Explain to me how a 50 amp connection works.

[quicky06]

This may be a stupid question but I’m tired and trying to answer A question for my father.

So a 30 amp Rv plug is a standard 110 v connection 1 hot, 1 Neutral, 1
Ground.

A 50 amp adds in an additional hot.

So in a house application 110 v circuits pull off of either hot. You loose a hot wire and half the 110 b will not work. 220 v gets nasty when you loose a hot.

So when you plug in a 50 amp Rv into a 30 amp plug using an adapter why does everything still work?


We are by no means in familiar with residential and commercial wiring. I am very familiar with automotive wiring.

We are looking at adding a small 30 amp inverter generator to his 42foot fifth wheel that has the wires ran for the generator but no transfer
Switch. All the transfer switches I am
Seeing are listed as 240v. So I am just trying to understand the system to see if this will work.

He wants the small generator to be able to stop and use the inside of the trailer to cook and eat lunch and one 1 of his 3 Ac units while on the road. Trying to make it as simple as can be for him to just fire the greater up and go inside the turn it off and get back in the road.

[CedarCreekWoody]

What exactly is your question?
By the way it is when you loose the neutral, not a hot leg, that causes problems in an RV. An adapter takes the single 120 volt leg and branches it to feed both legs in a 50 amp RV.

[quicky06]

Originally Posted by CedarCreekWoody

What exactly is your question?
By the way it is when you loose the neutral, not a hot leg, that causes problems in an RV. An adapter takes the single 120 volt leg and branches it to feed both legs in a 50 amp RV.

Does the Rv only use of of the 50 amp hot legs?
If it uses both I can’t figure out how.

[CedarCreekWoody]

It uses both legs, each leg feeding one half of the electrical buss with 50 amp at 120 volts. Total amperage in the box is 100 amps at 120 volts when connected to 50 amp RV service. When connected to a 30 amp adapter one 30 amp leg feeds both sides of the buss bar for 30 amps total in the box.

[quicky06]

So does someone make a transfer switch that can handle the 50 amp Service from shore power and 110v 30 amp generator input.

I would like at ovoid anything wfco

[cavie]

A 50 amp service in in fact 240 volts to the RV main breaker. That is where 240 stops. Most, except very high end MH, cannot access 240 volts.

50 to 30 dog bone picks just one leg of 240 and puts in on the hot wire of the 30 amp adapter.

By the same token a 30 to 50 adapter puts the hot leg of the 30 amps on both wires going to the RV 50 amp service.

RV generator will feed 2 30 amp circuits to a 50 amp service.

[babock]

Originally Posted by quicky06

So does someone make a transfer switch that can handle the 50 amp Service from shore power and 110v 30 amp generator input.

I would like at ovoid anything wfco

You just use a 30A to 50A adapter from your generator and a regular 50A transfer switch. The transfer switch doesn't care.

[cmysstailights]

Hope this helps a little

[wmtire]

This is always the link I refer to, to help memberS understand how 30 and 50 amp service work....including the adapter which will jump the ONE 30 amp hot leg over onto the other hot leg of the 50 amp RV, so both legs are powered by the one leg. THE LINK WILL FULLY EXPLAIN EVERYTHING


https://www.rvtechmag.com/electrical/chapter3.php

[mjbenedict]

The reason a 30A feeding both legs of a 50A breaker box works in a RV is most all RVs don’t have 240V appliances. If they do, you cannot run them when connected to the adapter and I would suggest shutting off that dual-pole breaker while using the dogbone adapter.

[CedarCreekWoody]

Originally Posted by mjbenedict

The reason a 30A feeding both legs of a 50A breaker box works in a RV is most all RVs don’t have 240V appliances. If they do, you cannot run them when connected to the adapter and I would suggest shutting off that dual-pole breaker while using the dogbone adapter.

This makes no sense. What double pole breaker are you referring to? The one on the camper circuit breaker box has to be on for power to flow to the buss.

[Swampy]

Originally Posted by quicky06

This may be a stupid question but I’m tired and trying to answer A question for my father.

So a 30 amp Rv plug is a standard 110 v connection 1 hot, 1 Neutral, 1
Ground.

A 50 amp adds in an additional hot.

So in a house application 110 v circuits pull off of either hot. You loose a hot wire and half the 110 b will not work. 220 v gets nasty when you loose a hot.

So when you plug in a 50 amp Rv into a 30 amp plug using an adapter why does everything still work?


We are by no means in familiar with residential and commercial wiring. I am very familiar with automotive wiring.

We are looking at adding a small 30 amp inverter generator to his 42foot fifth wheel that has the wires ran for the generator but no transfer
Switch. All the transfer switches I am
Seeing are listed as 240v. So I am just trying to understand the system to see if this will work.

He wants the small generator to be able to stop and use the inside of the trailer to cook and eat lunch and one 1 of his 3 Ac units while on the road. Trying to make it as simple as can be for him to just fire the greater up and go inside the turn it off and get back in the road.

quicky06, If I am understanding what you are asking, you want to hook up a 30A, 120V inverter generator to a 50A, double 120V RV.

If my interpretation is correct, then simply test to determine which of the 2 hot legs at the main RV panel go to the generator pre-wire Hot and Neutral ... once identified, mark with tape on both ends. Next, determine which half of the RV the A/C and microwave are fed from. That one will be the side of the mains you want to connect to the generator output. As far as the transfer switch goes, use a 50A, 240V model with a 120V control to sense the land power source as primary feed. be sure to verify the neutral wire is connected to the panel near the main bus as it must carry the full return current from the generator output.
Let us know how the project goes and be sure to ask more questions if you get confused. Above all, be careful while playing with electricity! Swampy

[babock]

Originally Posted by CedarCreekWoody

This makes no sense. What double pole breaker are you referring to? The one on the camper circuit breaker box has to be on for power to flow to the buss.

He was saying if the RV happened to have a 240V appliance. In that case, you want to turn the double pole breaker for that appliance. It's rare to have one of those but some large RVs do have them.

[Bigruh36]

A 30a plug has 1 hot 30a 120v wire and 1 neutral 30a wire plus a ground. For RV 50a you effectively have 1 hot line off of phase 1, 1 hot off of phase 2, 1 neutral and ground. If you measure the voltage from phase 1 to phase 2 it is 240v. But you are not going from phase to phase. You are using 2 separate legs of 120v to the neutral. So essentially you get 2 legs of 25a 120v hot combined for 50a on your neutral. You can tie those two hot lines together and run 1 50a hot 120v line to get the same results.

[babock]

Originally Posted by Bigruh36

So essentially you get 2 legs of 25a 120v hot combined for 50a on your neutral.

Wrong! Each leg is 50A. The most you would ever have on the neutral is 50A if only one leg was drawing 50A. If the other leg is also drawing 50A, the current in the neutral would be zero.

You are really an HVAC service technician?

[Bigruh36]

Originally Posted by babock

Wrong! Each leg is 50A. The most you would ever have on the neutral is 50A if only one leg was drawing 50A. If the other leg is also drawing 50A, the current in the neutral would be zero.

You are really an HVAC service technician?

If it was a 240v circuit you would be correct. But it is 2 50a 120v circuits. The neutral can only handle 50a, so the total amount of current flowing through both legs cannot exceed 50a.
The current could be divided between 1 or both legs however It cannot exceed 50a total. the neutral is the return leg.

[babock]

Originally Posted by Bigruh36

If it was a 240v circuit you would be correct. But it is 2 50a 120v circuits. The neutral can only handle 50a, so the total amount of current flowing through both legs cannot exceed 50a.
The current could be divided between 1 or both legs however It cannot exceed 50a total. the neutral is the return leg.

We ARE talking about a 240V service. That is what a 50A RV service is....240V split phase. You can have 50A flowing through both legs!

[rockfordroo]

One more pic that might help:

[itat]

Bigruh36, to clarify, the "split phase" part means that the 2 legs both can have 50A running through them but never simultaneously. When Leg 1 is energized, Leg 2 is not and vice versa. Therefore the shared neutral will never have more the 50A running through it.

I'm sure the electricians here will correct me if I'm wrong!

[Bigruh36]

Originally Posted by itat

Bigruh36, to clarify, the "split phase" part means that the 2 legs both can have 50A running through them but never simultaneously. When Leg 1 is energized, Leg 2 is not and vice versa. Therefore the shared neutral will never have more the 50A running through it.

I'm sure the electricians here will correct me if I'm wrong!

That is what I was trying to say.... sorry I am not a good writer