The low-voltage power supply is the unsung hero behind every video, access control, intrusion and fire system.

When systems integrators select the right power supply, they ensure the proper and reliable performance of all life-safety systems. Not choosing a unit carefully is tantamount to committing a critical mistake. One that can impact system operation and commonly result in rework, with the accompanying nonbillable labor and liquidated damages.

For the security industry, power quality has long been an immense issue. A power supply that is not suitable for a specific application has the capability of rendering a system ineffective. It can cause system slumps and shutdowns, not to mention burn up expensive control units.

The most common issues that impact power supplies are: excessive heat; surges, spikes and other line transients; ground problems; voltage drops that under-supply input energy; over-drawing the supply, taxing it beyond its design parameters; and noise that reduces video quality.

When selecting a power supply for a security system, the significant facets to consider range from the technical to the practical. And don’t fail to consider new government and regulatory requirements.

Selection Criteria Centers on Maintaining Reliable Performance
Most systems integrators tend to look for amp and voltage ratings as indications of an adequate power supply, and that is exactly why some falter in the process of choosing wisely. There is a better way.

First and foremost, a power supply should deliver clean, consistent power to system components. There are several factors that hinder superior performance to varying degrees. Let’s take a close look at some of these dynamics.

Load condition – Current traveling through long wire runs can result in significant voltage drop due to the inherent resistance of wire. Thus, voltage drop is defined as the amount of voltage loss that occurs through all or part of a circuit because of this resistance.

If the right wire gauge is calculated, voltage drop can be greatly decreased.

Consider an installer that places a surveillance camera 1,000 feet from the originating power supply, only to discover the camera won’t function. The installer takes a meter reading and finds 20V of current at the load end, while the camera requires 21V. Often the installer will mistakenly blame the power supply for not driving through and delivering sufficient voltage without correctly factoring voltage drop.  To determine the proper selection of wire gauge, integrators can reference a voltage drop table (see example on page 74 of the December issue).

Integrators should always use these types of calculators available from equipment manufacturers to determine current needs and wire sizing for the system devices to be connected.

The National Electric Code (NEC) says to load circuits to a maximum of 80 percent of the rated capacity. A good rule of thumb is to size for peak demand – not average loads – and to consider the power factor of loads.

Many times, peak loading occurs at system startup or when all devices are operating at the same time. Also, remember to consider the likelihood of future system upgrades. Finally, some experts say to add 30 percent to your answer as a safety factor.

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