Post by wisconsinjoe on Jul 6, 2021 4:17:03 GMT -8
Sorry for being confused, but I'm wondering why everything gets grounded to the trailer frame.
First, is there supposed to be a ground wire running from the 30 amp shore power breaker box (ground buss bar that is separated from the neutral bar) to a ground stud on the frame? If so, why? Isn't the frame isolated from the earth with rubber tires?
Then, also with the 12 volt systems: Is the original idea that the grounded frame acts as the neutral so that the entire system of metal parts (frame and skin) act as the neutral? Certainly, I've seen marker lights with only a hot wire running to it, with the skin acting as the neutral.
But, if you run a white wire (neutral/negative) to every light, why is that ground even needed?
I do understand the purpose of a ground in a home wiring situation. But that ground is literally connected to the earth with the ground wire clamped to a stout copper rod driven into the earth. I always thought that was a protection device to keep a short running wild electricity to the safer place of earth.
12 volt system and tow wiring: All 12 volt DC systems run with a "hot" and "ground". There is no neutral in a 12 volt system. Most of us add a ground wire to each tow light location because the skin is not considered a strong ground. When the trailer is new, the grounds work well. As time and vibration take their toll, the ground screws loosen and the ground can be lost. The light will not operate without a ground. The extra ground wires are INSURANCE that a good ground is always available. The skin and frame are your 12 volt grounds and the battery is connected directly to the frame as well. I use an extra ground bracket for inside system grounds.
110/120 system: The ground for the breaker box bolts directly onto the trailer frame, usually connected with a lug. This ground prevents power "leaking" thru and zapping you unexpectedly. In simple terms, the bleeding power stops at the ground. The campground recepticle provides the ground to Earth via that electrical system. Your power cord has a ground that connects the trailer to the campground recepticle as well as hot and neutral.
In the "old days", non-grounded trailers carried a sharpened copper rod to ground the trailer frame to Earth. This prevented zaps and was extra insurance that the trailer was well grounded. All of my 64 and newer trailers have had a 110 grounded system.
NOTE: 110/120 ground wires and neutral wires are ALWAYS isolated in an RV or trailer. The neutral bar is insulated from a metal box while the ground bar is not.
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The above is very difficult to explain in layman's terms. The best most of us can do is follow the codes and wire appropriately. I often have five 12 volt grounds on my trailers; each piece of skin is grounded directly to the frame. (just in case)
I think it would be easier to add the grounds and forget about the exact "whys" of grounding. There are quite a few electrical books and courses available that can certainly give you more on this subject.