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I have just recieved a call from a hospital maintenance man.He says that when they start their onsite generator.The entire radiology department goes down, and when they bring the power back up their wall clock runs backwards. To fix the clock they unplug it and then plug it back in. Any idea's. THANKS


I'm not clear on what happened.  Did they lose power to the radiology department while running on the emergency generator?  Is the radiology department supposed to be on emergency power?  If so, then what tripped to shut them down?  

As for the clock, I wouldn't worry about it too much.  These old clock motors typically have a shaded pole motor and can sometimes get confused about what direction to run.  Most ac motor driven clocks can run backwards if you give the second hand a little spin in the CCW direction.  A single-phase motor can run either direction - only the starting mechanism provides are direction preference.  


AS far as I know when they exercise their generator all of their computers and other equipment goes down. then everything has to be started back up. The gentleman also said that when they start the generator. The lights on emergency power only blink. So i take it that they have some sort of battery power also. But as for radiology nothing trips the equipment just shuts down.


First off, you may want to buy your maintenance contact a clock that is powered by a single AA-cell battery if he will agree to install it in place of the existing AC clock.

Second, as far as electric-service continuity for radiological gear, it’s necessary to determine what is legally required, whether it is designed properly and operating as designed.  In many regions inspection and enforcement of electric-system reliability in healthcare facilities is above and beyond the usual domain of building-inspection and fire-safety officials.

One very general reference may be IEEE Std 602 [white book.]


When utility power is lost, normally everything will shut down until the emergency generator starts and picks up load, unless a particular load is on a UPS.  For a hospital, the emergency generator must start and load up within 10 seconds.

I suspect the radiology wing loses power because it is not provided with emergency power.  Even in a hospital, not everything is powered by the emergency generator, only life safety related systems.  


dpc is probably right, but just in case, another issue may be the settings on the transfer switch. It sounds as if possibly the generator may be shutting down slightly prior to the switch transferring back, causing a slight loss of frequency. Switch-mode power supplies are sensitive to frequency drop and can cause problems, so most will shut down rather than allow corrupt data in microprocessors. Other hospital systems are probably on a UPS so they don't see it, but radiology is one of those not required to be on one. That may explain the clock phenomenon as well. I had this problem in hospital sterilization rooms, another non-critical area. When we went from relay logic to PLCs for the sterilizer controls, we had this come up a lot before we figured out what it was about.

Quando Omni Flunkus Moritati

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