120v/12v system ground

[Megadrop]

Hi,
I am building a metal framed camper instead of using wood. I Am a little concerned about having a common ground of the frame with 12v and120v. Specifically if my 120v shorts to ground will it harm my 12 v battery. I have never hooked up a dual voltage system so any help would be great.

Joe

[GuitarPhotog]

I'm wiring my all-metal trailer so that the 120 VAC ground is connected to the trailer chassis/frame, and the 12 VDC ground is floating. So I'm not using the chassis for "return" for 12 V.

I see no compelling reason to connect the -12 VDC to the trailer chassis.

My $0.02 worth.

<Chas>

[Miriam C.]

Not to re-start the oldest argument here but my 120 is not grounded to the trailer frame. If finds it's ground through the shore power source.

All 12v is grounded to the frame...

[GuitarPhotog]

Sorry, I didn't know this was one of those topics. I won't reignite the flames with my opinion.

<Chas>
-butting out, quietly

[chorizon]

:NC Not to re-start the oldest argument here but my 120 is not grounded to the trailer frame. If finds it's ground through the shore power source.

All 12v is grounded to the frame...

Yeah!

[eamarquardt]

As I understand it, if you have a wiring problem in your RV and the frame is grounded to the a/c ground, you could end up with a "hot chassis/frame" that is insulated from the ground/earth by your rubber tires. Sooooo, if you are touching/connected to the RV chassis/frame and a good earth ground, you may get the "shock of your life/death".

I think keeping the a/c ground off the frame may lessen the risk. Others can probably add to the discussion (and fan the flames).

On the DC side, I think it is "good form" to run ground wires to each load and not rely on the frame for a ground system. Corrosion, paint, loose fasteners can cause problems over time.

Cheers,

Gus

[Engineer Guy]

In my old age, I'm looking more to 3rd Party opinions rather than the old 'he said -> she said' stuff. Or, as I like to say, 'I'm right; just ask me'!

I 'thought' I'd understood prior that any RV Chassis should be Earth grounded, especially while on AC operation. So, I chased it down a little on line. From this lengthy Thread comes this point in Post #3:

RV Grounding vs. Residential Grounding

An RV 'shore' power plug should act like an auxilary breaker box. Neutral should not be grounded to RV chassis. RV chassis should be connected to shore power ground connection. Question to ask yourself is when you step off the step off the RV with a hand on the RV metal chassis will the RV chassis be at the same potential as the ground being stepped on. The best way to ensure this is use the shore power ground.

In the case of any short to RV Chassis causing the Chassis to be hot, you want it to be Earth grounded, just like any 'Old School' Saw or Drill or House Fridge Chassis, etc.. Today, Tools are double-insulated, of course, due in part to bad or broken Grounds at Construction Sites. One fine point is supposedly that you never want to have an Outlet 'appear' to have an Earth Ground, by the 3rd pin presence, when it doesn't.

In any number of weird scenarios, like something electrically 'hot' falling against a metal-skinned Trailer or the Chassis, you never want a scenario where those surfaces could go 'hot' and your Body is the only path to Ground. A grounded RV of any size wouldn't affect the Battery either way, unless someone can chime in with an interesting scenario...

Part of the whole safety 'thing' is to use a GFI Outlet first in any TD/TT/CT AC Circuit 'chain', and wire subsequent Outlets to also be GFI'ed. It's my understanding that if you touch a hot RV Chassis w/a bad Earth Ground with GFI'ed Outlets, the GFI will sense the 'goes inta' vs. 'goes outta' current unbalance as current diverts through your Body. It will trip and shut off power.

On not using the Chassis as DC current path return, what Gus said 2x. Mentally, I completely separate the 2 DC concepts. 1) Mechanical - a Chassis mechanically supports 'stuff'. 2) Electrical - a separate 2nd wire completes any/all DC Circuits; not the Chassis. The twain functions never meet... That is, the RV Chassis connects to DC Ground, especially in the case of Chassis Lights, but ideally is not used for 'high' current return paths.

[PaulC]

:NC Not to re-start the oldest argument here but my 120 is not grounded to the trailer frame. If finds it's ground through the shore power source.

All 12v is grounded to the frame...

Why?
I treat my 12v interior lights/radio etc just like a torch and earth back to the battery. The only earth to frame that is needed is for the trailer tail lights.

Paul

[Loader]

:NC Not to re-start the oldest argument here but my 120 is not grounded to the trailer frame. If finds it's ground through the shore power source.

All 12v is grounded to the frame...

Why?
I treat my 12v interior lights/radio etc just like a torch and earth back to the battery. The only earth to frame that is needed is for the trailer tail lights.

Paul

For what it is worth, I did my 12 volt wiring the same as Paul. Interior wiring goes to a combo fuse/ground block then to battery. Trailer lights are grounded to frame.

[Megadrop]

Thanks that helped now I will see if I can electrocute myself or maybe I will get a neighbor to be the first one to step inside.

Thanks Joe

In my old age, I'm looking more to 3rd Party opinions rather than the old 'he said -> she said' stuff. Or, as I like to say, 'I'm right; just ask me'!

I 'thought' I'd understood prior that any RV Chassis should be Earth grounded, especially while on AC operation. So, I chased it down a little on line. From this lengthy Thread comes this point in Post #3:

RV Grounding vs. Residential Grounding

An RV 'shore' power plug should act like an auxilary breaker box. Neutral should not be grounded to RV chassis. RV chassis should be connected to shore power ground connection. Question to ask yourself is when you step off the step off the RV with a hand on the RV metal chassis will the RV chassis be at the same potential as the ground being stepped on. The best way to ensure this is use the shore power ground.

In the case of any short to RV Chassis causing the Chassis to be hot, you want it to be Earth grounded, just like any 'Old School' Saw or Drill or House Fridge Chassis, etc.. Today, Tools are double-insulated, of course, due in part to bad or broken Grounds at Construction Sites. One fine point is supposedly that you never want to have an Outlet 'appear' to have an Earth Ground, by the 3rd pin presence, when it doesn't.

In any number of weird scenarios, like something electrically 'hot' falling against a metal-skinned Trailer or the Chassis, you never want a scenario where those surfaces could go 'hot' and your Body is the only path to Ground. A grounded RV of any size wouldn't affect the Battery either way, unless someone can chime in with an interesting scenario...

Part of the whole safety 'thing' is to use a GFI Outlet first in any TD/TT/CT AC Circuit 'chain', and wire subsequent Outlets to also be GFI'ed. It's my understanding that if you touch a hot RV Chassis w/a bad Earth Ground with GFI'ed Outlets, the GFI will sense the 'goes inta' vs. 'goes outta' current unbalance as current diverts through your Body. It will trip and shut off power.

On not using the Chassis as DC current path return, what Gus said 2x. Mentally, I completely separate the 2 DC concepts. 1) Mechanical - a Chassis mechanically supports 'stuff'. 2) Electrical - a separate 2nd wire completes any/all DC Circuits; not the Chassis. The twain functions never meet... That is, the RV Chassis connects to DC Ground, especially in the case of Chassis Lights, but ideally is not used for 'high' current return paths.

[86bigred]

all new trailers have the 12v ground the 120 ground to the frame.i work on these every day. heck the neurtral on the 120 volt side is bonded to the ground down the line.the metal propanes line are bonded to the grounds.these are all in place for your saftey,to prevent fires or electricution.
if you frame is not grounded it has the posibility to become energised and not trip the breaker leaving the frame hot and if your grounded and the frame is hot,you will get zapped.

[eamarquardt]

Live and learn. Guess it makes sense to bond the ground to the rv frame but certainly not the neutral. I don't see that the ground or lack thereof will protect from an overload as I seem to recall was suggested in one of the things I read while poking around looking for thoughts. While poking around I found a site where the fellow went into great detail on maintaining that ground connection (corrosion resulting in a high resistance connection being the problem). If that connection isn't good (ie has signficant resistance), the whole point of grounding becomes moot as YOU may be a better path to earth for the stray electrons than the "ground connection".

This whole string has convinced me I've no need/desire to wire a trailer for a/c power. The only devices I might run off of a/c are a battery charger, heater, or an air conditioner. I'll just use the factory cord and plug it into an extension cord connected to whatever is available (using a GFI for additional insurance). Propane for coooking/refrig and 12 V dc for my computer, charging my phone, running my lights, a Norcold chest, water pump, and any other incidental electrical needs.

Never had a/c on our boat and never missed it (but when sitting in 65F (max) water a/c is not a requirement). Toaster ovens, coffee pots, microwaves, blenders, crock pots, elecric frying pans, frabulizors, kreetasans, doomaflagees, freebises, etc are not part of our camping experience.

However, if I could fit a washer and dryer in a teardrop, I might consider a/c power.

Cheers,

Gus

[Miriam C.]

See, we all seem to do it different and we are all still here.

[PaulC]

all new trailers have the 12v ground the 120 ground to the frame.i work on these every day. heck the neurtral on the 120 volt side is bonded to the ground down the line.the metal propanes line are bonded to the grounds.these are all in place for your saftey,to prevent fires or electricution.
if you frame is not grounded it has the posibility to become energised and not trip the breaker leaving the frame hot and if your grounded and the frame is hot,you will get zapped.

I've never been zapped by a torch and that's how my 12v is set. No mains on mine, I don't see the need, personally.

Cheers
Paul

[86bigred]

Ok say your frame is not grounded to the 120v.some how a 120 hot wire rubs through the insulation and is touching the frame.it will not trip the breaker on the shore power.and whith rubber tires and most people using a wood block under the toung this will insulate the frame from the ground.you come walking up with your feet on the ground and touch any metal on the trailer.zap.that's why it is written in the electrical safety codes.ask any electrician they will agree.always bond the frame.