UPS Installation Safety Requirements (Smart Tricks to Improve Power Supply Reliability series)

Overview

IEC 62040-1 requires backfeed isolation of a permanently connected UPS within 15 s after loss of supply; a static switch alone is not adequate isolation. The paper compares internal backfeed isolation with external input-line isolation. With external devices, warning labels are required on all switchgear access points between the UPS and the isolator, responsibility moves to the installer, and the arrangement may force a dual feed with separate rectifier and bypass supplies.

A single external backfeed contactor shared by several static switches turns one switch failure into loss of all bypass lines; internal contactors per module preserve redundancy and also isolate a shorted static switch.

IEC 62040-1:2008 Amendment 1:2013 became mandatory in February 2016: the manufacturer must declare a rated short-time withstand current (Icw) or a rated conditional short-circuit current (Icc) with a specified SCPD. Withstand testing is mandatory unless the declared Icw is 10 kA or less, or the SCPD limits peak let-through to 17 kA or less.

Each bypass circuit must be independently safe at the available fault level; paralleling UPSs does not reduce the requirement per unit. Generator-parallel-with-transformer cases and future upgrades must be considered.

Key points

1. IEC 62040-1 requires backfeed isolation within 15 s after loss of supply for a permanently connected UPS; a static switch alone is not adequate.
2. With external backfeed devices, warning labels are needed on all access points between UPS and isolator, responsibility moves to the installer, and a dual feed may be forced.
3. One external contactor shared by several static switches loses all bypass lines on one switch failure; per-module internal contactors preserve redundancy.
4. Amendment 1:2013, mandatory from February 2016: declare Icw or Icc with a specified SCPD.
5. Withstand testing is mandatory unless declared Icw is 10 kA or less or the SCPD limits peak let-through to 17 kA or less.
6. Each bypass circuit must be safe at the available fault level; paralleling does not reduce the per-unit requirement; generator paralleling and future upgrades must be considered.

Using it in design

• Add backfeedProtection (internal or external), Icw/Icc rating and required SCPD to the UPS catalogue.
• Compare the prospective fault current at the UPS bypass input (worst case, including generator paralleling and future transformer upgrades) with the declared rating.
• If backfeed protection is external, add an isolator and warning-label requirement to the switchboard schedule.
• Warn when one backfeed device serves several static switches.

Who should read it

Electrical engineers designing UPS inputs and switchboard schedules, and commissioning specialists.

Related standards

• IEC 62040-1:2008+A1:2013
• IEC 61439-1/2

Publication details

Authors

Janne Paananen; Martijn Imming

Publisher

Eaton

Year

2018

Document language

English

Source type

Manufacturer

Access

Free to read

Licence

Copyright retained; citation only — the publisher’s terms apply to the original document

Citation