Understanding 50A in my RV

[RobWNY]

I understand there are two legs, each carrying 50 Amps to the RV but I'm having trouble understanding what gets serviced by L1 and what gets serviced by L2 of the 50A service and why are there two legs on a 50A service? I can just turn off one of the main breakers and check each outlet and AC unit and figure out that part of things but I'm more interested in knowing why it's done that way. I have two air conditioners. A 15,000 BTU AC in the living area and a 13,500 BTU AC in the bedroom. If I'm on a 30A service, I know I can't use both of them at the same time because of the start up surge needing too many watts but I can use both theoretically on one leg of a 50A service. So why are there two legs and why is that necessary? Why not just one leg of 75A or 100A to handle the loads from AC units, the Microwave, Washer/Dryer etc.? There are many homes with 100A services still so why are RV's different?

[Old-Biscuit]

Two Hot legs each capable of 50A to supply 6000W of power on each Hot Line

RV Main Panel is split into TWO BUSS works
Odd Circuit Breakers (#1, #3, #5 etc) are fed from one of the BUSS works
Even Circuit Breakers (#2, #4, #6 ec) are fed from the other BUSS Works

Each BUSS Works is Protected by ONE of the 50A Main Circuit Breakers in RV Panel


120VAC Appliances/services are staggered betweent the Two BUSS Works to try and 'balance' the LOAD on each Hot Line/50A CB

[BB_TX]

Here are two web sites to help understand the 50 amp side of life. And, yes, the RV power is the same as home power except only 50 amp instead of 100 or 200 amp. And the main two pole breaker is linked so that you cannot turn off one breaker without turning off the other at the same time.

http://www.myrv.us/electric/

https://www.rvtravel.com/rv-electricity-power-principals-50-amp-shore-power/

[rhagfo]

DownTheAvenue wrote:

RobWNY wrote:
There are many homes with 100A services still so why are RV's different?

RV's aren't different. They are wired exactly the same. Some homes have 200 amp service and are wired exactly the same as a 50 amp RV.

Well not quite correct, in a house panel you can tap 240 volt circuit simply by installing a double breaker for your panel that will connect one breaker to each leg. In an RV the legs split at the main breaker, giving two legs of 120 50 amp capacity. You can get one 240 volt circuit by using a double breaker with half size breakers in place of the main. Typicality you would install a 50/30 double half size breaker the 50 being the main and the 30 being a 240 volt feed for a dryer, or in my case my Cheap Heat system.

[jdc1]

If you had one 75 amp main curcuit, the wire size would be enormous....imagine trying to roll up a 00 4-wire cord!

[RobWNY]

Bobbo wrote:
Most countries in the world use 240v to power everything. The 240v uses 1/2 of the amps to power anything than an equivalent 120v circuit would use, so you are reducing the amperage draw by doing it that way. Also, you don't need a Neutral wire. Both wires to the outlet are Hot wires, and maybe a Ground wire. A 50 amp circuit has 50 amps at 240v, or 12,000 watts.

The US/Canada does it differently. We use a 120v/240v system. We have the same two Hot legs as everyone else, but, we have a "center tap" than comes in as the Neutral. (It is also tied to Ground voltage at your power entry point.) Now, on our system, we need the same two Hot wires as everyone else, and maybe a Ground, BUT, we also need a Neutral wire. We can wire for either 120v (use one Hot wire, either one as they are interchangeable for this purpose, and the Neutral), or 240v (use both Hot wires, but no Neutral), easily. You just alternate legs when wiring for 120v so you don't overload one leg. When we wire for 120v, we have 50 amps of power, or 6,000 watts ON EACH LEG. That totals the same 12,000 watts you get from the 50 amps of 240v power, if you choose to wire for 240v. Note that a 4 pin RV outlet has, well, 4 pins. It provides both Hot legs, the Ground, AND the Neutral. That means your RV can pick whether it wants to use the power as two 120v circuits, or as a single 240v circuit. Or, some rigs do both. Some higher end rigs have a 240v clothes dryer.

Why does the US/Canada do it differently than the rest of the world? Because, we can. It would have been just as easy to only use 240v here, then you wouldn't have, or need, two legs.

(And, the 50 amp 120v/240v RV outlet is identical to the 50 amp 120v/240v dryer outlet in your house. It is wired exactly the same.)

Thanks for the explanation. That makes sense now. So I assume where you say the "RV can pick whether it wants to use the power as two 120v circuits, or as a single 240v circuit" that is determined at the panel and how the RV has been wired at the factory?

[Bobbo]

Most countries in the world use 240v to power everything. The 240v uses 1/2 of the amps to power anything than an equivalent 120v circuit would use, so you are reducing the amperage draw by doing it that way. Also, you don't need a Neutral wire. Both wires to the outlet are Hot wires, and maybe a Ground wire. A 50 amp circuit has 50 amps at 240v, or 12,000 watts.

The US/Canada does it differently. We use a 120v/240v system. We have the same two Hot legs as everyone else, but, we have a "center tap" than comes in as the Neutral. (It is also tied to Ground voltage at your power entry point.) Now, on our system, we need the same two Hot wires as everyone else, and maybe a Ground, BUT, we also need a Neutral wire. We can wire for either 120v (use one Hot wire, either one as they are interchangeable for this purpose, and the Neutral), or 240v (use both Hot wires, but no Neutral), easily. You just alternate legs when wiring for 120v so you don't overload one leg. When we wire for 120v, we have 50 amps of power, or 6,000 watts ON EACH LEG. That totals the same 12,000 watts you get from the 50 amps of 240v power, if you choose to wire for 240v. Note that a 4 pin RV outlet has, well, 4 pins. It provides both Hot legs, the Ground, AND the Neutral. That means your RV can pick whether it wants to use the power as two 120v circuits, or as a single 240v circuit. Or, some rigs do both. Some higher end rigs have a 240v clothes dryer.

Why does the US/Canada do it differently than the rest of the world? Because, we can. It would have been just as easy to only use 240v here, then you wouldn't have, or need, two legs.

(And, the 50 amp 120v/240v RV outlet is identical to the 50 amp 120v/240v dryer outlet in your house. It is wired exactly the same.)

[joebedford]

My hot tub and water pump are both 240V with NO NEUTRAL.

[StirCrazy]

yup because it is pure 240V and not using it as 120V.  your kitchen range will be 240V with a nutral as it nees the nutral to tap 120V off the one leg for the controls.  any pure 240V heating element or motor doesn't utilize a nutral as the split phase acts like a nutral in thoes aplications.

[StirCrazy]

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@Bobbo wrote:
Most countries in the world use 240v to power everything.

almost, not quite, the rest of the world used to use 110V but the need for power caused them to switch to 220V buty they don't use bi phase like us.  they did it just so they wouldnt have to replace wires and could transmidt twice the power, probably more as they get a little less loss witht he higher voltage (now 230V but at 50Htz)  not  240V 60Htz We started out transmitting 240V bi phase and split it at the house to 120V , 

[DownTheAvenue]

RobWNY wrote:
There are many homes with 100A services still so why are RV's different?

RV's aren't different. They are wired exactly the same. Some homes have 200 amp service and are wired exactly the same as a 50 amp RV.