BPFox wrote:wlooper89 wrote:Hello BPFox, that is a very good web site for RV wiring. It appears my power cord may be a little under sized for 30 amps and 40 feet lenght with #10 wires. Maybe just barely enough. That was very informative.
Bill
Keep in mind that those rating are pretty much based on continuous usage at maximum power. That does not happen very often. Even when you buy extension cords at the store they tend to under rate them. A little C.Y.A. if you know what I mean. For instance they will rate 12ga cords at 15 amps and 10 ga cords at 20 amps. Besides, it's not like your cord will burst into flames. It will start to get hot first and then it will be too hot to pick up and then it will start to smell funny and then the cover will start to drip off the wire and then maybe you will start to see some flames. This process takes a while so no worries.
First post here, inspired by my sense of worry, so please take it in that spirit!
I would be a little more cautious...if this hot/smell/melt/flames process happens while you're out enjoying a hike, you may return to firetrucks and a smoldering mess. Or if it occurs while you're fast asleep inside the tear (and your sense of smell shuts down while sleeping), you may never return.
It's best to size cables conservatively. Age, the elements, continued flexing, poor coiling (how many of you know how to "over/under" or "figure-8" coil a cable to prevent it becoming twisted?) practices all cause a cable to lose its ability to work as designed.
The most important consideration (one I read and see being ignored a lot) is that your RV cable should be rated at or above the service's current. Adapters only make the plugs work together; most have no form of current protection and are not UL-listed devices.
If you have a 30-amp power post, use 30a rated cable, and don't use anything smaller in the circuit until you've got a fuse or breaker in line to protect the lower rated devices and cables. This is code, and it's important to observe. I often see people using 14 and 12 gauge cable with adapters, plugged into 30 or even 50 amp services. That cable, and the trailer's devices are now going to carry 30 or 50 amps before the power post's breaker will trip. It's a fire hazard.
Regarding the code I mentioned above, NEC states that all conductors and devices must have overcurrent protect rated at or below their rating. There are a few exceptions but none fall under the use we're discussing.
I recommend installing a 30 amp RV inlet and wiring 10 AWG stranded marine-rated wire from there to a small 120v NEMA box with a pair of breakers. Use 10AWG or larger feeder cable from RV to power post. You can then safely feed your tear with one or two 15 or 20 amp breakers, preferably GFCI breakers, and never worry about capacity or danger. If you need to plug into a 15 or 20-amp RV service, you can use adpaters without fear, as your 10AWG cable is rated well above the service current. Do not plug into a 50-amp RV service with this cable, unless you have an adapter with a 30-amp breaker inline.
I suggest using only finely stranded marine rated wiring in trailers. Marinco is a very good brand. The vibration, moisture and temperature extremes in trailers are tough on solid conductor wiring, and breakage or corrosion are a potential problem. Terminate all ends with crimped and shrink-tubes connections for corrosion and vibration resistance. Marine wiring costs a lot, but our tears are small with simple 120v needs, so it shouldn't be too much of a burden to provide the best possible wiring for a good long life.
