Melting extension cord

MEXICOWANDERER wrote:

Reading the voltmeter while switching on the A/C...

If voltage dips to 105

The show's over. Your calculation is belly-up. Time to retrofit.
Or make -real good- friends with your RV air conditioner seller.

Eso es correcto, muy bueno... :)

Here is an owners manual for Dometic AC units as an example. Duotherm

Starting inrush current of motors is typically around 6 times the full load running current (FLA) for a fraction of a second. Taking a look at the 13.5K unit with compressor FLA of 12.1, the locked rotor current (inrush starting current) is 59.0 amps (ignoring the fan current)!! That is why it is so important to keep all wiring back to the supply panelboard as short as possible and as heavy gauge as possible. In a house, you could easily have 50-100' of wire to the receptacle you're plugging into. If you are attempting to get the AC to run off a 15 amp circuit, you'll have #14 wire trying to provide 59 amps for a short time period. If it's also supplying other loads, the situation is even worse. Even though you have a #10 shore power cord, that will also have some voltage drop at around twice it's rated current. You could calculate the voltage drop if you know all the overall wire lengths and gauges and voltage at the supply panel. Depending on the neighborhood a house is in, voltage drop quite a bit at peak usage times.

Note the manual says min. 20 amp breaker is required and wire size is min. #12 gauge up to 24'. Cheapo 15 amp extension cords are usually #16 gauge, unless you buy a heavy duty one. Imagine trying to pull something like 60 amps through one of those... :E

With no loads on at the panel in your RV, the voltage may *seem* perfectly fine, but when you start the AC, the voltage can drop outa sight. That's why generators can struggle to handle starting of an AC. In marginal cases, a capacitor hard start kit may help because it reduces the starting inrush current. The voltmeter you are using probably won't indicate the actual amount of the drop, but if you see the needle kick towards zero, that's not good.

All electric appliances and equipment are required to have a data plate with electric, model. no. and other info. on it. I believe they are behind the shroud. Even if the power is off, do NOT touch any electrical parts inside as the capacitors hold a charge.

Don't forget to report what the eventual outcome is!