Sharing ground for DC systems?

[_Ryan_]

I have a couple questions about DC wiring and haven't seen it answered anywhere else on the forum. I am building a woody teardrop and will not be grounding anything to the frame as it is not accessible, instead I will be running 2 wires to every load for both the trailer lights, as well as the teardrop's own 12 volt system.

Should the trailer lights from the TV, and trailer's 12 volt system be completely separate, or can they share the same ground? For example I was thinking I could tap into the terminal strip for the ground wires which go to the trailer battery and then tap the TV ground for the running lights off of that. I believe I have seen this setup elsewhere as the negative terminal from the battery is tied to the frame, but I can't wrap my head around how this would work since 2 batteries would be involved (trailer and TV).

Also do the individual trailer light runs (green,yellow,brown) need to be on fuses if they are run through the trailer? I am wiring the turn/tail lights and license plate lights through the hatch so a short would be really bad. There will be a master fuse up at the positive terminal of the TV battery for the trailer light after market module kit I am installing.

Thanks in advance!
Ryan

[bobhenry]

GROUND IS GROUND


HOWEVER , if you have an on board battery return all your courtesy lighting and 12 volt interior goodies to the on board batteries ground post. You can then continue the ground circuit to the tow vehicle if you wish but unnecessary UNLESS you are charging the onboard battery from the tow vehicle then to complete the charging circuit it WILL be necessary

As to the tow package lighting it is sharing overload protection with the towing vehicle and these lights should have a return ground to the tow vehicle. Some wiring harnesses will do this some won't. I added a dedicated ground for the towing lights and a large allegator clamp to connect directly to the tow vehicles frame.

Were you to add additional fusing in the trailer wiring harness for the tow lights you could be without lights and totally unaware.

[Dale M.]

As Bob Henry says, you can ground both TV grounding for marker/clearance and stop/turn and tail lights and all interior DC circuits, even battery in TD to a single common ground point.... As long as you do not create a current path, from positive sides of TV battery through lamps or what nots to positive side of TD circuits through lamps and accessories you will be safe, this does not mean you can not charge while while towing, putting the two batteries in parallel doe not violate the forbidden current path rule...

I would just run everything that require a ground to single ground bar at convent location... Something as simple as this (available as most hardware stores in electrical dept) would be sufficient....



Maybe keeping all TV lighting grounds on one half of bar and all TD ground on other half of bar, just for some clarity and possible trouble shooting at some alter date....And you can double up by maybe putting two ground wires in single hole....

Dale

[_Ryan_]

I appreciate all the help guys!

Were you to add additional fusing in the trailer wiring harness for the tow lights you could be without lights and totally unaware.

Great point!

As Bob Henry says, you can ground both TV grounding for marker/clearance and stop/turn and tail lights and all interior DC circuits, even battery in TD to a single common ground point.... As long as you do not create a current path, from positive sides of TV battery through lamps or what nots to positive side of TD circuits through lamps and accessories you will be safe

Bingo, this is exactly what I needed to know! Thank you! I am using a Blue Sea fuse box with 12 ground terminals.

this does not mean you can not charge while while towing, putting the two batteries in parallel doe not violate the forbidden current path rule...

hmm, so in effect I would be setting up the system in parallel which a positive wire hooked up between the tow vehicle and the trailer battery. I could then charge when towing just by connecting this single cable. This brings up another question as I am planning on using a 4 wire flat connector which I believe uses 14/16 gauge wiring. Would this overload the wiring if I were trying to charge the trailer battery with this gauge wire as ground?

[H.A.]

[quote=]
This brings up another question as I am planning on using a 4 wire flat connector which I believe uses 14/16 gauge wiring. Would this overload the wiring if I were trying to charge the trailer battery with this gauge wire as ground?[/quote]

A flat four connector has JUST enough capacity for the bare minimum of US style trailer lighting, As well "flat fours", are cheesy construction at that.
14 or 16 AWG conductor is not suitable for a typical trailer battery to car battery connection either.
If the distances were short,one might squeeze by with 10 AWG. But 8 AWG or 6 AWG would be more suitable.

You should use a trailer connector with more conductors such as six or seven (as well it would need at least two pins suitable to serve the large size of the battery connection)
Or stick to the flat four for the minimal lighting it can serve, Adding an addtional two or more pins connector to serve the heavy battery connections.

[Dale M.]

A seven pin flat blade (RV style) is pretty much standard for most larger trailers and what nots.... Its the usual plug/socket combination found on most pick ups manufactured to day..... IT allows for all your required tow lighting, and for brake circuit and aux 12 volts supply (charge while towing) and a backup lights (or center high mount stop light)...

http://www.etrailer.com/faq-wiring.aspx

Dale