50 or 30 amp

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   The idea that all faults are low impedance (meaning direct line to line or line to ground short circuits that produce very high currents), is just not correct. There are numerous examples of high impedance faults on circuits that can produce limited current flows which either by themselves or in combination with actual loads result in currents which (for example) can be in excess of 30A but less than 50A.  Otherwise you could just use one circuit breaker size regardless of wire ampacity and call it good. But you can't. 
Heck, I had one of these faults in my house after the last hurricane corroded one of my outside receptacles. Tripped the breaker only after I turned on my skillsaw, which didn't trip on any other breakers. Couldn't figure out why for awhile. After I found the corrosion and replaced the receptacle, problem solved.  If I had had undersized conductors for my breaker I could easily have had a fire.

You can't really anticipate all the permutations you might run into with these kind of things. If you follow the NEC it will almost always save your bacon, its saved mine many times. And even if something bad happens anyway, if you follow the code you won't be giving lostagain grounds for a negligence suit 

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offgrid Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 23 Jul 2018 Online Status: Offline Posts: 5290	Topic: 50 or 30 amp Posted: 27 Jan 2019 at 12:59pm
	The idea that all faults are low impedance (meaning direct line to line or line to ground short circuits that produce very high currents), is just not correct. There are numerous examples of high impedance faults on circuits that can produce limited current flows which either by themselves or in combination with actual loads result in currents which (for example) can be in excess of 30A but less than 50A. Otherwise you could just use one circuit breaker size regardless of wire ampacity and call it good. But you can't. Heck, I had one of these faults in my house after the last hurricane corroded one of my outside receptacles. Tripped the breaker only after I turned on my skillsaw, which didn't trip on any other breakers. Couldn't figure out why for awhile. After I found the corrosion and replaced the receptacle, problem solved. If I had had undersized conductors for my breaker I could easily have had a fire. You can't really anticipate all the permutations you might run into with these kind of things. If you follow the NEC it will almost always save your bacon, its saved mine many times. And even if something bad happens anyway, if you follow the code you won't be giving lostagain grounds for a negligence suit
	1994 Chinook Concourse 1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold

offgrid Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 23 Jul 2018 Online Status: Offline Posts: 5290	Posted: 27 Jan 2019 at 2:40pm
	Yep, StephenH and GlueGuy each found one back in Sept. You could probably put a 50A male connector (with one hot not connected) on the input end and a 30A female on the output. The short 10 AWG cord on the input side wouldn't be rated for 50A unless you could get into the breaker enclosure and replace it with 6 AWG cord. But the rest of your circuit should be good to go. http://www.gordonelectricsupply.com/index~text~6019698~path~product~part~6019698~ds~dept~process~search?gclid=Cj0KCQjwrZLdBRCmARIsAFBZllELPAmgs86UJ-zDo2Nm-iIaP8NFonsn8lONX0TJymNO0kl_7kWSiTYaAkNjEALw_wcB https://www.amazon.com/Cooper-Wiring-Devices-GFI13M1NN-GFCI/dp/B00DUGWDOM/
	1994 Chinook Concourse 1995 RV6A Experimental Aircraft 2015 Rpod 179 - sold

Tars Tarkas Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 14 Jan 2013 Location: Near Nashville Online Status: Offline Posts: 1452	Posted: 27 Jan 2019 at 3:04pm
	There's a thread on another forum i read titled, "The last person to post to this thread WINS!" You don't win anything, you just win. It's been going on since 2006 and has almost 56,000 posts. That forum is somewhat more active than this one. Nevertheless, maybe we could get Furpod to change the title of this thread. TT
	2010 176 FJ Cruiser

mcarter Members Profile Send Private Message Find Members Posts Add to Buddy List podders Helping podders - pHp Joined: 07 Apr 2016 Location: Greenbrier, TN Online Status: Offline Posts: 3419	Posted: 27 Jan 2019 at 4:18pm
	T2 - +1. Maybe we could just go back and find OPs 4 months old and repost everything that was said then, come to the same solution that members had then and up our post count by rehashing the post again, or better yet wait 4 months and start the post again, to make sure you get your point across, to see if anybody is really listening, add another 10 posts to your history, reach same conclusion, then wait - you only have 4 months to wait and do it again. Much more beneficial than using the search function.
	Mike Carter 2015 178 " I had the right to remain silent, I just didn't have the ability."

lostagain Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 06 Sep 2016 Location: Quaker Hill, CT Online Status: Offline Posts: 2595	Posted: 29 Jan 2019 at 3:07pm
	Ok, so a dead short using my hypothetical 18awg lamp cord plugged into a 50A circuit would be one way to start a fire, but offgrid mentioned some high impedance events that could also create a fire hazard using a conductor not matched to the amperage of the circuit. What would cause high impedance that could light my lamp cord on fire? And I was only kidding about the horse recipe with mustard and thyme sauce. I'm not French and don't really eat horses. ;--) [the emojis don't work from here in Colombia.]
	Never leave footprints behind. Fred & Maria Kearney Sonoma 167RB Our Pod 172 2019 Ford F-150 4x4 2.7 EcoBoost

mcarter Members Profile Send Private Message Find Members Posts Add to Buddy List podders Helping podders - pHp Joined: 07 Apr 2016 Location: Greenbrier, TN Online Status: Offline Posts: 3419	Posted: 29 Jan 2019 at 4:06pm
	Lostagain, What is the difference is plugging a lamp into an outlet on a 30A compatible circuit and a 50A compatible circuit? At an outlet. It is very difficult to plug a lamp into a 50A plug, such as the power station in a park. In the case of an outlet the shorted wire will get HOT, draw amps and kick CB to the outlet. No fire. Circuit Breakers.
	Mike Carter 2015 178 " I had the right to remain silent, I just didn't have the ability."

mcarter Members Profile Send Private Message Find Members Posts Add to Buddy List podders Helping podders - pHp Joined: 07 Apr 2016 Location: Greenbrier, TN Online Status: Offline Posts: 3419	Posted: 29 Jan 2019 at 4:44pm
	Example: You have a standard outlet, we know most are circuit breakered at 15 or 20 A. Somebody wired this outlet to a 50A CB (STUPID), you plug a lamp into it. The lamp has a shorted wire. The wire will get HOT, it could cause combustible materiels near it to light. If the current draw exceeds the CB it will kick, probability is wire will burn in two before CB kicks at somewhere less than 50As. Example 2: When I first moved into my building, I was tracing outlets back to CBs in panel. I came across a standard outlet under a work bench that had 220 volts on it. Standard outlet. Traced back to panel and it had a double 100A CB on the line. I removed the double 100s, put in a single 20, went back to the outlet feed and removed the now disconnected 120. Now I had a standard 20A outlet.
	Mike Carter 2015 178 " I had the right to remain silent, I just didn't have the ability."

lostagain Members Profile Send Private Message Find Members Posts Add to Buddy List Senior Member Joined: 06 Sep 2016 Location: Quaker Hill, CT Online Status: Offline Posts: 2595	Posted: 29 Jan 2019 at 5:44pm
	Thanks, Mike, those are effectively dead short scenarios and in both, as was observed earlier, they would burn up the undersized cable possibly before the 50A breaker would trip since not a lot of heat would make it to the breaker due to limited wire size. That certainly presents a safety problem since there is no effective overcurrent/heat protection for the undersized cable. Of course in the RV setting we are talking about 10awg wire in the 30A compatible cable which is a lot closer to the 6awg for a 50A circuit so the danger is diminished. Wow, you had quite a danger there with the mis-wired plug. I had a similar experience when I worked in the grape sheds and a field box nailing machine arrived from Delano with a mis-wired 220. My co-campesino touched it and grounded himself when he touched a properly wired box skid. It nearly killed him. My question, though, is not the simple overcurrent dead short situation but other forms of impedance that offgrid alluded to. What other high impedance situations are within the world of possibilities that could also make an undersized conductor dangerous. I can think of, for example, running a hair dryer on high with 22awg wire. It may not trip the breaker, but it certainly would get the wire pretty warm. I got the impression there are other examples that it would be nice to know about.
	Never leave footprints behind. Fred & Maria Kearney Sonoma 167RB Our Pod 172 2019 Ford F-150 4x4 2.7 EcoBoost

mcarter Members Profile Send Private Message Find Members Posts Add to Buddy List podders Helping podders - pHp Joined: 07 Apr 2016 Location: Greenbrier, TN Online Status: Offline Posts: 3419	Posted: 29 Jan 2019 at 6:04pm
	Lostagain, Understand better. Hair dryer is an example, heaters, microwaves, anything that has a high current draw. The key in my mind is the CB and/or the GCFI, I'm just talking about a regular outlet device. In a shop for an example, heaters, welders any high current device. The key is the protective devices. Taking the example if I was to take a 50A stove and put it on a 30A circuit with 30A wire, is it going to cause a fire, in my opinion Nope. It's going to kick the 30A CB, due to over current, the chances of fire are less than the fact the apparatus won't work. Adding 50A wire won't effect the load of a 30A CB. In a standard RV, regardless of source, internally the RV is controlled by CBs on the outlets, for example. Example I can run one cube heater in my Pod if I run 2, I trip the GCFI. If you could hook a hair dryer up to a 50A circuit and the cord shorted the wire would burn in two before the CB would kick.
	Mike Carter 2015 178 " I had the right to remain silent, I just didn't have the ability."

StephenH Members Profile Send Private Message Find Members Posts Add to Buddy List podders Helping podders - pHp Joined: 29 Nov 2015 Location: Wake Forest, NC Online Status: Offline Posts: 6417	Posted: 29 Jan 2019 at 6:47pm
	It would seem that to mitigate the situation described of the lamp cord, an Arc Fault Circuit Interrupter would be the more appropriate protection device. Am I correct?
	StephenH Happy is the man that findeth wisdom,... ouR escaPOD mods Former RPod 179 Current Cherokee Grey Wolf 24 JS