30 amps is not enough

[Duckogram]

I’m laughing because the OP got his answer almost a week ago and departed. However there is some good info thereafter that stimulated a brisk conversation which is good. So I will throw this into the pot to see if there is fault with my thinking:
I use a 50-30 dogbone when I encounter a weak 30a breaker. I know that my house main is in good shape. I certainly understand that my 40’ power supply cable cannot handle 50a load for very long.
Now we have the capability of 50a coming into the coach. That brings us to the question of where does that capacity go? It does not go directly to the house main. That could be problematic. Mine goes to the automatic transfer switch then across the coach to PI PMS and then to the distribution panel. So now I have another 12’ of 10ga and two pieces of electronic gear exposed to overload.

So with that in mind, I am careful to monitor my power usage so as not to exceed a 30a load. I do not think its a good idea to use a dogbone without the capability of monitoring the load.

But even more important to me is voltage. Even 50a service is no good to me at 112v or less. It is because of that requirement (medical equipment) I use an autoformer before my power cord. That also gives me surge protection for my auto-transfer switch.

OK, maybe I exceeded .02¢ 😁

[mikel68]

Have you checked the breaker itself? We had the some trouble with a 5th wheel we had years ago. However I took it back to the dealer for service. They ended up changing the box and all the breakers and it never happened again. Check you amp draw on your AC. We have a 50 now, but always had 30s before this and never had trouble. Well, of course occasionally we'd trip a breaker, that also happens in sticks and bricks.

[Iwannacamp]

Originally Posted by Herk7769

So everyone seems to have an opinion here, so what the heck. Here's mine.



The 50 amp outlet on the pedestal is used less frequently than the 30 amp and therefore the sockets are usually in better condition (not always, but mostly true).



All things being equal, a 50 amp rated outlet has the potential to provide 50 amps on each hot leg. (TRUE)



When you use a 50 to 30 amp adapter, ONE leg of the outlet is used as the "hot" on a 30 amp style socket. That 30 amp socket has the potential to deliver 50 amps if requested; BUT your camper is incapable of asking for that much current for very long without tripping the 30 amp MAIN circuit breaker in a 30 amp service camper.



That is not to say that its impossible because depending on the overload condition, it may take seconds to many minutes (even hours) for the overload to reach a critical temperature in the breaker for it to trip OFF.



The biggest concern with using a 50->30 dogbone is that "slight" overload that sneaks past the main breaker in the camper over a LONG run like using a 30 amp extension cord could draw significantly more amps than the connections near the pedestal can handle.



This causes heat at the connections and can damage the cord or connections.



One solution to this problem can be fixed like this one enterprising camper by just fixing the breaker so it can't trip!



I attached the Training Manual on Circuit Breakers and excerpted the Time To Trip curve graph and text. The "In" in the graph is the rated current for the breaker. At a 1 multiple, the time to trip is infinite (ie a 30 amp breaker should not trip at 30 amps. At 90 amps (I3), a good quality breaker will trip in 3 seconds. At 60 amps it can take many seconds and maybe many minutes to trip as it is off scale. At 40 amps it could hold for a half hour or more.



Circuit breakers are SAFETY devices to back you up and not replace common sense when using electrical equipment. Ultimately, you are responsible for knowing what you are turning on and how much power it needs. Depending on a breaker to save your butt is really rolling the dice.



Does that mean you should never us a dogbone? Of course not. If you need an adapter you should not be afraid to use it. Just be aware that even if the breaker does not trip while running the AC, Water Heater on electric, and the coffee pot; it does not mean all is good. You may go to unplug in the morning and find your cord is melted to the socket.



Herk

Excellent post Sir. Thank you.

[Scrapper]

Maybe I'm not getting everything from this discussion,

But.....

If you have a 50A to 30A dogbone connected to your 30A RV cord, the cord will never carry the 50A current unless there is a demand. Once the demand reaches anything above the threshold of the 30A main breaker, it will trip. Your cord will only carry the demand until the main 30A breaker trips, thus eliminating that demand, unless there is a short in your RV's circuit up to the 30A breaker. The maximum current carried by the dogbone and your 30A cord will always equal the current load your RV is demanding at any given time. Current carried never equals current available without a dead short. As far as the question, "What happens to the amperage above 30A?", nothing as the amperage between 30A and 50A is not there as long as it is not needed.


Another way to look at it is to compare it to your 200Ah battery supplying power to your water pump, Just because your battery is capable of delivering 200Ah, your water pump will never pull that 200Ah when running unless there is a short in the circuit. If the circuit carried 200A, you would be replacing the fuse even if the pump was not running. Again, current carried never equals current available without a short.

[Duckogram]

Scrapper thats pretty much true but the issue is the part that is not exactly. I think Lou (Herk) outlined the issue very well and included some references of the results of not exactly.

[Herk7769]

Originally Posted by Duckogram

So with that in mind, I am careful to monitor my power usage so as not to exceed a 30a load. I do not think its a good idea to use a dogbone without the capability of monitoring the load.

But even more important to me is voltage. Even 50a service is no good to me at 112v or less. It is because of that requirement (medical equipment) I use an autoformer before my power cord. That also gives me surge protection for my auto-transfer switch.

OK, maybe I exceeded .02¢ 😁

Exactly. I also use an autotransformer when delivered voltage is problematic.