220 vs 240 volt

[jeff friedman]

Got it . Thanks

[Bill Dufour]

As a kid I was surprised that a lot of the war surplus ac motors were 400HZ. My Dad explanied that the higher frequency meant smaller and lighter weight transformers and motor coils.
High power transmission lines use dc now that it is much less expensive to switch ac/dc both ways. DC has almost no wasted energy by switching polarity and energizing all the nearby metal like the metal towers. this reduces energy lost to heating nearby conductive objects.
Bil lD

[John K Jordan]

... DC has almost no wasted energy by switching polarity and energizing all the nearby metal like the metal towers. this reduces energy lost to heating nearby conductive objects.
Bil lD

I once set up my telescope under some high power AC transmission lines. I was surprised at the odd feel when I ran my hand down the chrome legs of the scope tripod. Looking closer, there were tiny discharge arcs all around the tripod leg between the metal and my skin. Not enough to shock but definitely enough to see and feel!

JKJ

[Bill Dufour]

I learned in high school that you do normally get killed by touching a high voltage wire and getting sparked. instead you are on a metal ladder that gets near to the wires and it generates a voltage in the metal which is what actually zaps you. Birds are nowhere near ground potential so they can touch one wire at a time safely.
There are laws that outlaw runing wires under high voltage line sand generating power from the radiated emf fields.
Bil lD

Spark gap voltage is roughly 30,000 volts per centimeter in dry air. So a 120 kv spark is only 4cm long

[John K Jordan]

...
Spark gap voltage is roughly 30,000 volts per centimeter in dry air. So a 120 kv spark is only 4cm long

FWIW, the sparking/arcing I saw and experienced with my fingers all the way around the telescope tripod legs was way less then 1 mm in length.

The discharge voltage also apparently depends on the shape of the electrode. My buddy and I built a Van De Graaff generator that let him get continuous 11" arcs from the tip of a finger. Nice party trick when he used the tip of his tongue. Calculate that voltage Low current, though.

In a darkened room I could detect dimly visible continuous electron "spray" at the point of a pin held in my fingers feet away when approaching the globe of the generator.

Approach it with a broader part of the body, such as the side of the forearm, and you would get a single strong, bright, painful lightning zap from maybe 3-4" away. The less brave could hold a sphere or approach with the bottom of a metal bowl. The lack of the pointed "electrode" apparently allowed the generator to hold onto its charge longer then release it all at once.

JKJ