Which calculation is required to ensure alarm system operation during an extended power failure?

Which calculation is required to ensure alarm system operation during an extended power failure?

• A. Voltage drop
• B. VA rating
• C. Power factor
• D. Resistance

Answer: (B)

Sizing backup power for an alarm system hinges on the total apparent power the system will draw. This is expressed in volt-amperes (VA). To ensure operation during a power failure, determine the system’s VA demand by summing the VA of all loads (or, if you only know watts and power factor, sum watts divided by the PF for each device to get VA, then add them up). The backup source—like a UPS or battery—is rated in VA, so you must match or exceed the system’s total VA to guarantee continued operation for the intended duration. Voltage drop and resistance relate to wiring losses and component heating, not to sizing for extended outages. Power factor matters because it links watts to VA, but the essential step is establishing the total VA requirement and ensuring the backup can supply at least that amount.

Sizing backup power for an alarm system hinges on the total apparent power the system will draw. This is expressed in volt-amperes (VA). To ensure operation during a power failure, determine the system’s VA demand by summing the VA of all loads (or, if you only know watts and power factor, sum watts divided by the PF for each device to get VA, then add them up). The backup source—like a UPS or battery—is rated in VA, so you must match or exceed the system’s total VA to guarantee continued operation for the intended duration.

Voltage drop and resistance relate to wiring losses and component heating, not to sizing for extended outages. Power factor matters because it links watts to VA, but the essential step is establishing the total VA requirement and ensuring the backup can supply at least that amount.