From the RV Site
120 VOLT AC ELECTRICITYIt's not my intention here to write a book on AC electricity, but to cover those aspects that are peculiar to RV use. "RV Electrical Systems" (mentioned above under Sources and References) is your must-have reference for all things AC. It goes into much greater (and well illustrated) detail. (I'm interested in covering those things that can drive U Nutz.) First thing first: The neutral and ground in an RV electrical loadcenter are NOT to be bonded together. The RV chassis is isolated from ground by definition. Metal leveling jacks and such, mounted on the vehicle frame do not make an adequate ground contact. Therefore, in an RV, you always want to have a "floating" neutral, where the neutral and vehicle ground never come together. When you bond the neutral and ground together in an RV, you
have a "floating" ground (rather than neutral) and this will result in nutty things happening. Combined with ANY receptacle (at campground post or in RV) having reversed polarity, it may result in YOU becoming the path to ground in certain conditions (like standing on wet ground and touching metal vehicle parts). Usually you just feel a slight "tingle," but it can get serious. One result often seen is a dog, chained to a metal bumper, bouncing up and down. The above electrical faults result in breakers breaking and Ground Fault Interrupters (GFI's) that don't GFI (and pity the poor drunk who stands alongside the RV, with his hand leaning on the metal frame, and takes aleak). This shouldn't happen if there's no reverse polarity at ANY receptacle, because the ground wire is still grounded and does not become a hot wire by the fact that current of near-zero voltage is flowing in it. So, then, everything should still work OK and normal. The dog would still be happy right up to the time you drive off down the highway -- dragging
the whole affair -- dog and all. (I've seen this happen.) However, the whole purpose of the third ground is to be a fail safe, so current is not allowed to (normally) flow in this wire. Having more than one grounding point CAN make this possible. (See later.) RoVers can come on a bad electrical receptacle almost anywhere. Frequently in a camp ground, where the "electrician" is the guy who mows the grass and does other "high-tech" chores. They can also have one or more reverse-wired receptacles in their RV. (Factory RV wiring is not usually done by mental giants.) One inverter manufacturer's manual has a note about disconnecting a certain "pin" so this "double ground" won't happen. One inverter manufacturer now makes a "Marine" (same as RV) Model to preclude this (and it's not supposed to be sold for use in a fixed residence). 50 Amp and 30 Amp Electricity to the RV When the four wires from a 50 amp cable enter the RV, you have two "hots," a neutral and a ground. The wires then usually enter a dual "load center" (or two individual load centers). It's set up just like in a "house," EXCEPT the neutrals go to an insulated neutral bar. The ground wire goes to a separate "ground" bar.
While the neutrals are bonded together and common, the neutrals and ground wire are NOT bonded to the metal load center as a "common" (as is done in a house where there's an independent ground). The neutral and ground are common only at one place -- the meter and load center bars on a "house" or the power receptacles in the "box" you plug into at a camp ground. It's essential that the "neutrals" be floating (not connected to ground) throughout an RV.
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