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PAS 63100 vs BS 7671 A721

AJJewsbury

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.

Parents

  • Thanks guys. Yes, the use of "proper" cartridge fuses is becoming much more common with LiFePO4 due to the high PFC (well beyond what traditional automotive types can handle) (NH000 types seem popular) although some fuses seem to have a mechanical blown fuse indicator mechanism, which I wonder might compromise the seal around the fuse element? "Hose batteries" (especially the "rack mount" types) seem often to incorporate DC MCBs rather than fuses though ... which presumably aren't sealed at all.

    I'm not sure the voltage differences are as clear as they used to be "48V" (i.e. 51.2V LiFePO4) systems have been common on boats for a long time and seem to be making their way into the less weight conscious side of the caravan sector (i.e. "RV"s) in increasing numbers - most usually when feeding inverters for the 230V side. If you look at the likes of Victron systems it seems very clear that the stationary off-grid / mobile / new EESS sectors are merging very quickly. Likewise a lot of EESS system seems to be based on 48V (51.2V) systems.

    Even the ventilation requirements don't seem to differ much (e.g. A721.55.3.5 has ventilation requirements that look very similar to the PAS's) (even if they're sometimes not adhered to in practice in the caravan/RV world).

      - Andy.

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  • Thanks guys. Yes, the use of "proper" cartridge fuses is becoming much more common with LiFePO4 due to the high PFC (well beyond what traditional automotive types can handle) (NH000 types seem popular) although some fuses seem to have a mechanical blown fuse indicator mechanism, which I wonder might compromise the seal around the fuse element? "Hose batteries" (especially the "rack mount" types) seem often to incorporate DC MCBs rather than fuses though ... which presumably aren't sealed at all.

    I'm not sure the voltage differences are as clear as they used to be "48V" (i.e. 51.2V LiFePO4) systems have been common on boats for a long time and seem to be making their way into the less weight conscious side of the caravan sector (i.e. "RV"s) in increasing numbers - most usually when feeding inverters for the 230V side. If you look at the likes of Victron systems it seems very clear that the stationary off-grid / mobile / new EESS sectors are merging very quickly. Likewise a lot of EESS system seems to be based on 48V (51.2V) systems.

    Even the ventilation requirements don't seem to differ much (e.g. A721.55.3.5 has ventilation requirements that look very similar to the PAS's) (even if they're sometimes not adhered to in practice in the caravan/RV world).

      - Andy.

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  • in reply to AJJewsbury
    AJJewsbury said:
    Likewise a lot of EESS system seems to be based on 48V (51.2V) systems.

    Potentially, there is a rather inventive (or one could say cynical) reason for that. Take a look at Regulation 3(b) of the Electrical Equipment (Safety) Regulations 2016 (as amended). I do accept, however, that the General Product Safety Regulations 2005 (as amended) would continue to apply.

    However, more importantly, from PAS 63100 and BS 7671 perspective, lower voltage (for the same power delivery) means higher current ... and therefore when you move above about 30 V DC, increased arc flash risk, meaning fuses inside (or at the perimeter) of the enclosure makes most sense. 

  • in reply to gkenyon

    If product design really is going down a particular route drive only by regulation side-steps, then I'd expect 71 Volt or 1501 Volt systems to be popular with a gap in between. If there is much evidence that is the case, then really it suggests the regulations are not having the desired effect and should be either repealed if they are unnecessarily restrictive and not needed or amended to actually cover the case of equipment that is being made and used if there is a real risk to mitigate.
    But, given these are international products, a more serious question, are there similar limits in other countries ?

    Mike

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