Standards

BS 7827:2019, in our own words

What the parts of BS 7827:2019 cited in our articles say, explained in plain English, with the clause and table numbers so you can check them.

These are our explanations, in our own words, of the clauses our articles rely on. We do not reproduce the standard's text: the clause numbers are there so you can check each one against your own copy. They support the published standard and the judgement of a competent engineer, and replace neither.

The standard itself: BS 7827:2019 at BSI. Checked against BS 7827:2019 on 24 September 2026.

Clause 15: back-up power, and why sports grounds differ

The discussion that opens this clause explains that the sources disagree on how long back-up power should last. The Green Guide works to 3 hours at sports grounds, so that an event can run to its end after a mains failure rather than be abandoned in front of a crowd. BS 5839-8:2013, PD CEN/TS 54-32:2015 and BS EN 50849:2017 work to 24 hours of quiescent operation followed by 30 minutes of emergency operation.

Table 2: recommended back-up power

For sports grounds, Table 2 recommends back-up power for 3 h whether or not a generator is fitted, with a duty cycle of 3 h rather than 30 min, because the duty cycle follows the expected length of the event, including getting the crowd in and out. For voice alarm coverage in general it keeps 24 h (6 h with generator back-up) and a 30 min duty cycle.

Cited in: Peukert's law, and why the internet's version oversizes voice alarm batteries above 20 Ah

Clause and table numbers refer to BS 7827:2019.