4.7.3.3 OperationThe manufacturer shall, except when the UPS is intended for operation by a layperson,provide guidance on the level of competence necessary to operate the equipment. This may include reference for operators to undergo training or to be qualified and authorized to enter restricted access locations.4.7.3.4 MaintenanceExcept for minor routine maintenance that may be performed by the operator, safety instructions to be used during maintenance of the UPS are normally made available only to service persons.4.7.3.5 Distribution related backfeedFor the purpose of warning the electrical service person against backfeed situations not caused by the UPS but that may arise when a particular load fault is present while the UPS operates in stored energy mode or while unbalanced loads are supplied through a particular power distribution system, e.g. an impedance grounded IT system, the installation instructions for permanently connected UPS shall require the fitting of a warning label– by the UPS supplier, at the UPS input terminals and– by the user, on all primary power isolators installed remote from the UPS area and on external access points, if any, between such isolators and the UPS whena) the automatic backfeed isolation (see 5.1.4) is provided external to the equipment orb) the UPS input is connected through external isolators that, when opened, isolate the neutral orc) the UPS is connected to an IT power distribution system (see 1.6.1/RD).The warning label shall carry the following wording or equivalent.Before working on this circuit- Isolate Uninterruptible Power System (UPS)- Then check for Hazardous Voltage between all terminalsincluding the protrctive earth Risk of Voltage BackfeedNOTE Backfeed protection against faults occurring in the UPS is described in 5.1.4.4.7.4 Main voltage adjustmentThe provisions of 1.7.4/RD apply.