This is my first post. I have been lurking for weeks, trying to decide what kind of RV I want and how I want to set it up, so I am not going to pretend to be some kind of RV expert. HOWEVER, there are two subjects I am fairly well versed in, engines and electrical [including electronics].
You folks scare me to death. I won't get on the topic of engines, since your knowledge [or lack of knowledge] of engines will not kill you and this is not an engine thread anyway, but on the subject of electrical I am going to give y'all some fair warnings:
1. Almost water tight is not water tight. Lunchboxes do not a junction box make!! Almost dry is not dry! Damp can bleed current that will actually cost you money in a higher electric bill, but more importantly it can get someone killed.
To make a weatherproof connection between two cables, take a piece of 1/2 inch galvanized pipe about 30 inches long and bolt a small piece of plank to it. You can use wood or a scrap piece of Trex which will be forever rot free. U-bolts work well and don't require that you drill the pipe. Leave a few [2-5] inches of pipe above the plank. Screw an outdoor rated junction box to the plank. You can get one with a screw on cover for a tamper resistant set up or one with a door if you need frequent access. A small one is likely cheaper than the lunchbox described in the post above. Make your connection inside this nice, dry, safe, convenient box.
Now since the box is mounted on 1/2 inch galvanized pipe, you can stick it in the ground where it will not be kicked around, it will be above ground level where it can stay dry in the hardest rain and where it can be seen. It can also be easily moved. When you go to a new location, take a hammer and drive it back into the ground by striking it on that portion of the pipe you left sticking above the plank.
The whole thing weighs a pound or two.
You can get fancier for a price. You can use fiberglass or aluminum yard spikes, but they are not as cheap and take more space to store in your RV.
A 40 cent pipe cap can be used if you don't want any sharp edges and no hammer marks. 1/2" pipe is easier to drive than 3/4" and 1/2" is cheaper, lighter, and plenty strong. [The U-bolts are cheaper too].
If you place it close to where people drive -- or even walk, paint it bright yellow, international orange, lime green or hot pink depending on how obnoxious you want it to look.
2. Electrical Current Rules You can hook up a 30 amp RV to a 50 amp source without concern. But if you hook a 50 amp RV to a 30 amp source and draw more than 30 amps, there is going to be a problem. Often that problem is burned wiring or damaged motors [like the A/C compressor motor in your RV]. Sometimes that problem is a fire.
Don't count on circuit breakers to protect you. They certainly won't protect your A/C. Furthermore, circuit breakers can and do wear out! If your lucky, they will not close. If you are not lucky, they will not open. If you are Haley Joel Osment, you might "see dead people".
I have seen 20 amp breakers pass 50 amps without tripping. The wiring did not look very good afterward.
3. Heavy wires dude. 50 amp cables are thicker than 30 amp cables because?
A) Camping World knows if you have a 50 amp RV you can afford 50 amp cables.
B) Big RV, big tires, big money, gotta match it with big cables. It just looks cool.
C) It is a ploy by the IBEW [International Brotherhood of Electrical Workers] to keep the union workers employed by confusing everyone else with silly electrical codes.
D) A 30 amp cable cannot sustain continuous currents above 30 amps.
The answer is D. In the end it is all about heat. A 30 amp cable can take 50 amps for a very brief time [10-20 seconds?] and maybe even 100 amps for an even briefer time [2-3 seconds?], but the current will create heat. [In fact heat itself creates its own resistance - but that is another topic beyond the scope of this thread]. But the point is that a 50 amp cable is more EFFICIENT than a 30 amp one. When you approach the design limits of a cable you can use more electricity even though you are drawing less current [50 of you will argue this point. Hint: VxIxT=P(total)] and create a voltage drop across the cable [due to the resistance of the cable itself] robbing energy from high demand loads [such as your A/C] and converting electricity into heat across the cable. Is there such a thing as free heat generation? NO. Therefore, you are paying for energy that you are using to heat the cable.
Now some of you will argue that the heat generated on a 30 amp cable is the same as that generated on 50 amp cable but the heat is just spread out more. That is true to some degree, but not in real net terms. The total heat generated is greater.
Ever hear of someone burning up four starters in their car only to find out the starters were burning up because the battery output was too low? Hi resistance in the cable will cause the exact same effect. The current in the case of the starter was limited by low voltage and thus damaged the motor.The current in the cable was limited by the resistance of the cable and thus damage occurs again.
The motor can also suffer local damage. For example the motor can feel cool to the touch but the stator or brushes can be burned locally. So the motor may not seem hot yet it has suffered permanent damage. If you think a starter is expensive, check out the cost of that A/C motor.
Since voltage is a product of current across a resistance and vice versa then if the total impedance (Z) stays the same and the current drops then the voltage must also drop. When there is not enough energy to turn the motor at the proper speed then the motor creates excessive heat and the motor is damaged. Heat further robs the motor of kinetic energy. Again heat is not free.
===Technical===
Impedence Z = the resistance R plus the inductive reactance X(L), in the case of an electric motor.
Now this is all a bit of over-simplification so the average tinkerer can understand the process of risk. Somebody will probably run off and Google it all and try to post a more technically precise explanation that few will understand. The point in doing it simple like this is so that people can understand that the dangers of using lighter cords for the sake of a moment's convenience is not worth it.
For those who want to Google reactance, you can also look up "phase shift" and "power factor" which is often discussed with reactance and you can learn how a few capacitors can perform a phase shift on your motors to make your electrical meter 'see' that you are using less energy. This is perfectly legal. The current leads voltage in a capacitive circuit and trails it in an inductive circuit making your meter think you are using more power than you are. Clue: Match each Henry of inductance with one Farad of capacitance to correct the phase shift. Note that this does not save any REAL energy, so there is no need to do it when you are on a generator. It simply corrects the error causing your meter to tell the power company you are using more power than you actually are. So while it does not save REAL energy, it does save you REAL money. In fact, in an RV it would be very slightly less efficient as the hysteresis loses in the circuit would produce a very slight loss in net efficiency - but it still lowers your electric bill when you are on a meter.
===End Technical===
Why do most appliance circuits in your home have twice the rating of the appliance hooked to it? Just in case you get a bigger one someday? Nope.
I often use extension cords that are MUCH larger than required for my purpose. That is because everything works better on bigger cords. Obviously there are limits to the gain. If I am using a 60 watt bulb [about 1/2 amp draw] a 12 gauge extension cord will not provide any better results than a 14 or even 16 gauge one. But what if I am drawing close to 10 amps? You can bet the heaver cord is what I will use even though the 14 gauge cord is rated for 10 amps.
You want to run your 50 amp RV on a 30 amp cord? Go ahead. You can do it. As long as you are below a 30 amp draw it is "safe", but it is not what is best.
If you are so overwhelmed by the difference in weight of a 50 amp cord vs a 30 amp one, maybe you should consider if you are up to the rigors of RV travel. Seriously.
In all cases, if I HAD to run my 50 amp rig off a 30 amp source, I would:
1. Use a 50 amp cable on a 30 amp plug.
2. Carefully calculate the MAXIMUM load of all the appliances I intended using and assume they were running at the same time.
3. Turn of the breakers off going to any high draw appliances and unneeded circuits so they could not be accidentally switched on.
If the intended purpose is simply to keep the fridge cold and keep the batteries charged, I don't see a problem. Neither draws much current. But living in the RV would require careful calculations. You don't want to damage your equipment and you don't want a fire in your RV, just outside your RV, or at a remote location [such as your home] because it was just too inconvenient to prevent it.
There are reasons each source uses a different plug. I see RVers out on the road cheating safety all the time. Improper load distributions, compromises in visibility, improperly secured loads, hitches and couplers at the wrong height. It is frustrating the same disregard for safety and design exists when RVers are "camping" as well.
[I am also quite frustrated at how many RVs are built. Sure they comply with regulations, but if the builders had always built their products safely then the regulations (which are a minimum at best) would not have been required.]
I scuba dive, ride a motorcycle and have other dangerous hobbies. To enjoy these hobbies there is a need to take calculated risks. Yet I am not going to put myself at risk when there is a safer way to reach my goal. I COULD ride without a helmet in my state. I COULD wear sandals instead of riding boots. I COULD extend my dives by breathing into my air reserves, I COULD cut my decompression times by a few minutes and PROBABLY suffer no ill affects.
Likewise, you CAN run 30 amp cords on a 50 amp rig. Maybe you only will shorten the life of your A/C. Maybe you will harm nothing. Is it worth the risk?
A 50 amp 30 foot cord weighs just 21.1 pounds according to Camping World. A 30 amp cord of the same length weighs 8.1 pounds. That is 13 extra pounds of cable that you have to pull out and reel in ONCE at each stop. Is all that risk to equipment and human safety worth it for 13 pounds?
C'mon folks. There are plenty of dangers to be had to provide excitement for our lives without creating problems that could change your life or end someone else's.
While I have never pulled an RV, my last business used a 50 foot 5th wheel trailer. I logged over half a million miles pulling that trailer through 46 states plus Canada and Mexico and never had a a single insurance claim on my trailer. NOT ONE!
I drove in blizzards, tropical storms, sand storms and hauled that thing through the steepest mountains in the country.
The chain I used was THREE TIMES stronger than the DOT required [and you think that 50 amp power cord weighs a lot]. I had extra lights. I used better tires. I used better brake pads and synthetic brake fluid.
It was still very risky, but I minimized my risks wherever I could.
I understand that sometimes we need to fudge because the fudging option is all that is available. But using lighter cords and lunchbox 'plug protectors' when better, safer options are at hand makes no sense.
If you want to be a football coach, you better have the rule book. If you want to play electrical engineer, then you better understand the rules of the dangerous stuff you are playing with.
Sorry to have stood on my soapbox for so long. I just don't want to see any of you hurt for no good reason.
Best regards,
Steve
