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Old 03-31-2016, 03:17 PM   #1
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Use a Single Inverter to run Two 120v Breaker Bus for a 240 Volt setup

Hello All,
Does anyone know of an article where a single inverter, mounted away from the camper, is running a 240 volt setup to a 50 amp RV hookup box?
I do not believe I can run two inverters, one per bus, because they will not be phased.
Thanks for the help
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Old 03-31-2016, 03:22 PM   #2
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Use a Single Inverter to run Two 12oV Breaker Bus for a 240 Volt setup

A 50A rv runs on 110, not 240.

Edit: oops, bumped the send too soon.

As I was saying, the 50A trailer uses each leg independently, to provide 110 each. So you should be able to split your supply to both legs equally, just like a 30a to 50a dogbone adapter does.

Btw, when you say 'inverter' do you mean a generator? Or are you talking about a true inverter that turns battery power back into AC power?
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Old 03-31-2016, 03:26 PM   #3
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The phase issue on a 50 amp RV plug is commonly misunderstood. It is all SINGLE phase.
Yes, they are on separate buses and SPLIT but not different phases.

If all you are trying to do is be able to operate things on both sides of your 50 amp service from an inverter, get an adapter that feeds 110v to both sides of your 50 amp plug. (See wiring in lower right of schematic)

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Old 03-31-2016, 04:03 PM   #4
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Originally Posted by 2nd House View Post
Hello All,
Does anyone know of an article where a single inverter, mounted away from the camper, is running a 240 volt setup to a 50 amp RV hookup box?
I do not believe I can run two inverters, one per bus, because they will not be phased.
Thanks for the help
I too am extremely confused by your terminology (inverter, hookup box?). Are you perhaps meaning to ask how to connect two "inverter" generators to provide power to a 50 amp RV?

Honda and Yamaha have special cables for this, and you cannot parallel ALL of their generators.

What you would do, is parallel the two generators together, and then use an adapter like 5picker pointed out to hook to the RV if you only have a 30 amp 120 volt outlet, which then shares the generators power across both the L1 and L2 inside the RV. I think some of the generators parallel kits will have the 50 amp outlet too, where you won't have to use an adapter.

Here is an article on the Hondas:

http://powerequipment.honda.com/gene...lel-capability
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Old 03-31-2016, 04:46 PM   #5
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Hello All,
Does anyone know of an article where a single inverter, mounted away from the camper, is running a 240 volt setup to a 50 amp RV hookup box?
I do not believe I can run two inverters, one per bus, because they will not be phased.
Thanks for the help
I agree that perhaps you mean two generators or two inverters, both feeding your 50 amp power cable and panel. Now,

They don't have to be in phase (inverters or generators) since nothing in your RV is using the 240 volts across both of them, but rather one side of your panel is using one of the 120 lines and the other is using the other 120 volt line. Now, that being said, if the two sources are out of phase it really won't matter to either half of the panel anyway. Some inverters can be "grid tied" so that they will sync, and the same is true of inverter generators as others have suggested. Mechanical generators are more problematic since they would need mechanical governors to match phase.

Now, all that being said, if you put in a 3500 or 5000 watt inverter, you can use a dogbone adaptor as others have suggested to power both sides of the panel with a single source.
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Old 03-31-2016, 05:13 PM   #6
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The phase issue on a 50 amp RV plug is commonly misunderstood. It is all SINGLE phase.
Yes, they are on separate buses and SPLIT but not different phases.

If all you are trying to do is be able to operate things on both sides of your 50 amp service from an inverter, get an adapter that feeds 110v to both sides of your 50 amp plug. (See wiring in lower right of schematic)

I am not sure about this; every wiring diagram for 50 amp RV was 2 phase like the middle plug in your drawing.

I think you are confusing the issue (and yourself) by showing the 30 amp 110 single phase dogbone wiring diagram at the end. It is limited to 30 amps TOTAL on both legs added together. 20 amps on L1 and 10 amps on L2 for example.

This is an important point because if the 50 amp RV plug was not two phase, the neutral would have to be twice as large to handle the return current.

In a 2 phase system (both 110 volts), the hot wires alternate 180 degrees out of phase 60 times a second allowing the neutral to only "see" the return current on one leg at a time.

OK, yea, I am sure you misunderstood.
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Old 03-31-2016, 05:22 PM   #7
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Actually, virtually all home wiring is not two phase, but center tapped single phase, as shown in the diagram. In a two or three phase system, each leg is 120 degrees out of phase. Hence a residential "high voltage outlet" is not 208 volts but 240 volts, since both sides are derived from the same phase from the powerplant. The 208 volt version has reduced voltage from the phase difference between two 120 volt swine waves that are 120 degrees out of phase. The center tap is grounded at the power meter and becomes a "neutral" from there. Hence, the neutral can carry more current than each individual hot lead, but never more that the total current at 240 volts.
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Old 03-31-2016, 07:36 PM   #8
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Actually, virtually all home wiring is not two phase, but center tapped single phase, as shown in the diagram. In a two or three phase system, each leg is 120 degrees out of phase. Hence a residential "high voltage outlet" is not 208 volts but 240 volts, since both sides are derived from the same phase from the powerplant. The 208 volt version has reduced voltage from the phase difference between two 120 volt swine waves that are 120 degrees out of phase. The center tap is grounded at the power meter and becomes a "neutral" from there. Hence, the neutral can carry more current than each individual hot lead, but never more that the total current at 240 volts.


My head just exploded ...

Been a long time since school, and I don't remember it that way.
I am sure you are right, but I don't think it matters in the RV world.
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Old 03-31-2016, 08:06 PM   #9
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Lou,
I hope from your comments about ScottBrownsteins' post that you realize I am not confused about 50 amp R/V wiring and respectively, the schematic clearly points out that through an adapter, both sides of the 110v can be supplied from one feed. Keep in mind, this is typically used for temporary situations where a normal 50 amp (center plug of schematic) isn't available. And yes, you are limited to whatever amps are available by the breaker feeding that leg.

This is very commonly done by 30-to-50 amp adapters but can also be found in some pedastals to create a somewhat 'fake' 50 amp socket.

Again, a 50 amp R/V supply is not two separate phases. It is a split (single) phase from two separate busses in the breaker box.

My inclusion of the schematic was to simply show that the 50 amp plug can be (and often is by using a dog bone) fed from the same hot leg.
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Old 03-31-2016, 09:36 PM   #10
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Lou,
I hope from your comments about ScottBrownsteins' post that you realize I am not confused about 50 amp R/V wiring and respectively, the schematic clearly points out that through an adapter, both sides of the 110v can be supplied from one feed. Keep in mind, this is typically used for temporary situations where a normal 50 amp (center plug of schematic) isn't available. And yes, you are limited to whatever amps are available by the breaker feeding that leg.

This is very commonly done by 30-to-50 amp adapters but can also be found in some pedastals to create a somewhat 'fake' 50 amp socket.

Again, a 50 amp R/V supply is not two separate phases. It is a split (single) phase from two separate busses in the breaker box.

My inclusion of the schematic was to simply show that the 50 amp plug can be (and often is by using a dog bone) fed from the same hot leg.
I must not be thinking clearly obviously.

In a 30 amp RV (3 prong) outlet feeding a 50 amp RV dogbone:

The 30 amp limit on the dogbone adapter is limited by the neutral wire size and the pedestal breaker sized for that wire gauge. It does not matter what is on each leg (L1 and L2) so long as the sum does not exceed 30 amps.

In a 50 amp RV (4 prong) outlet:

If the two legs (L1 and L2) are "high" at the same time (in phase), won't the neutral see return current from both circuits? If they are each broken at 50 amps, won't the neutral "see" as much as 100 amps (if both legs are drawing 50 amps concurrently)?

Should not L1 and L2 be out of phase (L1 Vpeak when L2 is crossing zero) and L2 Vpeak when L1 is crossing zero) so the current on the neutral never exceeds 50 amps?

Still can't wrap my mind around them both being in phase and "high" at the same time. It has to be CRS at my age.
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Old 03-31-2016, 10:10 PM   #11
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The extra wires from the 50 is simply for the amps. Not volts. Same 110-125volts.

As far as connecting two inverters output together....don't try it as it will fry the inverter.

You can get a heavy enough inverter to power your needs. Just upgrade the inverter if you have the battery power for it. They suck power quick depending on your draw or usage.
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Old 04-01-2016, 05:30 AM   #12
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OK, let me try this again. Seems that everybody is right...and everybody is wrong in this discussion. First of all, the power pedestal in an RV park (and your house) is always single phase. However, the hot leads come off either end of a transformer winding that provides 240 volts AC. The neutral is a center tap for that transformer and is connected to ground. This is referred to as "split phase" wiring. Now stay with me here. Since the transformer supplies 240 volts and each "leg" is 120 volts above neutral and ground, when one leg is "high" at 120, the other is "low" at 120 so that between the two, they add to 240. If they were both high at the same time, the voltage between them would be zero!

So, in effect, the voltage on the two hot lines is 180 degrees out of phase. That means that if you load one with 50 amps and the other with 50 amps at the same time, the current in the common neutral will add to ZERO, hence the neutral conductor is generally way underloaded if the loads are balanced.

If someone who wired the pedestal managed to take both 50 amp feeds from the same side of the panel (not a double breaker), you would measure zero volts between the two hots in the incoming power cable. Most EMS's will try to automatically shed the load to 30 amps under this circumstance, since they measure the voltage between the two hot leads and get zero and assume you are using a 30 amp dogbone on a 50 amp rv cord and attempt to protect your system. If not, you technically would run the risk of overloading your neutral bus, cord and connector, since RVs generally have all 120 volt loads. The potential for overload, however, is eliminated by the fact that the pedestal is fused at 30 amps when a dogbone is used, giving the neutral sufficient protection since it is designed to carry 50 amps to begin with.

However, if both sides of the 50 amp rv plug come from the same side of the transformer, you can definitely overload your neutral since if you were to draw 50 from both hot leads, the current in the neutral would be 100 amps...and the breakers in the panel (and the pedestal) will neither see nor protect for this load.

In short, make sure you have 240 volts across the two hot leads in your 50 amp connection!
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Old 04-01-2016, 06:20 AM   #13
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OK, let me try this again. Seems that everybody is right...and everybody is wrong in this discussion. First of all, the power pedestal in an RV park (and your house) is always single phase. However, the hot leads come off either end of a transformer winding that provides 240 volts AC. The neutral is a center tap for that transformer and is connected to ground. This is referred to as "split phase" wiring. Now stay with me here. Since the transformer supplies 240 volts and each "leg" is 120 volts above neutral and ground, when one leg is "high" at 120, the other is "low" at 120 so that between the two, they add to 240. If they were both high at the same time, the voltage between them would be zero!

So, in effect, the voltage on the two hot lines is 180 degrees out of phase. That means that if you load one with 50 amps and the other with 50 amps at the same time, the current in the common neutral will add to ZERO, hence the neutral conductor is generally way underloaded if the loads are balanced.

If someone who wired the pedestal managed to take both 50 amp feeds from the same side of the panel (not a double breaker), you would measure zero volts between the two hots in the incoming power cable. Most EMS's will try to automatically shed the load to 30 amps under this circumstance, since they measure the voltage between the two hot leads and get zero and assume you are using a 30 amp dogbone on a 50 amp rv cord and attempt to protect your system. If not, you technically would run the risk of overloading your neutral bus, cord and connector, since RVs generally have all 120 volt loads. The potential for overload, however, is eliminated by the fact that the pedestal is fused at 30 amps when a dogbone is used, giving the neutral sufficient protection since it is designed to carry 50 amps to begin with.

However, if both sides of the 50 amp rv plug come from the same side of the transformer, you can definitely overload your neutral since if you were to draw 50 from both hot leads, the current in the neutral would be 100 amps...and the breakers in the panel (and the pedestal) will neither see nor protect for this load.

In short, make sure you have 240 volts across the two hot leads in your 50 amp connection!

Very good explanation!
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Old 04-01-2016, 09:18 AM   #14
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So, in effect, the voltage on the two hot lines is 180 degrees out of phase. That means that if you load one with 50 amps and the other with 50 amps at the same time, the current in the common neutral will add to ZERO, hence the neutral conductor is generally way underloaded if the loads are balanced.In short, make sure you have 240 volts across the two hot leads in your 50 amp connection!

Still trying to wrap my head around this.

"So, in effect, the voltage on the two hot lines is 180 degrees out of phase."
This is exactly what I said earlier.

"That means that if you load one with 50 amps and the other with 50 amps at the same time, the current in the common neutral will add to ZERO,"


This is still an issue for me. How can one side of the "split phase" and the "other side" of the split phase (two phase?) show zero current flow with a load on the circuit unless there is concurrently zero voltage?

In my mind this can only happen at the exact instant when the two wave forms (L1 AC and L2 AC) cross the zero on the voltage axis. Zero current only when there is zero voltage across the transformer. This occurs once every 1/120th of a second as the secondary current changes direction. At all other times, voltage is building on one side (or the other) and current is building as the voltage does till it peaks at 170 volts AC (Vpeak) - or more commonly called 120 volts RMS.

Since the Vpeak alternates between L1 and L2, the neutral current carries between zero and 50 amps assuming both L1 and L2 are "loaded" with resistance required to demand 50 amps of current.

50 Amp RV Service - the common four pin configuration used for larger RV's. The receptacles are ANSI/NEMA 14-50R and the plugs are ANSI/NEMA 14-50P. The half round pin is ground, the blade directly across from it is Neutral, and the other two blades each have 120 Volts. If wired per the National Electrical Code, the two 120 Volt feeds are of opposite phases so that you get 240 Volts when you read across them and 120 Volts between each of them and neutral or ground.

Source material:
V peak to peak to Vrms conversion calculator
Well, what is 50 amp service?
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Old 04-01-2016, 09:49 AM   #15
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Still trying to wrap my head around this.

"So, in effect, the voltage on the two hot lines is 180 degrees out of phase."
This is exactly what I said earlier.

"That means that if you load one with 50 amps and the other with 50 amps at the same time, the current in the common neutral will add to ZERO,"


This is still an issue for me. ...
Herk,

You have to dig deeper than that. Again both hot legs come from the same phase...not two phase...but split phase! As I said, in a multi phase installation, there are 3 separate phases and they are 120 degrees apart. This is a split single phase installation as are all residential services.

The issue is not the current that is induced in the neutral, the issue also relates to the direction of that induced current flow. One hot leg is trying to induce say 50 amps in one direction, while the other is simultaneously inducing current in exactly the opposite direction since one is at a plus voltage on the waveform and the other is simultaneously at the opposite and negative waveform voltage. As such, if the loads are exactly the same, they will neutralize in the common neutral and the net current will be zero! Now split phase loads are seldom that well balanced but even it one hot has no load and the other has a full 50 amp load, the current in the neutral will only be 50 amps. As they approach a balanced load the neutral current will drop to zero again. That way you can draw 100 amps at 120 volts and only load the hots at 50 and the neutral load will approach zero. The neutral only carries the difference in current from the two legs, not the sum!

The design allows smaller service entrance cabling for higher current levels.

Mind bending...but true.
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Old 04-01-2016, 10:01 AM   #16
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Sorry, I am just dumb I guess.

If there is 100 amps on the L1 and L2 wires and none on the neutral, aren't they undersized for that current?

Like I said, I am just putting all this in my too hard to fathom pile.
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Old 04-01-2016, 10:09 AM   #17
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Sorry, I am just dumb I guess.

If there is 100 amps on the L1 and L2 wires and none on the neutral, aren't they undersized for that current?

Like I said, I am just putting all this in my too hard to fathom pile.
Nope. EACH of the hot legs are carrying 50 amps, and they are sized for it. The neutral sees 50 amps in one direction from one of them and 50 amps in the other direction from the other, for a net current of...0 amps. Perfectly balanced load.

That is the whole idea.
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Old 04-01-2016, 10:14 AM   #18
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OK, I just read this Wiki article and I think I am now up to speed.

https://en.wikipedia.org/wiki/Split-...electric_power

"He can be taught!"

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Old 04-01-2016, 10:14 AM   #19
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Nope. EACH of the hot legs are carrying 50 amps, and they are sized for it. The neutral sees 50 amps in one direction from one of them and 50 amps in the other direction from the other, for a net current of...0 amps. Perfectly balanced load.

That is the whole idea.
What he said!
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Old 04-01-2016, 10:43 AM   #20
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Ok my question is that if you measure access L1- L2 with volt meter would i get 0,120,240? Im thinking im getting 0 with this set up . I have a 30 amp set up at this time but trying to get my head around 50 service for the future. Sorry for the mental block
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