Fire & Life Safety--Q&A on UPS

Dec. 19, 2012
Check the codes for power supply back up requirements

Q. My local fire inspector tells me that if I plan to use the existing phone line for my customer’s fire alarm system, I have to also install a Uninterruptible Power Supply (UPS) to keep the phone lines up. I have not ever had to do this before. What’s going on?

A. Prior to the 2007 edition of the National Fire Alarm Code, this communication issue was not addressed. Now that network reporting has become more common, the code has taken a look at all the links in the end-to-end communication methods employed in today’s high-tech industry.

There are four instances indicated in NFPA 72 where a UPS may be used. Where a computer system may be used at the protected premises to receive signals, such as a fire command center, standby power is required. NFPA 72 used to state that where a PC is used, the loss of primary power to the premises cannot allow required signals to be “lost, interrupted, or delayed by more than 10 seconds as a result of the primary power failure.” Ten seconds is for-ev-er when it comes to a computer. In these instances, a UPS was commonly used for standby power. However, you won’t find the term “computer systems” after the 1999 edition.

The next edition of NFPA 72, in 2002, provided more specific UPS requirements: “an uninterruptible power supply (UPS) arranged in accordance with the provisions of NFPA 111, Standard on Stored Electrical Energy Emergency and Standby Power Systems, shall be permitted to supplement the secondary power supply to ensure required operation during the transfer period.” [The old requirement for “at least 15 minutes” was changed to “during the transfer period”.]  This 2002 language remains basically unchanged through the 2010 edition (see

In our second example of UPS usage, the 2002 edition also inserted new language stating that if you are using “signal control and transport equipment (such as routers, servers) located in a critical fire alarm or fire safety function signaling path” as part of your fire alarm system, then you must provide power and supervision to this additional equipment. In the 2010 edition of NFPA 72, you can locate the rules for providing secondary power to the on-site network equipment used to transport fire alarm input and output signals throughout the facility in section “Operation on secondary power shall not affect the required performance of a system.”

Another major UPS section was inserted in the NFPA 72, 2010 edition for protected premise fire alarm systems and emergency voice communications systems. This edition began allowing a UPS system meeting NFPA 111 to provide primary and secondary power, as an alternate to the traditional “commercial light and power” which allowed batteries and generators for backup sources. This use requires application of all the same rules that apply to primary power for an FACP or FAPB panel, dedicated breaker, mechanically protected, etc., per section 10.5.5.

Check the codes

The last section of our UPS subject was also introduced in the 2010 edition as a requirement for adding backup power to customers’ communication equipment employing a data network or Internet (IP communicator) to transmit required signals off-site. However, this new section only requires compliance with the “capacity” requirements stated under 10.5.6, not the “mechanically protected” or “dedicated branch circuit” sections required of primary power for all commercial fire alarm systems. NFPA 72, A. explains: “This requirement is to ensure that communications equipment will operate for the same period of time on secondary power as the alarm control unit” [which is either 24 hours plus five minutes for most systems, or 24 hours plus 15 minutes for voice EVAC systems].

Therefore, if your Internet gateway (router-switch) is “listed” (merely for safety, not necessarily for fire alarm use), then a standard plug-and-go UPS system may be used. If your customer already has one of these in use, check it for capacity to see if it is capable of powering everything plugged into it. If you are asked to provide this UPS, you should know that there are two basic types of UPS units in general use.   “Illustration A” shows a standard, off-line UPS permitted by NFPA 72, for the customer’s on-site communication equipment. The AC sensing function causes the trickle-charged batteries to be switched into use should the primary power path be interrupted by loss of its commercial light and power source—like occasions where there is a local power outage. It is not intended that you supply a UPS for the infrastructure or pathway provided by the customer’s service provider! A more typical application is use the UPS to power the customer’s router/switch employed to access the Internet. While a UPS isn’t mentioned specifically in this section, it is the default choice for powering digital communication equipment. Also, under, meeting NFPA 111 isn’t required.

The true, online UPS unit in “Illustration B” is connected to the float charged batteries and charger during normal operation and continues working during common local power outages. The only switching to the backup path occurs when the charger, batteries, or DC to AC inverter fails. In those instances, the UPS sensor will switch in an attempt to use the commercial light and power source. However, NFPA 72 stipulates that the UPS be a “Type 0” (“Type 0” means zero seconds transfer time during a failure of the “commercial light and power”). An online type (or “true”) UPS is therefore required for compliance with “10.5.3 Power Supply Sources.” It must also be noted that by stipulating a NFPA 111 compliant “Class 24” UPS (“Class 24” means 24 hours of standby time), this new section doesn’t seem to require five or fifteen minutes of alarm time after the initial 24 hours of emergency operation, nor does it provide for an additional 20% battery capacity. I suspect this new primary power option will need to be cleared up in future editions of 72.