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Old 09-24-2017, 04:43 PM   #1
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220 single phase common neutral?

How are the two 110 supplies useful except there are at least two electrical "runs" in the coach. if you are in 30 amp a site, you only have one 110. Which of the runs powers up? and which "run" of appliances do you loose?
I store the mh at the plant where our incoming supply is 480 3 phase. In the back part of the plant where mh is stored, I have a transformer that outputs 110 and also 208 across any two lines. I don't have 220 single phase. Who cares Im not living there but in order to clean and work inside the mh,I want shore power. I can supply two 110s and common neutral but across the lines it is 208. Is there some need for 220 single phase that prevents my using the 208 ?
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Old 09-24-2017, 04:58 PM   #2
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in laymen's terms:

if your coach is a 50a coach, then it is provided power thru two incoming 50a breaker lines of power from the shore power post, which has a double pole 50a breaker(100amps total), to your TWO 50a internal breakers(or you might say 'sub breakers' within your breaker box)
but, when you use an 'adapter' to hook up to anything less, like 30a, 20a, or 15a, then your coach is provided the full power across both 'legs' of your breaker box, giving you power to ANYTHING you wish, as long as you don't exceed the shore breaker's own amperage.

Since 50amps per leg is typically what it is designed for, then anything less than that would never be an issue within your coach - only the shore power breaker is likely to trip should you ask for 'more power' than it can provide.
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Old 09-24-2017, 05:01 PM   #3
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Most coaches don't use 220/240 phased power, just two legs of 50 amp and share a common neutral. Unless you have a dryer or the like that combines the two legs, you will never see/care about the 208v combined. If just 30 amp plug, then the adaptor dog-bone splits the single 30 amp leg to power both legs in the coach. Do a search on this forum--there are hours of threads and posts on this subject--exhaustive!!!!!!
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Old 09-24-2017, 05:10 PM   #4
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Just a caution here, but if you are using a "dogbone" adapter, MAKE SURE that your line to neutral measures 110 to 120 VAC. Some old dryer and welder outlets are 220 or 208 as you are seeing! BAD IDEA! Will burn out your systems unless you have a surge protector in line.

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Old 09-24-2017, 05:34 PM   #5
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TLGPE,
your statement was hard for me to follow. i think a dog bone is an outlet changer from 110 30 amp service to use the same 110 line and split it off to supply both the 110 legs of the 50 amp shore cable. in my situation, i am going to wire up a receptacle with two individual 110 legs with a common neutral to plug in my 50 amp shore cable. Will this be alright? no dog bone for this campsite.
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Old 09-24-2017, 05:42 PM   #6
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i wish i knew how to successfully search these forums. give me an example like this electrical question. what words would you search for and where would you search? please
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Old 09-24-2017, 05:58 PM   #7
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To search the forums, use the Google Search box as shown in the image below. I entered "50 amp 220 volt" and got lots of hits.

To try to answer your question, an RV 50 amp outlet has two 110 volt live legs and one neutral wire. The important part is that the two live legs are 180 degrees out of phase with each other. That is what results in 220 volts live to live, and allows for up to 50 amp draw on each leg because the load on the neutral wire is cancelled out by the phase difference. Some older campgrounds have 50 amp outlets which have both live pins supplied from the same phase. The result is 50 amps on the neutral wire and a danger of the magic smoke leaking out. I have a home made tester which plugs into a 50 amp supply and tests for 110 volts on each line to neutral, and also for 220 volts line to line.

Hope this helps.
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Old 09-24-2017, 07:34 PM   #8
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That is a great explanation! I never thought of the "out of phase" in a neutral before. i don't intend to run much in storage. probably lights and a vacuum.

thanks for your thought provoking input.
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Old 09-24-2017, 07:43 PM   #9
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The concern about the three prong connectors is that welder outlets (and older dryers) apply 220 or 208 volts across L1 and L2, with the ground being there for safety. Just make sure the the two lines have 120V across them, NOT 208V.

This is serious. I don't want to alarm anyone; just check it.

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Old 09-24-2017, 07:50 PM   #10
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FWIW I think I would wire the box with the two hots connected together and the neutral and ground as usual. That will give you 50 A total without the phase issue. Both MH hots will have 120 VAC. Make sure your safety ground and neutral are connected at the box with a real safety ground. If you have anything that tries to use 240 VAC it will see zero - the difference between two lines in phase. The Neutral will stay at 50 A or less.

50 A will be enough to run an A/C and the vacuum and probably the coffee pot as well as keeping the batteries charged. Maybe even 2 A/C's if you alternate the percolate cycle with the vacuum with the microwave. ;-)
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Old 09-24-2017, 08:27 PM   #11
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Wrong picture, can't delete.
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Old 09-24-2017, 10:35 PM   #12
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Sound like you may have a delta transformer if you don't understand this. Get a qualified electrician.
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Old 09-24-2017, 10:47 PM   #13
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The issue you may run into is overloading your neutral. If using 220 if you have a ten amp load one one leg neutral carries ten also. If ten on each leg neutral carries zero. Using two 120 individual legs - ten amps on each leg will put 20 on neutral. As long as load is light will probably be ok. But as load increases maybe not.
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Old 09-24-2017, 10:59 PM   #14
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The 50-amp 120/240-volt 3 pole 4

http://www.myrv.us/electric/


Just look through this - should have all the answers.

Best of Luck,
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