Technically, our hardware can support an unlimited number of SSIDs. However, since each activated SSID (even when idle) has a negative impact on performance of all SSIDs, the maximum number of SSIDs any device can simultaneously broadcast is limited to 4.
To strike a balance between performance and advanced SSID features, the Plasma Cloud console allows to create unlimited SSIDs for your network and later assign them to individual Access Points (max 4 per device). By enabling some devices to broadcast SSIDs different from other devices, a wide range of custom setups can be accommodated.
Multi-SSID Performance Impact
For each enabled SSID, an Access Point needs to send additional beacon broadcast frames and respond to probe requests. These frames are part of the WiFi network discovery process, thus are required before any WiFi connection can be established. Consequently, each additional SSID causes more management & discovery frames to be in the air and leaving less time to transmit actual data. The team at Wireless LAN Professionals has published an excellent SSID overhead calculator visualizing the performance impact of multi-SSID deployments.