50 amp.... Why so big?

[Big Blue]

One of the more interesting threads on this forum.... The simple answer to the question.... is because the USA is wired for 120v... If you were to rent and RV in a country that was wired for 240v... ie: Australia.. microwave, Fridge, & air conditioner are all 240v... the power cord looked to be 14 gauge.....

[BobLandry]

That's because 240V devices draw much less current than our 120V appliances.

[Lane Hog]

Fulltmers I can see needing 50A.

Weekend warriors? We've "suffered" with 30A all these years just fine.

You're camping. You don't need every kitchen gadget and entertainment device known to Mankind....

Sent from my SM-G981U using Tapatalk

[mdwilliams44]

OK, I'm going to post this right here...it's a good explanation of the 50A RV Electrical Service to our campers. I wrote this about two weeks ago after getting into a discussion on one of the Facebook Grand Design pages where there were Soooo many comments that were all the way from a little wrong....to OMG wrong. Feel free to use it as you may need to explain to others about the facts of an RV 50A Electrical service.....

I have to admit....I'm still in shock (no pun intended) at some of the outrageous and totally wrong comments/info being given on this topic. The RV electrical systems have been engineered by professional folks, following an established method of electrical distribution that is not subject to your opinion or what you think on how it "should" work, it's based on how it DOES work. So in this case, opinion is totally irrelevant.....and FACT is the determining method of RV electrical systems.

And the fact is this. A 50A RV electrical system will be comprised of two hot legs, created by what is known as a Split Phase system, and thought of as L1 and L2, a neutral wire, and a ground wire. The two hot legs will be 180 degrees out of phase with each other (and if you don't know what that means, you likely are not going to thoroughly understand how it works) and they WILL IN FACT be able to provide 50 amps of 120VAC PER LEG. In the case of a 50A RV Electrical system, it is basically the exact same as the electrical distribution system INTO your house or home. The difference between the two (RV and your house) is in the electrical distribution panel....a.k.a. the breaker panel. Up to that point (disregarding that fact that your house will use a ground rod at the service entrance and your RV has a continuous ground wire from the pedestal to your RV) the two are exactly alike. Distribution of that power is where the difference is...not the power source itself.

The RV breaker panel is made so that the 50A Main breaker is located in the center of the panel and the associated bus work for each hot leg goes in opposite directions, so it is impossible to have a 240VAC circuit any place other than the Main breaker itself. In regard to the 50A Main breaker....the LEFT most half of that breaker feeds 120VAC (with respect to neutral) only to the LEFT side of the panel for the purpose of being able to install single pole breakers into the available spaces on the LEFT side of the panel. The RIGHT most half of the 50A Main breaker feeds the bus on the RIGHT side of the panel, providing 120VAC (with respect to the neutral wire) to all of the available slots on the RIGHT side of the panel. The left side of the panel can be thought of as Phase A...or L1.....and the right side of the panel would then be Phase B... or L2....and MOST IMPORTANTLY....L1 and L2 are electrically 180 degrees OUT OF PHASE with each other. The fact that the two hot legs are 180 degrees out of phase with each other, is what allows the neutral wire to NEVER have to carry any more than 50 amps of current.....even if each leg is pulling the maximum amount of current available to each leg.....50 amps each.

It's really pretty simple if you have been trained and or have knowledge of how a split phase electrical distribution system works.....if you don't, it might be a bit troublesome and cause you to make statements that may not be true at all. Sorry for the long-winded post, but hopefully it may help clear up some of the mis-statements made in this ongoing topic.

OKey Dokey then! I know I for one feel well and truly schooled on RV wiring now! Thank you for the lesson, it makes me fell like I know a little more about a huge investment I made!

[xrated]

OKey Dokey then! I know I for one feel well and truly schooled on RV wiring now! Thank you for the lesson, it makes me fell like I know a little more about a huge investment I made!

You're welcome.....glad I could help. BTW, do you know the difference between AC....and DC? AC = Always Confused DC = D@mned Confused!

[fez111]

The two hot legs will be 180 degrees out of phase with each other...

Please excuse my butting in, and I admit this is very petty, but I agreed with everything you said except for the above comment. All power distribution is generated from 3-Phase sources. "Single-phase" power for homes and other sources is been taken from any two of these phases. Think of a circle being 360 degrees. Divided by 3 phases means that the phases are 120 degrees out of phase.

Again, I agree with everything else you said, and obviously, this was very petty!

[xrated]

Please excuse my butting in, and I admit this is very petty, but I agreed with everything you said except for the above comment. All power distribution is generated from 3-Phase sources. "Single-phase" power for homes and other sources is been taken from any two of these phases. Think of a circle being 360 degrees. Divided by 3 phases means that the phases are 120 degrees out of phase.

Again, I agree with everything else you said, and obviously, this was very petty!

You are correct in the fact that power is generated using 3 phase, which is the standard in the US. You obviously though do not have a working knowledge of the distribution of that power to the final transformer which serves a house....which is typically One of the three phases and a neutral on the primary winding of that transformer. The secondary winding in that transformer is reduced down to the typical 240VAC and that secondary coil is center-tapped in order to be able to provide a split phase power to your house. Each of the hot legs, which are 120VAC as referenced to the neutral wire, are 180 degrees out of phase with each other. You should google this and see exactly how this is done. Here is a picture of what I'm talking about. Notice the primary winding of the transformer (the pole mount or the pad mount that services your house), that winding has ONE of the three overhead distribution lines (likely 7200 VAC) coming to the winding of the transformer, and the other side of the winding is grounded. The secondary winding is ONE coil of wire on the transformer and is center-tapped (That's your neutral lead), so there are two hot leads...L1 and L2, and the neutral lead.....all three are considered to be current carrying conductors. And because the two hot leads are 180 degrees out of phase with each other, the term split phase is used and the neutral current has a maximum current value of 50 amps, thus it is sized the same as the hot leads....normally a 6ga. conductor.

[Johnrb]

I've done some fairly extensive mods to my house on wheels and along the way I've wondered about how we got to 50 amp shore power. That question comes back up every time I drag out the huge heavy power cord to plug in. Why do we carry that beast around?

First, let's compare 30 and 50 amp service in terms of power. With 30 amp service, there is theoretically 3600 watts available and with 50 amp service there is 12000 watts available. How is it that almost overnight, the RV industry decided that we need more than three times the power to run the house. 12 kw is a lot of power! In my rig, 2 AC's, microwaveable coffee maker add up to less than 8 kw. And that's assuming no soft starts and all appliances start at the same time!

Yes, it's nice to have pretty much unlimited power available, but how much do we really need? And how much weight are we willing to carry to support that habit? Personally, my back and shoulders can't handle wrestling the 50 pound power cord in and out of its home, so I don't.

I haven't found my ideal setup yet, but most of the time I use a 10 gauge power cord that weighs about a quarter of what the beast weighs.

It seems to me, a little bit of thought in the industry would go a long way toward making things simpler and lighter.

Just my Sunday morning ramblings... I hope you enjoyed.

Since this was not mentioned in any replies, I would like to add that an electrical circuit would not be designed to be loaded to more than 80% of it's ampacity. So a 30 amp supply would not be able to safely and legally deliver 6000 watts of power. This is due to electrical codes and standards currently in use. There are exceptions to this, such as 100% rated circuit breakers, but in this case the wire would still have to satisfy the 80% rule. Hopefully this is useful information to all.

[xrated]

Since this was not mentioned in any replies, I would like to add that an electrical circuit would not be designed to be loaded to more than 80% of it's ampacity. So a 30 amp supply would not be able to safely and legally deliver 6000 watts of power. This is due to electrical codes and standards currently in use. There are exceptions to this, such as 100% rated circuit breakers, but in this case the wire would still have to satisfy the 80% rule. Hopefully this is useful information to all.

I'm not sure where you got your "6000" watts from a 30A supply, but is not correct. 120V time 30A is 3600 Watts of power.

[mdwilliams44]

You're welcome.....glad I could help. BTW, do you know the difference between AC....and DC? AC = Always Confused DC = D@mned Confused!

Dude, That was REALLY unfair! You made me spit my morning coffee!

Thank god it didn't get on the keyboard.

I shall remember that saying for life now....