Recently a question was raised about a mandatory annual exercise of each and all Life Safety and Critical Branch ATSs, to prove a minimum 10 second transfer time from a normal power failure until emergency power was available at the load side of each ATS.
According to NFPA 99, this type of exercise is not required unless, during any monthly/annual test of any one LS or CB ATS, there is a greater than 10-second transfer.
NFPA 99, Health Care Facilities Code, 2012 edition, 6.4.4.1.1.2: The 10-second criterion shall not apply during the monthly testing of an essential electrical system. If the 10-second criterion is not met during the monthly test, a process shall be provided to annually confirm the capability of the life safety and critical branches to comply with 6.4.3.1.
NFPA 99, 6.4.3.1: The life safety and critical branches shall be installed and connected to the alternate power source specified in 6.4.1.1.4 and 6.4.1.1.5 so that all functions specified herein for the life safety and critical branches are automatically restored to operation within 10 seconds after interruption of the normal source.
Be aware that when using an ATS test switch, and while normal power is still available, there can be a delay if an in-phase monitor is active in the ATS you are using to start your monthly test. Personally, I would use another switch.
Lastly, there is software now available which will verify “start wire connections,” passively.
