Why Squirrels And Electrical Systems Should Not Mingle
Originally published in Stanford White’s FYI Letter, a memo to clients.
During a recent summer, when the temperature outside was hovering around a hundred degrees in the shade, an incident occurred at a large eastern North Carolina hospital that gives all of us in the power distribution business reason to look closer at the way we see the world.
The facility in question is supplied from the utility by an automatic primary selective transfer switch. If power on one side of the switch fails, the switch automatically switches to the other side. Apparently a squirrel (believed to be Sciurus Carolinensis – there was not much left for the forensic boys to identify) became involved with the primary supply. During the incident the transfer switch transferred between sources several times; the lights in the hospital were observed to flicker but the power was not off for long enough for the emergency generators to start. No one thought much about the incident.
Later in the week it became necessary to run the hospital generators to support some maintenance work on the normal electrical system. It was discovered that none of the three generators would transfer to the emergency parallel bus. Not only would the system not operate in the automatic mode, but also the manual mode would not work. Apparently the squirrel had caused major damage to the facility’s automatic parallel switchgear while attempting to escape the late summer heat.
What is the moral to the story? If you notice anything peculiar happening to the electrical system or equipment in your facility, you should immediately verify the proper operation of the various components of the essential electrical system. While the above incident had a good ending – the equipment was repaired before it was needed in a real emergency – it was only the chance need of the generators that detected the problem. It is not too difficult to imagine a real power outage and a hospital in the dark from what appears to be no problem at all.