5TH Wheel Elecrical Description - RV-Dreams Community Forum

sdman · RV-Dreams Family Member

5TH Wheel Elecrical Description

Terry and Jo · RV-Dreams Family Member

Mark,

First of all, welcome to the RV Dreams forums. There is a wealth of information here in the forums, but Howard and Linda have also added a lot of knowledge gleaned from their process of becoming full-timers.

So, to start with, I recommend you go to the main page for RV Dreams and click on the button for "Site Map," under which you will find a lot of topics related to full-timing. Included will be the process they took, subjects with the electrical systems, and even their budgets and expenses.

The link provided here will take you to that page and if you go down about half way on the page to "Preparing for the Full-Time RV Lifestyle," you will find a start of an education about the electrical. From that beginning, you will have an idea of specific topics that you can search for on the internet.

RV Dreams Site Map Page

Good luck with all your research, and feel free to ask questions for anything RV and RV lifestyle related. Good to have you with us.

Terry

bjoyce · RV-Dreams Family Member

These were written many years ago, but they are still worthwhile - http://www.phrannie.org/phredex.html . Jack also has good info and more websites to look at http://www.jackdanmayer.com/rv_electrical_and_solar.htm .

My main piece of advice is to make the effort to keep the 12volt DC electric and the 110volt AC electric (also called 120volt) separate in your head.

The Bear II · RV-Dreams Family Member

Many shade tree mechanics start working on the RV electrical thinking it is similar to the 12V system in a car or truck.

The RV 120V system is like a house electrical system and so the 12V portion often use black and white wires instead of red and black like a car. On an RV the black is the positive and white is negative for the 12V system. Don't make the mistake of hooking the black to the negative side of the battery and white to the positive side it makes for a good smoke screen but lousy for the insulation on the wiring.

A guy in a spot next to us, replaced his batteries and thought the black wire should be the negative. He made the connections and I heard a bunch of comotion, I looked over in time to see smoke billing from his battery compartment as he tried to disconnect. By the time he had the wires off, he had to spend the rest of the weekend replacing all of the wiring leading into the battery compartment. All of the insulation on the wires had melted.

Howard · Host

Here is the direct link to our RV Electrical Page.

It starts out very basic and progresses into much more detail with generic diagrams of systems near the bottom. It also includes links to more sites if you need them.

Hope it helps. smile

sdman · RV-Dreams Family Member

Thanks for the sites to researh. I have an Electrical Engineering background, but like anything else need to understand what is in most RVs. I do understand that there is a 12v dc and a 120vac system and that batteeies are used for the 12vdc when the 120vac is not available. What I don't know about is the interfaces with the "shore" power, TV power, aux. generator, and just what is powered by which in the RV. Also, it seems that an invertor is used to creat the 12vdc from the 120vac, but is the 12vdc from the batteries used to create 120vac? I'm sure that the resources that you guys gave me will get me to a place where I can figure it out come back and ask better questions. Thanks: Mark

Bill Adams · RV-Dreams Family Member

Your coach may or may not have all of the power options available so you will need to find out what power options are available with your specific coach.

There are 30 amp and 50 amp shore power options. With 30 amp service you have one 30 amp leg of power and therefore a total of 30 amps of power available. With 50 amp service you have 2 50 amp legs making 50 amps available on each leg or a total of 100 amps of power available.

There are built in and portable generator options. With a built in generator you will also have a transfer switch. When you start the generator your transfer switch will provide the same power you could receive from your shore power connection up to the limit of the generator. These are generally referred to as 5K (5000W), 8K, 12K, 15K etc. and refers to to total wattage available. So a 5K (5000 watt) generator can provide around 40 amps. If you have a portable generator, these generally run in the 1-3K range and you just plug your shore power plug into the generator.

There may also be an option for an inverter in your coach. This unit takes the 12V power available from your house batteries (a separate battery bank from your engine starting battery) and converts it to 120V (110V) power. If this is a whole house inverter it will also go through a transfer switch and provide power to most (but likely not all) of the coach if, and only if, power from the generator or shore is not available. In most cases the transfer takes place automatically with the generator having #1 priority, shore power #2 and the inverter last.

Lastly, there may be certain things in the coach that are powered only by 12V. These are generally only the lighting circuits and these also draw their power from your house battery bank. These batteries must be charged to keep things running right so you must provide so source from time to time to prevent your batteries from going dead. Your coach will have some kind of a charging circuit that will charge the batteries (a converter, not inverter, that changes 120V to 12V+ and sends this charge to the batteries). Solar can be a good source for this charging as well as your regular shore power or generator power.

There's your power primer. Does that help?

sdman · RV-Dreams Family Member

Sorry Howard, sent by last post before I read yours. Your explanation for now was perfect for me. I may want more later, but for now that was perfect. We were at the Rally in TN in April and found that you have a gift of explaining thinks at the right level and for me from the perspective of a beginner RVer. Mark

sdman · RV-Dreams Family Member

Thanks to Bill also. Yes your explanation helped also. This IS a great forum and you guys are great. Thanks again: Mark

Bill Adams · RV-Dreams Family Member

I just visited your electrical page there Howard. What a nice resource to have available. It would have saved me a lot of typing had I gone there first and also referred him to that page.

-- Edited by Bill Adams on Thursday 1st of December 2011 01:39:39 PM

BandA · RV-Dreams Community Member

Bill Adams wrote:

There are 30 amp and 50 amp shore power options. With 30 amp service you have one 30 amp leg of power and therefore a total of 30 amps of power available. With 50 amp service you have 2 50 amp legs making 50 amps available on each leg or a total of 100 amps of power available.

I apologize for correcting you but a 50amp circuit is only 50amps total. Doesn't matter whether it's a double or triple pole breaker.
If the total amps were 100amp your power cord wire size would be #000 instead of #6

Bill and Linda · RV-Dreams Family Member

Bill Adams is correct in what he said concerning 30 and 50 amp service to an RV.

A “50 amp” service to an RV has 2 – 50 amp 120 volt circuits from a 2 pole 50 amp per pole breaker. You have a total of 100 amps available – 50 amps on each circuit hence #6 wire is correct as to capacity for each 50 amp feed. You have 100 total amps available in the RV.

BandA · RV-Dreams Community Member

Since the current in a 240 V circuit passes through BOTH of the breakers, a 20 amp, 2 pole breaker will only allow 20 amps to pass.

Bill and Linda · RV-Dreams Family Member

BandA wrote:
Since the current in a 240 V circuit passes through BOTH of the breakers, a 20 amp, 2 pole breaker will only allow 20 amps to pass.

As there is no 240 volt service in (most) RV’s I don’t follow what this has to do with 2 - 50 amp 120 volt circuits.

(And yes, at 240volts you are correct. But we are not using 240 volts in an RV. We’re using two 50 amp 120 volt circuits that, except for a shared neutral, don’t know the other circuit exists in an RV. Just like two 20 amp house circuits can provide 40 amp total - each at 20 amps / 120 volts.)

Bill Adams · RV-Dreams Family Member

Hopefully, readers will not get confused by BandA's incorrect correction of my correct post (grin).
50 amp RV service does provide 2 - 120V 50 amp legs to your RV allowing you to use up to 100 amps. If this were not true, why would I have a generator capable of outputting 125 amps (15K)?
Just because the RV circuit puts out 2 - 120 legs does not mean that it provides 240V service to your RV. In fact, it does not. Some will confuse a household 240V circuit with the RV 50 amp service and figure they can just plug their RV into the household clothes dryer circuit which is an actual 240V circuit. Please be sure that you never do this as the results would be disastrous!

-- Edited by Bill Adams on Thursday 1st of December 2011 08:02:59 PM

BandA · RV-Dreams Community Member

To Bill and the rest of the group I apologize for the need of an extended discussion and the confusion my "correction" has caused :]. I stand corrected you are right. 2 legs of 120v @ 50amp = 100 total amps.

My heat pump / air conditioner has 2 compressors that I “thought” for sure had to be 240v ( I work in the HVAC/R and LPG service field) WOW was I wrong, the heat pump is actually 2 120v. units that work simutaniosly in heating and individually in 1^st. and 2^nd. Stage cooling.

50 Amp RV Service:

To facilitate the larger loads placed upon the newer RVs the 50 amp service was brought out. Whereas the 30 amp service was a 120 volt service yielding 3,600 watts of power, the 50 amp service is a 120/240 split phase service. The split phase service means you have two 120 volt 50 amp poles, which gives you a total of up to 12,000 watts. So the perceived increase from 30 to 50 doesn't sound like very much but the real increase from 3,600 to 12,000 puts it into a more realistic perspective. Keep in mind that this assumes that you can utilize both of the two 50 amp poles effectively by balancing your load. If all of your loads are on one side of the panel you'll only be using one 50 amp pole, which means that you can only get 6,000 watts. So, it is important to split your loads and balance them between both phases on the breaker panel in order to get maximum capacity.

Very rarely will an RV have any 240 volt loads. Some RVs may have 240 volt stackable clothes driers or an electric heating element of some sort but it's rare. Still, the ability to split the load among two poles means that each pole can handle 50 amps. If all of the circuits were placed on a single phase, as in the 30 amp service, then you would need a 100 amp service to provide that same amount of power. That would require some massive wiring to the pedestal and also some very fat and heavy power cords to the RV. 50 amp lets you get by with a smaller #6 gauge wire. But what happens when you don't have a 50 amp service available?

Bill and Linda · RV-Dreams Family Member

Butch:

For what it is worth, it is not uncommon that people have trouble at first accepting that “50 amps ‘RV power’ is actually 70 amps more (100 total) then a 30 amp connection for an RV.” The fact that the trailers say 240/120 volts on the side panel further confuses the issue as well.

There are other RV electrical rules about neutral and ground bonding in an RV that are different from your HVAC training as well. In an RV neutral and ground wires should not bonded / tied together like they are in typical house wiring. RV’s are just different and interesting to study the differences between them and “house” wiring.

Now you know and welcome to the club.

Bill N.

BandA · RV-Dreams Community Member

Almost like learning a new operating system, the old rules are applied differently, kinda sorta ;)

Jim01 · RV-Dreams Family Member

Would you believe that now, in some of the high end coaches they're coming out with what they're calling 100 amp service?

Haven't run into any of them yet, but should be interesting.

Jim

Jack Mayer · RV-Dreams Family Member

There are high end RV parks that have 100 amp service at the pedestals....that is two 100 amp breakers....like 2x50 amp breakers in a typical pedestal. These rigs usually have isolation transformers built in and can run off of a single or dual 50 amp service if required. At reduced power of course. These critters are rare, though.

There are some that also have 2x50 amp service at the pedestal....that is two separate 50 amp plugs. Plus the 30 and 20. And you will see some that have GFCI on both the 30 and 50 amp services.

For the unbonded (floating) neutral in an RV...think of it this way. Electrically (from a NEC perspective) an RV is thought of as just a big appliance. Thus the unbonded neutral/ground.

Jim01 · RV-Dreams Family Member

What kind of power cord would you need for that service? A 50 amp cord is hard enough to handle when it gets cold.

Jim

Jack Mayer · RV-Dreams Family Member

It is typically a Marine twist lock on the RV. Some of these services are 3 phase and have a few more wires, but they really are not any bigger cords than the 50 amp ones - even though there are more and heavier wires in some. Also, remember that rigs like this have power cord reels on them....heck even my 5er has a powered cord reel so winding up the 50 amp cord is as easy as pushing a button. But as I said, these are rare beasts.....mostly you see 100 amp service for larger ships at docks.

Terry and Jo · RV-Dreams Family Member

We were at a SOITC rally in October and one of our immediate neighbors was Mike Salter and his wife in their Mobile Suites. (Mike is the administrator of 5th Wheel Forums.)

In showing us some of the improvements/modifications that he had done to their coach, he pointed out a very flexible electrical cord for his 50 amp. It is supposedly made up of 6 gauge wire and he made some comment that it was wiring used by MacDonalds restarurants for their deep fat fryers.

I can attest that it is a lot more flexible than our 50 amp wire. I guess I need to see if I can find some of that cable and literally compare it to normal 50 amp cable. I say that because I don't know what the gauge of normal 50 amp wiring is supposed to be.

If it really is the same but more flexible, I will definitely spring for some of that wiring cable.

Terry

Bill and Linda · RV-Dreams Family Member

Terry:

What you may have seen is what we always referred to as “welding cable” in our electrical group. It has many more but much finer copper wires in the wrap that make up the #6 size wire (for example.) It is much more flexible, and expensive. We used this type of cable “forever” on our TV remote mobile units. Worked quite well. But we needed cables in the 100+ foot range so we just spend the bucks to make is more functional as required.

Bill