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Whether you are adding a new UPS unit to your facility or replacing an old one, one of the firrst things you’ll need to determine is the needed UPS capacity. Units range in size from small enough to protect a single computer to large enough to protect an entire city – that’s not much help when you’re trying to find the right size for your facility; there’s too much choice!

So how can you narrow your choices down and select an appropriately sized UPS unit?

How to Factor Your UPS Needs

  • Make a list of every piece of equipment that needs to be protected by the UPS. It’s easy to jot down the big pieces, but remember, even a monitor needs power. Include everything to make sure you have appropriate power when you need it.
  • Determine the amps and volts for each piece listed. Find these ratings on the labels on the backs of the equipment. Determine VoltAmps (VA) by multiplying amps x volts. If the power ratings are listed in watts, you can convert watts to VA by dividing watts by the Power Factor (PF).
  • Multiply the VA by the number of pieces of equipment to get the VA subtotals.
  • Add the VA subtotals together.
  • Multiply the total by 1.2 to get the grand total. (This step accounts for future expansion).
  • Use the grand total to select your new UPS. Choose a UPS with a VA rating that is higher than your total VA requirements.

A Word About kW and kVA

The fact that UPS systems don’t have a standard rating system doesn’t make it any easier to appropriately size a UPS. Some UPS units are rated in in kilowatts (kW) and others are rated in kilo-volt-amperes (kVA). Kilowatts, represents the useful power available while kilovolt-amperes represents the apparent power. Learn more about kW and kVA, here.

The important thing to note is that neither the kW nor the kVA capacity of the UPS can be exceeded or the unit will fail and you won’t have power. That’s why it’s so important to account for the power needs of every piece of equipment that is to be protected by the UPS. A general rule of thumb is to plan to run the UPS at 80% of tis actual rated capacity. That will give you enough wiggle room to accommodate peak loads and handle growth before you need to upgrade your unit again.

One Last Consideration

One last consideration comes into play if you plan to use the UPS with a generator. Some UPS designs have different electrical characteristics from generators. You’ll need to have an electrical engineer double check both the UPS and the generator to make sure the generator won’t stall when the UPS kicks on in an emergency.

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