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Originally Posted by Footer4321
First... West Verginia... Watts*Volts=amps
Basically, amperage is a result of how many watts of electrcity is being pulled multiplied by the amount of voltage being supplied. A traditional (north american) household outlet is either 15 or 20 amps @ 120 volts, so they can supply a total of 2400 or 1800 watts.
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This is like half there and half not. West Virginia is
W=VA, which is how you did the math at the end of the paragraph. So, you only loose 50 points...
For M-C, in the united states the standard supply voltage is between 110v and 130v. Generally, as you sort of mentioned, at the power generation plant they send out 3 phase power. The most common 3 phase system is 3 phase Y (wye), this setup has each phase to neutral at 120v and the neutral is tapped from the center. The voltage between any two phases is 208v. From the generation station the electricity is transformed to a very high voltage at a very low amperage, which is best for long distance transmission. The transformer on your street or in your
theatre transforms the electricity back to a useable voltage.
After the transformer, you probably have some kind of power distribution system, this could be anything from one high amperage main breaker and sub breakers or a rack of high amperage breakers that feed other panels. It is common in theatre to see something like a 400 amp, 3 phase service. This means that on each phase you can load up to 400 amps for a total of 1200 amps on the service. In theatre terms, one
source four with an HPL575 draws 4.8 amps so you could put 250 units on the 400 amp 3 phase service.
As for your question on what the neutral line is for, it completes the
circuit. The hardest thing to fathom about neutral is that it doesn't run back to the generation station, it just runs into the ground and it works... Without completing a circuit from hot to neutral though, your devices wouldn't work, it would be like connecting a flashlight to only one end of the battery.
As for 60 cycle hum, this is most often caused, as you said by bad grounding. According to code, and best practice, every building is only supposed to have one path to ground. This means that there should only one connection point from the device ground (generally the green wire) to neutral, which is then connected to earth. In systems where there are multiple connections between device ground and neutral or where there are multiple earths this can produce a hum.
Hope that helps with your questions, and if I mis-spoke anything someone feel free to correct me.