The turbo pumping CP4 tripped off this afternoon.  As found, the turbo controller was de-energized and the scroll baking pump had isolated itself and remained running.  The power switch for the turbo controller doubles as a circuit breaker and was found in the OFF position.  This switch only has two states ON and OFF as opposed to the more common ON, OFF and "TRIPPED" states ->

None of the power cords appeared to be disturbed and my conclusion is that the turbo had likely tripped due to over temperature.  This pump is surrounded by hot, baking surfaces, has no fan but is, instead, cooled by a local chiller circulating 30C water through its electric motor.  For weeks leading up to today, the relevant temperatures have been non-changing and the turbo has been 80C at its inlet flange and 45C - 48C internally (as per the thermocouple read by the controller).  I think that the internal "trip" threshold is 50C.  Ambient conditions are getting warmer ->

I was able to restart the turbo and reach full RPM while the backing pump remained isolated.  Once at full RPM, I valved-in the baking pump.  Everything seems normal.  As a precaution, I added a small fan and folded back some of the aluminum foil to expose the turbo+RGA hardware and allow some, minimal, convection cooling.