Low Voltage Can Increase False Alarms in Life Safety Systems

Fire marshals and the National Burglar and Fire Alarm Association (NBFAA) say life safety systems can be rendered inoperable not only by lightning, but also by power surges from brownouts, blackouts, grid switching, and large equipment draw.

“Lightning storms rendered too many fire alarms inoperable, especially in multibuilding complexes connected with cable,” says Whitney Crahen, the veteran fire protection specialist who reviews fire alarm plans for the city of San Antonio, Texas. “When lightning hits, it can spread hundreds of feet until it finds the path of least resistance–all too often the highly conductive copper wiring that feeds into life safety alarm systems.”

Crahen’s solution has been to actively enforce NFPA 70 National Electrical Code(r), which requires surge-suppression devices on circuits that extend between buildings. “Proper surge protection for fire alarms is a requirement, and enforcing it will eliminate many future problems,” says Crahen.
The NBFAA also recommends surge protection. In its May 2000 brief titled “Surge Protection = Fewer False Alarms,” it states, “False alarms caused by lightning strikes are controllable through power and phone line protection. Surge protection has been used to protect sensitive electronics for many years. This protection can protect burglar or fire alarm panels from damage and prevent many false alarms.”

As system complexity and intelligence increase, requiring that parallel systems such as sprinklers, environmental controls, and critical condition devices be monitored, the probability of introducing damaging transients increases. Components are requiring voltages that are reaching new lows; this further increases the components’ susceptibility to transient damage and malfunction. A RS-485 data circuit running at three volts, for example, may be damaged or cause problems in the system when relatively small overvoltages are introduced. In contrast, the simpler analog components used in previous decades may not even have activated until the voltage reached 10 times that amount.

The power surges from brownouts, blackouts, grid switching, and large equipment draw can also wreak havoc with life safety systems mandated nationwide in stores, schools, offices, hotels, hospitals, and public spaces of all types, possibly subjecting these occupancies to increased scrutiny and fines from fire inspectors.

“Unmonitored systems could be unoperational for months–until they are discovered by a fire marshal or an alarm contractor,” says Craig Torrey, a fire inspector for the city of Anchorage, Alaska. Torrey notes: “Since a downed property without a life safety system would be at increased fire risk, the owner might be directed to fix the system in as little as 24 to 48 hours and may have to establish a continuous 24-hour firewatch by qualified personnel, such as off-duty firefighters in the interim, or face shutdown.”

Power fluctuations may also become more commonplace as a result of electrical deregulation, as was exemplified by the rotating outage numbers recently assigned to California Edison customers. The fluctuations may develop as supply and transmission issues are worked out in the “marketplace.”

David Burke, a senior executive at DITEK, a manufacturer of commercial, industrial, and residential surge protection, notes that when you see your VCR flashing 12:00 or your microwave giving the message “PF” (for power failure), that means there was a voltage spike large enough to reset your system. Also, Burke points out, if the lights dim and then return to full brightness when the building next door tests its backup generator, that’s a power spike as well. Air-conditioning units and other large equipment cause power fluctuations of a larger magnitude. For example, Burke recalls an Orlando, Florida, convention at which there was a 20-volt overcurrent each time the air-conditioner chillers kicked in. A demo unit with an audible alert and built-in surge counter registered the overvoltage each time the HVAC service cycled through. Even when systems continue to work properly, Burke explains, transients will take a toll on sensitive electronics over time and reduce the system’s life by as much as 30 percent.

Is it necessary to add aftermarket surge protection when most panels have the devices built into the control board? According to the May 2000 NBFAA brief: “By installing a surge protection device at the electrical outlet where the transformer is plugged in, the damaging transient can be bypassed to ground before it gets to the control panel, thereby greatly reducing the potential for false alarms or damage to the control board. The same is true when you install surge protection on the phone line prior to its entering the panel.”

The brief recommends that surge protection be added on both the AC (electric power line) and the phone line. “Many panels are zapped when transient voltage jumps the phone company’s lightning protector and sends 100s or 1000s of volts where only 48 volts normally reside,” according to the brief.

According to Burke, putting a surge protector on the AC power does not provide adequate protection. Only 30 to 40 percent of all damaging transients actually come in on the AC circuit, he says. “Most enter through the phone or data/communication circuits that run from building to building. Any wiring to the panel is a possible entry point for transients that should have adequate surge protection,” he explains.

What is adequate surge protection?

  • To start, surge suppressers should be UL-listed and installed a minimum of three feet from the control panel for a margin of safety. This usually requires aftermarket surge suppression. While most built-in protection meets minimum UL requirements, this usually takes the form of a small fuse or metal oxide varistor. Built-in protection allows damaging transients inside sensitive panels, which can disrupt function, including ground faults, trouble alerts, and communication failures. And if the voltage dissipation isn’t adequate, the damaged equipment may have to be replaced, which can cost tens of thousands of dollars in severe instances.
  • Use “surge protectors that self-restore after dissipating the surge harmlessly to ground,” recommends the NBFFA. This will prevent a false alarm, the NBFFA says. According to the NBFFA, “Self-restoring surge protectors wait for a predetermined voltage to be achieved, they then clamp the overvoltage, shunt it to ground, and automatically reset themselves to passive mode until it happens again.” These self-restoring protectors can stop hundreds of surges.
  • Buy the proper surge protector for your application; fire panels have different circuits that follow specific protocols. Using a generic model designed for scores of applications likely won’t work as well for your specific application.
    Burke warns against using the wrong surge protector on a circuit. He says, for example, that “a high-voltage surge protector used on a low-voltage circuit might not clamp until 30 volts or higher, at which point the circuitry will already be destroyed. Alternately, if you put a low-voltage surge protector on a high-voltage device, such as a horn/strobe circuit,” Burkes says, “the normal operating voltage of the horn/strobe may be seen as hostile current by the protection device. That’s a recipe for false alarms or ground faults.”
  • Choose surge suppressers that meet the latest codes, as fire codes at the national, state, and local levels may vary and are subject to change. At times, to meet specialized codes or mandates especially at the local level, Burke notes, it may be necessary to work with a manufacturer to build customized surge protection features.
  • Keep up with technological advances. “For convenience and continuous protection after a catastrophic surge, replacement smart module technology is worth looking into,” adds Burke. “This technology was originally developed for school and government use, where multiple buildings or campus-style system designs are common. It quickly identifies any sacrificed protectors with a red failure diagnostic light, which eliminates time-consuming, on-site troubleshooting. Its two-piece modular design enables quick replacement with no tools or test equipment: Just pull out the bad module, snap the new one into the base assembly, hit ‘acknowledge-reset,’ and the system is back in operation and fully protected.”
  • To protect data and video production devices from surges and “ghosting,” look into the new technology that protects the circuit from surge and isolates suppresser components from the circuitry of the system protected. The technology combines silicon avalanche diodes (SAD) with a diode bridge integrated into one component, providing protection and isolation in one package. With fewer components to fail and less circuitry on the PC board, this improves reliability in a more compact suppression design than typically available.

This article, written by technical writer Del Williams, was condensed. For additional information, email dburke@ditekcorp.com.

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