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 > Electricity? Never touch the stuff

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Dutch_12078

Winters south, summers north

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Posted: 08/14/19 05:52pm Link  |  Quote  |  Print  |  Notify Moderator

philh wrote:

Two questions,
1. I've heard of some wiring the same 120V phase to both sides. Wouldn't this drive twice as much current through neutral line?
2. Other than the problem of hooking to a single phase circuit, why wouldn't the AC units be 2 phase? Wouldn't that be much more energy efficient?


Yes, if a single 120 volt service is wired to both L1 and L2, the neutral carries the total load from both hot legs. Assuming a standard 50 amp single breaker though, the total load cannot exceed 50 amps.

Standard residential/RV 120/240 volt service is not "2 phase", it's a single "split-phase" service.


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Spridle

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Posted: 08/14/19 06:05pm Link  |  Quote  |  Print  |  Notify Moderator

These work out really well. You can be plugged in with the cover down in the rain.
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cougar28

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Posted: 08/14/19 06:13pm Link  |  Quote  |  Print  |  Notify Moderator

RLS7201 wrote:

philh wrote:

Two questions,
1. I've heard of some wiring the same 120V phase to both sides. Wouldn't this drive twice as much current through neutral line?
2. Other than the problem of hooking to a single phase circuit, why wouldn't the AC units be 2 phase? Wouldn't that be much more energy efficient?


What is being discussed(?) here is called split phase. The return path on the neutral line carries an inverted sine wave from L1 & L2. When L1 & L2 carry a balanced load, there is no current flow on the neutral path.
Maybe you can follow this.

Richard


RLS7201 is 100% correct. The neutral only carries the unbalanced load between the two line.


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Posted: 08/14/19 06:27pm Link  |  Quote  |  Print  |  Notify Moderator

Dutch_12078 wrote:

philh wrote:

Two questions,
1. I've heard of some wiring the same 120V phase to both sides. Wouldn't this drive twice as much current through neutral line?
2. Other than the problem of hooking to a single phase circuit, why wouldn't the AC units be 2 phase? Wouldn't that be much more energy efficient?


Yes, if a single 120 volt service is wired to both L1 and L2, the neutral carries the total load from both hot legs. Assuming a standard 50 amp single breaker though, the total load cannot exceed 50 amps.

Standard residential/RV 120/240 volt service is not "2 phase", it's a single "split-phase" service.
Good answer.

You may have read about using a cheater cord - ie one version has 2 male 30A plugs and a female 50A plug (ie 30/30/50). So yes this device can draw 60A on the 50A neutral. Not excessive but still over current. But what about the 30A neutrals that are now connected/shorted together? The current on the 30A neutrals is now determined by the impedance of each 30A neutral. As a result one 30A neutral could be carrying 50A and the other 10A resulting in significant overload of the one neutral.

The 20/30/50 cheater cord has the same problem.


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cougar28

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Posted: 08/14/19 06:28pm Link  |  Quote  |  Print  |  Notify Moderator

philh wrote:

Two questions,
1. I've heard of some wiring the same 120V phase to both sides. Wouldn't this drive twice as much current through neutral line?


That's what happening when when you plug a rv 50 amp using the dog bone into a rv 30 amp. To over current the neutral in that way you would have to be on a larger service and 120v breaker above 50amp.

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Posted: 08/14/19 06:37pm Link  |  Quote  |  Print  |  Notify Moderator

cougar28 wrote:

RLS7201 wrote:

philh wrote:

Two questions,
1. I've heard of some wiring the same 120V phase to both sides. Wouldn't this drive twice as much current through neutral line?
2. Other than the problem of hooking to a single phase circuit, why wouldn't the AC units be 2 phase? Wouldn't that be much more energy efficient?


What is being discussed(?) here is called split phase. The return path on the neutral line carries an inverted sine wave from L1 & L2. When L1 & L2 carry a balanced load, there is no current flow on the neutral path.
Maybe you can follow this.

Richard


RLS7201 is 100% correct. The neutral only carries the unbalanced load between the two line.
Yes the neutral carries the difference of the 2 loads for a 50A RV pedestal plug. I took the post to mean both hots are connected to L1 or L2 like the cheater cord allows.

time2roll

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Posted: 08/14/19 07:02pm Link  |  Quote  |  Print  |  Notify Moderator

philh wrote:

Two questions,
1. I've heard of some wiring the same 120V phase to both sides. Wouldn't this drive twice as much current through neutral line?
2. Other than the problem of hooking to a single phase circuit, why wouldn't the AC units be 2 phase? Wouldn't that be much more energy efficient?

1 yes however probably wired on a single 50a breaker and the two hots tied together. 50 amp 120v service. BTW this is NOT to code.

2 the air is configured for 120 for periodic 30 amp service and to match the generator power.


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cougar28

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Posted: 08/14/19 07:30pm Link  |  Quote  |  Print  |  Notify Moderator

philh wrote:

Two questions,
2. Other than the problem of hooking to a single phase circuit, why wouldn't the AC units be 2 phase? Wouldn't that be much more energy efficient?


No not any more efficient. Let say the a/c unit pulls 15 amps on 120v.That's a 15 amp draw on one line.
Now that same unit on 240v would pull 7.5amps. That a 7.5 amp draw on each one of the 2 hot line with a total of 15 amps.

STBRetired

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Posted: 08/14/19 07:47pm Link  |  Quote  |  Print  |  Notify Moderator

cougar28 wrote:


That's what happening when when you plug a rv 50 amp using the dog bone into a rv 30 amp. To over current the neutral in that way you would have to be on a larger service and 120v breaker above 50amp.


Not quite. The 30A receptacle should be protected by a 30 breaker, which will prevent drawing more that 30A, thus not overloading the neutral, which should be designed for 30A.


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12th Man Fan

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Posted: 08/14/19 07:51pm Link  |  Quote  |  Print  |  Notify Moderator

Boy, my stay at the Holiday Inn Express must have been a total waste.

Sorry for all the confusion. I guess I am the only one confused.


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