Fire Protection

Cracking the Code

Code changes force new notification technologies to conserve energy while reducing costs

• By Charlie Fisler
• Sep 01, 2006

ONE of the top attributes that building owners, managers and electrical contractors look for when choosing fire notification devices is compliance with local, state and federal building codes, which are created by organizations such as the International Code Council and the National Fire Protection Association. As these organizations implement and modify existing codes, organizations such as Underwriters Laboratories modify or develop product performance and safety standards that support the codes. Manufacturers, in turn, develop new products that comply with the codes and product standards.

Voltage ranges are now clearly specified and the worst-case current across the range must be used for the rating on the product. Surge-current allowances also have been reduced, requiring many manufacturers to now tighten up their designs.

Code Changes for Notification Devices
In May 2004, UL implemented significant changes in its standards for notification appliances. One of its goals was to force manufacturers of horns and strobes to publish operating specifications uniformly, making them easier to understand and easier to compare competitive offerings. Voltage ranges are now clearly specified and the worst-case current across the range must be used for the rating on the product. Surge-current allowances also have been reduced, requiring many manufacturers to now tighten up their designs.

The notification device ratings that emerged from the UL changes were more conservative than its predecessors, causing the current ratings on many devices to increase significantly, even though the devices themselves remained unchanged. Designers already accustomed to using worst-case ratings in their calculations encountered little or no impact, while those who typically worked with nominal values ran into trouble. The designers found themselves faced with increased installation expense because they had to either reduce device count on the loop or increase wire size to handle the higher currents.

Code Changes for Complete Systems
UL is currently implementing the ninth edition of UL 864, Control Units and Accessories for Fire Alarm Systems, which includes numerous additions and modifications to how fire alarm panels and systems are tested. While these changes extend into many areas unrelated to notification, many of the changes do affect notification. To a large extent, these changes mirror the changes made in the notification standards, with the intent of ensuring compatibility between the control panel and the notification devices that are connected to it. Under the new ninth edition rules, regulated panels must operate over the same voltage range as the notification devices and be able to supply worst-case currents, including surges, to the notification circuit. The end result is that the notification circuit design is a little simpler and less likely to fail under worst case conditions.

Obviously, it is still important for the designer to plan the notification circuit carefully. Wire size, wire length, number of devices on the loop and the current draws of each device must be taken into account. If loops are overloaded, then the voltage at the far end of the loop may drop below the rated voltage of the notification devices, causing failure in an emergency situation. Voltage drop calculators at the Web sites of leading manufacturers can simplify the layout process.

Beware of Complications
System designers also must carefully review the published current ratings for devices they plan to use because some manufacturers still publish specifications for their products that show nominal current draw, rather than worst case. The nominal specifications may look more attractive on paper, but the notification system may fail to work under worst-case conditions. When in doubt about the rating, refer to the installation manual that came with the product or the UL listing card itself, since these documents are controlled by UL and must provide the true rating of the product.

Another factor that complicates the design of a system is notification appliance synchronization, meaning all strobes flash simultaneously and all temporal pattern horns sound together. Synchronization is typically provided by pulses sent along the power line and detected by the individual devices attached to the circuit. The synchronization protocol may be incorporated into the panel software or provided by a module connected between the panel and the notification devices. There is no universal synchronization protocol, so each notification device system is unique to the manufacturer's product line.

Meeting UL's synchronization requirements is a lengthy process, as extensive testing is required to verify that individual products will work under all conditions. This testing must be repeated for every panel that is to be listed as compatible with a given product line. Again, system designers should review compatibility listings carefully during the device selection process to make sure that all of the components in their design will work together in the overall system.

The Net Result of the Changes
In the short term, the UL changes have led to considerable confusion in the field and, in many cases, increased installation expense. For replacement parts, changes in ratings potentially mean that a given device can't be used to replace itself because its published current rating has increased. In the long term, the new rules will be beneficial to the system designer and help to provide more reliable systems. Uniform specifications that are easier to understand will ultimately lead to lower costs and fewer problems with finished systems that don't work as expected.

Things to Come
Current draw is the main driving factor in the evolution of notification devices. Reduction of current means more devices on a single pair of wires, smaller wire sizes and lower cost power supply systems in the panel. While the straightforward method of reducing current through more efficient design of the notification devices plays a role in the evolution, the improvement has been achieved in other ways, as well. Devices with user-selectable candela settings now offer additional candela settings, for example, so that the candela level can be more closely tailored to the room size. Reducing the candela setting means reducing the current.

Ultimately, installers should be aware of new technologies, what they promise and how they will be impacted by those changes. Today's technology provides fire alarm systems with greater flexibility and the ability to offer improvements in fire and life safety, while reducing installation costs of complete systems.