ground question - Fiberglass RV


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Old 07-29-2007, 01:08 AM   #1
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I am rewiring my 85 burro. I decided to leave the previous 110V wiring in as it works ok, however, when I was taking out the 12V wiring, I noticed the 110V had a large green wire for the ground. Is this really necessary? Isn't that what the ground plug is for?

I also remember seeing someone say that this wire should be attached to the frame. But someone else said the frame is the worst place for a ground. Confused to say the least. I tried to use the previous grounds that went to the frame and have had nothing but heartache. Any suggestions?
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Old 07-29-2007, 03:20 AM   #2
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I am rewiring my 85 burro. I decided to leave the previous 110V wiring in as it works ok, however, when I was taking out the 12V wiring, I noticed the 110V had a large green wire for the ground. Is this really necessary? Isn't that what the ground plug is for?

I also remember seeing someone say that this wire should be attached to the frame. But someone else said the frame is the worst place for a ground. Confused to say the least. I tried to use the previous grounds that went to the frame and have had nothing but heartache. Any suggestions?
Randy,

Your confusion arises from mixing up "ground" and "return."

Ground is a term for safety connections. Both the AC and the DC should be grounded to the trailer frame at one point each. This ensures the frame stays at the same voltage level as the earth. The AC ground (the green or bare wire in AC circuits) is connected to earth at some point.

Return is a term for a part of the electrical circuit. In an electrical circuit, one wire goes to each load to supply current to that load, another wire goes to each load to return current to the source. All the current through a load is carried by the two wires, none of the current should flow through ground.

In AC wiring, the wire supplying current to the load is called high or hot (black), the wire returning current from the load is called low or neutral (white). The safety or ground wire (green) should not normally have current flowing through it; when current does flow through ground it is because of a fault in the circuit.

A ground fault may mean that your body has completed a circuit between hot and ground (i.e., in your house you get into the tub with a hair dryer running in you hand). Some of the current supplied by the hot wire is now flowing through your body through ground back to the source. This means that the currents in the hot wire and the neutral wire are imbalanced. This imbalance is sensed by the ground fault circuit interrupter (GFCI) which interrupts the hot side of the circuit in a fraction of a second, saving your life.

In DC wiring in our cars or trailers, the wire supplying current to the load is called +12 volts or positive, the wire returning current from the load is called -12 volts or negative or 12 volt return. Wiring colors for DC are not as well defined as for AC.
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Old 07-29-2007, 09:56 AM   #3
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In vehicle wiring the +12vdc has a hot wire to each light and the return is through a connection from the device to the conductive body or frame of the vehicle.

Because the conductive body or frame connection may get rusty, you will loose the return path and you will develop weird symptoms. Be sure that you have clean bare metal where the return wire connects.

The following is a great site. Notice the Ground symbol. This makes it easy to draw the circuit because instead of drawing a wire all the way from end to end, you just draw the symbol to indicate the connection to ground (Conductive Body or frame) This site is worth keeping in the how to file.

http://www.offroaders.com/tech/trail...ng-diagram.htm


Notice the notation: Ground to vehicle. The people who manufacture these items call it ground. It is easier to do it this way rather than running a separate return wire to each device. Just go from the device to the vehicle conductive connection.

http://www.accessconnect.com/trailer_wiring_diagram.htm
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Old 07-29-2007, 11:04 AM   #4
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Darwin,

Modern automobiles do not use the frame or chassis as a 12 volt return (except for the starter). For the reason you stated (corrosion), the old practice of using the frame or chassis as a return resulted in intermittent connections as the vehicles got older.
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Old 07-29-2007, 11:12 AM   #5
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Quote:
In vehicle wiring the +12vdc has a hot wire to each light and the return is through a connection from the device to the conductive body or frame of the vehicle.

Because the conductive body or frame connection may get rusty, you will loose the return path and you will develop weird symptoms. Be sure that you have clean bare metal where the return wire connects.

The following is a great site. Notice the Ground symbol. This makes it easy to draw the circuit because instead of drawing a wire all the way from end to end, you just draw the symbol to indicate the connection to ground (Conductive Body or frame) This site is worth keeping in the how to file.

http://www.offroaders.com/tech/trail...ng-diagram.htm
Notice the notation: Ground to vehicle. The people who manufacture these items call it ground. It is easier to do it this way rather than running a separate return wire to each device. Just go from the device to the vehicle conductive connection.

http://www.accessconnect.com/trailer_wiring_diagram.htm
Darwin---hmmm--did you happen to notice that the two sources you listed happen to use different color wires for the circuits? For example one says to use brown for a turn/stop and the other uses brown for the tail lite circuit (which is what is normally the tail/marker circuit on GM and Ford vehicles) Perhaps a word of caution is to carry a schematic in the trailer---especially for me as I can't remember everything anymore... Larry
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Old 07-29-2007, 05:19 PM   #6
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Modern automobiles do [b]not use the frame or chassis as a 12 volt return (except for the starter). For the reason you stated (corrosion), the old practice of using the frame or chassis as a return resulted in intermittent connections as the vehicles got older.
You know, I never really stopped to consider that. I just looked in my service CD for my 98 Ranger and indeed there are ground wires (that's what the manual calls them) all over the place, all eventually connected to the negative terminal on the battery.

BTW, when I was chasing an odd problem in my '82 D150 (engine would cut out and wouldn't restart unless key was cycled off; turned out to be a faulty run coil in the distributor), I pulled and cleaned all the underhood ground, wire and frame, that I could find and they were surprisingly clean, but it was essentially a nice-weather truck, not used on salted roads in frozen Northern climes.
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Old 07-30-2007, 12:46 PM   #7
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--hmmm--did you happen to notice that the two sources you listed happen to use different color wires for the circuits?...
There are well-established standards for trailer wiring, but that's the problem... there are standard[b]s, at least two. One for systems with 7-pole connectors, and a different one for systems with 4-pole connectors. My 1979 17' Boler was factory wired with colours which are consistent with the 7-pole RV/Bargman standard, but trailers vary.

There is no relationship between the colours used within a motor vehicle and the trailer colours. For one thing, a modern vehicle needs to distinguish between a dozen or more wires in the same harness, going to the same connector, so they use more colours and resort to stripes as well. Also, a specific colour may mean one thing in one part of the vehicle, and be re-used for an entirely different purpose elsewhere. If a truck manufacturer is nice to us, they'll be consistent about the colours they use for wires which we connect to, but you can't even count on that.

I think following the industry common practice for the type of tug-to-trailer connector is an important way to reduce confusion. If you've got a diagram for the trailer, I agree having that along would be valuable for on-on-road troubleshooting; I've got a copy of mine in the folder along with the trailer and appliance manuals, in a cabinet in the Boler.
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