Mains Smoke Alarms

Mains Smoke Alarms

Mains smoke alarms or mains powered smoke alarms are powered by the 230V from the mains wiring of the building. While replacement units and batteries can be easily changed, all wiring work should be completed by a competent person, such as an electrician, to ensure that it is safe and has been installed correctly. Mains smoke alarms can be wired into a special alarm wiring loop, which comes directly from the fuse box, or they can be fed from the nearest light fitting.

Retrofitting mains powered smoke alarms in older buildings, means that supply from a light fitting is often recommended and cheaper. However, care must be taken to ensure that the supply is wired correctly, and that the smoke alarm is not supplied by a ‘switched’ electric cable. Being wired to a ‘switched’ cable means that when in the ‘off’ position, the alarm may not function as it should and be only functional on its back-up battery. This is particularly problematic for sealed (Grade D1) smoke and heat alarms, as the battery cannot be changed, so the whole unit will need to be replaced if the battery is over-used.

Mains smoke alarms with any form of interlink (either hard-wired or using radio-interlink) fulfil BS5839-6 Grade D, which is required for extensions, new domestic buildings, let homes, HMOs, and many more applications.

Back-Up Batteries

All of our mains powered smoke detectors and heat alarms have back-up batteries, and therefore meet the Grade D requirements. Back-up batteries offer additional protection, by ensuring that the smoke and heat alarms still have a power supply, even if the mains power fails. Alarms with back-up batteries are either tamper proof devices for which the batteries last the lifetime of the alarm, or have and accessible battery compartment for the user to replace the alarms batteries within the alarm’s lifetime.

Replaceable back-up batteries (Grade D2):

These back-up batteries are often non-rechargeable, and specified as alkaline by the manufacturer. Usually, these require replacement every year or two, depending on how often they are used.

Non-replaceable back-up batteries (Grade D1):

These back-up batteries are a sealed-in rechargeable lithium cell, also known as a tamper-proof battery, which is designed to last the lifespan of the alarm. This type of back-up batteries are designed to trickle charge while there are connected to mains power and to provide full power, if the mains were to fail. These alarms are often found most useful in rented properties, in order to avoid tampering, deactivation, and the requirement for battery changes falling on the tenant.

Whether purchasing alarms fulfilling to Grade D1 or D2, the lifespan of any smoke or heat detector will usually be up to 10 years; the whole alarm must be replaced at this point. This is due to the sensor becoming less reliable, and more likely to falsely alarm.