30amp or 50amp

[KSBOWHTR]

As I wait for my cargo trailer to be delivered, I picked this panel up used.[img]rsz%20img%208763[/img]
It is a 50 amp panel. I had planned a 30 amp service, and if I ever chose to replace it, I think I would install a 30 amp panel. So my question is, should I, or can I, get a 30 amp plug and just use 30 amp service into my 50 amp panel??

[KSBOWHTR]

Sorry, pic didn't post. I cant figure out how to post pics

[GTS225]

Going by memory, here. As I recall, NEC says you may downsize the supply but never upsize. (I.E.; you can feed a 50 amp panel with a 30 amp supply, but not feed a 30 amp panel with a 50 amp supply.) I think I'd also drop a 30 amp main breaker in the panel, too. That'll limit your full draw to the rating of the plug and cord.

That being said, will there be an inspection done, by county code inspectors, to the trailer as you're building it?

Roger

[MtnDon]

Going by memory, here. As I recall, NEC says you may downsize the supply but never upsize. (I.E.; you can feed a 50 amp panel with a 30 amp supply, but not feed a 30 amp panel with a 50 amp supply.)....................
Roger

That does not seem logical. You can hook an incoming 200 amp sized set of wires (such as #2/0 AWG copper) to a 15 amp breaker box. It is the breaker size or the designed maximum load of the box that will limit the amps coming into and going out of the box circuits.

But if you connect 30 amp sized wire (#10 AWG) to a panel that is rated for 200 amps you cannot draw more than 30 amps without danger of overheating the 30 amp wires.

Make sense? NEC is about safety.

And NEC does not directly apply to RV's. There is a different association that sets the RV rules but they will be similar to NEC residential and commercial rules.

[GTS225]

That does not seem logical.

You're right, hence my disclaimer. I was going by memory, and it's been a number of years since I dug into an NEC manual. There could have been any number of changes to it since then.

You can hook an incoming 200 amp sized set of wires (such as #2/0 AWG copper) to a 15 amp breaker box. It is the breaker size or the designed maximum load of the box that will limit the amps coming into and going out of the box circuits.

Well, actually, you can't. The lugs in the 15 amp box won't physically accept the size of 2/0 wire. I think the best one could do is about 8 gauge.

But if you connect 30 amp sized wire (#10 AWG) to a panel that is rated for 200 amps you cannot draw more than 30 amps without danger of overheating the 30 amp wires.

Again, I doubt you could actually tighten down the lug screws to grip that 10g wire tight enough. But that's why you fuse/breaker upstream for the 30 amp wiring and panel/box. Remember, the NEC ampacity tables are about minimum sizes of wire to carry a known maximum current in certain conditions. You can legally run larger wiring.....it's just economically foolish to do so.

Make sense? NEC is about safety.

What you're saying does make a certain amount of sense, and does suggest one consult the latest NEC manual for guidance.

And NEC does not directly apply to RV's. There is a different association that sets the RV rules but they will be similar to NEC residential and commercial rules.

I remember a section pertaining to mobile homes. (Granted, a different animal, to a certain degree.) As I recall, there was discussion as to whether it applied to motor homes or campers. Again, I'd have to consult an NEC on that.
Either way, the NEC is part of the NFPA's rules and guidelines, which is a set of governmental agencies that will surely apply their authority as they see fit.

Roger