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Old 07-05-2011, 03:53 PM   #1
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30 amp plug into 50 amp welder outlet?

We are just starting to work with our recently acquired 19' Bambi. I have an old style 3 prong 50 amp outlet in my shop that I would like to use for our trailer A/C supply. I built a simple outlet-to-plug connector that acommodates the conversion, but before I plug it in, I thought I should find out if this is feasible or if I'm going to fry the air conditioner, instead.

Any advice? (Thanks, in advance...)
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Old 07-05-2011, 03:59 PM   #2
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30 amp plug into 50 amp welder outlet?

Greetings hipsters!

Welcome to the Forums and the world of Airstream ownership!

I suspect that your proposed plan has one flaw. If I am not mistaken that welder outlet is probably 220 or 240 volt - - your Bambi wants 30 AMP of 120 volt power. Sourcing the correct outlet to match your Bambi is as easy as stopping by the parts department of most any RV service center, and an electrician to properly install the outlet isn't terribly expensive (I have had these outlets installed at three different residences).

Good luck with your coach!

Kevin
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Old 07-05-2011, 04:00 PM   #3
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Most welders are 240V. You trailer is 120V. Confirm that you are not about to plug 240 volts into your trailer or you will toast EVERYTHING.
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Old 07-05-2011, 04:33 PM   #4
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Thanks!

I was in a hurry to get the AC running and forgot about the 110/220 issue momentarily. After I posted I went back to the shop and realized what I had almost done. Disaster averted!
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Old 07-05-2011, 04:40 PM   #5
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Needless to say, if you get the urge to drag that thing over to the nearest power substation and hook it up with jumper cables . . . DON'T!

If you need AC in Minnesota in July, the rest of us further south are doomed, i tell ya, doomed!
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Old 07-05-2011, 04:44 PM   #6
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A SHORT, heavy-gauge extension cord (or better yet, just an adapter if your shore power cord is long enough) from a socket on a 110v 20-amp circuit should be enough to run your AC temporarily. If you're also charging batteries, running all the lights and making popcorn in the microwave it would be too much. If you're going to be plugged in for long periods, it would be worth setting up a 30A dedicated RV circuit for your Airstream.
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Old 07-05-2011, 04:46 PM   #7
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Almost pulled a "Tim Allen"!

BTW...102 degrees here last Friday; hovering around 90 all this week. We're finally melting last winter's snow!
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Old 07-05-2011, 04:52 PM   #8
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The only time it is hovering around 90 here these days is around 9 a.m..... then it takes off like the proverbial cartoon thermometer.

DKB is right about the adapter and house circuit. We've run the 11K AC on our Safari for up to 8 hours while cleaning it up, readying for trip etc with no problem. I went and bought a second RV powercord to span the extra 15 feet to the curb from the front door outlet.
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Old 07-05-2011, 05:16 PM   #9
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Quote:
Originally Posted by hipsters View Post
I was in a hurry to get the AC running and forgot about the 110/220 issue momentarily. After I posted I went back to the shop and realized what I had almost done. Disaster averted!
Not sure if it is recommended, (so I'm not suggesting it!) but if you go between one of the two hot wires and the neutral wire on your 220v welding plug, then you will have 110v. I guess it will be fused at whatever the cartridge fuses or breakers protecting your welding plug equate to . IE if two 40 amp fuses protect the circult, then you are good for 40 amp -but the your cord and trailer wiring wouldn't be rated for that so you might want to use a 30 amp fuse.


I have used our dryer outlet and a home made extension to run a 220 welder now and then in our adjacent garage - and also used the same circuit wired as I mention above to give a heavy duty 110 volt source to run a 110v mig welder.

If you are not sure what you are doing with it though, may be best not to try!

Brian.
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Old 07-05-2011, 05:50 PM   #10
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Not sure if it is recommended, (so I'm not suggesting it!) but if you go between one of the two hot wires and the neutral wire on your 220v welding plug, then you will have 110v. .
This would work if you had a four prong dryer/welder/stove outlet. But a three prong outlet doesn't have a neutral.

I'd get an electrician to do the job right.
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Old 07-05-2011, 05:54 PM   #11
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There are two steps to the conversion:

1) Find the breaker that feeds the outlet and move one wire from the breaker to the neutral bus. Mark with white tape, and mark the other end of the wire (at the outlet) with white tape

2) Replace the outlet with a 30A 120v TT outlet being sure that the white-marked wire is connected to the neutral screw

If both the wires are the same color you may have to use a tester to figure out which is which. Call an electrician if there's any doubt in your mind although they sometimes get it wrong too.
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Old 07-05-2011, 06:45 PM   #12
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A three prong 220 outlet does have a neutral. Most, if not all welders have a cooling fan and the fan motor is 110 volt. The difference between the 3 and 4 prong outlets is that the neutral is grounded in the 3 prong setup.
If you are using the welder outlet for a welder as well. I wouldn't think you would want to modify the receptacle.
You just need to wire the plug for your trailer to one side of the welding outlet, then connect the neutral to the third pin on the plug. I tried a little sketch, hope it works

no connection \ / -hot leg
.....................l neutral
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Old 07-05-2011, 07:04 PM   #13
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Electrical receptacles are different for different amps and volts so you don't plug the wrong male plug into the wrong receptacle. You should not be able to plug a 30 amp, 120 v. receptacle into a 240 v., 50 amp or 30 amp one. A 50 amp, 240 v. is for a stove or a welder, 30 amp for for a dryer. You will need a twist lock receptacle for an RV plug.

This website has pictures of all sorts of receptacles used in the US and Canada: NEMA Configurations

If you just change the receptacle and get the wires right, you should change the breaker to a 120 v., 30 amp one. I think if you just use one side of a 50 amp breaker, I think you will get 25 amps. I could be wrong. One would have fewer amps than you want, the other too much and you could overload the circuit, but the breaker would not flip. This is how to overheat the wire and cause insulation break down and worse.

RV receptacles have two slanted and slightly curved female slots at the top and an L shaped on at the bottom. It may be mounted at 90˚ angle, but the pattern is the same otherwise. One is hot, one is common and one is ground. I haven't wired one in a couple of years, but the top ones are hot and common and the bottom (L), ground, I think. The cable should have color coded wires—probably black (hot for 120 v.), red (hot for 120 v., add them together and you get 240 v.), white for common and bare or green for ground. But maybe there will be no ground. I haven't taken apart a 50 amp. cable for a long, long time. The back of the receptacle should tell you which wire goes to which.

It can be hard to find a 120 v., 30 amp. receptacle in big box stores. I found one in a hardware store and if it is outside, it needs to be in a weatherproof box. Then you need to replace the breaker with a 30 amp, 120 v. one that fits into the buss bars inside the breaker box—figure out which wire is which and color code them with tape if the colors are different than they are supposed to be—maybe they are all black—it happens. Turn off the main breaker before you do anything. Write down the codes because we all forget what we just did. Take out the breaker (after you take the cover off) after you remove the wires and cap them to keep them from hitting anything hot (turning off the main breaker still means there are hot wires to that breaker), pull the breaker out from the outside end. Use a rubber or plastic handled screwdriver to do all this. Different manufacturers have different shaped breakers that don't fit in other boxes, so you have to get the right one and bring the one you removed with you.

I can figure this stuff out when I do it and test each wire a couple of times to make sure I got it right before I rewire, and after I do, and before I plug anything in. You test each hole in the receptacle from hot to ground and hot to common for voltage with a tester. The little neon units tell you only there is power, but not how much. You need a voltage meter or a multitester.

For some reason RV receptacles confuse people. They kind of look like 240 v. ones, but aren't. That seems to lead some people to hook up things incorrectly, electricians included, and fry the trailer circuits and electronics.

If you jury rig it, you may know what is what, but no one else will. It may be the next homeowner, or a friend hooking up something unaware of what is what and frying things.

If you are now intimidated, that may mean you shouldn't be doing this. You can get a book on household wiring and read it a couple of times; it may not have anything about RV circuits, but the principles are the same. Or, call an electrician and ask him or her whether he or she has ever done an RV receptacle for 120 v., 30 amps. Make sure you are shown the voltage on a tester once the new receptacle is wired. My guess the breaker, weatherproof box and receptacle should run less than $50.

Most countries have standard receptacles, voltages, cycles, but not all. Be glad you are not in Brazil where there are no standards.

Gene
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Old 07-05-2011, 08:24 PM   #14
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I agree with Crawford Gene on the compatability of the plug and receptacle and am not condoning the use of the welding outlet to provide power to an RV. Just pointing out that you can do it without getting 240 volts in the trailer.
As for the RV receptacle availablity. I bought mine at Home Depot. I have attached a photo. It has the words "For Travel Trailer Use Only" 120 volt 30 amp. written right on it. This is the same outlet that is used in campgrounds and RV sites around the country for 30 amp service. There is no twist lock to it.
If there is an electrician out there that wires it wrong. He or She should turn in their tool pouch.
The outlet even identifies the color of the wire to be terminated on each terminal.
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