[RE-wrenches] DC Fusing/Breakers for Battery Circuits

[Jerry Shafer]

I look at batteries the same way as modules each string gets it own
protection, its good for trouble shootings and for safety. we use the
magnum Energy Class T fuse and holder, its cheap and works very well. If
you have ever seen a short of a battery bank you would always install fuses
right there at the bank and even just one bank
Jerry


On Thu, Feb 6, 2014 at 3:20 PM, Jason Szumlanski <jason at fafcosolar.com>wrote:

> Allan's assessment matches my experience.
>
> Interesting note: Outback's IBR enclosures include string-level
> overcurrent protection "for added safety" according to their data sheet.
>
>
> http://www.outbackpower.com/downloads/documents/integrated_battery_rack/spec_sheet.pdf
>
>
> http://www.outbackpower.com/downloads/documents/integrated_battery_rack/integrated_battery_rack_installation_manual.pdf
>
>
> Jason Szumlanski
>
>
>
> On Thu, Feb 6, 2014 at 6:06 PM, Allan Sindelar <
> allan at positiveenergysolar.com> wrote:
>
>>  Dave,
>> I'm not really clear what your question is, but let me take a stab at it
>> anyway.
>>
>> Parallel strings of batteries are routine in PV systems; indeed, far more
>> common than single strings of large cells. Seldom are the individual
>> strings separately fused, and I have never seen it required as a Code
>> issue. The entire battery bank as a single entity is considered a single
>> current source. Overcurrent protection is sized in accordance with the
>> battery cable size - or rather vice versa: the overcurrent protection is
>> sized to the requirements of the inverter(s) and the cables are sized to
>> the overcurrent protection.
>>
>> Having said that, there are at least two cases where it's a good idea to
>> account for it, whether or not addressed in the Code:
>> 1) In smaller systems, such as with two or three strings of common
>> batteries, you will eventually have a cell failure. When that happens, the
>> amps increase on the other remaining strings. So it is good practice to
>> oversize series and parallel interconnects for that eventuality.
>> 2) For similar reasons, in large battery banks we have sometimes added
>> Class T fuses, appropriately sized to the application, to the B+ output of
>> each string before combining them on a bussbar. These fuses serve only as
>> catastrophic protection in case the entire load tries to exceed the
>> ampacity of one set of cells and thus one set of cables.
>>
>> When we have done what I think you have described - two parallel 48V
>> strings of 4 12V batteries each - we combine them with cables, without
>> additional string-level protection. That is in accordance with
>> manufacturers' instructions.
>>
>> Allan
>>
>>       *Allan Sindelar*
>> *Allan at positiveenergysolar.com* <Allan at positiveenergysolar.com>
>> NABCEP Certified PV Installation Professional
>> NABCEP Certified Technical Sales Professional
>> New Mexico EE98J Journeyman Electrician
>> Founder, *Positive Energy, Inc.*
>>
>> A Certified B CorporationTM
>> 3209 Richards Lane
>> Santa Fe, New Mexico 87507
>> *505 424-1112 <505%20424-1112> office 780-2738 cell*
>> *www.positiveenergysolar.com* <http://www.positiveenergysolar.com/>
>>
>>
>>   On 2/6/2014 3:23 PM, Dave Click wrote:
>>
>> All,
>>
>> I think that in the past, list discussions have talked about fusing of
>> parallel battery circuits as a best practice, but it's required per 690.9
>> right? (text below from 2008 NEC)
>>
>> Also, if someone (don't look at me) really wants to use 2 parallel
>> circuits of 12V batteries, what equipment is recommended to provide
>> overcurrent protection? The installer is using Outback hardware (FW500?)
>> and has two battery circuits combined in the battery enclosure and run to a
>> Big Bus feeding the two 125A dc disconnects for two GVFX3648s. If you've
>> read this far, this area is more your wheelhouse than mine. Thanks in
>> advance!
>>
>>
>> 690.9 Overcurrent Protection
>> (A) Circuits and Equipment. Photovoltaic source circuit, photovoltaic
>> output circuit, inverter output circuit, and storage battery circuit
>> conductors and equipment shall be protected in accordance with the
>> requirements of Article 240. Circuits connected to more than one electrical
>> source shall have overcurrent devices located so as to provide overcurrent
>> protection from all sources.
>>
>> Exception: An overcurrent device shall not be required for circuit
>> conductors sized in accordance with 690.8(B) and located where one of the
>> following apply:
>> (a) There are no external sources such as parallel-connected source
>> circuits, batteries, or backfeed from inverters.
>> (b) The short-circuit currents from all sources do not exceed the
>> ampacity of the conductors.
>>
>>
>
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