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OT: Wiring 50 amp RV Plug


SuiteSuccess

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My shore power cord for the trailer needs a new plug which I have purchased. Just want to be sure I do this absolutely correct. I know the green wire is ground and white is neutral and go to respective top and bottom sites. Question is does red (hot) go to x plug or y plug to maintain proper phase. Black(hot) will go to other. This is the plug I have.

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Agree - which red or black wire goes to X or Y makes no difference. Just as an added comment for anyone not totally familiar with RV supply wiring: A 50 amp supply is really a 100 amp supply when compared to a conventional 30 amp supply thus providing 70 additional amps to the camper. This is why I always refer to it as a 50-50 amp supply. The 50-50 amp supply is really a 240 volt supply (measure between the red and black and you should get 240 volts) with a neutral so that you have two 50 amp 120 volt circuits in your camper.

 

Carl mentioned maintaining the proper phase. While the 240 volt feed in campgrounds is known as a single phase, there is a 180 degree phase differential between X and neutral and Y and neutral. But, the differential is not an issue when connecting a new plug.

 

Sorry - it is extremely hard for me to give a simple one word answer after teaching this stuff for most of my professional life. The WHY was always expected with an answer ;) .

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And always one in the crowd - we have stayed in a 120/208 3 phase park. They are out there. We have the standard 50-50 that Randy mentioned but a neighbor was having fits with things. Seems his high end MH had some 240 volt appliances (dryer, stove) and his power monitor was going ape-ship.

 

120/208volt is very common in apartments and most of the equipment can handle it with noting more than longer heating times. Monitors do just that, monitor and they were not happy.

 

We did bypass a few things after talking with and reading manufacture literature.

 

the old check and verify routine.

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Stekay - think of it as a circle. single phase is the 2 poles (phases) at opposite sides of the circle.

 

3 phase is the same circle divided into 3 parts 120 deg apart. You do the old trig thing -- 120 volt (one leg) * square root of 3 (1.732) and 208 between all the phases.

 

LOL - Don't even try to think of wild legs, open deltas and a host of other transformer configurations. Books have been written and courses taught.

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In one of my former lives, we used either 2 phases of a wye-connected three phase system or 220 single phase , which ever the customer provided for us. The only way we could tell 3 phase wye-connected from single phase was that single phase line to line was the sum of the 2 legs and 3 phase wye-connected line to line was less than the sum of the two legs. Each had 2 hots, a ground and a neutral. I once arrived after an electrician had wired the recepticle with true 3 phase and the customer leaked all the smoke out of our equipment in short order...it did not like having 3 hot legs at all. I surely would not want to hook up my camper to that. I have run across a couple of park outlets that were wired with L1 and L2 off of the same wire, so L1 to ground and neutral was 120, L2 to ground and neutral was 120 volts and L1 to L2 was also 120 volts. Campground pedestals can have some wierd connections in them. Charlie

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Stekay - think of it as a circle. single phase is the 2 poles (phases) at opposite sides of the circle.

 

3 phase is the same circle divided into 3 parts 120 deg apart. You do the old trig thing -- 120 volt (one leg) * square root of 3 (1.732) and 208 between all the phases.

 

LOL - Don't even try to think of wild legs, open deltas and a host of other transformer configurations. Books have been written and courses taught.

Your exactly correct on this and is why in the three phase 120/208 they are called phases. The single phase 120/240 the are called lines as in L1 and L2. Luckily we don't use 240 rated things in our RV's usually. Putting 208 on a resistance device such as a heater makes no deference other than 208 heats a little slower than 240 volt. Now on a motor it could make and does make some difference. There is by code a plus or minus voltage above and below the rated nameplate motor voltage of 10% as I recall been a long time. Now if you put 240 volt on a 208 rated motor it is with in the plus 10% and the same on the low side when putting 208 on a 240 volt nameplate motor. I won't say who but there are motor manufacturers who sell 208 and 240 volt motor which are in fact the same motor with different nameplates they was all 208 volt motors(cheaper to manufacturer). I was doing a study at the time on how much the electric utility could reduce voltage for power reduction during emergencies without damaging customer equipment. Now we felt we could do a 10% reduction and would still be providing voltage within national guidelines. As you can see if the utility did a 10% reduction from their nominal those motors basically with false nameplates would be damaged. The question became who would pay to replace the motors and some are high horsepower and high cost motors. Lot of legal discussions; the motor manufactures would be and where held responsible. There was other problems but none germane to this discussion. I have a feeling a lot of people here like me lived, breathed and even taught this stuff and it can get really involved. Won't even go into efficiency, power factor, harmonics gee-sh the topics can be endless.

 

Bottom line makes know difference which hot leg you connect to L1 and L2. Just don't accidentally put one on the neutral or ground!!!!!!!

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Like Bill said, "3 phase is the same circle divided into 3 parts 120 deg apart. You do the old trig thing -- 120 volt (one leg) * square root of 3 (1.732) and 208 between all the phases."

Except, when you have 3 phase wye with a neutral you also have three 120 volt circuits serving the CG power pedestals rather than the two you find with 240 single phase using a neutral. The electrician or engineer that designs the CG distribution system will do it in a manner that evenly distributes or balances the loads between phases. When colored wire insulation is used we typically find a 4th conductor that is blue. For a CG and our typical 50-50 amp power it won't make a diddley-squat whether there is a 180 or 120 differential between red to neutral and black to neutral . Some plugs will be fed by white, blue and either red or black. What is important is the type of outlet in the CG power pedestal and if it is wired according to Code. Now, if someone with one of those big bus motor-homes hooks up with two 50-50 amp cords and one of the two is set-up to provide what would be a typical single phase 240 volt feed they are not going to find what some fancy monitor thinks it should see.

 

3 phase 208 VAC wye is, as noted, the standard for low end industrial/commercial areas and certain apartment complexes. If a CG is located in or near one of these areas it will most likely be served by 3 phase wye power system. Conversely, if it i in a rural or all residential area it will most likely be served by single phase lines.

 

Cheeze - simple question threads always seem to evolve as they grow. All Carl wanted to know is if it made a difference whether red or black went to X or Y. Now look where we are :rolleyes: and it is still growing.

 

I've observed some totally inadequate, unsafe, jury rigged wiring run to RV plug-in's, both 30 and 50 amp - I assume to satisfy customers who only look to see if the plug fits and leave it at that. In most instances they get away with it unless the customer is running two big air conditioners, a microwave, electric water heater, electric dryer and other everyday powered gear. If the circuit breaker doesn't trip the wiring and the outlet get extremely hot and RV power plugs can melt - which is often the reason for having to replace a plug on the RV power cord.

 

Below are some examples of "plug melter's"

 

Oh, and Charlie...... that wasn't your head I saw you scratchin' :) :)

 

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Two 30 amp outlets on the same pole with no disconnect or covers. Wiring was #12AWG and a 50 amp outlet on the next pole was bridged. At one time the outlet was probably a 20, then replaced by a 30 and finally by a 50 with no improvements to the supply. <_<

 

unnumbered%20site%20outlet%20hot.jpg

Yes, this is an active site and that is a 30 amp outlet which, incidentally, was looped over to another similar outlet on the site next door.

 

10%20AWG%20wire%20to%2040%20amp%20breake

This one has a 40 amp breaker with #12AWG feed wire (rated 20 amps) going to a 50 amp outlet.. Note both the neutral and grounding wire are bonded in the pedestal box which is in violation of codes for the place where the photo was taken. (yes, I took the cover off the box.)

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Randy, those are great pictures!! I can not tell you how may "issues" caused by things like that I have addressed in the 15 years we have been fulltiming. It is simply amazing to me what campgrounds have in them for power. I find it quite "interesting".

 

At least here (at Diamond) we now have a power distribution system that is pretty good. It has taken 10 years to get it fully repowered. I'm putting in the last of the metered 50-50 service (as you call it) right now....in fact the last six pedestals go in this afternoon.

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I have run across a couple of park outlets that were wired with L1 and L2 off of the same wire, so L1 to ground and neutral was 120, L2 to ground and neutral was 120 volts and L1 to L2 was also 120 volts. Campground pedestals can have some wierd connections in them. Charlie

 

 

If L1 and L2 were connected to the same wire. L1 to L2 world be 0 volts.

 

This would be a True 50-50 amp condition. That would be a real good way to melt a power cord or plug. If you tried to load both L1 and L2 to 50 amps each that would result in 100 amps in the neutral (White) wire. The only protection would be melting or possibly a low L1 or L2 voltage if so equipped with a power management system.

As mentioned previously L1 and L2 should 180 degrees phase separated (120 degrees on 120-208 Volt system), this would result in currents near zero on the neutral wire for balanced loads.

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I'm putting in the last of the metered 50-50 service (as you call it) right now....in fact the last six pedestals go in this afternoon.

Jack, I hope you and other readers recognize why I am calling it a 50-50 service - we do not use 240 volts in our rigs. It is one center tapped buss fitted with one 50 amp 240 volt service breaker via a tie bar In fact, the outlet and service is identical to the 50 amp 4-wire outlet used by residential electric ranges. The 50-50 nomenclature was only used to emphasize that we use TWO 50 amp 120 volt circuits equaling 100 amps @ 120 volts while a 30 amp TT outlet is a single 30 amp 120 volt outlet. I am not sure why the 50 amp standard was adopted at the time of inception rather than the (then existing) 60 amp mobile home standard or even a lower amperage dual feed value like 30-30 amp which could have saved mucho $$$ in copper or aluminum triplex cables. Anyway, I am glad that they did as one of today's rigs would be hurting for power with all of our bells and whistles, One more comment though - I would hate to think of trying to roll up a 34 foot, 60 amp power cord with thermoplastic insulation. I needed a pipe bender for a 50 amp 4-wire thermoplastic jacketed cable in cold weather - a rather daunting task for an old man, I quickly configured the OEM thermoplastic for an occasional use extension cord and adopted a nice rubber jacketed SOOW class cord for daily use. Much more bendable and lighter in weight thought somewhat more susceptible to damage from abuse. Getting an OEM thermoplastic cord attached to one of the plugs Carl showed is a somewhat frustrating to impossible experience. It is a whole lot easier with SOOW cord.

 

Gotta go, I have an electron associated with a hurricane knocking at my door. I need to batten down the hatches around the ranch before it hits :mellow: .

 

 

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