Standing Up to the Elements
Outdoor notification appliances must face extreme heat/cold; water spray testing required
LOCAL
and national fire codes oftentimes require notification appliances in areas that are very inhospitable to electronic devices. These devices are installed in areas that are unheated, unsheltered and completely exposed to the elements -- snow, sleet, driving rain or blazing sun.
These conditions demand a product designed -- and stringently tested -- to operate flawlessly during emergencies, even though it is installed in less-than-optimum conditions. Just as important, this type of installation requires a unit that is compatible with the control panel for the facility's interior audible notification or voice evacuation devices, including horns, horn/strobes, strobes, speakers and speaker/strobes.
Underwriters Laboratories outlines the stringent requirements of UL 1638 for strobes, UL 464 for horns and UL 1480 for speakers. All UL-listed notification products for outdoor use must be able to operate in environments that range in temperature from -40 to 151 degrees Fahrenheit. The UL standards also require that the products operate properly after enduring a rigorous one-hour water spray test. In the case of the speaker, the product must be operational after it is completely submerged for 24 hours and then dried out.
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UL Max Denotes Current Ratings
In May 2004, Underwriters Laboratories revised UL 1971, regulating how operating currents are to be measured and how voltage ranges are to be listed and published.
Historically, fire alarm system designers used 24-volt current draw for computing voltage drops on audible and visible (AV) circuits. However, voltage drops based on 24-volt current draw only provide an illusion of lower current draw, placing the reliability of the circuit in question.
UL recognized confusion within the industry because AV appliance circuit calculations were being performed with the wrong current draw. They saw the potential for circuit failures.
Seldom is the voltage for AV devices exactly 24 volts. This is due to the natural voltage drop in the circuit. Depending where the device is located on the circuit, the voltage could drop to its lowest operating voltage. Despite UL's efforts, some manufacturers are still printing 24-volt current draws on their data sheets. Current draws based on 24 volts can confuse industry professionals who don't realize that these specifications shouldn't be used for circuit calculations.
This means that because device currents vary with applied voltage, the only way to ensure the power supply will provide enough current to the entire circuit is to measure the current for each device at its highest value.
Based on this logic, UL now requires that current ratings published in installation manuals are to symbolize the maximum current draw (UL Max) over the listed voltage range. These true current ratings will:
- Reflect device power usage more accurately.
- Ensure compatibility between devices and outputs on the control panel, regardless of manufacturer.
- Present comparable current draw data amongst manufacturers.
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Although limited in application, outdoor notification devices may be installed in a wide range of settings that vary in luminescence and in size of the coverage area.
For example, exterior notification devices for parking garages, stadiums and balconies will not have the same protection parameters. Therefore, it is important to look for a product line with multiple available candela options and for products that have the capability to recognize and self-adjust for either 12- or 24-volt operation.
For strobes, products that have field-selectable candela settings, including 15, 15/75, 30, 75 or 110 cd, are ideal. Typically, strobes can be operated at 12 volts for the 15 and 15/75 candela settings, while 24 volts is usually required for 30-, 75- or 110-cd selections. These also should be installed in conjunction with a weatherproof back box.
Outdoor notification devices also should be designed to emit low total harmonic distortion and wide frequency response. This allows for the highest levels of intelligibility to provide an accurate and clean broadcast of evacuation messages. Speakers should feature field-selectable 25- or 70.7-Vrms operation at 1/4, 1/2, 1 and 2 watts.
While the need for outdoor notification devices is limited to select applications, it is important to remember that more often these days, safety codes are being recognized as the minimum for safety. That creates a great potential in the market for this important type of product.
This article originally appeared in the February 2006 issue of Security Products, pg. 24.