 or UPS, kicks in and begins a complex series of events designed to protect service in the office. First, it recognizes that the build- Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Telephony Telephony ing is now isolated and is on battery power exclusively. The batteries have enough current to power a typical CO for several hours before things start to fail. Second, technicians begin overseeing the process of restoration and of shutting down nonessential systems to conserve bat- tery power. Third, the UPS system initiates startup of the building's tur- bine, a massive jet engine that can be spun up in about a half hour. The turbine is either in a soundproof room in the basement or in an enclosure on the roof of the building (see Figure 3-29). Once the turbine has spun up to speed, the building's power load can slowly be shed onto it. It will power the building until it runs out of kerosene, but most buildings have several days' supply of fuel in their underground tanks. As Al Bergman, a data center design engineer and friend told me several years ago, "If we're down SO long that we run out of fuel, our problems are far worse than an office that's out of service." The cables leave the cable vault via fireproof foam-insulated ducts and travel upstairs to whatever floor houses the MDF. The MDF, shown in Figure 3-30, is a large iron jungle gym sort of frame that provides phys- ical support and technician access for the thousands of pairs of wire that interconnect customer telephones to the switch. The cables from the cable vault ascend and are hardwired to the vertical side of the MDF, shown in Figure 3-31. The ends of the cables are called the "cable heads." The vertical side of the MDF has additional overvoltage protection, shown in the diagram. The arrays of plug-ins are called "carbons;" they are simply carbon fuses that open in the event