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

[Dave Click]

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.