This part of IEC 62040 applies to uninterruptible power systems (UPS) with an electrical energy storage device in the d.c. link. It is used with IEC 60950-1, which is referred to in this standard as "RD" (reference document). NOTE UPS applications generally make use of a chemical battery as the energy storage device. Alternative devices may be suitable, and as such, where “battery” appears in the text of this standard, where applicable, this may be understood as “energy storage device”. When a clause is referred to by the phrase "The definitions or the provisions of item/RD apply", this phrase is intended to mean that the definitions or provisions in that clause of IEC 60950-1 apply, except any which are clearly inapplicable to uninterruptible power systems. National requirements additional to those in IEC 60950-1 apply and are found as notes under relevant clauses of the RD. The primary function of the UPS covered by this standard is to ensure continuity of an alternating power source. The UPS may also serve to improve the quality of the power source by keeping it within specified characteristics. This standard is applicable to UPS which are movable, stationary, fixed or for building-in, for use in low-voltage distribution systems and intended to be installed in any operator accessible area or in restricted access locations as applicable. It specifies requirements to ensure safety for the operator and layman who may come into contact with the equipment and, where specifically stated, for the service person. This standard is intended to ensure the safety of installed UPS, both as a single UPS unit or as a system of interconnected UPS units, subject to installing, operating and maintaining the UPS in the manner prescribed by the manufacturer. This standard does not cover UPS based on rotating machines. Electromagnetic compatibility (EMC) requirements and definitions are given in IEC 62040-2.