Add second air conditioner to 30 amp RV

Always smarter to use 50 amp if you got it (My opinion)

BUt I have a 50 amp rig. I "Broke out" (Technical term) the bedroom A/C so that when I'm on a 30 amp site I open a door pull a plug and now the Rear A/C is independent of the RV. I use a 12ga cord to the park's 20 amp breaker

Suggest the following hookup for the added A/C also suggest you go 15000 BTU I mean for a few dollars more you get more cooling and as the world warms. YOU WILL NEED IT.

A/C----Single breaker box, 20 amps----- 20 amp (Twist lock) Inlet

20 amp (Twist lock) 12ga cord----------- Park 20 amp outlet .


ON a 50 amp site you have choices

1: will need to buy or build a "Break out" box 50 amp male plug. Two breakers (1-20 1-30) TT-30 outlet and a 15/20 Duplex receptacle

I'd add a few neon Lamp indicators to show things like good safety ground and such but hey that's technical stuff.

The other.. Use the park's 20 amp outlet for the A/c
Feed the RV by either using a 30-50 Dogbone or off the park's TT-30

You won't overload the circuit using any of those methods.

rickfraza wrote:
Would it be smarter to use the 50 amp service with one of those 50A pigtails that provides 2 x 30 amp outlets?

The cheater cord does not work with a 20A GFCI plug. There are also safety issues that need to be considered. But RV stores are happy to sell you one anyway.

Knowledgeable CGs will not allow it even though most really don't understand why.

With some panning it's straightforward to modify the A/C with a plug so you can connect it to a 20A pedestal plug.

I would not use a 50-30/30 adapter, as that would be running that cord and air conditioner on a 50 amp breaker- not safe. If you like, you can build a breakout box with breakers like John said.

Chris Bryant wrote:
I would not use a 50-30/30 adapter, as that would be running that cord and air conditioner on a 50 amp breaker- not safe. If you like, you can build a breakout box with breakers like John said.

Basically agree but would say not as safe. The chance of drawing say 49A on one leg is very slim. But a defective cord etc could cause a problem. Ditto for a 50/30 adapter.

I do just as you describe, with my 2 A/Cs on a 30 amp coach. A 20 amp cheater cord WILL work with a GFCI if you make sure the ground and neutral are not bonded. Much easier than rewiring your coach for 50 amp.

Richard

RLS7201 wrote:
I do just as you describe, with my 2 A/Cs on a 30 amp coach. A 20 amp cheater cord WILL work with a GFCI if you make sure the ground and neutral are not bonded. Much easier than rewiring your coach for 50 amp.

Richard

What is a 20A cheater cord? I'm familiar with 50-30/30 and 50-30/20 cheater cords which will trip a GFCI. Nothing to do with neutral/ground bonding which occurs in a service panel.

Are you referring to incorrect ground/neutral bonding in the rig?

Some comments:

- Running two AC units on 30 amps is a bad idea. You're looking at 2 units at 13 amps, plus at least a few amps for the converter, plus whatever else might be running on 120 volts. While a 30 amp breaker (in your RV or pedestal) technically speaking can run indefinitely at 30 amps, it will get very hot due to the thermal elements in breakers. To make it worse, RV panels have the 20 amp AC breaker right below the 30 amp main breaker. Besides the heat, the breakers can eventually trip.

- AC units have a 20 amp breaker which is sized to ensure it won't trip on the momentary startup inrush current, it's not based on the full load running current.

- Momentary startup inrush current is in the 50-60 amp range.

- Voltage is extremely important when running AC units. If the voltage gets down to 105 volts or less, that will cause damage to the motor windings. AC units will draw more current as the voltage goes down which will exacerbate voltage drop.

- Voltage may *look* okay when running, but can drop very low during startup and lead to AC damage.

- AC unit damage is cumulative over time and it can fail prematurely one day for no apparent reason. AC units are expensive to replace.

- Running a 2nd AC unit off the 20 amp breaker in pedestal may or may not work. "Modern" CGs have loop-fed pedestals on large amperage wire (like say 200 amps) and the possibility of excessive voltage drop is significantly reduced. Older CGs have distribution panels spread around the property with small gauge wire to pedestals, which can be as small as #10 wire and thus voltage drop can be high plus wiring runs to the pedestals can be long, further increasing voltage drop.

- If you plan to travel around a lot and not stay exclusively at newer CGs/RV parks with loop-fed pedestals, do not expect running a 2nd AC unit off the pedestal 20 amp breaker to work.

- Installing a permanently mounted voltmeter inside an RV is highly recommended. An EMS unit is also recommended.

- Choosing a site close to a pad-mounted transformer in a CG can help in some cases.

Running a pair of A/C means every so often in a hot climate they BOTH will want to high head pressure re-start simultaneously.

That's when compressor motors will fry and other electrical has to deal with an 80-volt brownout.

Use a pair of 30-amp relays in the feed line. And an ON/ON toggle switch. Either or. This is the only safe way when a single 30-amp service is the only power available.

Your basic plan is solid. An EMS, as suggested, is a good thing to have but would not cover a separated, add on power supply. I added a seperate 15/20 amp inlet on my TT that supplies one duplex outlet inside. So I can separately run a power hog off that while running my Air Conditioning or microwave (not at the same time). I can run an electric heater, toaster, electric fry pan, or coffee maker off the new power supply and not drag down the main power.