50 amp rig using 30 amp pedestal

cross country wrote:
when plugged into 30 amp pedestal, the monitor panel shows 2 legs (or at least 2 separate 120 volt readings. Now I understand, I think, why 50 amp power plug would show 2, 120 volt lines because there are 2 hot wires of 120 coming into the mh. for a total of approx 12000 watts...but when plugged into 30 amps with one hot wire of approx 3600 watts, why would the monitor show two?

Is the motor home electrical system splitting the 30 amps to 2 15 amp lines for distribution in the coach where when plugged into 50 amps the monitor would split into 2 50 amp circuits of 120 volts? Thanks very much. Tom

You didn't mention using a converter cord, but most likely you are, which provides a jumper to the other side, so without elaborating further and to the point of confusion, the difference is, instead of having two opposite potentials as you would with the 50amp service, you now have the same potential. Reading between two opposites, will produce 240vac and between two of the same will read 0, but in either case, each leg will read 120vac to neutral or ground, so the previously described 0 reading is still hot and definitely not safe to the touch.

For an Energy management system to "SEE" 2 legs, those legs must NOT be on the same "Phase" from the electrical supply. Since you are combining 1 phase of the supply (The Y), That is why your EMS system (any EMS system) does NOT sense and show separate power on each leg. 30 amp service is on 1 phase/leg. 50 amp service is on 2 separate out of phase legs. Doug

The reason the monitor panel on a 50 amp rig always shows 120/120 (or close to it) even when plugged into 30 amps is simply.. Think about the letter "Y"

The top of the Y is your RV, two feeds of 120 volts totaling 30 amps between them

The bottom of the "Y" is the park pedestal.

the Y,, well that's the dog bone connector.

Now, when on 50 amps.. Each leg is 120, but leg-leg is 240 volt (This is how your energy manager can tell 'em apart by the way).

Unless some of the idiots in some of the threads I read wired it, But that is a topic for those threads.

If I was on 30 amp I'd only try to run 1 A/C unit. Microwave, toaster and 1 A/C is a good load by it self on 30 amps. The 2nd A/C is often the reason for the upgrade to 50 amp service. A 15,000 BTU A/C unit is around 15 amps running.

You have received a good explanation. Remember that when on 30 amp you can have what is called a brown out because you do not have enough amps to run every thing. AC use more amps (called starting Amps) when first spinning up. On 30 amps we have problems when one one AC, micro wave, and toaster and then the second AC kicks on. Normally the pedestal breaker pops. Not much 50 amps in CN.

"Is the motor home electrical system splitting the 30 amps to 2 15 amp lines for distribution in the coach where when plugged into 50 amps the monitor would split into 2 50 amp circuits of 120 volts"

NO, The previous explanations stand, but the system combines to ALL the breakers in your panel. No split at all but the 30 amp feeds all 120 systems equally. This is why you see Burnt/pitted prongs on 50 to 30 amp adapters on the 30 amp side. People run more current thru their RV (on 30 amp adapted) than the Supply can handle and the weakest point is that 30 amp end plug. Which heats up and then burns/discolors. ALWAYS replace your 50 to 30 adapter when you see this problem. Doug

Consider these DMBRUSS pictorials of a typical 50AMP setup using an RV30A-50AMP Adapter.



The RV30A-50A adapter has a wire that runs from the two hot legs to feed both 50A circuits in your trailer. Everything in your 50AMP distribution will work as before except the most current you can draw is only 30AMPS



Hope this helps...
Roy Ken

Hi,

The adapter has two wires going into it, then has three wires (plus ground too) going to the 50 amp plug. What happens is the white wire goes to the center neutral of the 50 amp plug, while the black 30 amp wire goes to both sides of the 50 amp plug.

The black wire is protected by a 30 amp circuit breaker, and is feeding both sides of the 50 amp plug. Your monitor is reading 120 to ground on both legs of the incoming wire, but it is all protected by the 30 amp wire, so be sure to not exceed the 30 amp limit.

It is easy to exceed the 30 amp limit, though I never did in years of RVing. the coffee maker can use up to about 12 amps, a toaster or toaster oven about 8-10 amps, microwave despite it's 1,000 watt output can have a 1,500 watt input or about 12.5 amps.

Each air conditioner can use 12.5 amps on a cooler day, while upwards of 14 or 15 amps on a hot day.

Fred.

new to this but anxious for someone with knowledge to educate us, i have a 50 amp MH but just bought the adapter for the 30 , everything works just not at the same time on 30 so what you said below makes sense to me..