[RE-wrenches] Current limiting fuse at battery bank

[William Miller]

Tom:

Here's how I approach this subject:

In general there are two places to insert OCPDs to protect wire and
devices:  Upstream or downstream.

For a vast majority of circumstances, it is preferred to place protection
upstream, for obvious reasons.  This is not to say protection cannot be
placed downstream.  This is done for taps and service entrance conductors.
The philosophy is to minimize the probability of failure on the upstream
side of the protection and the OCPD protects the upstream circuit from
downstream faults.

I think the same criteria applies for battery lead protection as it does
for taps and SE cables:  Minimize the risk by keeping leads short and
protected from damage.

If you follow these practices you can eliminate the need for fuses in
proximity to the batteries.

William

PS:  This relates to my complaints about the Sunny Island systems lack of
BOS.  If you use the Midnite Disconnect, it mounts right under the SI
inverter.  This can often be too far from the battery bank.

Wm


Lic 773985
millersolar.com
805-438-5600


-----Original Message-----
From: RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org] On
Behalf Of Tom Ruscitti
Sent: Thursday, October 22, 2015 6:27 PM
To: re-wrenches at lists.re-wrenches.org
Subject: [RE-wrenches] Current limiting fuse at battery bank

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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