myredracer wrote:
Some things to be aware of:
First, check the AC manufacturers specs and you should find that a min. wire size of #12 is required and also for runs above 50' (overall) min. #10 is required.
Check the voltage when the AC units are running. Low voltage below 105 volts will lead to premature failure. If it gets down to 105, shut off the AC units and wait for it to go back up (if it does) or get a Hughes autoformer. Use a plug-in voltmeter inside or install a permanent wall mount. Better, install an EMS so that power will be automatically disconnected if too low (except that the AC on the 20 amp recept. would need it's own EMS for this to work).
Voltage at your camper will depend on how good the CG/RV park wiring is, how old it is and how long the runs are between a pedestal and CG main supply. AC units draw more current the lower the voltage gets and running two simultaneously could substantially increase voltage drop, especially in older CGs that have panels distributed around the property with individual runs to each pedestal. (Newer CGs have loop-fed pedestals). An older 30 amp pedestal could have just #10 wire supplying it and then you'd be trying to run up to 50 amps on it.
Note that the NEC does not provide for simultaneous operation of a 30 & 20 amp receptacle in a pedestal for load calculations and sizing of wire from the pedestal to main supply. Running two AC units could result in an undesirable and significant increase in voltage drop.
Just because an AC unit(s) *seems* to start and run okay, it doesn't mean that the voltage isn't too low and causing damage to it/them. If they struggle to start on generator, a hard start capacitor might help and in some cases can help when on pedestal power.
Lots of good info.
While the NEC doesn't adress the use of both the 20 and 30A receptacles in a panel, that doesn't mean it isn't perfectly fine to do so.
If your using what is commonly referred to as a 100A panel with one each 50A, 30A & 20A outlets, the 20A and 30A outlets are *wired (by the manufacturers of the box) on oposite sides of the 240V circuits. So they don't both run off the same side of the 50A.
This makes it perfectly safe to use both circuits at their max potential. That is UNLESS the 50A is also in use. Then all bets are off. The NEC rates the panel based on use of the 50A. So you can skip that part and use the 20/30 with no issues.
So the bottom linie is, it is perfeclty safe to use the 20/30 at the same time as long as the 50 isn't in use.
*Connection not actually made with wire but rather with solid metal, formed bars.
