Customers often ask us to explain the difference between a surge protector and an uninterruptible power supply (UPS) — and which device is better suited for their environment.

The fact is that neither UPS nor surge protection devices (SPD) alone will provide complete protection forcommercial systems. The most effective installation is ensured by utilizing a combination of both forms of power conditioning.

Surge protectors (or suppressors) provide just that: a line of defense against surges, which are short-term high voltages above 110 percent of nominal. They are often associated with lightning strikes and utility switching, but in fact, 80% of surges originate inside a facility. These occur due to electrical switching or other disturbances created by various devices within the building. Regardless of the source, increased voltage from surges can damage components in electrical systems, such as computers, networks, and process control equipment.

Even if nothing is immediately destroyed, the increased strain over time can cause premature failure of expensive components. It’s important to note that surge protection will not keep your equipment operational during a blackout, but damaging surges occur much more frequently than power outages. A properly designed backup power system should always incorporate a cascaded surge-protection approach (i.e., a two-layered approach) working in conjunction with a UPS. The first surge unit (upstream SPD) mitigates the brunt of the surge energy while the second SPD reduces any remaining surge energy to an inconsequential level.

A UPS provides second-level protection against catastrophic surges; it should never be considered a primary surge-protection device. It also continually regulates incoming voltage and provides an internal battery that allows connected equipment to continue running even if the power supply is cut. To keep your electronic devices functioning even when power is unavailable, you need a UPS and often a backup generator as well.

How do you apply these devices coherently? Surge protection should be installed on the utility side of your UPS, ideally on the bypass line.

Surge protection installed on the utility side of a UPS will also help protect the UPS. A dramatic surge event, such as a lightning strike, can be associated with over 20kV and 5kA. The typical let-through voltage of a surge device at this surge level would be roughly 2000V, which is still high enough to cause equipment damage. To eliminate this, we install an upstream unit and allow the UPS to mitigate the effects of the remaining surge energy, i.e., driving the final let-through voltage down to around 200V, which is well below the point that would cause damage.

Additionally, an SPD must be installed between the UPS output and the load distribution system. This is especially true if the load panel is located far from the UPS. The greater the distance, the higher the likelihood that an internally generated surge could impact the load.

So, which form of power protection is best suited for your environment? The answer is both. Critical servers, workstations, PCs, POS and VoIP equipment, and other key business devices are protected by attaching a UPS, ensuring they can function during a power outage and, if needed, shut down cleanly if power remains out for an extended period. Surge devices are also required to protect both critical equipment and the UPS itself.

For further explanation of common power-related questions, check out our UPS FAQ page.

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