Class T fuse source request [RE-wrenches]

[Christopher Freitas --- OutBack Power]

Sorry for not responding sooner - Allan actually reminded me to respond 
after I forgot about this... Thanks Allan!  

So - I have included additional fusing of the battery on a few large 
battery system installs I was involved with.  I have found that the 
inspectors are more comfortable with them if you refer to these as 
"catastrophic" and "additional" protection and emphasize that you are 
going beyound the NEC in providing them.  This worked well at the large 
off-grid system which was I helped to install two or so years ago near 
Pasadena and was not objected to by the chief electrical inspector who 
came out for the final inspection. 

The fuses where mounted in fuseholders and enclosed behind a protective 
lexan cover inside of the battery room / closet - the battery system was 
5000AH at 48 vdc sealed Absolyte IIP - four strings total of 24 cells 
each.  The cabling from the battery to the fuses was as short as 
possible and should be done with equal length cables IMHO.   This system 
had eight OutBack VFX3648 and something like 10 MX60s

I have looked a the devices called "cable limiters" and am more 
comfortable with using Class-T fuses for these applications.  I have 
always liked the idea of putting in one 400 amp Class T fuse PER SERIES 
STRING of batteries prior to the point that they are paralleled 
together.  On some systems a smaller fuse might make sense even - 
depends on the size of the battery.  The fuse is really meant to handle 
a short circuit - so the trip current rating is not as critical.  

These fuseholders also can be thought of as "bolted disconnect" points 
to allow isolation of a section of the battery for testing and or 
individual string equalization, etc.  Sort of like a PV array combiner 
box for the battery. I would use a similar practice here as well - that 
is that when there are more than two strings of batteries being 
paralleled,  individual battery strings should be fused.        

I agree that the NEC is very conservative on cable ratings - I too have 
done many EV conversions and have used much smaller cables without 
problems.  In many ways the UL and NEC standards result in multiple 
safety margins being applied - which just makes things more difficule 
and expensive, not actually safer.  Can you imagine how much innovation 
would occur if the automakers had to get cars UL listed each year? Think 
about it... 

Christopher  


Ray Walters wrote:
> Hi Allan;
> I too have pondered these same issues, and would like some 
> clarification from Outback. 


Christopher Freitas
OutBack Power Systems, Inc.
cfreitas @ outbackpower.com  
www.outbackpower.com
Arlington WA USA
Tel 360 435 6030  


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