Single phase inverter hot wires

[anees]

why in single phase ac output there are 2 hot wires( L1 and L2 )
In text book it should be one hot wire and neutral

 

[480sparky]

Two ungrounded (hot) conductors would be single phase.
Two hots would be a phase-to-phase voltage. One hot and one grounded ('neutral') is phase-to-ground voltage.
Two hots is NOT '2-phase'.

 

[Carultch]

why in single phase ac output there are 2 hot wires( L1 and L2 )
In text book it should be one hot wire and neutral

L1 and L2, when measuring volts to neutral, are equal and opposite. When measuring between each other, you get twice the voltage difference. This is how the 120/240V single phase delivers power to both 120V loads like receptacles, and 240V loads like electric ovens. Line-to-line circuits, line-to-neutral circuits, and circuits containing both lines and neutral, are called single phase when connected to a 120/240V service.

You might instinctively think, as I did, that it would be called "two phase", because it is mathematically equivalent to two sine waves that are out of phase by half a cycle. Just like 3-phase is 3 sine waves that are out of phase with each other by a third of a cycle. But the reason it isn't called "two phase", has to do with how it is derived, and historical reasons. It is pulled from a single phase off of the utility distribution, which is then stepped-down and center-tapped to produce equal and opposite L1 and L2 voltages. The center tap is bonded at the service disconnect to define neutral to the same voltage as ground.

 

[Carultch]

Line-to-line circuits, line-to-neutral circuits, and circuits containing both lines and neutral, are called single phase when connected to a 120/240V single phase service, also known as split phase.

Correction.

 

[synchro]

why in single phase ac output there are 2 hot wires( L1 and L2 )
In text book it should be one hot wire and neutral

One thing that may be confusing to the poster is that the single phase (aka split-phase) 120V/240V system shown in the schematic is common in the U.S. and some other places, but not in Pakistan or most of the rest of the world. These countries instead typically have 230V/400V which provides 230V L-N single phase, and this configuration is likely to be what your text book is describing as "one hot wire and neutral".

As was described above, L1 and L2 are still single phase but have opposing polarities because they are derived from a center-tapped transformer secondary winding. If you have a transformer driven with a single phase input, then you could have many output lines tapped from the secondary winding that have various voltages and polarities, but they all would still be single phase.