H.A. wrote:Hmm.
I think I just did.
Not really, how about something like this?:
Grounding the Frame
There needs to be a path from the frame to AC ground, in case a hot wire contacts the frame. Without such a path, a person entering or leaving the trailer could become the path to ground and be electrocuted. Run a green wire from the ground bus to the frame.
There needs to be a current return path from the frame to your AC power source. This ensures that the breaker opens if the hot wire ever comes in contact with the frame. Without it, the breaker wont open and the frame is energized at 120V. A person touching the frame would become the return current path and be electrocuted. Run a #12 green insulated wire from the ground bus to the frame. Strip the paint off the frame where you connect the wire so there's a good connection. Be careful not to connect the neutral and the ground together inside the converter. This can cause the frame to be energized if the campground receptacle has the hot and neutral reversed. Keep the neutral and grounds separate in all your wiring for the same reason. Its a good idea to carry a receptacle tester with you and check the campground receptacles to make sure the hot and neutral aren't switched before you plug in.
Grounding DC
This is controversial. Because all the DC goes through the converter, which is grounded via the AC ground wire, some say there is no need to ground the various appliances and fixtures to the frame. Others say that it is a must, but I’m not clear on why.
Bonding the battery to the frame is not as clear as the AC approach. Trailer manufacturers will use the trailer frame for the DC current return path to save money on wiring. A connection from the trailer battery to the frame is not needed when the trailer is connected to the tow vehicle as all the power for lights and brakes comes though the the trailer connector. A bond from the battery to the frame also provides the same function as it does with the AC system; it provides a return path for current to blow a fuse if a 12V positive wire touches the frame. Most people omit the connection to the frame if they're
not using the frame as a current return path to the trailer battery as the risk of electrocution death at 12V is much less than at 120V. However, it's a good idea to provide the connection as it's an easy way to provide another level of safety in your electrical system. The green wire from the battery negative terminal to the frame should be the same size as the positive wire from the converter to the battery. And don't worry, stray AC currents won't charge your battery through the frame connection. The AC ground wire only carries current during a fault if you've installed your wiring correctly.
Bruce
P.S. There's a general perception among specifiers that tandem breakers are of lesser quality than single breakers, FWIW.