same thing, just use red and black wires for everything (per mfgs. recommendations via phone call to Analytic Systems and Raymarine).
I would like to know if anyone has put in a true grounding system in their boat, and if it actually helped with noise, etc.
Thanks again, Griff
posted 07-28-2007 02:56 AM ET (US)
My example is Raymarine. All of their equipment has black, red, ground wires. And, in the manuals it specifically says to hook the ground wire to the ship ground or the batt. negative. Northstar has ground wires as well, but they say in their manuals to cut and insulate them. Go figure! So much for standards- I wonder which is better, cutting and insulating or running to ground (pardon the pun). ;>)
posted 07-28-2007 08:50 AM ET (US)
In response to your "I wonder which is better, cutting and insulating or running to ground".
The engineers that design the installation of electronic systems usually connect as much of the available shielding to the ship's hull, the negative side of DC power, or ground as possible.
The shielding is always connected to the equipment chassis. And in turn, the equipment chassis is bonded or grounded to ship's hull. Some electronic equipment enclosures provide a grounding post on the outside of the container. All electronic system installations should have these grounding/bonding connections hooked up.
Obviously, without a metal ship's hull, the only alternatives for shield connections are to use a dedicated grounding/bonding system or the negative side of the DC power distribution. Ultimately, most of the grounding/bonding connections also connect to the negative side of the DC power distribution.
Most of the new multiconductor cables used for electronic system hookup utilize a shield of some sort. Some have wire braid shields and some have foil shields with bare drain wires used for electrical connection. All shields should be connected including both ends of the same cable.
About spare wires within multiconductor cables, the prevailing installation methods have the conductor ends insulated and tied back into the wire harness.
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