Newbie 50/30 amp adaptor question

[NCFischers]

Except for Exnavydiver who wired his differently, the dryers for RV's are 120 volts.

[KathyandDave]

Are the two legs of 50A CG power off the same or different phases?

[NCFischers]

Dave,
The 50 amp power in campground pedestals is two 120 volt 50 amp phases. That is what is provided to your circuit breaker panel in the trailer. You only have single pole breakers in the trailer and each breaker pulls power from one or the other phase. The problem comes when you plug into 30 amp power. That is a single 30 amp phase and is split into two legs with a 30 to 50 amp adaptor. If you use a two pole (240 volt) circuit breaker to power an appliance like a dryer with 30 amp campground power and don't remember to turn off the two pole breaker, you will create a cross phase situation. There will be a large bang and and a flash of light and the dryer will be fried. If you are lucky, there won't be a fire and you won't get hurt.
Any time there is 240 volt power, there are two phases that can't be crossed.
I hope this helps,
Jim

[Tom S.]

What Jim said except..... Unless you put in a non-rv washer/dryer, you don't need to worry because RV units are only 120v, not 240 like stick house units.

[farmboy]

Dave and kathy, please do not cofuse phases and legs when refering to 50amp. service. They are completly different animals. 240v service in your home or rv is in fact single phase service with with both a + and - in reference to 0 or nuteral. Phases are in fact 3 different cycles of the electrical sine wave 120 degrees apart and mostly used in indusrtial and light commerical applications. I know this is confusing to a non-electricl type, but I hope it helps a little. Another way to look at it is if you look at the poles in front of your house and you see 2 then it is single phase, if 4 then it is three phase, but the power company only taps one of the hot legs and the grounded leg to your home. Happy travels and have a good day.

[KathyandDave]

Thanks for the correction on phases and legs. Here is my understanding. I would appreciate any corrections you all can offer.
240V is delivered as a leg of +120V and a leg of -120V . They are single phase because they are at 180 degrees polarity. Each leg runs through the service entrance panel separately on its own buss. Neutral is tied to ground in the panel. Any individual circuit uses a single-pole breaker connected to one buss or the other and routes 120V (+/- doesn't matter) to the appliance or lightbulb, then returns it to the panel via the neutral wire. In the case of a dryer or baseboard heater (or oven?), each pole of a two-pole breaker is connected to a leg, so we get a circuit of +120V and another of -120V running together out to the appliance, where they are wired to the two ends of a heating coil, driving the coil at 240V. The neutral is not involved, so this can be a three-wire circuit/plug, but appliance wiring includes a neutral because the other parts of the appliance, like the clock and controls, use the the 120V circuits independently without joining them together. If the separate 120V legs get accidentally connected, you get a shower of sparks and the two-pole breaker will snap (a good thing), but each leg is still only 120V, so is considered safe if fused and wired to code.
A campground 30A circuit is one 120V leg, + or -, with a neutral and a ground (we hope). An adapter to 50V just splits the 120V leg into two wires having the same polarity, then sends them into the RV as if it was + and -. The available current is still only 30A total, unlike the total of 100A that is available from two separate 120V 50A legs. The circuits all operate normally. However, I expect NOTHING to happen when a 240V dryer is plugged in conventionally, since both ends of the heater coil are connected to the same leg, so no voltage difference. This is different than Jim (NCFischers) reports, so I need help with it.
Connecting a house or RV to three-phase power means taking two of the three phases as legs. The phases will be 120 degrees apart and the voltage difference will be about 208V. The household appliances and light bulbs will see what they expect and the dryer will be a bit less hot. A true three-phase panel for industrial use has three separate busses. The ordinary circuits work as expected but three pole breakers can be mounted to power motors.
Is this correct?

[NCFischers]

Dave,
Maybe I confused you a bit when I used the term "phase" instead of leg. I was trying to stay with your terminology. I also had a brain fart this morning and can only blame it on not enough sleep last night. You are right that nothing will happen on a 30 amp campground service and a house dryer since you are only providing 120 volts from the same leg to both busses of the circuit breaker panel. The two legs of a 240 volt circuit touched together will cause a direct short.

[Countryfolks]

Phases are a timing thing. An example is singing 3 blind mice in rounds, the 1st person starts [1st phase] then the 2nd [2d phase] then the third starts [phase three]. This is determined at the basic power source. The power we start with is a single phase, 240V, [pressure] at 50A, [volume]. The legs are nothing more than a splitting or division of the original 240V, with the zero point, the reference or neutral, being in in the center, and lowering the volume to 30A. The phase remains the same.
Another way to see this is to draw 3 lines 1 1/2" long, one above another, make a dot at the start, the center and the end of the middle line and label them [1,2,3]. Make another dot 1/4" to the right of each of the first set and label them, [a,b,c]. Make another set of 3 dots a 1/4' to the right of the of the 2d set and label them [d,e,f]. Extend the original line through the new dots. Draw a sideways "S" thru each of the labeled sets of dots and have the top and bottom touch the upper and lower lines, you should have 3 lazy S's that overlap. Each "S" is a phase. The distance between the top and bottom lines is the starting voltage, 240V. The center line is the zero/reference/neutral point. A leg is the distance between the zero and either the top or bottom lines on one of the S's.
The 50A connector end/side of an adapter has a contact for all three of the lines and an additional line [ground] that is separate, the 30A end/side only connects the zero line, one of the legs and ground.

OP- I suspect you have to set your generator up for the 240V output. I think I would use a standard 120V, 30A [rv]cable because most of what you'll use is off of 1 leg. [30A twist lock to 30A rv cable].

edit. Dave the ground and neutral are tied together in a stick house but not in our rigs.

[KathyandDave]

Countryfolks: I like the 3 Blind Mice analogy! Thanks for the reminder about tying the neutral and ground together. That's been the topic of another thread.

[1ViciousGSX]

The generator had both the 3-prong 30 amp twist lock and the 4 prong 30 amp twist lock receptacles. But the 4-prong side had two 20 amp breakers, one for each side of the connector. The 3-prong 30 amp would have to supply both sides of my 3380RL connector for a total of 30 amps. But by using the 4-prong 30 amp I got a pair of 20 amp feeds to supply my 3380RL for a total of 40 amps.

The generator was built as 120v on each side of the 4-prong receptacle. It would become 240 volt if I tied the to sides together. But the 3380RL keeps them separated.

[mcgiver2]

WOW iam glad all i do is just plug in to the rv park power with my power surge and then i have elec and i dont have to understand how it works.

[Art-n-Marge]

Be careful mcgiver2. Don't get too comfortable with shore power. There have been plenty of horror stories with RV park power even with power surge and power conditioners in place. In a way, 1ViciousGSX is controlling his own destiny.

Let's all keep our fingers crossed. Wait a minute, maybe don't cross the fingers. I can never remember which one gives us the good luck.

[1ViciousGSX]

Well I hope that my initial lack of knowledge on this subject and what I have found out along the way will help others. By all means, what ever you do, use a volt meter to determine how the power is being supplied by your generator and/or shore power. Don't take the chance without checking first.

[KathyandDave]

While we're on the subject, we got a site this fall that promised 50A. The pedestal turned out to be much further away (50 feet across the very big campsite) than our 50A cable could reach AND there was no 30A on the pedestal! I went to the park office and they said it happens all the time and handed me a 50A to 30A adapter. I assume the adapter takes one 50A leg and connects it to the 30A socket, while leaving the other 50A leg disconnected. I plugged it in and metered it. It was fine on the 30A side, so I plugged in 50 feet of 30A cable, then the 30A>50A adapter bone into our 50A cable and it was good. After a few hours, I got a creepy feeling about the arrangement. The pedestal breaker is 50A for each leg. Similarly, the Monty panel is breakered for 50A. If we had turned too many things on in the Monty, no breaker would have popped, so it could have drawn close to 50A through a wire (my extension cord) that was rated for 30A. It could have melted the cable and/or the connectors. So, we were very careful what got turned on. In conclusion, the park was very dumb to hand out that adapter without asking what was to be hooked up, since it voided the effectiveness of the pedestal breaker. Any fire or damage would be their liability. If I, the camper, did a dumb thing like that, it would be my problem. So, be careful about adapters, even if they meter fine.

[Countryfolks]

Why do you say 50A in each leg?

[KathyandDave]

It's a two-pole breaker?

[Countryfolks]

I agree about using a 30A cord in a 50A circuit but the leg part is confusing me.

[KathyandDave]

One leg = one of the two circuits that are present in the 50A socket on the CG pedestal. It's slang that I picked up somewhere along the way...