990-5992D-001

Backfeed Protection

DANGER
Hazard of electric shock, explosion, or arc flash
In systems where backfeed protection is not part of the standard design, an automatic isolation device (backfeed protection option or other device meeting the requirements of IEC/EN 62040–1) must be installed to prevent hazardous voltage or energy at the input terminals of the isolation device. The device must open within 15 seconds after the upstream power supply fails and must be rated according to the specifications.
Failure to follow these instructions will result in death or serious injury.

When the UPS input is connected through external isolators that, when opened, isolate the neutral or when the automatic backfeed isolation is provided external to the equipment or is connected to an IT power distribution system, a label must be fitted at the UPS input terminals, and on all primary power isolators installed remote from the UPS area and on external access points between such isolators and the UPS, by the user, displaying the following text (or equivalent in a language which is acceptable in the country in which the UPS system is installed):

DANGER
Hazard of electric shock, explosion, or arc flash
Risk of Voltage Backfeed. Before working on this circuit: Isolate the UPS and check for hazardous voltage between all terminals including the protective earth.
Failure to follow these instructions will result in death or serious injury.

An additional external isolation device must be installed in the UPS system. A contactor can be used for this purpose. In the shown examples, the isolation device is a contactor (marked with a MC1 for single mains systems and marked with a MC1 and MC2 for dual mains systems).

The isolation device must be able to withstand the electrical characteristics as described in Specifications.

NOTE: The 24 V source should be generated from the switchgear input source in single mains configurations and from both the switchgear input and bypass source in dual mains configurations.

Single Mains UPS and External Isolation Device

Single Mains UPS with Backfeed Box

Dual Mains UPS and External Isolation Device

Dual Mains UPS with Backfeed Box

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