The EP2500 has two downstream RS-485 ports that are each capable of supporting 32 downstream devices. Then another 32 network-based downstream devices are also supported.
The EP1502 has a single downstream RS-485 port that is capable of supporting 32 downstream devices. It can also support 32 network based downstream devices.
The EP1501 supports a total of 16 downstream devices, up to 8 of these can be on the downstream RS-485 port and the remaining on the network.