120V AC Wiring

Wiring Considerations

I used standard 10-2 Romex cable with ground wire and ran two such Romex cables between the inverter (located under the second row passenger-side seat) and the electrical cabinet (located under the driver-side rear couch), about a 14 foot run each way. One cable is to bring shore / generator power to the battery charger. The other is to bring the inverter output (or shore power - depending on the DPDT switch position) to the electrical sub-panel. I again covered these cables with split wire loom for protection. I used 10 gauge wire because my original inverter was rated for over 20 amps of output. If you keep output below 20 amps, you can get by with 12 gauge wire, which is easier to work with. I secured the wire loom up out of the way in its path through the rear storage compartment using plastic zip ties with built-in screw holes. These worked nicely.

In the above 120 volt wiring diagram, the visualized connections are for the hot (black) wires. I left out most of the neutral (white) wiring, as all the neutrals are tied together whenever they meet up (such as in the neutral bus bar in the circuit breaker boxes or at switches). All the ground wires are also connected together wherever they meet up (including the grounding bus bar in the circuit breaker boxes) and any metal parts are also grounded using their grounding screws. The main panel box and sub-panel box are both grounded to the van chassis. The inverter and charger are also grounded to the van chassis, all using a 8 AWG green covered wire.

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 plan to do this in the future). Another circuit in the new main panel feeds power to the battery charger.

Neutral Bonding:

You may have wondered why I used a DPDT (double pole, double throw) switch to select between shore power or inverter power. Why not just use a common single pole, double throw switch, otherwise known as a three-way switch? The reason 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 (or else the ground wire becomes a conductor of electricity). When you are plugged into shore power, the campground electrical system provides the required neutral bonding. Your generator should also provide a neutral bond whenever it is running. The same is true for your inverter. Whenever your inverter is supplying your power, it needs to bond neutral to ground. However, when it is not supplying power, it should not allow any connection between neutral and ground. This would violate the single site of neutral bonding rule.

Now lets look at the diagram of my DPDT switch. When the switch is in the up position (shown), it connects the hot wire from the inverter to the hot wire going to the sub-panel. It will also connect the neutral wire from the inverter to the neutral wire going to the sub-panel. My inverter has neutral bonding inside, so everything is working the way it should.

Now let's move the switch to it's down position. The hot wire from shore power (or generator) is now connected to the hot wire going to the sub-panel and the neutral wire from shore power is now connected to the neutral wire going to the sub-panel. MOST IMPORTANTLY, the neutral wire coming from the inverter has been disconnected. If I had used a SPDT switch that just switched between the hot wires, I would need to connect all the neutral wires together. This would have kept the neutral wire from the inverter connected to the circuit. Since the inverter provides internal neutral bonding (neutral connected to ground), this would violate the single site of neutral bonding rule. We would have neutral bonding at both the shore power and at the inverter. This is not safe and it would trip any ground fault circuit interrupter (GFCI) plug you tried to plug your RV into.

Some inverters have an internal relay that will automatically switch over to shore power when they sense that shore power is available. These relays will also cut off the internal neutral bonding. My original inverter had this. These are great from a safety perspective, but they suffer from a significant flaw. The problem is that the neutral bonding cutoff relay within the inverter takes a short 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 inverter's neutral bonding nearly instantaneously and perceives it as a fault, thereby tripping the breaker before the inverter has a chance to activate the neutral bonding disconnect relay. 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. My solution was to install a DPST switch (double-pole, single-throw) on the power output from the inverter. This will allow you to temporarily disconnect both the hot and neutral wires from the inverter so the GFCI cannot sense the brief neutral bond. After you are plugged in, you can turn this switch back on, since the neutral bonding cutoff relay has been activated. I have not found this transient neutral bonding to be a problem at most campgrounds.