30 amp for duel AC

westernrvparkowner wrote:

valhalla360 wrote:

Mandalay Parr wrote:
I can run both of mine on 30. They draw about 27-28 total. One is a 15 and the other 13.5.

Keep in mind a 30amp is really only rated for 25amps continuous. Drawing continuous 27-28 amps is a good way to burn out equipment. If you are lucky it just trips the circuit breaker.

You may or may not be able to get both units going but it's really a not a good idea.

Huh? What gets damaged drawing 27 amps? A breaker only has two positions, on or off. If it is on, the power being delivered will be 120 volts +/- 5 percent per NEC. If it is tripped to off, the power being delivered will be zero volts +/- an infinite percent (zero times anything is still zero). Where things get damaged is when voltage fluctuates high or low. The only possible damage would be if something gets harmed by the power suddenly cutting out due to a breaker tripping. Almost all appliances are built with that potential in mind so they aren't going to be damaged. The biggest threat would be if something got harmed because the appliance stopped working. Pets might overheat if the AC quits and the Chicken Fried Steak is going to be mighty greasy should the electric frying pan cut out in mid fry, but the skillet and the AC unit will almost assuredly continue to work once power is restored.

I agree.. Only thing I can figure is valhalla is assuming an 80 percent of total for safety margin. From what I just read online, this is probably how he comes up with his rationale.

The 1996 NEC recognizes that overcurrent protective devices will be affected by heat in the system. As such, it defines the concept of continuous loads and the 80% rule to try and offset the effects of heat in the system when sizing a CB.

A CB either carries a standard rating (80 percent) or a 100 percent rating. CBs that are 100%-rated are permitted to be loaded continuously at their full rating as long as the assembly is listed and conductors are properly connected.

But, I assume that if the CB was incapable of sustaining 100 percent, then it would trip. So, if one was using 27 amps continuously, and it was incapable of keeping up with that, it trips, and then you go to zero. Not sure where the equipment damage comes into play. You are still going to draw 27 amps, even if the CB is rated for 80 percent continuous. It's not like the CB is a smart system and can throttle the output.

Mike