Backfeeding relates to electricity flowing in the reverse direction to its usual direction of travel.
In terms of uninterruptible power supplies, current could feed back from the UPS to isolated circuits in the event of a mains failure or a fault with the UPS itself. Without the necessary backfeed protection in place, it would be extremely dangerous for any service engineer to handle a circuit in such circumstances.
This whitepaper examines the safety standards and regulations UPS installations must comply with to ensure suitable backfeed protection is in place.
According to the BS EN 62040-1:2019 Uninterruptible Power Systems (UPS): General and Safety Requirements for UPS quality standard, backfeed protection devices “must be capable of preventing hazardous voltage or energy from being present on the UPS input AC terminals”.
In practice, this involves installing backfeed isolation devices either inside the UPS or externally, for example a magnetic contactor or circuit breaker with UVR (undervoltage release) functionality.
Such backfeed isolation devices can be electronic or mechanical – this whitepaper explores the differences (and the pros and cons) of each type and their use.
Backfeed Protection And Impact On Fault Tolerance
As well as their primary purpose of preventing hazardous voltages downstream, backfeed protection devices also often provide a secondary role in boosting overall UPS system resilience.
This is because the backfeed protection device isolates the UPS output from the incoming supplies, which provides a safeguard against any faults within the static switch.
Normally, if a static switch faults, power feeds between the UPS output and the supply. Such an unexpected current flow could lead to an overload.
But with backfeed detection installed, the UPS will detect this current and immediately open the device to isolate the fault, eliminating a single point of failure from the system and enabling the UPS to keep protecting the critical load.
Backfeed Protection As Standard?
While Riello UPS incorporates internal backfeed protection as standard across our entire range, some manufacturers don’t.
In an effort to reduce costs, there’s a recent trend where some suppliers place the burden of complying with EN 62040 in the hands of electrical installers and contractors, who may not have the necessary product-specific knowledge.
That’s why it is essential to clarify whether any backfeed protection devices will need installing before buying and commissioning any new UPS system.