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Old 07-31-2014, 09:02 AM   #29
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Originally Posted by LakeKerrGuy View Post
The difference between (2) 50 amp 120vac circuits (4 load carrying conductors) and a single 50 amp 240vac circuit (3 load carrying conductors) is the neutral (grounded conductor). In the 240vac 3 wire circuit the neutral carries the unbalanced current. Exanple: Line A current = 30 amp; Line B current = 12 amp; neutral current will be 18 amps.
Exactly. This is why the elec code changed for elec household dryers. They started using 120 VAC control circuits. This unbalanced the load on the neutral and the "balance current" was being returned by an uninsulated return since most older homes were wired with two insulated and one uninsulated wires. Now the code requires a 4-wire device with an insulated neutral.
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Old 07-31-2014, 09:05 AM   #30
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Originally Posted by pasdad1 View Post
Correct. And since the neutral wire is not sized to carry that much current, bad things happen.
True. Normal wiring is typically THHN type and is rated for 90 deg C. Once that temp rise is crossed....better get the extinguisher ready.
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Old 07-31-2014, 09:08 AM   #31
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Originally Posted by Dr4Film View Post
Glenn,

No, do not worry, you are not missing anything. If you have and use a good multi-meter that will accomplish the same task.




Bob,

The basic wiring is found at THIS web site. I substituted a 3-way switch for one duplex allowing to switch between Leg #1 & #2.

If you are adept in electricity & electrical connections, you can figure it out easily.

If you would like one built for you, please PM me.




4X4 Dually,

A good simple post and explanation of "Phase".

There are many RVer's who don't understand 50 amp RV service nor do they want to. All they want is to plug in and enjoy. Unfortunately, there are many ways to destroy hundreds if not thousands of dollars worth of electrical items inside an RV.

I always HIGHLY recommend those RVer's who are inept in regards to RV 120/240 VAC power that they read and bookmark THIS website.

Hopefully, after reviewing it they will be a little more knowledgeable about their RV's.

Thanks for posting.

Dr4Film ----- Richard
Richard the pedestal tester you built for me works great. Before I even pull in to the site I take it and plug it in to the pedestal to make sure all is OK. If it is then I pull in get in the position that I want and then plug in the coach with my hard wired PI 50amp EMS to take over monitoring from that point forward. I would be protected for sure with the PI 50amp EMS even with out the pedestal tester but with the pedestal tester I save a lot of time and effort if there is a problem, and I can then move on to another site if need be.

I am happy.
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Old 07-31-2014, 09:49 AM   #32
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I imagine a person could put a test load on each leg and use an LED to illuminate if the net current on the neutral was less than 1 VAC or what ever the upper limit would be.
Do not understand. You say net current but then say 1vac.

Am I to assume the load placed on each leg is equal. Which is not likely with multiple 120 volt loads.
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Old 07-31-2014, 10:07 AM   #33
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Do not understand. You say net current but then say 1vac.

Am I to assume the load placed on each leg is equal. Which is not likely with multiple 120 volt loads.
I was just meaning that if both legs pull equal current, the net current on the neutral will be close to zero. Ideally it would be zero. Real world, it will probably be .3 or .7 or something. So basically, if it is less than a volt, you are good.

Don't let my multiple phase comment earlier confuse anyone. On three phase power, each phase is shifted 120 degrees. On standard 240/120 VAC single phase, there is only one phase, not multiple as my earlier comment could have inferred. It is a single winding on a transformer that is center tapped for the neutral.

So in summation, if you take a $5 pocket multi-meter from radio shack and L1 to L2 says 240 VAC +-3%, you are good. If it reads 0 volts L1 to L2 then it is either both wired to the same input wire and your neutral current will be an addition of the two or they are both un-connected. Clear as mud?
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Old 07-31-2014, 10:36 AM   #34
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All - If the park construction crew was electrical qualified to work RV wiring, then the wires (2 hot's - 1 neutral - 1 ground) in all the pedestals will be at least #6AWG (again depending on the length of the run from the main supply panel) to supply the power/voltage/amperage needed for a 50A circuit. The 30A circuit is one hot, one neutral and the ground, which is usually is taken off one of the 50A legs in the pedestal. All those circuits will have their own breakers to control that power. That is why in large parks you see transformers periodically and will see circuit panel and pull boxes. Many older parks (older could mean as new as 2000 or back to the 60-70's) are dubious in the wiring and how good it is, that would be from the transformer to the end pedestal. One of the nicest wiring parks I have been in is the 7-Feathers in Canyonville, OR. The park is great, expensive too!

I know of one park in TX where all the wiring from the transformer to the circuit panel is AL. From that panel it's CU, but, it was direct buried, no conduit, and it fails all the time, and they have to dig them up, the soil is very rocky, and hard to break into. It would cost couple million to rewire and bring up to code. The park is very nice with the exception of its wiring, and that is why, regardless of what tester you use, you need to test BEFORE you plug in, regardless of if you have the Surge Guard or some other device. I challenge you to (if you are electrically trained) to take the cover off your SG device and look at how small the sensing wires and circuits are in that device, and if something is really bad, it could cook that thing before it has the time to sense the issues and stop the SP coming in. A 10-170 dollar device is cheap insurance instead of having to replace all the devices in your rv, and lots of wiring damage.

As "Melissa Frances" said on the Fox Business Channel, It's always about the money, always!!!!
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Old 07-31-2014, 11:18 AM   #35
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Originally Posted by 4x4dually View Post
I was just meaning that if both legs pull equal current, the net current on the neutral will be close to zero. Ideally it would be zero. Real world, it will probably be .3 or .7 or something. So basically, if it is less than a volt, you are good.

Don't let my multiple phase comment earlier confuse anyone. On three phase power, each phase is shifted 120 degrees. On standard 240/120 VAC single phase, there is only one phase, not multiple as my earlier comment could have inferred. It is a single winding on a transformer that is center tapped for the neutral.

So in summation, if you take a $5 pocket multi-meter from radio shack and L1 to L2 says 240 VAC +-3%, you are good. If it reads 0 volts L1 to L2 then it is either both wired to the same input wire and your neutral current will be an addition of the two or they are both un-connected. Clear as mud?
Your description of three phase vs a center tapped single phase transformer is perfectly understood and correct. Where my confusion comes in is we are talking current flow but you keep using the term volt instead of amp. I know I'm being picky, but it is pretty obvious there are some on here who do not know the difference. I hear watts used when amps is intended; volts when amps is intended; and the inverter vs converter story as a few examples
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Old 07-31-2014, 11:27 AM   #36
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Originally Posted by Dr4Film View Post
Bob,

The basic wiring is found at THIS web site. I substituted a 3-way switch for one duplex allowing to switch between Leg #1 & #2.

If you are adept in electricity & electrical connections, you can figure it out easily.

If you would like one built for you, please PM me.
Dr4Film ----- Richard
Richard,
Thank you very much for the information. I had the site you reference bookmarked, but failed to realize that your unit was basically the same. I like your design better. Thank you for your offer, but the DIYer in me makes me want to make one of these myself.
Bob
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Old 08-31-2014, 01:24 AM   #37
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Richard -- Dr4Film,

Thank you for all your pictures and other information on the Pedestal Power checker. I unabashedly stole from your design for my unit. I have checked out everything with an ohm meter and all looks good. But, I will have to wait for an RV park to give it a real trial. My one modification, since I am right-handed, was to move the switch to the right side and have the "meter" on the left.

You are a saint if you build these for people. Just locating and getting the parts for this thing turned out to be a challenge. But, between Amazon, Wal-Mart, a local electronic parts store (for the 250 volt pilot light) and Lowes I was able to get all the parts I needed for this beast. This will be one of the first things I take out of the RV when we get to a new spot.

Thanks again,
Bob
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Old 08-31-2014, 08:35 AM   #38
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Richard -- Dr4Film,

Thank you for all your pictures and other information on the Pedestal Power checker. I unabashedly stole from your design for my unit. I have checked out everything with an ohm meter and all looks good. But, I will have to wait for an RV park to give it a real trial. My one modification, since I am right-handed, was to move the switch to the right side and have the "meter" on the left.

You are a saint if you build these for people. Just locating and getting the parts for this thing turned out to be a challenge. But, between Amazon, Wal-Mart, a local electronic parts store (for the 250 volt pilot light) and Lowes I was able to get all the parts I needed for this beast. This will be one of the first things I take out of the RV when we get to a new spot.

Thanks again,
Bob
Hi Bob,

I don't own a patent on these devices nor on any one type of design. The one that I own has morphed into what you had seen in an earlier post.

I offer to build these for people who are electrically challenged or don't have the time to spend gathering the parts and assembling it.

I do it more as a hobby to keep busy and make a little money on the side.

Glad it worked out for you!

Dr4Film ----- Richard
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Old 08-31-2014, 12:10 PM   #39
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I built one too. An easy project. I got the parts from Amazon and Home Depot. That digital line meter is great. I bought an oven cord for the pre-wired 50 amp plug.

I haven't found any bad pedestals yet, but it has only been in use for a couple of weeks.

Bob,

Thanks for the pictures. I was about to copy the one from the website but liked your mods better.
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Old 08-31-2014, 03:01 PM   #40
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Fake Pedestal--new term???? Since nothing on most coaches actually requires 220/240 [like elect stoves or resid A/C, I am not sure why in or out of phase matters? Curious -- does having both legs off the same 120 phase cause a problem? For spreading amp load, its nice if each leg of a 50 amp plug is a separate 50 amp circuit [for 100 amps total], but not phased--what am I missing?
Correct with one omission..... With both legs being identical (Same side of the transformer) the NEUTRAL wire can be ask to haul up to 100 amps... now, it is usually the same size as the L-1 and L-2 wires... So it's a 50 amp wire,, and here you are asking it to haul twice it's rating.. Can you see where this is leading.... If not... Visit a fire house.. Cause what is parked there WILL be visiting you if you try to haul 100 amps on a 50 amp wire.

And there is indeed one (JUST ONE) thing in many motor homes (not so many trailers but it will work there too) that needs 240 volts...


To the O/P. 169.00 for a few dollars more you can get a progressie Industries HW-50C and hard wire it in, With that you simply plug in. If the post is wired properly 2 mintues give or take a bit later you get power.. If not, it tells you way it is refusing.
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Old 09-01-2014, 08:59 AM   #41
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Correct with one omission..... With both legs being identical (Same side of the transformer) the NEUTRAL wire can be ask to haul up to 100 amps... now, it is usually the same size as the L-1 and L-2 wires... So it's a 50 amp wire,, and here you are asking it to haul twice it's rating.. Can you see where this is leading.... If not... Visit a fire house.. Cause what is parked there WILL be visiting you if you try to haul 100 amps on a 50 amp wire.

And there is indeed one (JUST ONE) thing in many motor homes (not so many trailers but it will work there too) that needs 240 volts...

To the O/P. 169.00 for a few dollars more you can get a progressie Industries HW-50C and hard wire it in, With that you simply plug in. If the post is wired properly 2 mintues give or take a bit later you get power.. If not, it tells you way it is refusing.
People who own the Power/Pedestal Testers don't have to wait until they are fully backed in, parked, setup and plugged in only to find that there is a problem with the pedestal and will need to move. They can test it PRIOR to doing all of that work. Plus if you plug in your Power/Pedestal Tester and hear "Snap - Crackle - Pop" along with smoke and fire, you simply remove the 50 amp plug that most likely looks like a toasted marshmallow and install a new one. Sure hate to do that to my 30 foot shore cable with a molded plug on the end.

If they own a Progressive Industries Portable EMS unit, then YES, the Power/Pedestal Tester is redundant.

Dr4Film ----- Richard
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Old 09-01-2014, 02:50 PM   #42
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The majority of motorhomes do not have a use for 240V so the phase thing is irrelevant. In fact many 50A to 30A plug adapters do connect both legs to the same source and possibly some pedestals do too. The only difference is you will have a total of 50A or 30A instead of 100A. For that reason your generator does not produce 240V anywhere. My 8K Onan produces a total of 85A. Check the single breaker on the gen set.

Another reasonable tester is a Kill-A-Watt for about $20 it will show you frequency, voltage and if you plug something in to it, amps, watts and watt-hours.
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