Alan_Hepburn wrote:
By your reasoning, plugging a 50A rig into a 50A outlet is dangerous - if both breakers malfunction you can draw more than 50A per line.
That is not what I am saying at all. Maybe you should reread my post.
You can count on YOUR circuit breaker. Most likely you know its condition. So when you plug YOUR 30 amp rig into their 50 amp service, you are fine. When you are plugging in YOUR 50 amp rig into their 50 amp service you are still fine because you know the condition of your 50 amp breaker.
However, TWO problems can arise when you plug YOUR 50 amp rig into THEIR 30 amp service.
1) You can count on your 50 amp breaker tripping somewhere around 50 amps, but because POSSIBLY HUNDREDS of other guys before you "adapted" their 50 amp rigs to work on their 30 amp service, many of them pressing the absolute limit of their supply, THEIR breaker may not work as designed. Your rig won't catch fire. But their side may burn.
2) As your demands approach THEIR 30 amp limit, a voltage drop will occur. The limited current capability of THEIR supply could damage YOUR rig if you are close to the limits.
I hope that clarifies the situation for you.
I used to be employed working on aircraft power supplies for our military aircraft. These power supplies cost tens of thousands of dollars and the engineers made some mistakes. Once our company put a diode in a simple rectifying circuit that was just a hair too small. Fortunately, the diode never failed in flight. But on the ground, as the systems were powered up, a counter EMF was produced that would burn out the diode because the PIV spec on the diode was fine for the operating design but was not high enough for the surge that accompanied the power up of adjacent systems. In other words if the system that the power supply supported was turned on it worked fine, but nearby systems could damage this system and thus we had to retrofit hundreds of rectifying diodes to withstand the counter EMF generated by other systems.
That RV park or that 30 amp home service was likely installed by a qualified electrician who followed a code, but who is NOT an engineer. How much more likely is a failure to occur?
Think about it this way: When do most residential electrical fires occur? Answer: Christmas season.
Why? Christmas lights are engineered to be safe. The home is built to meet all local electrical codes. Yet every year many fires occur and many people are killed when perfectly well intentioned people believe that if they plug in too many lights those circuit breakers are going to prevent a fire.
Who are these people? There are people who say things like:
Alan_Hepburn wrote:
Similarly plugging a 30A rig into a 30A outlet can be disastrous. If you go through life with that attitude you need to stay in bed rather than go off driving in an RV.
As I said in my first post. I scuba dive and ride motorcycles too. I also fly airplanes too. But that does not mean I am going to bet someone's safety or risk damage to my equipment by plugging my equipment THAT I KNOW already exceeds the design limits of the supply that I know nothing about.
Would you pull a 35 foot fiver with a Dodge Dakota pickup? If you were just going a few blocks in good weather it could be done. But is that safe? For a short distance you would PROBABLY avoid injury or damage to the tow vehicle if you HAD to go just a short distance and a proper truck was not available for the job.
But doing that is not unlike plugging in a rig that can draw 50 amps into a 30 amp supply. If you carefully monitor your load you CAN do it if 50 amp service is not available.
On the other hand with the cavalier attitude you express above, YOU would probably be better off staying in bed so as not to join the hundreds of people killed and injured every year by simply plugging in too large a load and counting on circuit breakers to protect them from harm.
Remember, as circuit breakers are repeatedly tripped, they fall out of spec. I knew a HAM radio operator that had tripped one circuit in his home so often the breaker would no longer trip at all. He had to install a new breaker to be sure his house would not burn down.
Alan_Hepburn wrote:
There are more important things to watch our for, such as uninformed electricians who install an RV 30A outlet and wire it for 240V!
How does one do that? 240V has two legs and a 30 amp breaker has just one. Unless you are talking about wiring the breaker in series with the two legs but you could not do that from within a standard breaker box. However, even then the breaker would still trip when the current reached roughly 30 amps.
Circuit breakers are tripped when the metal strip inside of them heats up and pushes against the switch. That metal strip can become deformed and fatigued which is why when they are repeatedly tripped they fall out of spec. IF you took the trouble to wire 240 volts into a 30 amp circuit, most likely it would cut the current when tripped because 240 VAC RMS actually produces a peak voltage of about 340 volts on the sine wave and under MOST circumstances that is not enough voltage to arc over the gap of a 120 volt switch.
So why would you concern yourself with such a thing. The risk is relatively small, probably smaller than plugging in a 50 amp load into a 30 amp service. Of course you have no ground leg but you don't really need a ground leg do you? I mean if you have a common then the ground is just redundant, right? Most things will run just fine without a ground. If you make sure the appliance or the rig never becomes hot then nobody will ever know the difference. And while you are at it why don't you just forget all those expensive GFCIs? I mean all you have to do is be sure your appliances don't get wet and be sure you never get close to electric circuits with wet hands, right? It will still work just fine 99% of the time.
You have the brass to talk about "uninformed electricians" - who are not at all uninformed if they are licensed, and then you will tell me I should not get out of bed because I caution the forum on plugging in a load capable of 50 amps into a 30 amp source? WOWEEEE!!!!
Ironically, you will worry about the actions "uninformed electricians" but you will plug your 50 amp rig into a 30 amp source that you know nothing about. Do you open THEIR breaker box to make sure they did not use an "uninformed electrician"? Do you test the functioning of THEIR breakers? Do you inspect THEIR wiring to be sure it will DELIVER the 30 amps YOU plan to use?
What do you know about THEIR supply? And your big concern is "uninformed electricians"?
If you think THAT is your biggest concern, bigger than plugging in a potential 50 amp load into a 30 amp supply then you should NEVER trust an electrical source that is not your own. How do you manage to get out of bed in the morning?
The problem is that we live in a dangerous world and it is not practical to second guess that the 30 amp supply is not properly set up to handle 30 amps. But when you plug in a 50 amp load you KNOW that the circuit you are plugging into is NOT designed for that potential, even if the wiring is perfect, the breaker is brand new and it was installed by the most conscientious, well informed, hardest working electrician in the world. When you do that YOU are playing the role of the "uninformed electrician".
