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Old 09-29-2016, 09:08 PM   #1
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2 x 20 amp to 50 amp connection

I'm trying to find more than 20 amps for my 2005, 45' Country Coach when I'm visiting someone's home. Would it work if I used two separate 20 amp circuits from the home and wired them to my 50 amp RV cord? An electrician showed me how to do it. He said to make sure the two home circuits are separate so they add up to 240 V. Would these two 20 amp, 120 V legs work? I've seen another thread where there is a 30a/20a to 50a conversion cord, so I'm thinking this may work.

Thanks, Doug
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Old 09-29-2016, 09:32 PM   #2
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Done correctly you can power up both legs of your 50 amp coach systems.
BUT, you will only have 20 amps on a 50 amp circuit . RV site plug supplies 50 amps to each side , so power use management is in order.
And that's if the two circuits you plug into are 20 amps , you'll have to go back to the circuit breaker panel to check , as most older homes will only be 15 amps per circuit , and you'd need to check for all other loads in the house.
Could be a lot of tripping of C/B s going on.
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Old 09-29-2016, 09:48 PM   #3
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I am not sure I would do that to my worst enemy. For starters you have to think that maybe the home owners may also be using these circuits to run things in their home. Next you will have to run extension cords after finding two separate circuits. The longer the run the more voltage drop and these cords need to be good heavy duty probably 12/3 wire which will run you in the neighborhood or $100 each. You really don't want to burn down their house do you.
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Old 09-29-2016, 09:51 PM   #4
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I agree. You have to know your usage balance to know if it is going to do you any good. As long as you have breakers that limit the pull to not exceed the wire you can put any plug you want. The limit is the breakers, and I would also suggest spending $20 and putting in fresh breakers for such an "implementation". Remember that just because something is rated for 50 does not mean it is using 50. Limit your inputs and as long as your needs do not exceed it you are fine.

It is not the optimal solution but depending on the rig needs is possible if you are ABSOLUTELY SURE on the wire and limit the inputs based on the wire.
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Old 09-29-2016, 10:09 PM   #5
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What you propose will work but you shouldn't have make sure they add up to 240 volts.

If you find 2 separate circits, even on the same leg, you will only be supplying 40 amps, so you won't be overloading the shared neutral line.

Modern homes, 1980s and up, wire kitchens and dinning rooms with, at least 2, 20 amp circuits. Then you can try the laundry room for a 20 amp circuit.

As pointed out, you may have some breaker tripping, sharing the loads with the house. That would be the case using only one circuit anyway.

Another option is to adapt to a 240 volt electric dryer outlet, if it's a 4 prong plug. You would have more power and could go to generator when laundry needs to be done.
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Old 09-29-2016, 10:17 PM   #6
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...most older homes will only be 15 amps per circuit , and you'd need to check for all other loads in the house.
Could be a lot of tripping of C/B s going on.
If the home owner will let me, and they're not already loading up those circuits, two 15 amp lines are better than one
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Old 09-29-2016, 10:22 PM   #7
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The longer the run the more voltage drop and these cords need to be good heavy duty probably 12/3 wire which will run you in the neighborhood or $100 each. You really don't want to burn down their house do you.
Ha ha. I bought a thick $100 cord about 10 years ago. Finally I have a use for it. I'll have to make the second cord a short run. The breaker should prevent an overload and possible fire.
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Old 09-29-2016, 10:30 PM   #8
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Ha ha. I bought a thick $100 cord about 10 years ago. Finally I have a use for it. I'll have to make the second cord a short run. The breaker should prevent an overload and possible fire.
Though it does not sound like an issue in this case note should be taken that a 100' braided (flexible) cord and a 100' of solid wire cord are completely different. The reason we only use braided cord on short segments and that it requires a much thicker wire is because of the energy loss. Solid wire which is not flexible can safely carry much more power then the same gauge wire if braided.
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Old 09-29-2016, 10:31 PM   #9
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You have to know your usage balance to know if it is going to do you any good.
By "usage balance", do you mean what each leg of the 50 amp RV cord supplies in the coach? This would be a good question. For example, if one leg just supplies the A/C units (I have 3), and it's cool like where I am now (Canada), then this might not help much cause I don't need the A/C. But in a warmer climate, I may be able to run 1 A/C unit on the one leg.
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Old 09-29-2016, 10:36 PM   #10
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What you propose will work but you shouldn't have make sure they add up to 240 volts.

Another option is to adapt to a 240 volt electric dryer outlet, if it's a 4 prong plug. You would have more power and could go to generator when laundry needs to be done.
Yes, the electrician told me to test the 2 black wires (small prongs) for 240 V.

Good idea about the electric drier outlet. Might be more difficult to access.
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Old 09-29-2016, 10:39 PM   #11
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Though it does not sound like an issue in this case note should be taken that a 100' braided (flexible) cord and a 100' of solid wire cord are completely different. The reason we only use braided cord on short segments and that it requires a much thicker wire is because of the energy loss. Solid wire which is not flexible can safely carry much more power then the same gauge wire if braided.
Mmm... the cord is thick and not that flexible. How can I tell if it's solid or braided?
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Old 09-29-2016, 10:40 PM   #12
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"Balance" can mean many things depending on your rig and configuration and you need to know that before you wire it. It could mean something as simple as do not run both AC and the clothes washer at the same time or you need a special schema. At the end of the day the critical piece is know the source wire and make sure you can not exceed its limits.
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Old 09-29-2016, 10:42 PM   #13
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Mmm... the cord is thick and not that flexible. How can I tell if it's solid or braided?
That's an easy one. If you strip the cover and it is one wire.. that is solid. If you strip it and it is "many" wires that you can "twist" around.. that is a braided/standed wire.

Example: http://www.cableorganizer.com/images...-wire-core.png
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Old 09-30-2016, 05:40 AM   #14
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No, as an electrical engineer....this will not work. I'll give you a short summary, and then the more detail info if your stomach is up for it.

The reason this won't work is because of the GFCI circuits that you will be plugging into. The GFCI breakers will trip and turn the power off.

By code, to avoid electrocutions, any outlets that are near water, outside, garages, etc are protected by a GFCI breaker. The two common installations are either a GFCI circuit breaker in your circuit breaker box (which then protects all of the sockets downstream on that breaker), or the outlet which has the two little buttons on them and a light which are typically found in bathrooms (which also then protect all downstream sockets that are daisy chained off of them).

A socket has three wires to it, the power leg (black or red), a neutral leg (white), and a ground (green or bare copper). The alternating current normally goes out the power leg to the item being powered, and then returns on the neutral leg going back to the breaker box. The ground should have no current on it, and ties the frame to earth ground. Electrocutions occur when the power is able to find it's way to/thru your body to earth ground, a path different than thru the cable. The way a GFCI breaker works, is that it very closely monitors the current of both the positive leg and the neutral leg. If it detects that those two current streams are different, it quickly trips the breaker at a current less than will kill you, and quick enough so that it doesn't. If the current coming out the positive leg, does not match the current coming back on the neutral leg, then it must have found a path to ground somewhere other than it should have, and the GFCI is tripped.

Here's your proposed connection on a 50amp RV: A 50 amp plug has two power legs, one neutral leg, and one ground cable. When you make your cabling dongle that you are talking about, you would have to bring together two circuits, each comprised of a pos/neut/grnd. Pos #1 would connect to Leg#1 of a 50amp plug. Pos#2 would connect to Leg#2 of the 50amp plug. Both Neu#1 and Neu#2 would have to connect together and attach to the single neutral of the 50 amp plug. Both Grnd#1 and Grnd#2 connect together and are attached to a single ground lug on the 50 amp plug.

Here's why it won't work in operation: Once connected, you turn something on (a lamp) in the coach, and lets say it happens to be a circuit that is getting powered from your house cable #1. The Alt Current flows from your house circuit breaker box out on the positive leg #1, thru GFCI#1 in your garage, to your dongle, thru the coach power cord, to the coach circuit breaker box, and to the lamp. That same current returns on the neutral headed back to the house. When it reaches your dongle, it will get to where you tied the two neutrals together, and current will always take the path of least resistance, effectively splitting it's current. Half the current will go back towards your house thru GFCI#1, half thru GFCI#2. When the GFCI sees the minutest difference in current ("all" of the positive leg lamp current vs. "some" of the negative return lamp current), it will trip to prevent electrocution. You will never legitimately get this dongle to work under the electrical code standards.

What you CAN do, is use one house/garage socket to connect a normal 20amp to 30amp dongle, and then a 30amp to 50amp dongle, then connect your coach power cord. Then run a separate extension cord out to the RV from a different house/garage circuit, thru the slide to the kitchen area, and plug the refrig or microwave into it (make sure the extension cords are rated at 20 amps). Remember however, the extension cords will have an internal resistance to them, and using high current devices will result in a drop of voltage at the device (V=i x r). Incandescent lamps don't care if the voltage isn't high, electronic control boards and motors do.

You may say....but wait, the house and socket I'm plugging into is circa 1940 and doesn't have any grounded outlets or GFCI sockets, and I'd like to plug into it. Then you take your (and your spouse/kids) life into your own hands. Don't be a fool, the GFCI's are made to protect your life.

As a side note, if you read the fine print of that 20a/50amp dongle that you referenced in the very first post, you will see that it will say does not work with GFCI sockets. Unless you are at a VERY old campground which isn't up to electrical code standards, it won't work. For example: "This versatile adapter enables RV users with 50-Amp service to run more appliances when 50 amp service is not available. Simply plug the 50 AMP Adapter Cheater Box into a 120 volt/30 amp and a 120 volt/20 amp source on two separate circuits to achieve a 240 volt/50 amp output. "Will not operate on a gfci circuit." Includes a 30 amp to 20 amp adapter and is made of high impact plastic. For outdoor use, and comes with a one year warranty. Features & Specifications 1 year warranty Plugs into a 30 amp and a 20 amp source Great for RVs Requires two separate circuits Able to run more appliances"
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