How Do I Know Whether to Use 2-Wire or 4-Wire Smoke Detectors?

You will know whether to use 2-wire or 4-wire smoke detectors based on your wiring needs. This is an important decision for anyone who owns a hardwired system. Most DIY users choose 2-wire smokes since they are easier to setup. But 4-wire smokes offer greater flexibility in choosing a zone.

System sensor 2wt b 2 wire smoke detector with fixed heat sensor

If you have existing smoke detectors, you will usually want to find some way to integrate them into your security system. This may be possible using a wireless takeover module, such as an Encore FireFighter FF345. But if you are purchasing new smoke detectors, then choosing the best type for your needs is very important. If a user has a hardwired system, then they will usually choose wired smoke detectors. These include both 2-wire and 4-wire smokes. But if they have a wireless system, then using wireless smokes is often much easier.

If you have a hardwired alarm panel, then you will most likely be integrating hardwired smokes. The thing to understand about hardwired smokes is that the power to these devices must be dropped as an alarm is being cleared. This is necessary for resetting the smoke detector. Both 2-wire and 4-wire smoke detectors must be powered down to reset. But the process for accomplishing this differs greatly between the two different types of smokes. This factor is ultimately why most DIY users select 2-wire smokes over 4-wire smokes.

The nice thing about 2-wire smokes is that they can be automatically reset by the panel once an alarm has been cleared. Many hardwired panels, including the Honeywell VISTA Panels, use Zone 1 as a supervised zone that is specifically designed for 2-wire smokes. These normally-open smokes are wired in parallel with an end-of-line resistor (EOLR). When an alarm is cleared, power to Zone 1 is briefly cut. This allows every smoke to automatically reset following an alarm. The panel will reset he smoke detectors and stop them from sounding on its own, with no additional equipment needed.

Meanwhile, 4-wire smokes require much more equipment than 2-wire smokes. These smoke detectors require a relay that temporarily cuts power to the smoke detector when an alarm is cleared. If the panel has a built-in relay, then that can be used. Otherwise, a user will need to add an external relay. Beyond that, a 2nd relay is also required for smoke power supervision. An additional power supply may also be needed if the panel cannot supply enough current on its own. However, there is one main advantage to using 4-wire smokes. The advantage is that 4-wire smokes do not require a special designated zone, and they can be used with nearly any hardwired zone terminals.

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