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Old 04-29-2010, 05:15 PM   #1
2Wanderers
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50 Amp legs for AC

Had my unit wired for a second air conditioner in bedroom. When I had the fuse/circuit breaker panel cover off I noticed both AC circuit breakers for the air conditioners were on the same side of the gang tripped dual 50 amp circuit breakers. I thought the whole idea was that each AC used a different input to spread the current drain over the two wires. Maybe the circuit breakers, although side by side, are using staggered bus bars from the two 50 amp circuit breakers. Any thoughts on this?
 
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Old 04-30-2010, 01:51 AM   #2
Jdrobone
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You got it. Typically adjacent breakers are out of phase with each other. In a house panel where you would actually use 230V power this is how you obtain it - by mounting a 2-pole breaker across the 2 phases.
Jerry
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Old 04-30-2010, 03:28 AM   #3
SlickWillie
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Quote:
quote:Originally posted by Jdrobone

You got it. Typically adjacent breakers are out of phase with each other. In a house panel where you would actually use 230V power this is how you obtain it - by mounting a 2-pole breaker across the 2 phases.
Jerry
Don't think the RV panel is set up like that tho, at least not the panel I have. One phase one side, one phase the other side. I would say the two AC units the OP has are on the same phase.
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Old 04-30-2010, 07:41 AM   #4
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[quote]quote:Originally posted by SlickWillie

Quote:
Originally posted by Jdrobone
Don't think the RV panel is set up like that tho, at least not the panel I have. One phase one side, one phase the other side. I would say the two AC units the OP has are on the same phase.
I believe Jerry is correct on this. First you have to be hooked up to 50A Service, not using 30A adapter. RV's are setup for 110V, but if you measure across the two breaks next to each other you will find 220V. Most breakers are doubles (so both output are same phase).
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Old 04-30-2010, 12:27 PM   #5
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[quote]quote:Originally posted by 7.3Ford

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quote:Originally posted by SlickWillie

Quote:
Originally posted by Jdrobone
Don't think the RV panel is set up like that tho, at least not the panel I have. One phase one side, one phase the other side. I would say the two AC units the OP has are on the same phase.
I believe Jerry is correct on this. First you have to be hooked up to 50A Service, not using 30A adapter. RV's are setup for 110V, but if you measure across the two breaks next to each other you will find 220V. Most breakers are doubles (so both output are same phase).
You might want to take a closer look at your panel. I have a GFCO, but I have worked on the Iota panel, and I believe it is the same. Each side of the double pole single throw 50 amp main supports a single buss. One to the left, one to the right. If it were as you suggest, like a residential panel set up to supply 240 volts, it would have to have two buses across the whole panel.



I pulled a couple breakers out of my panel where you can see the left side of the 50 amp main, and the last two breaker slots on that side. Perhaps the Iota is different, but I don't believe it is.
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Old 04-30-2010, 02:02 PM   #6
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Not sure what that I can see that pic very clearly,but here's how mine(IOTA)(and most)work. The small handles in the pic go to mini-breakers. The form factor in this case is to save space - both of those breakers (in the pic a 15 and a 20) are in the same phase - if you look at the rear you will see only one attachment to the buss. The next adjacent pair of mini-breakers (if they exist) will be in the opposite phase and so on. If you use full size breakers then adjacent breakers will be out of phase with each other. Typically, these panels will be what a tradesman would call "back-fed". In this scenario the "feed" - probably a red and a black #6 type TW wire (part of a 6-3 with #10 ground piece of Romex (type NM) cable)anyway, the red wire will go to the bottom of a full-size 50A breaker and the black #6 will go to the bottom of an adjacent full size 50A breaker. This will feed voltage from the red #6, thru the breaker (limiting the current to 50A) to the buss feeding every other stab. The black will do the same to alternating stabs. Or black, red then black, red, etc. If you put an adapter on the end of your 50A cable to hook up to 30A then what happens is that there is an internal jumper built into that adapter (dog-bone). You will only have 1 30A hot wire from the pedestal but that jumper feeds voltage from that single hot source to both 50A breakers in your RV panel so everything in the RV will still work, BUT the total wattage available will be about 3600W versus the 11500W or so available with the 2-pole 50A source - result, you can't run as much load.
It is very important that if you hook up to a 50A source you make sure (read with voltmeter) that there is indeed 230-240 volts between phases - my pedestal, for example, was wired wrong when I checked it in Florida. What can happen, no, what will happen if both 50A hots are in the same phase is that you run a very real chance of overheating the neutral wire (white wire)in your panel. Extreme example - pedestal is wired wrong - both hots in same phase- and you have, say 35A on one phase and 45A on the other phase. Result: neutal caries 45 plus 35=80A which will overheat the neutal wire, possible causing a fire. Neither breaker will trip because the amperage is within the rating of the breaker and there is no current limiter on the neutral so . . . smoke city. On the other hand, if you have a 230 (out of phase) source you will still have the 2 50A feeds but, the neutral will carry 45 minus 35=10A, which is well within the rating of the neutral. What really happens here is that the neutral is a center-tap on one winding of a delta-connected transformer and carries the difference in current from both sides of the center tap. Or, as Richfaa pointed out, in a Y connected transformer you will have 208V and 117V at
the tap, versus 230 and 120 + or - a couple of volts. Most appliance with motors will tolerate around 8 to 10 percent below rating, so if voltage goes below 110 you are treading in dangerous territory in keeping your AC or any motorized device alive.
Phew, got more technical and long-winded than I meant to but, just be careful with those pedestals was my intent.
Jerry
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Old 05-01-2010, 04:09 AM   #7
SlickWillie
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Ha! I'm not gonna quote all that, but I don't know what you mean by mini breakers. These are standard residential Square D Homline breakers. In fact, the last one I put in was a tandem 15 amp from Lowe's. It was one of the two I pulled for this picture.

I don't know what you have, but I know the panel you see in the picture has a phase to the left, and a phase to the right. Voltage from left to right buss is 240 volts. If it had two busses, they would be fingered together with flash guards in between. Never had any reason to use the 30 amp adapter.
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Old 05-01-2010, 03:50 PM   #8
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Mini-breakers are common, what makes them a "mini" is the fact that there are 2 circuits attached to a single stab on the buss. Typically each half of a "mini" (one circuit) is half the width of a standard breaker, thus allowing more circuits in a limited amount of space. Good idea to avoid that dog-bone, but if that's all the CG has, then that's all there is.
Regards,
Jerry
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Old 05-02-2010, 04:21 AM   #9
SlickWillie
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Okee dokee, I just always knew of them as tandem breakers. I always knew of the little push button type as mini. I think the Iota must be different than the WFCO. The one I did a little work on was an older unit. In fact, Iota tech support told me the 12 volt panel was obsolete. I never did think the WFCO electrical panel, converter and such had the quality I saw in the Iota.
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Old 05-02-2010, 07:29 AM   #10
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Roger that, no problem. Another methodology used by our friendly EE's in designing these bad boys is to make them of standard width and then stack 2 seperate circuits, with their respective handle-ties, from inboard (buss-side) to outboard (field wiring side). Same result . . . 2 circuits on the same stab, thus in the same phase - saving space.
Downside?? - heat, the enemy of elec circuits & ultimately your coach! If at all possible do not put two heavy loads (such as those 2 AC's that started all this) on the same buss, let alone on the same tandem. The heat from the two are additive, lowering them below their ratings. In fact we did studies at one of the industrial manufacturing plants we serviced, using recording ammeters with both rtd and thermocouple temp monitoring and found that continuous loads of > 80 per cent lowered not only the rated current carrying capacity of the breaker carrying the large load but also adjacent breakers by as much as ten per cent.
Regards,
Jerry
If they made a fusible panel that would fit, cost effectively, in my coach I'd buy it in a NY second. Sure fuses are one-time but they are so FAST!
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