10 Considerations When Selecting Power Supplies

May 23, 2011
Calculating the power requirements of each system's components and how they integrate with one another is critical

Want to select and install the power solutions that are most appropriate for your installation? It is critical to calculate the power requirements of each system’s components and consider how they integrate with one another. This information is essential in determining the selection of the power supplies that will be required to keep your system running efficiently over the long run.

As part of the evaluation and selection process, end-users should consider the following 10 issues when choosing power supplies:

1. Compliance: Each state, county and even municipality has its own requirements regarding agency approvals. There are a variety of compliance issues, such as UL listings for video, access control and fire/life safety that need to be adhered to, along with specific local codes. It is imperative that you check with the local AHJ (Authority Having Jurisdiction) to find out what agency listings you must conform to during the design process to ensure your system is in compliance before installing any components and power supplies.

2. Analyze Existing Systems: Before starting the design process, a comprehensive analysis of the facility’s security systems are required to determine feature sets of the power supplies. Up until recently, selecting power supplies often required the need to combine various components to deliver the functionality desired. For example, does the system need battery back-up in case of a power failure? All that has changed with the introduction of a new breed of integrated power solutions that deliver both cost and installation advantages.

3. Determine Power Requirements: Determine the number of devices in the system, the power requirements for each, and their physical location. This information is necessary to determine the size and quantity of the power supplies, how many devices they will run, and where they will be physically located. It is always a good rule of thumb to add 20 percent more power to your calculations as a safety factor.

System-Specific Steps:

4. For Fire Alarm Systems: Power consumption is a primary issue when configuring fire alarm systems. One of the most critical considerations centers on how alarm signals are activated. When an alarm condition exists, Notification Appliance Circuits (NAC) are output from the Fire Alarm Control Panel (FACP) to activate notification appliances such as strobes and horns commonly used to indicate an emergency situation. The number of notification appliances to be activated, along with the current draw for each device and its distance from the FACP, sometimes makes the deployment of NAC Power Extenders a necessary system component.

For example, in large commercial installations or multi-tenant buildings, the total current draw of the notification appliances may well exceed the power output of the FACP. In these instances, one or more NAC Power Extenders need to be installed for those notification appliances where the wire runs are too long for the FACP to deliver sufficient power.

Features to consider when selecting a NAC Power Extender:

• Number of Class A or Class B indicating circuits.
• Total power rating (ex. 6.5 amp, 8 amp or 10 amp).
• Number of Aux. power outputs with or without battery backup.
• Programmable outputs (synchronization, Temporal Code 3, and Input to output follower mode)
• Enclosure capacity (room for battery backup; ample knockouts and room for wiring)
• Agency approvals, including UL, MEA, CSFM and FM.

NAC Power Extenders are available with programmable features that maintain horn/strobe synchronization by either producing internally generated sync protocols utilized by major signal manufacturers, or by electronically repeating these sync protocols from the FACP outputs.

5. For Access Control Systems: NFPA requires that any device or system intended to actuate the locking or unlocking of exits must be connected to the facility’s fire alarm system so that all doors will release when an alarm signal is generated.

To comply with NFPA requirements, there are two classifications of locking devices that need to be addressed: Fail-Safe and Fail-Secure. Fail-Safe locking devices, such as magnetic locks, release when they lose power. Fail-Secure locking devices, such as electric strikes, unlock when power is applied and may be manually released from inside a secured area. This determines the manner in which your power solution removes or provides power and the sequence and timing of each action.

Some systems may also require the installation of panic hardware devices. Upon activation, the devices’ high current power demand can reach up to 16 amps, but not all power supplies can handle these high inrush currents. As a result, you need to specify a power supply designed for this type of application. Some operate a single panic hardware device and require optional modules to add features like timing functions, output relays, fire alarm disconnect or power for additional panic hardware devices. Therefore, these "base" models almost always require additional modules to deliver the functionality you need and may not be cost-effective. More advanced models offer integrated features and supply a comprehensive solution.

6. For Video Surveillance Systems: Video’s constant operation typically places high demands on power supplies. These video power supplies need to deliver a clean and consistent source of 24VAC or 12VDC power to ensure uninterrupted operation. Depending on the video component’s specific power requirements and its location, there is a wide selection of power supplies. They can be wall- or rack-mounted, designed for use indoors or outdoors, and feature AC or DC outputs. Configurations typically range from 1 to 32 outputs and some models offer additional features like 115 or 230VAC input with current ratings as high as 25 amps, power LED indicators, and PTC or fused protected outputs. Certain models provide both 24VAC and 12VDC to power both types of cameras simultaneously.

7. Temperature: Temperature differences due to change of seasons, day or night can often be extreme and can have a direct affect on the performance of both the video components and the power supply when located outdoors. Enclosures for outdoor power supplies should be rated to withstand the elements.

8. Ground Isolation: In some cases, cameras are not equipped with internal electrical ground isolation. Should this be the case, it is important to specify a power supply with this feature.

9. UTP Transceiver Hubs: The use of structured cable has been an inexpensive method for transmitting video and data between head-end equipment and camera systems. The introduction of UTP transceiver hubs with integral camera power make it possible to transmit both video and data via structured cable along with the power needed for the cameras. This is accomplished via video balun/combiners which pass the power and data to the camera and send the video back to the head-end equipment. These devices greatly reduce the time and expense of configuring and installing separate components while helping to minimize bandwidth requirements for large systems.

10. Find Help: Selecting power supplies is a complex process given all the individual equipment and system variables, functionality requirements and compliance issues to be considered. The safest practice to follow is to consult with your dealer/installer and draw on their expertise and field experience.

Paul Rizzuto is Technical Sales Manager for Altronix Corp. All trademarks are the property of their respective owners.