On Wed, 06 Jul 2011 15:06:08 -0700, Rich Grise
wrote:

Spehro Pefhany wrote:

I wonder why 400Hz though, rather than 360 or something that's an
integer multiple of 60Hz.. perhaps ...

Nobody knows, but at least 2,150,000 people think they have an
answer:
http://www.google.com/search?hl=en&q...t+power+400+hz

Cheers!
Rich

You can get MUCH better results if you learn to use advanced search
options and better keywords (such as 'history'). Also, if you search
books as well as the web-- but I don't see anything remotely
authoritative yet.