"Spehro Pefhany" wrote in message
...
On Mon, 14 Feb 2011 14:04:57 -0600, John Fields

I would be extremely reluctant to f*ck with the design of an
commercial elevator. A stuck contact, for example, might do Bad
Things, and there could be consequences:
http://www.jurispro.com/category/ele...calator-s-312/

That said, fairly recently I did modify the design of a residential
elevator somewhat (they didn't do a very good job, as it turns out)
but the regulations for residential elevators are essentially
nonexistent, and I'm comfortable with assuming the liability for my
changes in any case. The relays used to switch the motor etc. were at
least quite robust and were not the source of the problems (more of a
symptom when they chattered).

Yeah, liabilities understood.
Was chatting with the elevator tech that comes once a month and seems to do
nothing more than scratch his head. Mentioned that would be interesting to
see if a cheap PLC would replace the rack of 29 relays. He offered to send
me the regulations for elevator design. Will see if he delivers.

Hydraulic elevator, 2 floor.
Reversing contactors wired for powering the pump 3 phase for up and shorting
the motor for down to give drag.
Rest of the system consists of low voltage relays running the logic and a
handfull of relays that handle the 110/208 vac interfaces.