I've been pondering battery systems at home and noticed an apparent discrepancy between PAS 63100 and BS 7671. I know the two are for (slightly) different situations (a home on wheels vs a home on solid ground) but I'm presuming the underlying physics is similar - they're both (usually) ELV rechargeable battery systems in domestic type situations (indeed the differences between the two are getting more and more blurred, as traditional "off grid" system are finding their way into traditional houses as battery storage systems).
A case in point is the position of the main battery fuse (or CB) - traditional caravan rules prohibit this entirely from the battery locker - presumably on the assumption that lead acid batteries are liable to liberate hydrogen gas and a fuse (especially the open automotive types) or a circuit breaker is very likely to create an arc when opening the circuit - and arcs and explosive hydrogen aren't a good mix. Maybe there's also a worry of acidic vapours from the battery corroding contacts. BS 7671 A721 agrees with that (A721.533.1.8). PAS 63100 on the other hand seems to take the opposite approach "6.1.1 Batteries shall comprise non-combustible enclosures containing the overcurrent protection
with the cells/monoblocs." - backed up by Figure 1. While I can see both pros and cons to both approaches - it does seem somewhat inconsistent.
Perhaps differing battery chemistries are an influence? I presume A721 was written with only lead-acid in mind - whereas the world has moved on and the majority of EESS these days use lithium (or Sodium) which have a much lower chance of evolving hydrogen (or acidic fumes) ... but as I understand it they can still emit hydrogen in some fault conditions - quite possibly the very conditions you'd want the fuse to open under.
Or are there any other reasons for the difference?
- Andy.
