A colleague of mine says he read in bs7671 that equipment in lofts may need an Arc Fault Detection Device.
I can't find such a requirement, perhaps someone here has heard of it?
A colleague of mine says he read in bs7671 that equipment in lofts may need an Arc Fault Detection Device.
I can't find such a requirement, perhaps someone here has heard of it?
when charging the charger uses voltage to determine battery charge state - too long/thin cables and charger/inverter will think the battery is full well before it is, and empty while there's still some charge in it. (There are methods to compensate for that, but they have limits - e,g. max 1V difference).
This isn't always the case with modern battery management systems, which can measure voltage, temperature, etc, and regulate current, locally at the battery, and communicate local metrics to the EEMS at the inverter via EIA-485 (modbus/canbus or similar) - it really depends on the manufacturer's approach.
The big problem with DC, is arc flash, and arcs being drawn on disconnection, meaning fire protection of the wiring system etc. is more difficult.
Given the advances in miniature circuit breaker design and manufacture since DC was last widely used in domestic installations, I didn't see that as the biggest problem.
I was thinking the bigger challenge comes from the protection arrangements which need to accommodate challenges like high source impedances / low fault currents insufficient to operate over-current protection when being supplied from current-limited devices like PV panels or possibly some inverter systems, multiple sources of supply when cables are connected to a potential source at each end, and potentially a variety of earthing arrangements for the DC systems.
But then it's all still relatively early days for this technology, unclear as to where the standard arrangements will converge, it could go down the route of DC cabling between panels on the roof, central hybrid inverters, remote outdoor batteries. Equally it could go down an AC route, local inverters near the panels (in the attic, or micro-inverters on the roof) with batteries with integral inverters, with DC limited to the roof space and battery enclosure, retaining AC cabling around the home.
See PAS 63100:2024 https://www.bsigroup.com/en-GB/insights-and-media/insights/brochures/pas-63100-protection-against-fire-of-battery-energy-storage-systems/
It's not actually a British Standard, and isn't law, but a lot of people are taking note of it.
It's not actually a British Standard, and isn't law, but a lot of people are taking note of it.
It is a standard published by BSI, but it's not a British Standard.
Most standards are voluntary, and not mandated by law. Even 'designated standards' are not mandatory ... there is an alternative approach, although the designated standards route, especially if supported by independent testing and endorsement, is probably the safest route for products 'placed on the market'.
Worth noting, though, that, contrary to popular opinion, BS 7671 is mandated by legislation for certain installations (including those with Solar PV or battery storage). See ESQCR Regulations 21 and 22 ... or ESQCR (NI) Regulations 22 and 23.
Given the situation that standards are generally voluntary ... and therefore PAS 63100 is little different in that respect ... what one would have to be sure of if choosing not to follow it, is how one might respond when asked "why did you do something contrary?" if anything went awry.
LiFePO4 seemingly are much more difficult to get into a thermal runaway state than other types
Quite so ... but as far as I'm aware, all of the electrical energy storage system battery fires we've had in the UK are LiFePO4, starting with the Carnegie Road fire in Liverpool ?
I also believe at the moment these are limited to grid-scale (probably because of the storage power install base). Who knows what statistics will show as the storage power install base increases in other categories of installation?
Indeed - that was one of the "methods" I obliquely referred to (others include separate voltage sensing cables from the charger/inverter to the battery) - but even if the charger/inverter knows better the state of change, it doesn't necessarily mean it can compensate for it entirely - a Victron system I'm looking at at the moment for instance is only capable of increasing the charge voltage by 1V (0.5V for each of the +ve and -ve cables?) and I suspect in discharge mode there will be similarly be limits to what the inverter will accept.
- Andy.
Im more used to dealing with and looking at electric vehicle battery fires, or certainly the impact of those. Now I appreaciate lots of diffrent types of Lithium battery packs in the market place, so others on here may be better placed to say if Im making same comparrison or not. When an electric vehicle Lithium battery starts exothermic runaway. Before there is any serious heat or naked flames, the battery discharges various very nasty gases including flammable gases. Those that have been close or seen an EV battery fire actually comment that those gases look like "Steam" they are actually toxic and flammable electrolyte gases and average ignition of those flammable gases occur in 5% of EV battery fires.
So my question is albeit possbly smaller scale, if you had a battery event in a loft of a dwelling, are we likley to see the same flammable and toxic gases be produced? If they can be produced given confined space of the attic and non Ex certified electrics and all sorts of ignition sources in the loft, could we have those gases being ignited? The flammable gases produced can be both heavier and lighter than air, so again penetrations in the loft floor/ceiling allows ingress into the rooms below?
I know I sound like prophet of doom this morning, and manufacturers will say everything ok and it would be an extreme event, but future safety standards and regulations often come about because of a tragic event. If inverter lithium batteries behave in a similar way to an EV battery fire, I would not be putting them in any loft or confined space.
Regards GTB
I would not be putting them in any loft or confined space.
So, GTB, would you have one anywhere indoors?
If the battery cables should be as short as possible, then perhaps a gable end, but it would look rather unsightly.
Chris,
If it is my own home, then I wouldn't have battery storage within my main dwelling building, would be external to the building structure, in a suitable ventilated metal enclosure, unless the battery housing already met those conditions.
For other properties, it would be the "Designers" responsibility taking into account manufacturers instructions, and standards, including all appropriate electrical standards and building standards applicable at the time for size and type of system and type of property where the battery storage should be located. The "Designer" would I hope take into account use of the building and type of persons within taht building and what the fire risk assessment indicates.
One would hope better chance of things being considered in a industrial and commercial property and pushing it a retail one. But for general dwellings, sadly dont see the battery storage being considered.
Regards GTB.
It's odd how we "feel" about risk. Now my HP is in and seems to be working well I'm about to have the gas supply disconnected - so it occurs to me: what if the situation was reversed? How could I persuade someone to accept a mains gas supply that they hadn't had before - an almost infinite uncontrolled supply of highly flammable/explosive invisible gas, fed through single skin copper pipes (probably with soldered joints that will likely melt during a house fire) feeding appliances that can turn that gas into something that's very toxic (carbon monoxide) and involves flames at hundreds of degrees contained in a flimsy metal box within living spaces of the home. Doesn't sound that good even before you add in regular evidence of whole houses simply disappearing in a gas explosion. Yet most of us find that perfectly acceptable.
- Andy.
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