My take on this device is that you *could* be increasing voltage drop using it leading to AC damage. NEC requires a demand load of 3600 watts for a 30 amp pedestal and does not take into account a 30 and 20 amp recept. running simultaneously (a 30 amp pedestal has one hot and one neutral, unlike 50 amp ones). A 13.5/15.0 BTU AC draws around 15-16 full load amps at
120 volts (
for ex., Dometic info.). By running 2 AC units off a 30 amp pedestal you will be drawing 30+ amps plus any other loads running inside. A run of 30 amp pedestals gets derated to 55 percent for 7-9 pedestals. Depending on how old the CG is and how it is wired and/or where you are on a run of pedestals, you could be seeing low voltage that can damage an AC unit. If the voltage goes down, AC units will draw more current and exacerbate the voltage problem. AC units draw around 5-6 times their full load current during startup and can cause an AC unit to struggle to start or trip a breaker. Sometimes the voltage may look okay before you turn on an AC unit but can take a big dive when started/running.
If you're going to use the transfer switch, I'd at the least use a permanently mounted voltmeter inside and keep an eye on the voltage. Better still, use an EMS so you are automatically protected. But then you've got two hot circuits coming into your RV...
If you consider the NEC and AC unit manufacturer's specs, running two AC units is over the min. requirements for a 30 amp RV and that's *if* you have a full 120 volts and aren't running any other loads. It may seem like it's all okay but damage is cumulative over time and an AC can fail for no apparent reason, akin to heat damage in ST tires. Are the AC manufacturers okay with using a 20 amp recept. for running a 2nd AC?
FWIW, all 30 and 50 amp pedestals are required by code to have a 20 amp GFCI receptacle. Old CGs may have no 20 amp recepts. (or 50 amp) because they could have pre-dated code requirements. It wasn't until the 2005 NEC edition that they increased the no. of req'd 50 amp pedestals from 5 to 20 percent. Unless you stay in higher end RV parks or an owner has intentionally built above. min. code, finding a 50 amp pedestal can be next to impossible in the high season. So much for all the 50 amp RVs manufacturers are selling.
