Hi Schnem-If both wires are the same voltage and the same phase, then the voltage between them will be zero, so the bulb will not light. It will not be short-circuited either. There will be voltage between the wires and ground (or neutral), but no voltage between the two wires. Think about it this way- the voltage on both of the wires will be going in the positive direction the same amount and at the same time, and then during the next half-cycle they both go negative the same amount at the same time. The bulb only lights when there's a difference in voltage between the two wires, which causes current to flow. In this case there can be no current. -Rick
Further to Rick's response - a good way to visualize this sort of thing is to use a water analogy. Suppose we have two tanks of water that are connected at the bottom by a pipe. Now suppose that each tank has its own water feed coming in as illustrated below. In this case, if we add water to one tank, then water will flow through the pipe connecting the tanks until they are filled to the same height. This would be like feeding the two sides of your bulb with separate phases.
Tanks fed by separate pipes Alternatively, now suppose that both tanks are fed via the same source -- in this case the water in the tanks may rise (or fall), and they will be connected together, but no water will flow through the pipe connecting the two tanks. This would be like feeding the two sides of your bulb with the same phase.
Assuming that the light is represented by the circle with the X in it, you're showing three wires going to it. Assuming that the wire in the middle and the one on the left are connected to the same terminal, then you've got a short across Q1, so the answer is- nothing happens.This is really not the same as having two sources of the same phase, though.-Rick
In your diagram above you show (I think) both wires that are supposedly of the same phase going to the same side of the bulb, and another wire (in blue) going to the other side of the bulb. in this case, the bulb will light.If you take away the wire shown in blue, and connect one of the remaining wires to one side of the bulb and the other wire to the other side of the bulb, the bulb will NOT light.
-Rick
