How long to backup batteries have to last?

[Guest JohnFree]

What would be the time required for Standby battery Back up in fire alarms for Warden Aided premises which is manned 24 hours a day.

Regards

John

[Tom Sutton]

Is it the battery in the control panel (CIE) of a BS 5839 part 1 system which should last 4 years. Is it domestic smoke detectors which could use standard batteries which last about 1 year or you can get ten year batteries. All will give a warning indication when the voltage falls below the optimum level.

[Guest JohnFree]

Thanks, Tom

How many hours does the battery have to last after mains power failed?

Regards

John

[Tom Sutton]

In most parts of the United Kingdom most failures in public electricity supplies are relatively short in duration and prolonged failures exceeding 24 hours are uncommon. The recommendations in this standard are based on this assumption, and for category M and Category L systems the duration of standby batteries need not therefore normally be capable of supplying power to the system for longer than 24 hours. A greater duration might, however be necessary if the probability of failure of a public or private electricity supply for periods exceeding 24 hours is considered to be significant.

As you can see from the extract from the British standard above the minimum is twenty four hours but could longer depending on circumstances.