Running 2 AC units on 30 amp

I can only offer what my actual experience has been. Thousand Trail's is not known for upgraded equipment yet, for one example, at Rancho Oso in Santa Barbara, Ca their 30 amp service has run my two 15,000 btu units on most every occasion I've needed them. And Yes, I do monitor voltage..our MH just happens to have Voltage and amp meter's for each leg of pedestal power and in this case the single leg and never did I get to a critical low voltage situation. Here again, maybe I was just lucky, maybe the compressor's never started together, maybe the sky is falling.....I say the only way to know for sure is to try it WHILE watching your voltage easy enough??? :)

This is exactly why I'm so fond of hybrid inverters, energy management, and autoformer technology. The combination of the three more or less eliminates shore power breaker overloads while leaving full function to the RV.

Veebyes wrote:
The DW is going to turn the microwave on without thinking anyway. /this could result in a trip out to the post to reset the breaker. Head her off by turning the microwave off at the circuit breaker.

The short answer is NO you can't. The long answer is YES you can but it takes power understanding & management. The fan of the A/C needs very little power. It is the compressor, especially at startup, that needs the power.

Running one or the other, but not both on cool, is a plan. Running only one on cool & the other on fan only is a plan. For extra security turn the waterheater off & only use it on propane if using the A/C combos. Also reduce the A/Cs to fan only while using the microwave.

50amp units need 50amp service so that all that stuff can run at once. 30amp service simply cannot provide for full load demand.

The DW is going to turn the microwave on without thinking anyway. /this could result in a trip out to the post to reset the breaker. Head her off by turning the microwave off at the circuit breaker.

My 'guess' is that you may have a problem trying to run both a/c's on 30 amps, especially if both are 15K Btu. They can draw between 12 and 15 amps each or about 1500 watts each while running. A 30 amp RV system is 3600 watts while a 50 amp system is 12,000 watts. These RV a/c's have a peak of about 3500 during the startup phase. Now with these simple numbers - maybe, but then, maybe not. I don't try to run both of ours since replacing an a/c with a failed motor/compressor or even a failed pigtail is not in my dollar or time budget. My recommendation - run the main area during the day, starting the BR a/c a half hour before bedtime and after shutting down the main area unit. I'm not even going to get into a CGs power delivery system as there are way too many variables with surges and over/undervoltage spikes

Yes I agree. Just some perspective. RV is not considered a continuous load because everything is on a timer or thermostat. However when the intended use is to max it out for hours on end IMO it is best to watch for issues such as the plug getting hot. NEC rule is just for a single dedicated item(not RV) but the issue still exists. And while new equipment should have less issues the typical RV park connectors are not close to new.

Hi,

This is a bit of a red herring. Most Breaker Panels in homes would not power all the circuits at once at 80 percent of their respective loads. Where I am at this moment has a 200 amp panel. There are 2 feeds of 30 amps each to out buildings, a 50 amp circuit for a water heater, a 50 amp RV plug, and a 30 amp RV plug. That already adds up to more than the 200 amp panel could power at full continuous loads.


Just because NEC doesn't say it is illegal is no reason to not respect the 80 percent of load that is recommended for continuous loads. I choose to limit my 30 amp input to 24 amps, unless I'm plugged into a 50 amp shore power supply.

NEC doesn't require code to be followed for ANY item that plugs in. Hence a hardwired autoformer breaks the code, but a plug in autoformer does not.

A far greater issue is voltage drop. I do monitor voltage and use an autoformer. At the location I am now (rural Saskatchewan) it is a long run from the power companies transformer, so even though I have access to 50 amp outlet, I still am using my Sola Basic autoformer, and I have load support active from the Magnum 3012 hybrid inverter/charger.

myredracer wrote:


If you stop and think about it, there is no way that demand in a 30 amp RV can possibly be restricted to max. 80 percent (24 amps). If you added up the available load per branch circuit in the panel, it would far exceed 30 amps.

error...

time2roll wrote:

myredracer wrote:

We Cant Wait wrote:
Also pulling a full 30 AMPS for an extended period of time could in all likely hood over hear and melt the pedestal plug or your cord plug as shown above.

A receptacle and a circuit breaker are designed to operate at their rating indefinitely.

NEC says for continuous load circuits the supply should be 125 percent of the load. Or rather 24 amps is the maximum continuous load that should be on a 30 amp circuit. IIRC continuous is defined as 3+ hours. Air conditioner is not generally considered a continuous load as it should cycle. In reality we all know they can run 12+ hours without cycling the compressor.

Just some perspective.

To clarify that, the NEC circuit loading only applies to buildings and facilities that have permanent/fixed wiring systems and components and the 80/125 percent rule doesn't apply to RVs. The NEC doesn't cover "portable" plug-in loads and restrict the load relative to the recept. rating it's plugged into. NEC article 551 requires a demand load of 3600 watts (30 amps) for an individual 30 amp RV/site and there is no provision for continuous/non-continuous loads. Art. 551 specifies how wiring within an RV is to be done but does not restrict the total demand on the 30 amp (or 50 amp) shore power connection. I'd post some links to the NEC but can't find a free online version lately.

If you stop and think about it, there is no way that demand in a 30 amp RV can possibly be restricted to max. 80 percent (24 amps). If you added up the available load per branch circuit in the panel, it would far exceed 30 amps. The way you find out if you are drawing too much is simply that you end up with a tripped breaker - you unplug one or more items and reset the breaker and hopefully won't do it again. :) An RV is kinda like an extension cord with a few receptacles on the end of it and it's not possible to restrict how much you plug into it.

myredracer wrote:

We Cant Wait wrote:
Also pulling a full 30 AMPS for an extended period of time could in all likely hood over hear and melt the pedestal plug or your cord plug as shown above.

A receptacle and a circuit breaker are designed to operate at their rating indefinitely.

NEC says for continuous load circuits the supply should be 125 percent of the load. Or rather 24 amps is the maximum continuous load that should be on a 30 amp circuit. IIRC continuous is defined as 3+ hours. Air conditioner is not generally considered a continuous load as it should cycle. In reality we all know they can run 12+ hours without cycling the compressor.

Just some perspective.

Might be okay, might not... Some good advice above.

If trying to run 2 ACs on 30 amps, you better know how the voltage is doing. Actually, even with just one is important. Low voltage causes an AC unit to draw more current and can cause even greater voltage drop and possibly prevent one or both AC from starting. Most importantly, if you use an AC unit(s) often enough under low voltage conditions (105V and below), you can cause cumulative irreversible damage to the AC resulting in premature failure. You *might* get one or both AC units to run and all seems okay, but you won't know how much damage has occurred and how much sooner it will fail.

An AC unit draws about 13-15 running amps and the momentary inrush current at startup will be about 50-60 amps (per manufacturer's specs) at 120 volts which is the industry/code nominal system and equipment/appliance voltage. It's important to know that these figures will increase as voltage goes down. *IF* you got the 1st AC to start and voltage was 120, the total current at startup of the 2nd AC will be 15+60 = 75 amps, plus any other loads that are running when trying to start the 2nd AC. That's a lot, even at full nominal voltage. As mentioned above, depending on a number of various factors, the 2nd unit might not start. If the voltage is already low after the 1st unit is running, it's very likely the 2nd unit will not start. Installing a "hard start" capacitor can help in some cases.

At a min. I'd use either a plug-in LED voltmeter or permanently mounted one on a wall to monitor voltage. The best thing of all is to use a Progressive Industries EMS unit that will shut power off at 104 volts. The "other" brand shuts down at 102V which is too low IMO. Note that voltage may look okay before you turn high load items on but can drop quite a bit with more loads running.

Older RV parks have pedestals wired in a star arrangement to a remote panel. Newer parks have pedestals wired in a loop-fed arrangement from one to the next. The newer parks are less likely on avg. to have voltage drop issues because of the heavy wire to the pedestals (typically around 200 amps). Older pedestals usually have 30 amp wire to them and can be a long run. As well, the older editions of the NEC required demand allowances were much smaller. I can almost guarantee that you won't be able to start a 2nd AC on 30 amps in an older RV park, esp. with high occupancy.

Running a 2nd AC off the 20 amp recept. in a pedestal may or may not work because the NEC does not require wire size to pedestals to be based on 20 amp + 30 amps running together and this could cause the voltage drop to be too high. A newer CG would have more of a chance of this working.

We Cant Wait wrote:
Also pulling a full 30 AMPS for an extended period of time could in all likely hood over hear and melt the pedestal plug or your cord plug as shown above.

A receptacle and a circuit breaker are designed to operate at their rating indefinitely. If a pedestal recept. or shore power cord plug gets warm/hot, the cause will be dirty contacts inside the receptacle, a dirty plug and/or weak contact pressure inside the recept. Always make sure your plug blades are kept clean (use emery cloth or sandpaper). As noted above, if a pedestal recept. looks in rough shape, try and find another site or run on minimal loads. Avoid plugging into a pedestal with the power on as this causes pitting and dirt buildup on plug blades.