We were somewhere around Barstow, on the edge of the desert, when the
drugs began to take hold. I remember Jonathan
saying something like:

In recent musings about generators, UPS systems etc. I have been
thinking about transfer switches.

Is there much difference between a "transfer switch" such as this:
http://www.mowers-online.co.uk/itm01417.htm

and a suitably rated contactor such as this:
http://cpc.farnell.com/MC00148/elect...-k2-30a10230ac
(rating would need to be sized according to electrical load)

Obviously one comes in a nice box, with accessories - but as long as
the contacts break before they make, surely these will both do the
same job?

The Briggs changeover switch is all in one and being manual, is
relatively foolproof.

The contactor needs to be a changeover type - much pricier and you need
detection, timing and activation relays or circuitry to make it work
reliably and, more importantly, safely. It's not so much your safety,
it's the life of the bloke working on the power line that's important.
By the time you've built a safe changeover panel you will probably equal
or exceed the cost of the B&S switch and if your diy panel kills
someone, your arse will be in a sling.

I used to make these things for a living - trust me on this, it's not
worth making one from scratch unless you can fully test it and guarantee
it will fail safe. If I cocked it up, I was covered by my employer's
insurance - you could lose your house.

There are plenty of old changeover panels knocking around on the used
market as gensets are ripped out or upgraded, you could pick one up
cheaply enough, but since you're here asking, I must assume you don't
have the knowledge to fault find and rectify on a used one - and they do
develop faults.

Seriously - if you really want one, bite the bullet and go for the fully
manual B&S - it's much safer.
--
Dave
GS850x2 XS650 SE6a

"It's a moron working with power tools.
How much more suspenseful can you get?"
- House