Backfeed protection is an essential safety mechanism against dangerous electric shocks and arc flashes as outlined in the quality standard BS EN IEC 62040-1:2019 Uninterruptible Power Systems (UPS): General and Safety Requirements for UPS.
Backfeeding refers to the flow of electricity in the reverse to its normal direction of travel.
Whenever there’s a mains supply failure or a fault within the UPS, current can start flowing back from the UPS to isolated circuits. Without the security of a backfeed protection device, this would be exceptionally dangerous to any person handling that circuit.
Different Types Of Backfeed Protection Devices
The EN 62040 standard stipulates that a backfeed protection device must prevent hazardous voltage from being present on the UPS input AC terminals.
Such devices can be located in two locations:
- Internal backfeed isolation device inside the UPS itself
- External input line isolation device (for hardwired UPS only), such as a magnetic contactor or circuit breaker with undervoltage release capability
Internal backfeed protection devices can be either mechanical (a relay or contactor-based solution) or electronic, where the UPS continually monitors the current flowing through the bypass and detects any faults, at which point it automatically shuts down the inverter.
External backfeed protection devices come in the form of a motor-operated circuit breaker or magnetic connector. Clear warning labels stating “Hazard Of Electric Shock, Explosion, Or Arc Flash” must appear on all switchgear access points and switching devices between the UPS and the external isolator.
Riello UPS incorporates internal backfeed protection as standard on its entire range of UPS solutions. However, in a bid to reduce costs, there’s a trend amongst some other UPS manufacturers to no longer incorporate complete internal backfeed protection.
This places ultimate responsibility onto electrical installers and contractors, who may not have specific product-related knowledge.
Further Reading:
- Whitepaper: Backfeed Protection In UPS Systems
- What are the main components of a UPS system?
- Why install a Bypass Isolation Transformer?
- What does an Automatic Transfer Switch (ATS) do in a UPS system?
- When should you use Emergency Power Off (EPO) with a UPS system?
- What does a Bypass Switch in a UPS system do?