How many transfer switches does an emergency power supply system require?
According to the 2002 version of the National Electrical Code, any transfer switch that serves “Emergency” class load must serve no other loads. If loads other than Emergency class are to be served by a standby power source, at least two transfer switches will be required. Furthermore, a larger number of smaller-ampacity transfer switches provides greater protection against branch circuit failures, so “more and smaller” is a good general principle.
