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Old 05-04-2013, 05:16 AM   #1
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Can a 30AMP 240v provide 2 30AMP 120v??

Hi guys, looking for some enlightenment from the electrician here in the forums.
just wondering is based on the same concept that:
1) 50AMP 240v provides 12000W (50A x 240 V) We see very often the Y adapters for 2 30Amp 120V
2) Can a 30Amp 240 that provides 7200W (30A x 240V) be used to split 2 30Amp 120V??
According to our obvious limited knowledge in the electrical field isn't the same principle?
thanks for your time!!
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Old 05-04-2013, 07:31 AM   #2
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Not sure where your going with this but I'll try.
Campers use a 120V / 30 amp hook up OR a 240V / 50 amp.
Have never seen a 240V / 30 amp at a campground, or
a camper wired for 240V / 30 amp.
All 240V systems are two 120V legs to a common "neutral" regardless of amperage.
The adapters that allow a 240V / 50 amp camper to use a 120V / 30 amp outlet has an internal jumper wire that ties both 120V legs together. This allows all the 120V circuits to be powered in the camper, but too much demand will overload the 120V / 30 amp supply and trip the circuit breaker.
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Old 05-04-2013, 07:48 AM   #3
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Many generators have 30a 240v outlets. If you want to run two separate trailers from a single generator, make sure ther is only one N-G connection and you have a good ground at the generator.
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Old 05-04-2013, 08:10 AM   #4
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I think you can get two 120V 30A connections out of a 30A 220V connection but I am having trouble with the current in the neutral. I would think that two 120V connections would draw 60A through the neutral but I think it is probably 30A. I am having trouble with this. When you are running 220V nothing is going through the neutral. You definately need to make sure the nuetral feeding the recepticle is the same gage as the two hots. Which should be #10. So you would need 10/3 and preferably an independent ground. I run my trailer off a stove outlet in my dad's utility shed by pulling one leg off that. But if you ran two trailers one off each leg, I am worried about running too much current through the neutral.

I know that the feed coming into a house has 3 conductors of the same gage.

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Old 05-04-2013, 09:10 AM   #5
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No, you cannot use a normal 30 amp 120 volt RV cord to supply two 30 amp circuits. There are only 3 wires in the cord. One is the hot leg, one the neutral and the third is the ground.

In a 50 amp cord there are 4 wires. Two hot legs, one neutral and one ground. When wired properly the neutral only takes the difference current between the two legs, not the sum current as in effect the two hot legs are the outside of a center taped transformer and the neutral is the center conneciton. If incorrectly wired, the two legs are connected to the same half of the transformer and the neutral then would have to take the sum of the currents (60 amps) and if the same size, would overheat.

But, in short, the RV cord cannot be used for two 30 amp 120 volt circuits.
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Old 05-04-2013, 09:17 AM   #6
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That is what I was worried about. So to do it right you would need a nuetral that would handle 60A not 30A?

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Old 05-04-2013, 09:22 AM   #7
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Originally Posted by perryg114 View Post
That is what I was worried about. So to do it right you would need a nuetral that would handle 60A not 30A?

Perry
Yes, if both hot lines were connected to the same half of the transformer wired to the power supply.

The real point is that you don't have enough wires in a normal 30 amp RV cord.
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Old 05-04-2013, 09:56 AM   #8
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When I had the back off my trailer I put in a 10/4 pigtail going to a 4 pole twist lock with the hopes of upgrading to a dual 30A system running off a 50A RV recepticle.

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Old 05-04-2013, 10:23 AM   #9
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Originally Posted by perryg114 View Post
I think you can get two 120V 30A connections out of a 30A 220V connection but I am having trouble with the current in the neutral. I would think that two 120V connections would draw 60A through the neutral but I think it is probably 30A. I am having trouble with this.
The two hot pins of a 240 V, 30 A outlet (for example a welder outlet) are 180 degrees out of phase, so if you connect two 120 V loads to the outlet the current flowing in the neutral is the difference between the two 120 V load currents.

That's why the neutral line coming into your house is the same size as the two hot lines. The most current the neutral ever sees is equal to the current flowing in one of the hot lines when there is no load on the other side.

So in answer to the original poster's question, there is no reason you couldn't fan out a 240 V, 30 A outlet to two 120 V, 30 A RV outlets, as long as the 240 V, 30 A outlet has a neutral line (a 4 prong outlet). Not all 240V outlets do.
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Old 05-04-2013, 12:05 PM   #10
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I thought there was something I was missing. It has been 25 years or so since I took Circuits 1.

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Old 05-28-2013, 06:20 AM   #11
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thanks for all the replies, as always Airforums is a great community!!
Well the whole issue here is that we have a generator cord rated 30AMP 240 (4prongs) and we were wondering if we can use that cable & install a 30Amp 240V Outlet to have 2 trailer plugged with full 30Amp.
I see that there is still a split decision whether "yes" and "no".
We are planning on installing a 50AMP 240 and have the "Y" adapter to 2 30Amps 120V but since we have the generator cord that could save us a ton of funds that can be very useful for some aluminum...
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Old 05-28-2013, 07:15 AM   #12
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Originally Posted by Nuvite-F View Post
The two hot pins of a 240 V, 30 A outlet (for example a welder outlet) are 180 degrees out of phase, so if you connect two 120 V loads to the outlet the current flowing in the neutral is the difference between the two 120 V load currents.

That's why the neutral line coming into your house is the same size as the two hot lines. The most current the neutral ever sees is equal to the current flowing in one of the hot lines when there is no load on the other side.

So in answer to the original poster's question, there is no reason you couldn't fan out a 240 V, 30 A outlet to two 120 V, 30 A RV outlets, as long as the 240 V, 30 A outlet has a neutral line (a 4 prong outlet). Not all 240V outlets do.
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Nuvite-F has it correct.
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Old 05-28-2013, 08:35 AM   #13
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You should have an electrician check the wiring of you 240/50 amp circuit.
Not all 240 circuits were provided with a neutal line that was large enough to carry the 120 neutral. What you need is a 4 wire circuit. Two 120 hot leads, one neutral and one ground circuit.
A 50 amp circuit would be a 8 AWG wire. You need at least a 8 AWG neutral and a ground wire (usually green or bare wire).
Some 240 vac circuits only provide two hot leads and a ground. This would not be suitable to split for two 120 vac circuits.
Have it checked out.
And,yes, I am an industrial electrician.
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Old 05-28-2013, 08:46 AM   #14
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So, I have a 4 prong 240V outlet for an electric stove (unused, I have gas) right on the other side of the garage wall. What do I do to convert it to a 30 amp, 120V RV outlet if I moved it through the wall?
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Old 05-29-2013, 08:31 AM   #15
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Great; you can run two SEPERATE 120 vac 30 amp curcuits.
You may not use two outlets to provide power to a single trailer.
L1 - Neutral = 120 vac
L2 - Neutral = 120 vac
Neutral to Ground = 0 vac
BUT :
L1 to L2 will always be 240 VAC
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Old 05-29-2013, 06:16 PM   #16
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So, I have a 4 prong 240V outlet for an electric stove (unused, I have gas) right on the other side of the garage wall. What do I do to convert it to a 30 amp, 120V RV outlet if I moved it through the wall?
any pics of the outlet?
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Old 05-29-2013, 08:50 PM   #17
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So, I have a 4 prong 240V outlet for an electric stove (unused, I have gas) right on the other side of the garage wall. What do I do to convert it to a 30 amp, 120V RV outlet if I moved it through the wall?
Safety First! If you do not know how, you should get a qualified electrician to do this for you.

If I were in your situation, I would remove the 4 prong outlet (relocate wires as needed) and use the existing wire to feed a small 240v sub-panel. If the existing wire is to short you might add a junction box and extend this set of wires to where you would like the sub-panel to be. Add a 30 amp single pole GFCI breakers to the sub-panel to feed a 120v 30amp RV outlets. You could add additional 120v circuit breakers if you need more than one outlet. You can extend the wires from the sub-panel to where ever you want the outlets, if at a different location. #10-2 copper with ground will carry the load of 120v 30 amp, if you are not extending a long distance.

edit: to be legal the person doing the work must be licensed and a permit is required.
edit 2: I assumed the existing outlet for a stove is 30 amp 240v. If the breaker controlling this wire is less than 30 amp double pole it will not work.
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Old 05-29-2013, 10:28 PM   #18
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thanks for all the replies, as always Airforums is a great community!!
Well the whole issue here is that we have a generator cord rated 30AMP 240 (4prongs) and we were wondering if we can use that cable & install a 30Amp 240V Outlet to have 2 trailer plugged with full 30Amp.
I see that there is still a split decision whether "yes" and "no".
We are planning on installing a 50AMP 240 and have the "Y" adapter to 2 30Amps 120V but since we have the generator cord that could save us a ton of funds that can be very useful for some aluminum...
If you are installing a 50 amp circuit, you should add a sub-panel with breakers, not a 50 amp plug with a splitter adapter. You probably could rig something using that 30 amp cable that would work, but it might be dangerous.
1. You should get a qualified electrician to do the work if you are modifying any portion of the existing permanent electrical system you are connecting to. Or, if just plugging into an existing outlet, have someone look your work over before you power it up. You could damage your home and/or your trailer.
2. The chord you have for your generator should not be used as permanent fixed wiring inside your house or garage. It is meant to be a temporary drop chord.
3. If you spit the wires on a 240v 50 amp circuit without using breakers to protect any extensions from it, you will have 50 amps on the wires rated for 30 amps. The chord is probably has #10 wire rated for 30 amp.
4. The 240v circuit is protected by a double pole breaker. A 120v circuit extended from a 240v circuit should be protected by a single pole breaker with amp rating no larger than the amp rating the wire extending from it.

PM me if you have additional questions.
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