Choosing a UPS (Uninterruptible Power Supply) for your phone system or other telecom / data equipment can seem like a daunting task. In this post, I’ll tell you how to navigate the choices to select the UPS that meets your needs.

UPS Types

There are many different types of UPS systems. How can you choose the model that’s right for your application?  Some are more appropriate than others for small- and medium-sized businesses (SMBs).  Cost, power conditioning and capacity are primary decision factors. The most common UPS systems used by SMBs are:

  • Standby
  • Line interactive
  • Double conversion on-line

Please Stand By

The Standby UPS is small, efficient and inexpensive. However, the Standby unit applies building AC directly to the load most of the time so you are not getting any power conditioning at the device. The Standby UPS is often used to power individual PCs. They typically have  capacities ranging from 50-500VA. An example is the APC Back-UPS.

Going On Line

The Line Interactive UPS is very common for SMBs, providing conditioned power to the load. Capacities range from 500VA to 5000VA (5kVA). They are not as inexpensive as Standby units, but they are more appropriate for protecting your more costly servers, phone systems, etc. An example is the APC Smart-UPS.

Double or Nothing

The Double Conversion systems are more appropriate for larger loads, having capacities ranging from 5kVA to 5000kVA. So, you might use this UPS type when your load consists of several devices like a data center application. An example is the APC Smart-UPS Online.

Watts A Volt-Amp??

When you read your electric bill, you can see the power you are consuming. Typically, they will use kiloWatt-hours (kW-h) to measure your usage. The kW-h is equal to 1,000 Watts used for an hour. The Watt is the standard measure of actual power consumed by a device. If you look at a piece of electrical equipment, it will usually have a tag that shows maximum power consumption for that device in Watts. Remember that this is a ‘maximum’ value. You may want to look at a spec sheet for the equipment to get a more realistic ‘typical’ value. It would be easy if UPS systems were specified by the number of Watts they would support. But things are never that easy. UPS systems are sized in Volt-Amps. Well, if you remember your basic Ohms law, a Watt is equal to 1V x 1A, so they must be the same thing, right?

Watts the Difference?

Not exactly. The Volt-Amp is a measure of apparent power usage. You can determine the Volt-Amp rating for a piece of equipment by multiplying the voltage by the current drawn by the device. You might think this is just a semantic difference. For many cases, you’d be right. Watts and Volt-Amps for many kinds of electrical devices are identical. However, when it comes to many devices in your IT department (including your phone system), W and VA ratings can differ significantly. When they do differ, the VA rating will be higher. Why do they differ for these devices? Because of their switching power supplies.

It’s All in the Percentages

It is essential that you size your UPS so that neither the W or VA maximum is exceeded. Say you want to power a load of 400W. You find a UPS rated at 500VA. You should be good to go, right? Not so fast. Typically, the actual Watt rating of the UPS is 60% of the VA rating. So the 500VA UPS will only support a 300W load. Always use 60% of the VA rating on the UPS to determine the load (in Watts) for which the UPS can be safely used.

Other Considerations

When sizing a UPS for a phone system, use either the ‘maximum’ power rating of the equipment (for a conservative estimate) or adjust the ‘typical’ value for the number of ports and devices connected to the system (for a more realistic estimate). When you connect multiple devices to the same UPS system, you can usually feel more comfortable using typical values, as peaks will tend to average out among the different devices. It is more appropriate to use maximum values when sizing a UPS for a single device. And remember, those UPS batteries don’t last forever. Having a UPS with old batteries is as bad as having no UPS. Especially here in New Mexico, heat is the enemy of battery life. Check your batteries periodically for swelling and plan to replace them every 3-5 years.

You can find more details on UPS types here. Click on the link for UPS Systems (pdf).

What UPS systems do you use at your facility? How have they handled our many power outages here in New Mexico? Share your thoughts in the comments.

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