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Understanding Field Service Reports Part 3: Balancing UPS Loads

Our third entry in our series on field service reports concentrates on understanding balancing UPS loads. Before we dive in, let’s start by defining what it means to balance UPS loads. The definition of balancing UPS loads means to distribute loads evenly across the total output of the UPS.

Balancing UPS loads is normally recommended in order to avoid overuse on any one phase of the UPS equipment. In an example with a 3-phase UPS, the UPS puts out a certain amount of amperage, which can be separated into thirds of the total kVA rating across the three phases. When properly executed, balancing UPS loads avoids overuse and increases the useful life of the UPS by maximizing its output.

UPS units can be more susceptible to the issue of unbalanced loads than other equipment. Capacitors in UPS units are used 24 hours a day, so there is more demand on this equipment by its nature of use. Utility power also is not “steady state” power coming into most businesses.

“Steady state” power means an equilibrium condition of a circuit or network. Therefore, balancing UPS loads is necessary to avoid consistent power fluctuations.

If balancing UPS loads is ignored or not consistently done, there is plenty of risk to doing nothing. Some of these risks include:

  • Premature equipment failure due to overuse of specific components. This is the biggest risk and the most important reason to balance loads, as it is costly and also time consuming to replace equipment.
  • Problems syncing between the UPS inverter and the utility. Aside from load imbalances, this can potentially cause damage to the UPS and other connected equipment, instability on the grid, and potential power outages on the grid itself.
  • Potential fault overload. This situation occurs when the load is lower than the total threshold of the UPS, though the UPS “thinks” it is not, and it causes an issue, such as a transfer to bypass.

Many examples of failure related to improperly balanced loads can show up in a client’s field service reports. Some of these examples are:

Load Imbalance UPS FSR

This field service report shows load imbalance on each phase of a 3 phase unit.

  • Insulated Gate Bipolar Transistor (IGBT) or other component failures due to overwork.
  • Syncing problems due to load imbalance. In this case, the (equipment) does not “think” it is safe to transfer load to the UPS and keeps it locked in bypass, therefore rendering the UPS temporarily useless.
  • False overloads signaled when loads are within tolerance.
  • Failed components of the UPS due to overuse.



Clients should always be aware of the condition of any new or additional critical power equipment they maintain, and how adding equipment, and the power factor of that equipment, affects the total load on the UPS. Just because your UPS can handle the load of your original equipment configuration, doesn’t mean it will continue to handle that load in the same way as new equipment is added. It is very important to know at all times which devices are being supported, along with their corresponding load, on the UPS distribution panels.

Not sure about how to properly balance UPS loads? Contact the experts at QPS to help you determine the best equipment and configuration to keep your operation running smoothly.

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  1. […] can potentially fail, and what will be recorded on your report if they are needing replacement. Our third installment in the FSR series focused on understanding balancing UPS loads, the dangers of not consistently balancing them, and how examples of failure related to improperly […]

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