I agree installing a fuse at the battery bank is a good idea. However
actually doing it right is tough. Putting the class T fuse and holder
in a battery enclosure with flooded cells is going to cause more trouble
than it solves. I've seen class T fuses oozing green goo out the ends,
and the fuse holder contacts get corroded to the point that they are
causing significant volt drop.
If it is installed outside, then you need an enclosure. Then there is
the requirement that fuses be serviceable, requiring disconnects on both
sides. The Boltswitch pullout system solves that problem, but then you
have to custom fabricate an enclosure for the Boltswitch disconnect.
End of story, is we aren't usually ever installing that fuse at the
battery. Instead we keep the distance from the DC Load center to the
battery as close as possible. The number one danger is a wrench falling
across the battery terminals, and neither the breaker or a class T fuse
at the main terminal is going to stop that. We would need fusing at
each exposed positive terminal of each battery to truly protect against
short circuits.
R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760
On 10/22/2015 7:26 PM, Tom Ruscitti 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
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