Our S4K-C UPS can be bypassed using either the Dynamic Bypass Switch (Internal Bypass Switch) or the Maintenance Bypass Switch.
The Dynamic Bypass Switch is built into the UPS and automatically transfers the connected load to AC utility power if the UPS experiences an overload, an over-temperature situation or a UPS failure condition. Manual transfers can be accomplished by pressing the Standby/Manual Bypass button just once on the front panel of the unit. This Dynamic Bypass uses a MAKE-BEFORE-BREAK (MBB) Transfer Switch which establishes a new connection path before the previous contacts are opened. It momentarily parallels both sources to provide a seamless transfer of the load from one source to another during the transfer period.
The Maintenance Bypass Switch is an external bypass which is available on the Power A/C Distribution (PAD) options of our S4K-C UPS. It allows for complete shutdown and isolation of the UPS for scheduled maintenance or UPS replacement without powering down the connected load. Our Maintenance Bypass uses a BREAK-BEFORE-MAKE (BBM) Transfer Switch which breaks the first set of contacts before engaging the connection to the second source. This takes a maximum transfer time of 4-6 milliseconds.
The technical question and answer above were featured in the April 25, 2012 edition of the SolaHD Wednesday Weekly online newsletter.