vax thermostat?

[Dave Martindale]

The three VAXes in the math building at Waterloo are protected by a very
simple overtemperature shutoff.  The main circuit breakers feeding the
electrical panels which supply the machines' power are a special sort
known as "shunt-trip" breakers.  They will trip on overcurrent like
any ordinary breaker, but can also be tripped by the momentary application
of 120V to a pair of terminals on the breaker.  We have thermostats which
close at a set temperature (25 or 30 degrees Celsius) located in the machine
rooms and connected to these trip terminals.  Thus if the airconditioning
dies for any reason at any time, all power to the machine will be shut
off before the room temperature gets high enough to cause damage.
We haven't had any airconditioning failures yet, but it's cheap insurance.