Electrical Question

[pablor]

Hi

My furuno network sounder asks for a chassis ground connection. The manual says that in fiberglass boats one shouls add a 8x10 metal plate to the bottom of the boat to get a good ground connection. Obviously I am not adding a metal plate to the bottom of the boat. The only other place I can think of is the engines, but this is too far away and cumbersome. Where do you think i can get a good ground connection on a 360 near the elec box?

Thanks!

 

[catch22]

If you don't have a grounding plate, I think the best thing is to run a dedicated ground wire, (16 or 18 gauge) back to the negative post on one of your batterires.

 

[Capt Bill]

Catch22 is right about using the battery negative for your ground, but it should be much heavier gauge than 16-18. If your boat has a power buss under the helm or in the electronics box, it is probably fed directly from the batteries with an 8 or 10 ga wire, which should be fine.

 

[pablor]

do larger grady's have a grounding plate built in? I have a 360...

Can I run it to the fuse box in the helm directly? I read somewhere that furuno if you need to ground it to the battery, dont ground it at all.

 

[catch22]

Catch22 is right about using the battery negative for your ground, but it should be much heavier gauge than 16-18. If your boat has a power buss under the helm or in the electronics box, it is probably fed directly from the batteries with an 8 or 10 ga wire, which should be fine.

I think when it comes to a chassis ground, (rf ground) there's really no current draw, so the 16 or 18 should be ok. It's for preventing, (grounding out) noise and interference. It can't hurt to go bigger though.

I thought about suggesting a local ground, but on one of the units I just installed, (Raymarine autopilot), it said not to. It specifically said a dedicated wire to the battery ground, (if there's no ground plate).

 

[Grog]

There normally isn't current draw to the "ground" but in case of a lightning strike larger is definitely better. Also if there isn't a good bond, the manufacturer can use that as an excuse (you should see some of the old Allen Bradley specs for grounding).

 

[Jasom]

Wish you all the best on youre boats, can anyone tell me where the other end of these go to, I retrieved the othe end of these apparent bonding wires but no clue where they go, any help would be greatly appreciated.

 

[seasick]

If you have thru hulls or sea cocks that have bonding wires, the place where they ALL interconnect is where you want to get your 'ground'.

If no bonding, I would ask the company what they recommend to do with that ground assuming that the sounder has a pos 12 v connection, a neg 12 v connection and a separate ground connection. They may recommend connecting it to the neg wire or even leaving it disconnected. Maybe they will say to run a separate wire to the battery compartment.
I am hesitant to run ground wires to a negative battery feed since that can create a condition called a ground loop. Ground loops are caused when there are two paths for a current to flow but the voltage at the ends of those two paths are different. Yes you would assume that the voltage on a negative battery feed would be 0 volts but under load it may be really close but not exactly zero volts. The difference which could be in the thousandths of volts (milivolts) but nevertheless creates a small current and that current is similar to what happens with sacrificial anodes. Something is going to experience electrolysis.

If you speak to Furuno, let us know what they say. I need to get educated