[RE-wrenches] Current limiting fuse at battery bank

[Dan Fink]

Esteemed Wrenches;
This creeps me out too and sometimes causes lack of sleep.
The Midnite Solar power panel install manual shows no OCPD on in DC + main
from battery bank to power panel. Easy to wire the main DC breaker to
control those conductors, but then you have a "self destruct" switch if
system shutdown and restart is not done in the proper order, IE PV and wind
turbine shut down first before battery bank.
For a class T fuse on the battery bank, it's a big $ ordeal because it has
to be outside the battery box in an enclosure per NEC.
So, recently I've just been making sure the conduit from DC battery mains
is sound up to the power panel. The only issue I can see is mice chewing
2/0 cable inside the battery box -- which means the box wasn't designed
right to exclude rodents, or the owner has a lazy cat.
I'd feel much  better if there was an OCPD NEC legal to attach right to the
main battery DC + and wire from there to power panel, but I don't think
that exists.




Dan Fink
Adjunct Professor, Ecotech Institute
IREC Certified Instructor™ for:
~ PV Installation Professional
~ Small Wind Installer
Executive Director, Buckville Energy
NABCEP / IREC / ISPQ Accredited Continuing Education Providers™
970.672.4342



On Thu, Oct 22, 2015 at 11:26 PM, Mbalchowsky <max at seesolar.com> wrote:

> It's ALWAYS good practice to install a current limiting fuse at the
> battery bank, if fact it's very poor practice not to. We're working with a
> lot of larger lithium ion phosphate manganese systems and I would not
> install them without it. As far as working on someone else's install, make
> your  contract very clear as to what the customer can expect as far as your
> liability when working on an existing system. The more detail, the
> better.....
>
> Sent from my iPhone
>
> On Oct 22, 2015, at 7:25 PM, Jerry Shafer <jerrysgarage01 at gmail.com>
> wrote:
>
> I agree, fuse it
>
> Jerry
> On Oct 22, 2015 3:26 PM, "Tom Ruscitti" <truscitti at taitem.com> wrote:
>
>> On battery based systems I always install a Class T fuse as close to the
>> battery bank as possible. 690.71(C) is a little vague in requiring a
>> current limiting fuse only where the available short-circuit current from
>> the battery bank exceeds the interrupting ratings of the inverter breaker.
>> Inverter breakers vary in their interrupting ratings and battery banks are
>> big current sources when things go wrong, so it's just a sensible best
>> practice. My question is about service work on systems we didn't install.
>> We're quoting the second job this year for battery replacement where there
>> is no current limiting fuse installed. It's always a tough question to
>> judge what extra work might be required when you touch another contractor's
>> system, but does anyone have an opinion about recommending or requiring the
>> installation of a fuse at the battery box as part of the battery
>> replacement?
>>
>> Thanks,
>>
>> - Tom
>>
>> --
>> Tom Ruscitti
>> Senior Engineer
>>
>> Taitem Engineering, PC
>> 110 S. Albany Street, Ithaca, NY 14850
>> Mobile: (607) 220-7022
>> www.taitem.com
>>
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