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High Voltage Wiring Tips
Compared to low voltage wiring, high voltage wiring isn't all that much different. However, the higher voltage does make it much more dangerous. While a 12 volt wire may short out, smoke a bit and then pop a fuse, a short in a high voltage circuit can have more severe consequnces. The potential for personal injury and burning down your RV is greater so you need to be careful when working on high voltage circuits. If you feel you are getting in over your head it's best to enlist the services of someone who knows what they are doing.
High voltage wiring is generally rated with a 300 volt or 600 volt insulation. Either will work in an RV situation. The insulation keeps the current inside the wire so that it doesn't short circuit. However, any damage to that insulation creates a hazard so a layer of protection must be used to protect the wire's insulation. That layer can be conduit or a number of wires can be molded together in a vinyl jacket, as in boat cable, or any other non-metallic shielded cable. The actual size, or wire gauge, of the wire determines how many amps it can carry. It is not dependant on voltage so a #12 wire can carry 20 amps, whether it's 12 volts DC or 480 volts AC. The insulation does change with the voltage rating though so don't use 12 volt automotive wire for a 120 volt AC application or the current will jump the insulation. Refer to the Wire Gauge Capacities table for more details on wire gauge capacities.
In the 12 volt DC category we listed a selection of tools in the 12 Volt Wiring Tips topic. These tools are pretty much similar to what you will need for AC work. Refer to that listing for reference. Certain tools, like a 12 volt test light, won't be needed when working on AC circuits but the multimeter should have AC voltage test circuits as well as DC. A utility knife is also handy for slitting the cable shield jackets to expose wires near the end and wire nuts or other high voltage connectors will be needed rather than your low voltage crimp terminal selection.
AC power is dangerous. Always be sure to disconnect any power at the source when attempting to service any electrical device. Be sure that you have totally disconnected all power. It doesn't pay to pull the shore power plug when working on a receptacle if that outlet is now being fed by the inverter. Always use your voltmeter and test for presence of power before working on any electrical device. Also, be sure that your power source is locked out. You don't need a "helpful" person coming along and turning something on while you are working on that circuit.
Whenever possible, try to have a wiring schematic of the item you are going to be working on. By reading this diagram first you'll gain a better understanding of how it works before you start poking around.
When you need to replace a wire always leave plenty of extra. Whenever you measure an existing wire and cut a replacement the exact same length it will invariably be too short. Just pull plenty of extra wire. It's not that expensive and you can always cut it shorter but it's pretty hard to make it longer once it's been cut. The same holds true for shielded cable. You want to leave the cable shield jacket on far enough so that it is held in the retaining clamp on the electrical box. When you strip back the jacket with your knife, set the blade shallow so that you don't cut into the insulation of each conductor. You also want to be sure you have enough wire exposed to comfortably reach the device.
High voltage wiring is dangerous. If a wire connection falls off it can cause sparks, which in turn can cause fires. That's why they always place wire nuts inside an electrical box, which is capable of containing those sparks. Unlike automotive wire, it is generally not necessary to solder these connections. It is a good idea to tape your wire nuts though so that they cannot unscrew. My particular Allegro Bus uses Wago Wall-Nuts, which are push-in connections. These connectors are very fast and solid for assembly yet the wires do not pull out unless an insertion tools is used. Plus, they're not threaded so they can't unscrew.
Remember, if you are checking for continuity with your ohmmeter be sure that there is no 120 volt power on the area you are testing. If you apply power while in ohms mode you'll blow your multimeter.
Submitted by Mark Quasius - 2/24/06
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