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Old 03-04-2012, 09:23 PM   #15
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Yep. Have one and used it, but it won't tell you that they Y ed both hots off the 30 amp. It will still give you 110 to grnd on both legs and 220 across the 2 hot legs.
I don't think that's correct. If what you say is correct then I should be able to get 220 from both hots on a residential duplex receptacle.
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Old 03-04-2012, 09:34 PM   #16
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Yep. Have one and used it, but it won't tell you that they Y ed both hots off the 30 amp. It will still give you 110 to grnd on both legs and 220 across the 2 hot legs.
If they connected both hot sides of the 50A socket to a single 30A line you would get 120V to gnd, but will get 0V across the 2 hot sides. If the pedestal happened to have two separate 30A sockets they would have to connect the output of the 30A breakers to the input of the 50A breakers to cause a 50A load to trip the 30A breakers. Maybe I'm not picturing something here...
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Old 03-04-2012, 11:11 PM   #17
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If they connected two 30a to a 50a and they used the same phase in both 30a , would you not get 240v across the hots? Two different phased would cancel each other and you would get 0 across the hots. I'm just learning this (I hope) - what am I missing here?
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Old 03-04-2012, 11:28 PM   #18
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If they connected two 30a to a 50a and they used the same phase in both 30a , would you not get 240v across the hots? Two different phased would cancel each other and you would get 0 across the hots. I'm just learning this (I hope) - what am I missing here?
You've got it exactly backwards. If the two hots are the SAME phase, the difference between them is 0. If they're opposite phases, and each is 120v, then the max difference between them is 240v (one is 120v, the other is -120v).

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Old 03-04-2012, 11:45 PM   #19
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If one is +120 and one is -120 are they not different phases? I have a lot of problem understanding this electrical stuff.

Oops, now I see it. The DIFFERENCE between the two. Thank You
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Old 03-05-2012, 07:33 AM   #20
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If a 50A socket has both hot legs wired to the the same leg of the split phase, the resulting voltage across the hot legs will be zero because, essentially, both legs have been shunted together. It's the same as just hooking both leads of the your meter to the hot leg of the 30A socket, or for that matter, just connecting both leads of the voltmeter together.

While it may seem harmless because you would have 120v hot to neutral and most RVs use only the two 120v legs instead of the 240v, if both hot legs of the 50A socket are connected to the same leg of the incoming split phase, then the neutral would have to carry as much as 100A, 100% more than it was designed for.

Checking a socket for correct wiring is as easy as checking the votage from each hot leg to neutral and to ground (all four should 120v) and across the hot legs (should be 240v).
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Old 03-05-2012, 08:40 AM   #21
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Yep. Have one and used it, but it won't tell you that they Y ed both hots off the 30 amp. It will still give you 110 to grnd on both legs and 220 across the 2 hot legs.
If you got 220V across the the legs then they didn't "Y" it.

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Old 03-05-2012, 08:56 AM   #22
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I stand corrected on the Y = 220, sorry (senior moment ). Still trying to understand then how a 30 amp to 50 amp pigtail works other than providing 110 to both lugs with common ground (single phase).
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Old 03-05-2012, 09:00 AM   #23
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I stand corrected on the Y = 220, sorry (senior moment ). Still trying to understand then how a 30 amp to 50 amp pigtail works other than providing 110 to both lugs with common ground (single phase).
That's exactly what it does. It does NOT provide 240v. But it does give you power on both legs, so that all the circuits in the RV work (except for anything requiring true 240v). But it's easy to overload that circuit, so you need to be careful what you turn on.

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Old 03-05-2012, 09:25 AM   #24
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I stand corrected on the Y = 220, sorry (senior moment ). Still trying to understand then how a 30 amp to 50 amp pigtail works other than providing 110 to both lugs with common ground (single phase).
Use of the 30 to 50 Y adapter can result with several possible configurations dependent on how the pedestals were wired.

1) The two pedestals are wired to the same phase (line, or leg).... Then you get the same 120 V to each of your coaches legs. In this case the neutral of the coach can get over loaded by 10 amps under max loading(30 +30=60A). Probably not likely or an issue.

2) The pedestals are of the opposite phases....
Then you get the equivalent of 30 amp 220V power and that should cover most of your requirements depending on balancing to each line of your bigger users. The neutral of the coach only sees normal currents.

3) If your Y box is used with a 20A and a 30A outlet on a lone pedestal, case 1 above probably applies. Except that no overload of the neutral occurs.

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Old 03-05-2012, 09:32 AM   #25
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Please note that there are two different wiring adapters being discussed here. The original discussion was for a "pigtail", which is a simple 30amp male to 50amp female connector. Used to plug a 50amp cord into a SINGLE 30 amp receptacle.

The other is a "Y adapter", which is used to plug a 50 amp cord into TWO 30amp (or one 30amp and one 20amp) receptacles. This is the device Marty is talking about.

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Old 03-05-2012, 09:55 AM   #26
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I don't know how this thread morphed into a discussion on how adapters are wired. I'm sure the op has since lost interest and purchased a commercial adapter being assured it is wired correctly should he need it in a campground.
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Old 03-05-2012, 10:00 AM   #27
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Well, if you don't know how the commercial adapter is supposed to work, how would you know if it's not working properly?

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Old 03-05-2012, 03:38 PM   #28
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I hope this drawing will make things a little clearer

First plug is a normal 30 amp service plug

In the middle is normal 50 amp service

On the right is using a 30 to 50 amp dogbone (30 amp supply service)



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