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

[Ray Walters]

Boltswitch used to make pullout discos for the smaller R fuses too.  You 
can use them, but they are a time delay fuse, so you need to look at 
trip curves for sizing (don't just substitute the same amp rated RK5 for 
a T)
The R fuses are physically much larger, and are rated to 300 vdc, class 
T to 160 vdc.  The AIC ratings seem to be similar 20,000 amps, though.

I would favor the Boltswitch pullout with T fuses for these reasons:
1) its lower cost
2) It will trip faster than any breaker or RK5 in an actual fault.
3) It takes up much less space than 3 breakers in their own enclosure.
4)  It disconnects 3 strings with one move.
5) The fuses and holder would handle corrosion better than the 
complicated internal workings of a breaker
(my opinion: not proven fact)

I should also add that I'm normally a big fan of breakers, and would 
still have inverter disconnect breakers in the system as well.  I'm only 
advocating the class T Bolt switch solution for fusing separate parallel 
battery strings, close to the battery box.



R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760

On 2/11/2014 11:32 AM, August Goers wrote:
>
> Hi Wrenches,
>
> I've seen a lot of posts lately all mentioning Class T for battery 
> fusing. Does anyone know if Class R is acceptable for battery fusing? 
> I looked back at an old John Wiles doc and it seems like RK5 is fine, 
> but would like to hear your opinion.
>
> http://www.nmsu.edu/~tdi/pdf-resources/cc67.pdf 
> <http://www.nmsu.edu/%7Etdi/pdf-resources/cc67.pdf>
>
> -August
>
> *From:*August Goers [mailto:august at luminalt.com 
> <mailto:august at luminalt.com>]
> *Sent:* Friday, February 07, 2014 4:36 PM
> *To:* 'RE-wrenches'
> *Subject:* RE: [RE-wrenches] DC Fusing/Breakers for Battery Circuits
>
> Hi All,
>
> Correction: Another Wrench member contacted me off-list and noticed 
> that we have a class RK5 in one photo and a T in the other photo. This 
> opens up the question of whether one or both are correct or incorrect. 
> I think both are rated for 20k AIC for DC voltage but I'll have to 
> look through my order records to be certain. The R is slow acting and 
> the T is fast acting.
>
> Best,
>
> August
>
> *From:*August Goers [mailto:august at luminalt.com]
> *Sent:* Friday, February 07, 2014 3:32 PM
> *To:* 'RE-wrenches'
> *Subject:* RE: [RE-wrenches] DC Fusing/Breakers for Battery Circuits
>
> Hi Dan,
>
> I've been wondering the same think. We've been fusing with a class T 
> in the battery box and grounding the negative side of the batteries. 
> See attached pics. Do you feel that the fuses should be outside of the 
> battery box?
>
> Best,
>
> August
>
> Luminalt Energy
>
> *From:*re-wrenches-bounces at lists.re-wrenches.org 
> <mailto:re-wrenches-bounces at lists.re-wrenches.org> 
> [mailto:re-wrenches-bounces at lists.re-wrenches.org] *On Behalf Of *Dan Fink
> *Sent:* Friday, February 07, 2014 9:27 AM
> *To:* RE-wrenches
> *Subject:* Re: [RE-wrenches] DC Fusing/Breakers for Battery Circuits
>
> Does anyone have any elegant solutions to this? It's really time 
> consuming and ugly to run big parallel battery string wires *out* of 
> the battery enclosure to class T fuses, then back into the battery 
> box. It looks very ugly and DIY, and in conduit adds a few hundred to 
> the install cost just for labor. The Class T fuses and blocks 
> themselves are not particularly expensive.
>
> I have been recommending parallel fusing on battery banks of 2x8 L16s 
> and over now, after a nearly tragic incident with a bad cell that 
> shorted. The (perfectly legal) wooden battery box made the fire much 
> worse. A pet peeve of mine.
>
>
> Dan Fink,
> Executive Director;
> Otherpower
> Buckville Energy Consulting
> Buckville Publications LLC
> NABCEP / IREC accredited Continuing Education Providers
> 970.672.4342
>
>
>
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