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What Size UPS System Means

Having a clear understanding of power terminology is crucial when selecting the appropriate amount of power. Power capacity is commonly expressed in kilowatts (kW) and kilo-volt-amperes (kVA). For example, a 1 kVA uninterruptible power supply (UPS) can handle 1,000 volt-amperes.

The formula for AC power is “watts = volts x amps,” which may lead one to believe that a 1,000VA UPS can handle 1,000 watts. However, UPS systems have inefficiencies, and some power is lost in the transformers and circuitry, known as reactance. As a result, most UPS manufacturers specify a “power factor” used to calculate the maximum wattage the UPS can handle. Therefore, the formula becomes “watts = volts x amps x power factor.”

For instance, a 1kVA UPS from N1C has a power capacity of 900 watts for connected equipment, indicating a power factor of 0.9.

Operating a 1 kVA UPS at 100% of its capacity (900 watts) is not recommended as it can cause the UPS to fail due to a short circuit, rendering it useless during outages. Instead, it is better to use a lower wattage, such as 450 watts, which would result in the UPS running at 50% of its power. This not only prolongs battery runtime during outages but also increases the UPS’s lifespan by reducing the need for maintenance and repairs.

kVA Sizing FAQ 3kVA-40kVA

How much power do I need?

To establish the maximum load capacity for your UPS, it’s crucial to examine the wattage rating on the label of each device you intend to connect to it. After adding up their wattage usage, it’s essential to leave a 20% margin of error. Therefore, you should only run the UPS system at 80% of your calculated maximum load. This allows for a safety buffer during peak conditions, like when some devices may require a sudden surge in wattage usage, such as when a hair dryer is initially turned on. Adhering to this guideline will prevent overloading the UPS and ensure that it runs smoothly.

UPS runtime

Another crucial consideration is your battery runtime requirements.

Suppose your equipment is located on a different floor or wing of your office building, or at an offsite location. In that case, you may need a longer battery runtime for your UPS to safeguard your load and keep your devices operational. Conversely, if you’re aware that your building has a generator that will swiftly activate during an outage, you might be able to manage with a shorter battery runtime.