Maintenance Bypass feature

Maintenance Bypass provides the ability to power the load from an unprotected side path when the UPS is disconnected from the circuit for service or repair.

Some UPSs have a Maintenance Bypass circuit internally, while others do so using off-line wiring.

Internal Maintenance Bypass

The figure above shows the isolation system in a high power UPS and three phases on-line equipped with an internal maintenance bypass path.

This diagram shows that although the power units of a UPS can be completely isolated during the maintenance (during this time it supplies power through the Maintenance Bypass route energy), it is still in the isolation section. The UPS has electricity and connections to its inlet / outlet terminals.

External Maintenance Bypass

The figure below shows an UPS with an External Maintenance Bypass with three isolators connected to the UPS system. This combination is often called the ‘wrap-around’ route because it is outside the main block.

This figure clearly shows that when the SW1 and SW2 are open and the SW3 is closed, the UPS will completely exit the circuit. This method completely isolates the UPS from the power supply and can even replace faulty UPS with healthy UPS. In this method, the circuit breakers in a cabinet are usually the same. It is designed to come close to the basic UPS equipment.

Bypass Interlocking

There must be a mechanical connection between the Maintenance Bypass and the UPS separator keys to ensure that the load shift between the two energy sources (UPS output and city electricity) is controlled. The first is to ensure uninterrupted power transmission, the second is to prevent damage to the inverter output (when powered by the inverter) in order to prevent damage to the city’s power supply.

The isolator keys inside the UPS have non-replaceable mechanical connections that prevent the keys from being misplaced, but appropriate maintenance or electrical switches must be used for the Maintenance Bypass keys installed outside the UPS.