Navico autopilot wiring

[mrangry]

I am in the process of installing a Navico NAC 3 autopilot and B&G T2 ram. Looking at the (poor) installation instructions it advises that the main course computer should have and adequate power supply (+ve and -neg) for its electrical load which is all fine. It then states that there should be a separate ground wire in addition to this. It seems odd (to me) that a separate -ve cable would have to be run to the unit when I am already supplying one. Am I missing something here?

 

[wonkywinch]

I am in the process of installing a Navico NAC 3 autopilot and B&G T2 ram. Looking at the (poor) installation instructions it advises that the main course computer should have and adequate power supply (+ve and -neg) for its electrical load which is all fine. It then states that there should be a separate ground wire in addition to this. It seems odd (to me) that a separate -ve cable would have to be run to the unit when I am already supplying one. Am I missing something here?

I'm not as familiar with boat electrics as I am cars and houses but in some situations it could be possible that the negative is not the same as "ground". In cars, they are mostly negative earth and in houses the neutral is at earth potential (but not the same thing). I recently replaced an AC42 with a NAC3 and saw the requirement for the earth but since the wire wasn't there on the AC42, I didn't bother adding one for the NAC3. It all worked fine.

I don't know if the Navico manual is different from the B&G one but I found it straightforward so maybe the B&G manual is different for the same product?

Downloads | B&G Sailing Electronics

 

[mrangry]

I'm not as familiar with boat electrics as I am cars and houses but in some situations it could be possible that the negative is not the same as "ground". In cars, they are mostly negative earth and in houses the neutral is at earth potential (but not the same thing). I recently replaced an AC42 with a NAC3 and saw the requirement for the earth but since the wire wasn't there on the AC42, I didn't bother adding one for the NAC3. It all worked fine.

I don't know if the Navico manual is different from the B&G one but I found it straightforward so maybe the B&G manual is different for the same product?

Downloads | B&G Sailing Electronics

Interestingly the "system wiring example" in the instillation guide doesnt show the separate ground wire.

 

[PaulRainbow]

I am in the process of installing a Navico NAC 3 autopilot and B&G T2 ram. Looking at the (poor) installation instructions it advises that the main course computer should have and adequate power supply (+ve and -neg) for its electrical load which is all fine. It then states that there should be a separate ground wire in addition to this. It seems odd (to me) that a separate -ve cable would have to be run to the unit when I am already supplying one. Am I missing something here?

Ground is not -ve, as such, it's a grounding wire, as it says on the tin. If the boat has a ground plane (not common) you connect to that, if not you can connect it to the battery negative.

 

[mrangry]

Ground is not -ve, as such, it's a grounding wire, as it says on the tin. If the boat has a ground plane (not common) you connect to that, if not you can connect it to the battery negative.

Thanks Paul. I dont have a grounding plate just -ve bus bar which goes to engine block. Can I then just piggy back of the -ve connection next to the +ve feed on the NAC3 supply as I just dont see what running another -ve cable is achieving?

 

[PaulRainbow]

Thanks Paul. I dont have a grounding plate just -ve bus bar which goes to engine block. Can I then just piggy back of the -ve connection next to the +ve feed on the NAC3 supply as I just dont see what running another -ve cable is achieving?

It's supposed to go back to the -ve, but in the real World, it usually works fine as you describe.