RV 12 volt negative lead to battery...Just grounded to closest steel?

[dlshunter]

I'm surprised I have to ask this, but are most 5th wheel 12 volt systems just grounded from the neg battery post to the closest steel/iron part?  Like a typical car/truck?

 

[Lou Schneider]

Usually there will be a negative wire run back to the negative buss in the 12 volt fusepanel, then from there to the chassis. There may be exceptions, but 12 volt house components have their own negative wires running to this buss, the only things that may be connected to the frame are the automotive components (brakes and lights) and the 120 volt safety ground.

 

[Rene T]

Mine runs to the frame about 18? away.

 

[John From Detroit]

THey do it both ways.. By the way.

I have some radios around here that can suck serious current.  one is 5/25/50 watts one is 5-100 and one is zero to 5 (That's the one I use the most and yes ZERO (Transmitter is actually disabled and just the other parts working talks to a computer via a data cable and Wi-Fi from there to.. Throw a dart at a world map and a good chance where the dart sticks.. IE: Toyoko, Hong Kong, South Korea.. Germany. England.  All over USA they call it "Termial mode)

Well that last one is hand held so it has its own battery

But the big ones they tell you to run both positive and negative all the way back to the battery and to fuse both leads as well. 

 

[Gary RV_Wizard]

Short answer is yes, the chassis is the ground reference for the 12v system and the negative battery base is wired to it.  In most of the systems I see the battery negative goes direct to solid chassis steel, but it may be tied through the converter or inverter panel negative because that also needs a solid connection to chassis ground. Either way works as long as the cable is of sufficient size and the connections are high quality.

 

[Mark_K5LXP]

THey do it both ways..
...
they tell you to run both positive and negative all the way back to the battery and to fuse both leads as well.

Yes "they" do and for the simple reason is chassis grounds aren't always a direct path back to the battery.  I've measured over an ohm from the equipment location to battery negative which is a lot of voltage drop for a high-ish current device.  Not so much an issue for a vehicle with a frame like an RV but with unibody cars that have thin metal and glued seams, there's no telling what the DC path through the body will be back to the battery chassis ground point.

The hazard here is connecting anything directly to the battery negative terminal which also has a chassis frame ground connection.  If for some reason the battery chassis connection becomes compromised (corrosion, damage, loose hardware) then ground currents will start to flow through your equipment ground leads instead of the frame.  This results in anything from weirdness (lights getting bright or dimming, equipment malfunction) to failures (equipment ruined, circuits burned).  The stopgap "they" use is to put a fuse in the negative lead which will blow in the event of a "large" fault (like starter currents) but most faults I've seen aren't enough to blow the fuse.  They just sit there at some nominal amount of current getting things warm and causing problems until you figure it out.

The "best" way to do it is to ground your battery to the frame with a single cable, then connect any high current separately grounded equipment cables to the frame nearby the battery ground point.  This offers a low impedance return path for the equipment without risk of an inadvertent ground fault going through the equipment grounds.

I would make an exception for something like an inverter drawing possibly hundreds of amps, where a direct low impedance battery connection is paramount to operation.  You just have to accept that with that application the connections have to be perfect for everything to work right.

Mark B.
Albuquerque, NM

 

[dlshunter]

Solved with y'alls help!
Grounds connections were slightly oxidized. 
Used Dremmel to grind down to bare copper and steel, reconnected everything and now
all is good.
Lesson here is that you don't have to see white powder on battery connections to have a problem, slight enough
oxidation can disable your system.

Thanks guys!

 

[John From Detroit]

To Mark B. .Thanks for explaining what I typed about  (I was hoping that either A: nobody would ask or B: Your post) so thanks

And yes.. I've had to do that several times on some connections....  THe "Starting" battery on this rig is a "maintenance free' Side terminal (Supposed to not need cleaning or so they advertised long ago)  Biggest pain in the dremel I've got.