Like Top said in the classroom and here and even in the cab of the truck ok, but I've seen guys talk all about how they tamed the world years ago and they are still wet behind the ears. . . so I was giving that young buck a pointer or two on how to get along in this business. I want them to be smart not smart a$$e$.
any 3 wire circuit that has a neutral works like this.
The 3rd "neutral" wire is responsible for the return of any unbalance amperage to the source.
120/240v house service... if leg A carries 30 amps and leg B has 20 amps of load the neutral carries the unbalance difference-10 amps.
If you balance the load A-50 b-50 there is no unbalanced current to return... In fact-all the current travels in series-through every device that is turned on inside that house.... sort of. O amps is read on the neutral at that time
In theory what happens is that the current ...curent is seen as moving through the transformer winding in the direction of the "hot bushings" (x1 and x3.. (the neutral connect to the middle of said winding or x2)
If the current was actually moving through the house load as a true series circuit.. many of the devices would drop voltage based on the resistance contained in the device itself (ohms). The 120 volts need a grounded reference to work correctly (they need 120 volts of potential to work correctly-it has to see ground) if they were is series we would see the same damage as we would if we "lost the neutral"-- some stuff (like your low resistance computer or TV) would get too high a voltage... and stuff like your hairdryer (high resistance) would not drop enough... Expensive stuff burns up...cheap stuff survives.
You get a zero reading on a balanced neutral because the neutral current form leg A...actually travels past the current from Leg B--- in opposite directions. As a vector problem... if the return current is equal they would cancel each other out... and the ampmeter reads '0".