Where can I find T&B (Thomas & Betts) circuit breakers, or compatible?

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I bought a 30A 100' 10g wire power cable to run from the shed to the trailer. I've got a 50A to 30A adapter at the shed, and an adapter from the 3 wire cable plug to mate with the 3 prong hook up on the trailer, which uses the 2 "bent" connectors (hot and neutral), along with the 'flat' ground. I'm getting 120v at the hot connector on the cable there, with 0 on the white/neutral. All good up to this point. 

But when I try to take readings at the breaker box on the inside of the rear wall where the input is, which is only about 18" of main wire between the outer socket and the breakers, I'm getting no voltage coming out of the breakers, and power only coming into one of them. Something else I don't quite understand is that there are 4 wire's coming into the box. Black and red, which I would normally say are the hot wires, one feeding each of the two breakers, a white neutral and a green ground. How can there be 4 wires coming off of a 3 wire prong? At first I thought, well maybe one is feeding the converter to charge the batteries??, but both the wires are feeding into the inputs of the two breakers in the box. 

These two breakers are both T&B breakers. One is a 30A single pole SR-100 type TB, and the second is a 20A double pole YF-6738 type TBBD. 

so I was just re reading this and I think you have more going on than breakers, and they may not be the issue, or at least only a small part.  

10amp extension cord isn't rate for 30 amps over 100 feet, at that distance it is only up to 20amps.

RV 50amp outlets have 4 cables, two hot, one nutral and one ground.  the reason for this is it is real two 120V circuts not a 240V, so you need the nutral.  it would be handy to see a picture of the two wires you are talking about that are feeding the panel breakers, both at the panel and where they start.  once you get into a RV the colors can be what ever the manufacture had availble at the time 😁

Thanks stircrazy and opnspaces- that's a new one on me. I'm thinking the idea of the PO needing a breaker fast and this was the one on hand. Funny thing happened this morning, though. I got an email from e-trailer.com asking how the adapter I bought from them a year ago for the 100' rv power cord was working. I'd sent the first one back because it wouldn't connect correctly. (it wouldn't seat completely so that the fastening ring was not able to screw in.) I've checked the power at the cord at the trailer, and inside the trailer, but I did not consider checking at the adapter, which is after the cord and before it enters the trailer. Maybe that's the problem?? Kind of doubt it, but I'll have to put the multimeter on that too. Meanwhile, I've got the 30A breaker from Menards and am waiting on the 20A from ebay. Thanks again, everybody! Lee

It's just two breakers in the traditional space of one breaker. Double pole breakers are typically used where you need to add a new circuit and are out of slots in the box to add a breaker.  So you remove one existing single breaker and replace it with a double pole breaker. If the double 20amp breaker you pictured has only one wire to it then it's using only one 20 amp breaker. And you have a spare 20amp breaker that is not being used.

As to why? Could be a plethora of reasons why there is a second unused breaker. It could be that they ran out of single breakers on the assembly so the installer just used a double. Or the original failed while on vacation and the  owner could only get a double in the small town they were in.

The breaker you show is not a double pole breaker. It is two single pole breakers in a single  1" space, often called a twin breaker.  They are made in 2-15 amp, 15-20 amp, 2-20 amp, 15-30amp, 20-30 amp and 2-30 amp and others.  If you have two wires hooked up to the breaker, you have two separate 120 volt circuits. Be careful what you do, you may cause a fire, or worse zap yourself.  Former electrical contractor.

While I'm on this subject, can anyone tell me why there is a double pole breaker in this box? There is only one wire coming into it. What good is a double pole breaker that's only being fed on one side? 

There's a piece of tape just to the right of the two breakers in the box labeled "water heater", but the label was placed pretty much in the center of the two, so I don't know which one is the water heater and which is the rest of the trailer's AC circuit. Or did someone replace a breaker along the way with a double pole incorrectly? They are both T&B's. I'm going to try to trace them down once the power is flowing again, but I'm still skeptical about the dual pole breaker. AND the 4 wires coming into the breaker box from a 3 wire input socket on the 5th wheel's exterior port. 

Thank you, Stircrazy! After posting yesterday, I spent some time searching the subject and found both of the breakers online. The single pole 30A breaker had to be replaced with an Eaton CL type, but it's exactly the same. The other, a double pole 20A breaker, which is in a single pole size casing, I actually found a new T&B breaker. Hopefully, this is the problem. I don't see what else it could be, short of a bad socket on the 5th wheel, since that's all there is between the 100' cord and the breaker box. I'll report back after I get back down to the property and install them. I also need to hook up the generator and see what happens with that. 

What is so strange about this is that just a month or so ago, after I finished firing up the system after having to get two new breakers for the PV input into the charge controllers, I hooked it up and everything worked fine. I'll report back after I try the breakers when they arrive. Thanks again!

Siemens or Eaton breakers are compatible with Thomas and Betts panels.  just take a old breaker to Home Depot and look for a Eaton and make sure they look the same.