The Honeywell 4208SN Zone Expansion Module increases the number of hardwired zones that can be used with a wired polling loop system. It will only work with polling loop systems, and it will increase the number of available zones by eight. The 4208SN supports serial number programming only.
Zone expansion modules are very important for hardwired systems. If no zone expanders are added, a commercial polling loop panel, such as a VISTA-128BPT or VISTA-250BPT, will only be capable of supporting a small number of hardwired sensors through its on-board terminals. But by adding some zone expanders, these commercial-grade systems can provide support for an impressively large number of hardwired zones. Please note though that the 4208SN can only be used by panels with a polling loop. It will not work with non-polling loop alarm systems.
There are some key reasons as to why being able to use a polling loop offers advantages when setting up a wired system. Most users will benefit from the more flexible wiring options. For non-polling loop panels, the keypad bus is used for expansion. Depending on the panel, the keypad bus only offers a wiring limit of somewhere between 1,500 and 2,000 feet. But the polling loop can provide a much further wiring distance of up to 12,000 feet. Another difference is that polling loop expanders like the 4208SN only require two wires to connect with the system. But a non-polling loop expander needs four connecting wires.
The SN in the 4208SN stands for "Serial Number". This is because it can only be used for serial number programming. The module will not support traditional dip switch programming. This is important to remember if the user has an older alarm panel that relies solely on dip switch programming. In that case, the user should use the Honeywell 4208U Universal Zone Expansion Module instead of the 4208SN. The 4208U also works best when the panel is only capable of supporting 128 wired zones or less. This is the case with the VISTA-128BPT. In order to maximize the number of wired zones for a VISTA-250BPT, a user will need to add 30 of the 4208SN Expansion Modules.
Keep in mind that the 4208SN does not include any wiring. In order to connect the module with the system, a user will need to add their own wires. And of course, the user will also need wiring for setting up any sensors that are used.