According to one aspect, embodiments of the invention provide a method of operating a UPS system having a first UPS, the method comprising powering on the first UPS, detecting a first signal at a first I/O of the first UPS using a first detection circuit of the first UPS, detecting a second signal at a second I/O of the first UPS using a second detection circuit of the first UPS, based on a status of the first signal and a status of the second signal, configuring the first UPS to operate in one of a master mode of operation and a controlled mode of operation.