BCP (Business Continuity Procedure)

A progression of preordained tasks aimed at enabling an organization to continue serving its customers during and after a disaster.

back-up time

Time during which the UPS can supply the rated load with nominal-quality power while utility power is down. This time depends on the battery and the efficiency of the UPS. Typical backup ranges from five minutes to several hours.

battery (recombination)

Battery with a gas recombination rate at least equal to 95%, which means that no water need be added over the battery life. Usually called “maintenance-free.”

battery (tier-mounted)

Battery cell installation system whereby the cells are placed on tiered racks

battery (vented)

Battery with cells equipped with a filling port for distilled, demineralization water to top up the free electrolyte

battery cells

The interconnected battery elements that supply electrical power created by electrolytic reaction

BMS (Building Management System)

System used for controlling and monitoring building utilities and systems. It is generally composed of sensors, actuators, and programmable controllers connected to a central computer or computers equipped with specific software.


The act of taking the UPS offline and feeding the critical bus from utility power. This can be done either manually, for service, or automatically in the event of failure or overload.


Device associated with the rectifier and used to supply the battery with the electrical power (DC current) required to recharge and/or float charge the battery

circuit breaker (battery)

DC circuit breaker that protects the battery of a UPS

electromagnetic compatibility

Possibility of a device to operate normally when installed near other devices, given the disturbances emitted by each device and their mutual sensitivities

EOL (end of life)

Term for when a product has reached or is near the end of its supported life

filter (phase-shift)

Filter used to reduce, if necessary, the overall distortion from current harmonics injected into the utility upstream of a UPS by its rectifier/charger. Filtering is superior to that of a traditional filter of the L or C type.


UPS subassembly that recomposes a sine-wave output (regulated and without breaks) using the DC current supplied by the rectifier/charger or the battery. The primary elements of the inverter are the DC/AC converter, a regulation system, and an output filter.

inverter (off-line or stand-by)

UPS configuration in which the inverter is parallel mounted to the load supply line and backs up the utility. This configuration offers a substantial cost reduction but is applicable only to low outputs (those under 3 kVA), because it results in an interruption lasting up to 10 ms during transfer and does not filter inrush currents.

inverter (on-line)

UPS configuration in which the inverter is in series mounted between the utility and the load. All power drawn by the load passes via the inverter. This is the only configuration used for high outputs.

kVA (kilovolt amperes)

A measurement of apparent power expressed in thousands

kW (kilowatts)

A measurement of real power expressed in thousands

load (linear)

Load for which voltage form and current form are similar or in phase

load (non-linear)

Load (generally with a switched-mode power supply) generating major harmonic currents. Current wave form is out of phase with the voltage wave form. Ohm’s law is not applicable. The impedance changes with the applied voltage.

load power

Apparent power (Pu) that the UPS inverter supplies under given load conditions. It is less than or equal to the rated output (Pn). The ratio Pu/Pn defines the percentage load of the inverter.

maintenance bypass (wraparound)

Manually operated series of circuit breakers creating a make-before-break (preferably) parallel path around the UPS and static switch. Once energized, all load power is supplied through the bypass, and the UPS can be completely de-energized, allowing any service activity. 

micro-outage (or micro-interruption) 

Total loss in the supply of power for 10 ms

MTBF (mean time between failures)

Mathematical calculation of the duration of normal operation of a repairable device between failures. The result, expressed in hours, is an indication of the reliability of the device.

MTTF (mean time to failure)

Mathematical calculation of the duration of normal operation of a non-reparable device, i.e., for which a MTBF is not possible. The result, expressed in hours, is an indication of the reliability of the device.

MTTR (mean time to repair)

Mathematical calculation (or statistical average if available) of the time required to repair a device

noise level

Acoustical decibel level of a source of noise, measured according to the applicable ISO standard

output (rated)

Apparent power (Pn) that the UPS can deliver under given load conditions (power factor = 0.8).

percent load

Ratio between the power drawn by the load and the rated output of a UPS system (Pu/Pn). Sometimes referred to as the load factor.

power factor (l)

Ratio between the active power (true power), P, supplied to a load and the apparent power, S, supplied to said load by an AC power supply

power source (alternate)

Backup source used in the event of a mains failure. The connection time and the duration of the source depend on the type of source used.

power source (safety)

Power source for loads defined as critical by applicable safety regulations. This supply must not be affected by a mains failure and is generally separate from other supplies.


UPS component that draws on the incoming power required to supply the inverter and to float charge or recharge the battery. The alternating input current is rectified and then distributed to the inverter and the battery.

redundancy (active)

Parallel UPS configuration in which several UPS units with equal outputs are parallel connected and share the load. In the event one UPS unit fails, the other units pick up its share without any interruption in the supply of power to the load.

redundancy (standby)

UPS configuration in which one or several UPS units operate on standby, with no load or only a partial load, and can immediately back up a faulty UPS unit by no-break transfer of the load, carried out by a static switch


Reliability of a power system refers to the probability of its satisfactory operation over the long run. It denotes the ability to supply adequate electric service on a nearly continuous basis, with few interruptions over an extended time period.

RPO (recovery point objective)

The amount of data that can be lost before the business is unable to recover the system in question

RTO (recovery time objective)

The amount of downtime that can be tolerated in the event of a disaster

safety installation

Installations supplying electrical equipment that may have a direct effect on the safety of users and must therefore remain energized even in the event of a mains failure. In general, characteristics concerning the power supply and conditions for transfer to the safety source for such electrical equipment are covered by applicable regulations.

static bypass switch

Power-electronics device that can be used to switch from one source to another without interruption in the supply of power. In a UPS, transfer is from mains 1 to mains 2 and back. Transfer without interruption is possible because there are no mechanical parts and the electronic components have ultra-fast switching capabilities.

Thevenin generator

For a given load, it is possible to consider the power supply as a voltage generator, called a Thevenin generator.

tolerance in percent

Limit for allowable variations for a given quantity, expressed as a percent of the rated value

UL (Underwriters Laboratories)

Underwriters Laboratories is a non-governmental, non-profit product safety certification and compliance organization. Following certification, a product may bear the UL label.

UPS (uninterruptible power supply)

An electrical device providing an interface between the main power supply and sensitive loads (computer systems, instrumentation, etc.). The UPS supplies sinusoidal AC power free of disturbances and within strict amplitude and frequency tolerances. It is generally made up of a rectifier/charger and an inverter together with a battery for backup power in the event of a mains failure.

UPS (parallel with redundancy)

A UPS made up of several parallel-connected (n) UPS units with equal output ratings (P) and each equipped with its battery. If one unit fails, one or several of the others pick up the resulting excess load. If a UPS has a rated output and is made up of n + k units, k is the level of redundancy for the entire set.

UPS (parallel without redundancy)

A UPS made up of several parallel-connected (n) UPS units with equal output ratings (P) and each equipped with its battery for large loads. The total output is equal to the number of units multiplied by their individual output. In this configuration, no UPS unit is redundant.

UPS (single)

A UPS made up of a single UPS unit (rectifier/charger, inverter, and bypass) and a battery

voltage (float)

DC voltage applied to the battery to maintain its charge level. This voltage depends on the type of battery, the number of cells, and the manufacturer’s recommendations