I read up on it bit it isn’t clicking for me.
In: Engineering
High leg has higher voltage to neutral. One phase is split and grounded in the middle for a neutral.
Power is carried from power plant to home on very high voltage power lines. Think 100,000 volts for very long distance. As it gets closer and closer to your home, that voltage is lowered by big transformers at substations. But when it gets to your house it’s still at about 5,000 volts, far too high for every day use. It often comes in on a single high voltage line with a ground return, but we need to step it down to roughly 100 volts for home use. The trick is that we actually need it to be more like 200 volts so we can run our driers and water heaters and things that require higher voltage. But a lot of things will burn up or explode at that high of voltage.
So here’s the trick: transformers are just two sets of wire windings around some sort of magnetic core material, iron works great for this. If we have one coil of wire with 100 turns around the core and another winding with only ten turns around the core, and we apply the high voltage to the 100 turns side, we have a 10 to 1 step down transformer, meaning if we had 1000 volts on the high side we would get 100 volts on the low side.
But the cool thing is that we could actually have one 100 turn winding and two 10 turn windings. Then we would have two circuits with 100 volts each from a single 1000volt line. If we were to take one end of each of those 10 turn windings and connect them, then we would have 200 volts across both coils and a common point in the middle which we call the neutral. This is essentially how residential transformers are built!
A high leg is when the voltage on one coil is higher than the voltage on the other coil creating an imbalance in the system. This can be caused by a shorted winding in the transformer or a short in an appliance in a home. It can also be caused by a poorly connected neutral which can cause power to flow back to the transformer in funny ways.
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