How does 50 amp work?

[David0725]

Can someone explain how the 50 approach system works? Normally 50 amp is 220 but the rv is not 220 its 110 riright? So how does this work?

[enblethen]

MedCad: Some adapters do not tie the two legs of power. You maybe able to run both AC units on a thirty-amp power feed.
I say again that 50-amp system is 120/240-volt four wire!

[Racklefratz]

2 legs of 120v...it's not complicated.

[MedCad]

My 50 amp RV are two 110v, one 110v feeds the front of the RV and it's AC and the other 110v feeds the rear and rear AC. If I plug into a 30 amp only the front AC will work.

[pianotuna]

enblethen,

Great clarification. Thank you.

[enblethen]

I will refer you to the National Electrical Code Article 551-46 (C)(4) for correct information.
Paragraph (D) gives information on how the rig is required to be labeled.
It is not two legs of 120 volts. If supply is wired in this manner the neutral will be overloaded if wired from same phase.

[dodge_guy]

Technically a 50A service is 220V. It just depends on how the power is pulled from the service panel I some the RV. Most RV systems use 110V appliances.

An RV uses 2 50A legs of 110V.

[rgatijnet1]

https://i0.wp.com/makezine.com/wp-content/uploads/2016/11/figure_2-240v-1.png?w=450&ssl=1

[dougrainer]

ScottG wrote:

dougrainer wrote:

RCMAN46 wrote:
The 50 amp 220 volt is the same as the 30 amp 220 volts at your home.
Most RV's loads are 110 volts thus only use one side of the 220 volts as do most of the loads at your home. Most homes only the water heater, electric range and electric furnace use 220 volts and most are 30 amps or less with the exception of some heat pumps. A heat pump in a RV may be wired for 220 volts.

NO HP in a RV is wired for 220 volts. No such HP for an RV has 220 volts. ALL are 110 volts.

220/240 volts in an RV is supplied by 2 separate 120 wires OUT OF PHASE. EACH side is on a 50 amp breaker for 100 amps total supply. The RV does NOT separate the supply. The supply is already separated at the POLE. If the Supply is in phase, the RV will not function correctly all the time. For instance, you have a built in EMS (energy management system) . IT sees if the supply is out of phase. IF IT IS, then you have full 100 amp capacity. IF same phase at supply the EMS will only allow 30 amps total operation. It assumes you have connected a 50 to 30 amp reducer dogbone. IF you think you are connected to a 50 amp service and your EMS shows 30 amp, you have what I call CHEATED 50 amp service. The RV park did not upgrade their supply and wiring for true 50 amp total 100 amp service. This is theft by the RV park. You are paying for 50 amp service and they are NOT giving you what you pay for. The simple test ALL RV'ers need to do is have a multitester and at the Park Pole test the voltage between the 3 and 9 o clock spade slots. 50 amp will show 240. ANY OTHER reading, the pole is NOT 50 amp. Doug

A good explanation. Only thing wrong with it is that the "out of phase" part - a common misconception.
They (the two legs) are in-phase with each other and maybe easier to understand as two halves of the same phase. On an oscilloscope the signal would look like one complete sine wave. That phase is then split into the two, 120VAC legs.
So your 240VAC service is referred to as Split-Phase.

I think my explanation is better on the Phasing. Please explain in your definition, why, when people try CHEATED 50 amp. They use the same "leg" and then attempt to split that leg onto BOTH sides of the 50 amp RV breaker box, you are still on one phase. This is the Electrical definition of this, NOT MINE. "Two 120 V AC lines are supplied to the premises that are out of phase by 180 degrees with each other". Doug

PS, the definitions also state Split Phase as the same, but I feel stating OUT OF PHASE is better to let lay people understand WHY 50 amp is as it is. It helps explain the 240 between the legs.

[pianotuna]

Best practice is to use not more than 80% of the capacity for continuous loads.

I set my inverter charger to that level (24 amps; 2880 watts) and use the load support feature.

On 50 amps each leg would be set at 40 amps; 4800 watts.

NEC suggests this for sticks and bricks homes. RV's are considered a plug in device and so there is no requirement to follow the 80%.

[rgatijnet1]

It is also necessary to remember that some inverter/chargers use "pass thru" current when hooked up to shore power. Just because you have x amount of power available from the shore connection does not mean that you can actually use all of it. If I tried to use too many high power appliances it would pop the break on the inverter/charger first. I never tripped a breaker in my main panel or on the shore panel.

[time2roll]

valhalla360 wrote:

time2roll wrote:
12,000 watts of electric power available.

Minor nitpick.

You have 2legs @ 6000w.

If you try to pull 8000w on leg 1 and 4000w on leg 2, expect it to pop the breaker.

Of course, that's a lot of power, so unless you are running several space heaters, it's not likely to happen.

Yes the 12,000 watts would have to be split perfectly half to each side. Still available and would be eight 1500w space heaters if all are on separate branch circuits and four on each side.

I throw out the 12kW power to compare to 30 amp service at just 3.6kW. Big difference.

[ScottG]

dougrainer wrote:

RCMAN46 wrote:
The 50 amp 220 volt is the same as the 30 amp 220 volts at your home.
Most RV's loads are 110 volts thus only use one side of the 220 volts as do most of the loads at your home. Most homes only the water heater, electric range and electric furnace use 220 volts and most are 30 amps or less with the exception of some heat pumps. A heat pump in a RV may be wired for 220 volts.

NO HP in a RV is wired for 220 volts. No such HP for an RV has 220 volts. ALL are 110 volts.

220/240 volts in an RV is supplied by 2 separate 120 wires OUT OF PHASE. EACH side is on a 50 amp breaker for 100 amps total supply. The RV does NOT separate the supply. The supply is already separated at the POLE. If the Supply is in phase, the RV will not function correctly all the time. For instance, you have a built in EMS (energy management system) . IT sees if the supply is out of phase. IF IT IS, then you have full 100 amp capacity. IF same phase at supply the EMS will only allow 30 amps total operation. It assumes you have connected a 50 to 30 amp reducer dogbone. IF you think you are connected to a 50 amp service and your EMS shows 30 amp, you have what I call CHEATED 50 amp service. The RV park did not upgrade their supply and wiring for true 50 amp total 100 amp service. This is theft by the RV park. You are paying for 50 amp service and they are NOT giving you what you pay for. The simple test ALL RV'ers need to do is have a multitester and at the Park Pole test the voltage between the 3 and 9 o clock spade slots. 50 amp will show 240. ANY OTHER reading, the pole is NOT 50 amp. Doug

A good explanation. Only thing wrong with it is that the "out of phase" part - a common misconception.
They (the two legs) are in-phase with each other and maybe easier to understand as two halves of the same phase. On an oscilloscope the signal would look like one complete sine wave. That phase is then split into the two, 120VAC legs.
So your 240VAC service is referred to as Split-Phase.

[valhalla360]

time2roll wrote:
12,000 watts of electric power available.

Minor nitpick.

You have 2legs @ 6000w.

If you try to pull 8000w on leg 1 and 4000w on leg 2, expect it to pop the breaker.

Of course, that's a lot of power, so unless you are running several space heaters, it's not likely to happen.

[wa8yxm]

David0725 wrote:
Can someone explain how the 50 approach system works? Normally 50 amp is 220 but the rv is not 220 its 110 riright? So how does this work?

Ok think of your house for a moment.. Most everything in it is 120 VAC but the "Drop" is 3 wires. 240 volt "Divided" as a cook would say (and that is the best term for it.) If you want the technical description Well.. I can do that. Most folks get it wrong by the way.

The divided means you have to "Hot" legs and a "neutral" which is bonded to Ground.. Your devices. Computers. Cloths washer, Fridge, TV/Radio. lights.. Draw off one of the hot legs with respect to neutral. Now some things.. Like a cloths dryer or a Centeral AC use the full 240 volts.. (This is not so in an RV but it is in a house)

So why 240 volts divided?

Imagine that between your electric coffee maker and the power company transformer there are 2 volts of drop. due to the resistance of the wire EACH WAY.. This means you only have not 120 volt but 116 so it takes a but longer before the Elixer of the Gods is ready to drink.

On 30 amp service this is how it works

Now on 50 amp.. let's say that coffee maker is working opposite your Water heater.. IT also has 2 volts drop each way.. but it's on the OTHER LEG. Since the current is nearly balanced the power say comes in Leg 1. losing 2 volts. passes to leg two where it again looses two volts. but now each appliance has not 116 but 118 volts (The voltage drop. like the voltage, is split is.. "Divided")

This means they can use less copper and get better performance.

But due to the neutral wire (the divider) everything gets close to 120 volt.


Think of a water system.. You have two water pups pushign 120 gallons per minute.. both pushign to the right.. in the middle is a "T" and that T is hooked to a tank holding 50 gallons.

So long as both pumps are pumping the fill flow. the 50 gallon tank water level is static.

But what happens if you are only using power on one leg?
Well then the neutral carries that back to the transformer and of course you get voltage drop both ways.

And the level in the tank change in the water example (The rate of change is affected by the size of the pipe by the way.. and the length)

On a good system it takes a very good Digital meter to see the voltage chagnes properly.

[AllegroD]

A link and pic as sometimes the visual helps.

RV 50amp

More reading



One thing the pic provides is how your RV handles L1 & L2, at the RV distribution panel. You can, therefore, audit what is wired to each leg, such as ACs, inverters/chargers, and 110 plugs, in case you wish to use high load items, such as space heaters.