Electrical compartment AC detail - The new main circuit breaker box is installed to the left back of the compartment. Attached to the top of this box is my bypass switch. I attached a label on top explaining its function and labeling the two switch positions. I had to move an existing junction box to the front floor of the compartment to make room for the new circuit breaker box. I removed the old 12 volt Parallax 7300 converter since my new battery charger can provide more than enough power to both charge the batteries and run any 12 volt appliances. I confirmed this with Xantrex. The original circuit breaker panel and 12 volt distribution panel remains in place.
First I installed a new main circuit breaker box. I looked for the smallest box I could find that would hold 4 separate circuits. If you use the half-size circuit breakers, where two breakers fit in the space of one normal breaker, you can get fairly small. The box I used is rated for 60 amps, which is more than enough since the van electrical system is maxed at 30 amps anyway. I rearranged the electrical cabinet in the Roadtrek so that I would have room for this new box. Also, I completely wired up the box with all the connections before I secured it in the compartment. It would have been a nightmare to try to wire things up within that small space. The wires were left long enough outside the box for me to do this. All wires outside the box were covered with split wire loom for protection and neatness.
Since I did not want the air conditioner to run off the inverter, I removed its wire from the existing sub-panel and moved it to my new main panel. You could do the same for any other circuit you don't want powered by the inverter (note: in retrospect, I should probably also have moved the electric hot water heater over to the new main panel - I forgot about that high current draw). Another of the circuit breakers in the new main panel feeds power to the inverter. The inverter uses this for its battery charger. While I could have used a 30 amp breaker for this circuit, I preferred to limit the charger to 20 amps max. You can program the inverter⁄charger and tell it what size breaker you used so it will not exceed that current draw.
I wired things so that the power input to the existing sub-panel comes from a bypass switch. This is a 20 amp single-pole, double-throw (SPDT) switch that is commonly referred to as a “three-way” switch in lighting applications. This switch is very important. First a word about how inverters operate. When you are not connected to shore power (and not using the generator), the inverter will automatically generate 120 volt power and send it through its output. If you should either plug into shore power or turn on your generator, the inverter senses this input power and stops generating electricity. It also has an internal relay that will activate and shunt the incoming power to its output. If you later unplug shore power, the relay opens up and the inverter seamlessly starts generating electricity again. So far, so good. Everything is behaving the way you'd like it with power always maintained at the inverter output. The problem arises when you turn the inverter off. Lets say something happens to your inverter and it stops working, or you have a problem with one of your batteries and have to remove it temporarily?
When you have the inverter turned off, the relay within it no longer works. It is not capable of shunting the incoming shore power to its output. If you permanently wire up the existing power distribution sub-panel to the inverter output, nothing will get power if the inverter is turned off – even if you are hooked up to shore power or use the generator. That's the reason you need a bypass switch. This switch allows you to select whether you get your power from the inverter output or directly from the main circuit panel. Interestingly enough, the installation manual never mentions the need for such a bypass switch.
Another switch that I found you need is a cutoff switch on the inverter output. This switch needs to cut off both the hot (black) and neutral (white) wires and therefore should be a 20 amp double-pole, single-throw switch (DPST). The key here is that you want to be able to interrupt the neutral (white) wire coming from the inverter output in addition to the hot (black) wire. The reason for this stems from something called neutral bonding.
For safety reasons, any device that generates 120 volt alternating current (AC) electricity is required to have its neutral wire connected (bonded) to ground. This neutral bonding keeps the neutral wire from becoming a shock hazard. Furthermore, this bonding must only occur at the source of the electricity. You cannot have the neutral wire and ground wire connected anywhere else in the system. When you are plugged into shore power, the power company provides the required neutral bonding at the transformer. Your generator should also provide a neutral bond whenever it is running. The same is true for your inverter. Whenever your inverter is supplying power, it needs to bond neutral to ground. However, when it is not supplying power, but merely passing through shore power, it should not provide neutral bonding, as this would violate the single site of neutral bonding rule. Fortunately inverters are smart, and contain a relay that will automatically cut off neutral bonding whenever they sense power coming into their input. So what's the problem?
The problem is that the neutral bonding cutoff relay within the inverter takes time to activate. So for a fraction of a second after you plug into shore power, you have neutral bonding present at the inverter. Normally this would be no big deal. The problem arises when you are plugging into a GFCI (ground fault circuit interrupter) outlet, such as most people have on their outdoor outlets at home. The GFCI outlet can detect the inverters neutral bonding nearly instantaneously and perceives it as a fault, thereby tripping the breaker before the inverter has a chance to disconnect the neutral bonding. For this reason, I found it impossible to plug my RV into my protected outlets at home. Every time I plugged in, the ground fault breaker on the outlet would pop open. The solution to this problem is to place a cutoff switch on the inverter output line that opens both the hot and neutral wires. By turning off this cutoff switch, the neutral wires beyond the switch are no longer bonded to ground. Now I can plug into my home GFCI power without tripping the outlet. If desired, I can then turn the cutoff switch back on, since the relay has now had time to open and internally disconnect the neutral bonding within the inverter. In practice however, I always turn off the cutoff switch before I plug into shore power at home and leave it off until I need inverter power again. I have not found this transient neutral bonding to be a problem at campgrounds.
[Note: As an alternative to having a separate cutoff switch, you could use a double-pole, double-throw switch for your bypass switch to cutoff both hot and neutral wires, but such switches are hard to find in 20 amp capacity. I also find that in my setup, my cutoff switch is much more accessible than the bypass switch and thus easier to quickly turn off the neutral bonding.]