50 amp 120v or 240v

[Mr_D]

Originally Posted by docj

The volts CAN and DO change. The meter is measuring the energy sent through it, NOT the amps. If you were having a power brown-out the energy used (watt-hours) would be different. For example, during a brown-out many motors will draw more current (amps) but the energy used will still be governed by volts x current and, in this case, the voltage will be reduced.

Unless you have an autoformer, then the voltage will be boosted so the amps drawn will go down. Much better than low voltage.

[TonyMac]

Originally Posted by twinboat

You need to accept that it is a 50 amp 240 volt service.

In the RV that 240 volt is split to 120 volts at 50 amps each leg.

There are many, many internet references that will explain it.

Really? Why does my Surge Guard show two legs of 120vac, as tho' the voltage coming to the rv is two legs of 120vac before it enters the cord, and the motorhome splits nothing? My Surge Guard must be wrong...

[iamblum]

Love it everytime the 50 amp 240 or the 30 amp outlet comes up��

[docj]

Originally Posted by TonyMac

Really? Why does my Surge Guard show two legs of 120vac, as tho' the voltage coming to the rv is two legs of 120vac before it enters the cord, and the motorhome splits nothing? My Surge Guard must be wrong...

One last time......

No one is denying that each of the two legs will measure 120V on a meter, but what the meter doesn't show are the oscillations that actually describe the instantaneous voltage of our standard 60Hz electricity.

If you connected the two 120V connections to a dual-trace oscilloscope you would see that the phases of the two voltage waveforms are exactly 180 degrees out of phase with each other. What that means is that one is at its positive-going peak when the other is at its negative peak. This is why your meter says that there is 240V across the two blades of the outlet you are plugging into.

Despite what your Surgeguard reads, if you opened up the breaker box in your MH and measured the voltage across the two incoming conductors, your meter would also read 240V. The 240V continues to exist because each of the two 120V inputs is out of phase with each other. Nothing any device can do will change that.

It would also be possible to have two 120V circuits that are in phase with each other rather than being out of phase. A voltage meter would show that each of them had a 120V but a scope would show that their waves add rather than subtract from each other. If you tried to wire an RV pedestal using two such circuits, you would need to have a much larger neutral conductor because the current through it from the two circuits would no longer cancel. It would provide no benefit and would be a serious inconvenience.

[FlyingDiver]

Originally Posted by TonyMac

Really? Why does my Surge Guard show two legs of 120vac, as tho' the voltage coming to the rv is two legs of 120vac before it enters the cord, and the motorhome splits nothing? My Surge Guard must be wrong...

The Surge Guard is showing the voltage from the hot lead to neutral. It's 240V between the hot leads. There's really no splitting going on anywhere (except at the transformer feeding the pedestal). Both 240V (hot to hot) and 120V (hot to neutral) are present on the shore power cable.

[MisterT]

Originally Posted by FlyingDiver

Not quite right. It's incorrect to refer to the incoming power as two "different" 120v lines because they're not independent. It's 240V with a center tapped neutral. And some coaches certainly do use the 240V. Mine has a residential 240V dryer in it. So the main breaker panel is a standard (if small) 240V breaker panel and one 240V double breaker for the dryer in addition to the 240V double breaker for the main (input).

true, thanks for the correction...

I think my true intention was to eliminate the discourse of what 50a RV service versus 100amps really is, at least for us common folks, in a more easily understood way. Most RVs will never have or use 240v service, or have that type of 240v breaker box panel, so the conversation from most who ask the question is to try to understand why the RV industry has 'defaulted' to 50a double-pole service, vs a more 'simple to understand' 100amp, similar to easy 30amp service.


enjoy!

[FlyingDiver]

Originally Posted by MisterT

true, thanks for the correction...

I think my true intention was to eliminate the discourse of what 50a RV service versus 100amps really is, at least for us common folks, in a more easily understood way. Most RVs will never have or use 240v service, or have that type of 240v breaker box panel, so the conversation from most who ask the question is to try to understand why the RV industry has 'defaulted' to 50a double-pole service, vs a more 'simple to understand' 100amp, similar to easy 30amp service.


enjoy!

We would all be better off if no one ever used the term "100 amps" referring to RV service. You can't ever get 100 amps from an RV 50 amp setup, to a single circuit. People understand that S&B homes have 240V service, with 120V circuits inside. An RV connected to a 50amp pedestal is basically the same thing. So why try and make it something that it's not? A house with gas appliances and no central AC units won't have any 240V loads either. The house I grew up in didn't. Heck, it had screw in fuses and no breakers.

[iamblum]

We can use the term "100 amps" just fine. It's just that people need to understand the terminology of they are going to put their "2 cents in". I went to school for 4 years to understand electrical theory along with many many others. So when I see this thread pop up every few months it makes me laugh. A bunch of people "who know everything " chime in where they shouldn't.

Don't get me wrong, I've posted things without knowing, or actually without thinking. But I will not tell someone they are wrong or argue with them without knowing the theory, or truth behind the matter

[MisterT]

agree, but most folks new to '50amp service' in an RV don't 'get' what that really means, and trying to tell them that they really have up to 100amps of total power messes with their minds, but it's true.

The RV industry calls it's '50amp service', but if it was called '100amp service', it would carry much less angst for those new to RVing to understand it, whether it's really TWO 50amp hot lines, or if it was all along just a single 3-wire cord to a 100amp outlet and breaker.

if your RV's breaker box has two sides, each with a 50amp 'Main Breaker', then you have two 50a lines coming in to service those breakers within each 'side', for a total usage of up to 100amps.

if, instead, your coach had TWO shore power cords to plug into two 'true' 50amp outlets, going to each 'side' of your breaker box, it would be no different.
a single 50amp shore power cord, plugged into a 50amp double-pole breaker, just shares the NEUTRAL, giving you a simpler way to hook up to 100amps of power.

getting into the 120v vs 240v conversation, technically speaking, is what muddies the subject, though it's understood that some really understand it well, and finding a way to help the rest of us understand it is the difficulty.

[twinboat]

Originally Posted by TonyMac

Really? Why does my Surge Guard show two legs of 120vac, as tho' the voltage coming to the rv is two legs of 120vac before it enters the cord, and the motorhome splits nothing? My Surge Guard must be wrong...

It is two legs of 120 volts !

L1@120 + L2@120 = 240 volts, with a shared single neutral wire.

Take your volt meter inside and measure between L1 and L2, at the TWO 50 amp breakers. You will find 240 volts.

[Sbrownstein]

But the real problem is...it is not the RV industry who coins these terms. The same model is used in 200 amp service to homes. 200 amps at 240, two 120 legs and a neutral from the transformer's center tap, each leg fused at 200 amps.

They need to get over it. I think a lot comes from hooking up to old style dryer outlets that were 240 with a ground and no neutral.

[followingsea]

I was a mechanical with 40 years in the power industry including 10 years as a nuke trained officer. Things do not always work according to theory.

What do you want to do and how do you know it is safe? I did the wiring for a house I built. I used the same 12 gage wire for 15 and 20 amp circuits. The building inspector 'red flagged' my 15 amp breakers. The breaker should protect the limiting component on the expected on the circuit but is conservative to use a heavier gage wire.

So you match individual 15 and 20 amp breakers to the load and the main breaker to the total load.

More often than not shore power is on 20 amp kitchen circuit with a 50' extension cord through the window. Measured voltage with the microwave running 95 volts. Not good!

With generator running power comes from one 20 amp breaker and 30 amp breaker for a total of 50 amps. Voltage is maintained at 120 volts and stays close to that at the loads. Some load management is required by putting loads on propane.

On shore power, power comes from two 50 amp breakers with a possible total of 100 amps on the common wire. Voltage drop depends a lot on the loads that include other RVs in the park. We like to be at the far end and often we are back down to 90 volts.

So yes you may have 100 amps service but I do not recommend burning out your AC unit.

RV power democracy.

[FlyingDiver]

Originally Posted by followingsea

On shore power, power comes from two 50 amp breakers with a possible total of 100 amps on the common wire.

Not if the pedestal is wired according to code. A properly wired 50 amp shore power connection will have a max of 50 amps on the neutral, and it would be damn hard to get anywhere near that with any conventionally wired RV.

[doublechevy]

With 49years of electrical experience and the holder of a Master electrical Lisc. I have never seen so much misinformation on electrical as I have seen reading this forum post. some of the responders truly know what they are talking about a very few of them. to the last poster you will never have 100A
on the common (Neutral ) if connected to a properly wired shore power pedestal. On ( 2) 120V lines on separate phases, the neutral will only carry the unbalanced current.

Sample Only

L1 20A L1 20A
L2 10A L2 20A
N 5A 0A

Do yourself a favor If you are not sure what you are doing Hire a qualified Lisc. Electrician