[GreenKeys] History - Why voltages and frequencies are chosen (5v & 3.3v logic, 6.3v filaments, 120/220 VAC, 50/60Hz etc)

[Keith Lueck]

I think 60 Hz was chosen b/c it's above the human perception for flicker - although you'd think that the thermal time constants of incandescent filaments (the only light source at the time) would've tended to smooth that out anyway.  Certainly a low frequency was chosen to minimize the rotational speed of large generating equipment.  IIRC, there used to be some industrial systems that used 25 Hz, here in the US.   Don't know why we ended up w/ 60 Hz and the Brits used 50...  

Early (mechanical) RF alternators had a nasty habit of flying apart - literally sending shrapnel everywhere b/c of their high rotational speeds and large numbers of poles....  but that's another story.   

JM2CW,

Keith

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