Help me understand 50amp

[ependydad]

Ok, I’m piecing bits and pieces of information together.

(Please y’all- keep this civil. If you disagree, say so- provide a link and then be like Elsa & “let it go”. These conversations tend to turn into pee contests and I’d love for this one to not end in a site team closure. -ependydad)

The general saying is that a “50amp RV is really 100amps because you have 2 x 50amp legs.

But, if it really is 100amps, how is it possible to be protected by a 50amp breaker at the pedestal?

So, I asked an RVing electrician (master electrician in 15-20 states) and he explained that it IS 50amps per phase but each phase can’t be used at the same time. It alternates between L1 gets a micro-moment of juice and that wave dips and L2 then rises and gets its micro-moment of juice.

With all of these ups and downs, a grand total of 50amps is consumed- since neither leg can consume more than 50amps and only 1 leg ever has electric for that momentary micro-moment in time.

—-

First, do I understand this correctly? 50amps really is just 50amps (even though it sure pretends to be 100amps)?

[elind]

The RV 50 amp service is two 50 amps 120 volt circuits. Nothing runs on 240 volts in the RV. That way when you use a 30 to 50 amp dog leg adapter you only get 30 amps because both hot lines are tied together. In a 30 amp cable you 3-10 gauge wires feeding the RV and in a 50 amp cable there is 4-6 gauge wires (2 hot wires).

[TheGerman]

The breaker at the pedestal is a double pole type. It will disconnect both phases if either phase exceeds 50A. It supports up to 100A in total but split over the two phases so a single leg can not exceed 50A or ~6000W.
The way it is used in an RV you can think of it as two separate 120V/50A feeds carried in one cable. The different feeds power different sets of equipment in the RV.

[andymil]

Think of it as two different extension cords plugged into two different receptacles which are protected by two different breakers. You’ll get 120 volts on both cords. Let’s say they are 15 amp cords and both breakers are 15 amp. That would give you 30 amps total.

If you start wondering how the neutral can carry 100 amps, you better wrap your head in duct tape. It might explode! (Hint: it only carries 50 amps.)

But the two lines (black and red) carry 50 amps each protected by two 50 amp breakers mechanically tied together.

[Skyliner]

This is a 50 amp thread and not a "best oil for my truck, best tow vehicle, overweight towing, or does my RV make my wife look fat thread" so I'm pretty sure it will remain civil ;-)

Please please please do not rely on an electrician for advice or WORSE wire you a 30 or 50 amp pedestal at your home. Two many of them have fried electronics in campers for hooking up 240 volts to the RV.

What previous posters have said is accurate but i will reiterate it? A 50 amp service actually has two 50 amp hot lines/feeds going to the camper giving you basically 100 amps of service. This differs a lot from a 30 amp RV service where max power is 30 amps and nothing more.

I think the reason why the neutral carries only 50 amps instead of 100 amps is probably related to the fact that the two separate hot wires are 180 degrees out of phase with each other.

Regardless, you have 12,000 watts to play with, 6000 watts per each hot line in a 50 amp service.

[Scrapper]

ependydad, maybe these will help.

RV Electric and click on "50-amp Service".

wmtire will be able to help you better than anyone I know of, he knows how to put his thoughts into words anyone can understand. Sorry cavie.

[My17Ram]

To be clear:
The neutral would only be carrying 50A if one phase was loaded to the max 50A current draw and the other phase had zero amp load. For example if both legs had a 20A draw at the same time, the neutral would be carrying zero amps.
If one phase was carrying 30A load and the other phase was carrying 10A load, the neutral would be carrying a 20A load.

[wmtire]

Doug, everyone is correct to a point, we just need to put it all together.

However, you need to understand how the current flows in a 120/240 SPLIT phase service, in which a 50 amp service is.

This link explains it in layman terms better than most (without getting too technical on alternating current), and explains load balancing and the neutral wire.

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

Please read the above link. It may take a few times for it to really sink in. Only after you understand it, should you proceed to the following post, which has diagrams that Scrapper provided. You should then understand how the current flows from the 120/240 split phase service to the outlet...thru the shore power cord....and then how the RV utilizes it in it's electrical distribution panel.

[wmtire]

Here is how the 120/240 50 amp is provided via the power company and a double pole circuit breaker, which is one breaker providing 50 amps from the L1 side/pole, and another circuit breaker providing 50 amps from the L2 side/pole. :

Now, here is an example of how the 120/240 volt 50 amp split phase service is fed into your RV's electrical distribution panel (which may vary somewhat depending on the panel):

[Briyoung]

I didn't want to start another post about this and I did use the search feature but have a related simple question. Our TT has 50amp wired service for an optional 2nd A/C unit, we only have one 15k but a/c and the typical microwave etc. My question is what can I run before something blows.

[ManlyMan]

Without getting too technical the best explanation is this, "It's magic."

[SeaDog]

Originally Posted by Briyoung

I didn't want to start another post about this and I did use the search feature but have a related simple question. Our TT has 50amp wired service for an optional 2nd A/C unit, we only have one 15k but a/c and the typical microwave etc. My question is what can I run before something blows.

You can run what ever you want your rig is wired to handle the normal loads. Optional AC means nothing other then wiring is there, without the AC installed and running you have more power available for what ever you want.

[Bama Rambler]

Originally Posted by Briyoung

I didn't want to start another post about this and I did use the search feature but have a related simple question. Our TT has 50amp wired service for an optional 2nd A/C unit, we only have one 15k but a/c and the typical microwave etc. My question is what can I run before something blows.

It's impossible to for us to say 'what' you can run before "something blows" because we have no idea what you have or how much current each device draws. However, we can say that you can run several things until you reach the limit of the branch circuit breaker on that circuit and then the breaker will trip. So, theoretically if you're running several appliances on a single 20 amp circuit, as soon as you exceed 20 amps, the breaker will trip. If your RV is wired with several branch circuits and the loads are somewhat balanced, you can run up to 50 amps on each leg.

[nc-canuck]

Great information. Ependy my apologies in advance but I have a similar question to understand my 30 amp RV. I never use a 30 to 50 dog leg. My understanding is that there really is no benefit to plug a 30 amp RV into a 50 amp receptor. I only have it in case there is no 30 amp receptor available. Is this true or would there be a benefit?

[ependydad]

Originally Posted by nc-canuck

Great information. Ependy my apologies in advance but I have a similar question to understand my 30 amp RV. I never use a 30 to 50 dog leg. My understanding is that there really is no benefit to plug a 30 amp RV into a 50 amp receptor. I only have it in case there is no 30 amp receptor available. Is this true or would there be a benefit?

No worries. I got good info and a better understanding.

As for you, the only real benefit is that the 30amp receptacles are sometimes worn out from use and the 50amp isn’t. If you get a tighter connection with the 50 vs the 30, then it’s “better”.

You lose in that you lose the protection of the 30amp breaker at the pedestal.

[myredracer]

A 50 amp RV service is identical to a residential service except they are 100, 200 or sometimes 400 amps. The total amount of power you can get from 50 amps is 12,000 watts while 30 amps will give you 3600 watts. Unless you have a larger RV, are maybe running all electric heating or have 2 or more AC units, 30 amps is adequate. I installed an LED ammeter and rarely see it go much above 15 amps.

There is one thing about 50 amp RVs to be aware of and that is that the NEC only requires 20% of pedestals in a CG to be 50 amps and the balance 30 amps. Prior to the 2005 edition of the NEC, only 5% of the pedestals had to be 50 amps. Unless you are staying at some casinos or a CG where the owner intentionally built above the min. code requirements, 50 amp pedestals can be extremely hard to find, and especially in older CGs that have not been upgraded and in the high season. I have seen many, many 50 amp RVs plugged into 30 amp recepts all over the place. RV manufacturers and dealers will gladly sell you a 50 amp unit and not tell you how hard to find a 50 amp pedestal can be...

Originally Posted by nc-canuck

Great information. Ependy my apologies in advance but I have a similar question to understand my 30 amp RV. I never use a 30 to 50 dog leg. My understanding is that there really is no benefit to plug a 30 amp RV into a 50 amp receptor. I only have it in case there is no 30 amp receptor available. Is this true or would there be a benefit?

There are a couple of good benefits to using a 50/30 dogbone adapter. One is voltage drop can be a lot less because the wiring to pedestals is heavier gauge - especially in an older CG because of how they used to wire them compared to today's loop-fed pedestals.

Another is that 30 amp receptacles tend to get a lot more abuse than 50 amps and using a 50 amp receptacle means you may be less likely to have a poor connection that can lead to overheating, smoke and a meltdown.

[ependydad]

Originally Posted by myredracer

RV manufacturers and dealers will gladly sell you a 50 amp unit and not tell you how hard to find a 50 amp pedestal can be...

Honestly, in my travels with a 50amp rig, we haven't seen this. We don't mind getting a 30amp spot but it is the exception vs. the norm for us.

[Jeanguypataterubberboot]

Originally Posted by wmtire

Here is how the 120/240 50 amp is provided via the power company and a double pole circuit breaker, which is one breaker providing 50 amps from the L1 side/pole, and another circuit breaker providing 50 amps from the L2 side/pole. :

Now, here is an example of how the 120/240 volt 50 amp split phase service is fed into your RV's electrical distribution panel (which may vary somewhat depending on the panel):

But won't the neutral have to be able to handle 100 in this case? 50x2 if everything is on.

[ScottBrownstein]

Originally Posted by Jeanguypataterubberboot

But won't the neutral have to be able to handle 100 in this case? 50x2 if everything is on.

Nope, current in one leg is going one way and at the same time current in the other is going the other way. If you load both legs to 50 amps...there is no current in the neutral at all.

[Jeanguypataterubberboot]

I see thank you.