[RE-wrenches] Current limiting fuse at battery bank

Fri Oct 23 08:55:36 PDT 2015

HI Dan,

All the big three have the same wiring diagrams  with a positive buss and then breakers going out from there.
And yes there is no main disco for the DC branches.  

But if your point was that the fuse could/will blow and then you have the PV/wind connected to the inverter and could over volt it, then yes I agree.
This was actually a problem that happened to a friend using some rapid shutdown with a trip/breaker at the battery.  It shut down the battery but the system continued to work as the PV had enough energy to feed the inverter/loads.  And in the really old days of the first power panels from Trace, they did wire them the way maybe you are taking about Dan.  With the main breaker as a main, and the PV/inverter connected on the switched side.  But then PV is connected directly to the inverter and those old CC didn’t clamp that fast, and poof dead inverter.  Amazingly I just “updated” a  trace PP from way back a few months ago.

I am of the opinion ( in the minority here) that fuses are not a good addition for protection of the conductors. They add complexity and more failure modes.  ( I’ve seen class T fuse holders almost catch on fire).  And now you are going to have to leave extra fuses $$$ and then insulated tools as well?  And as others have pointed out, where do you mount them etc. 

And in my defense, mostly my conductors are pretty short so I don’t worry about that.  If they were going a long ways, then I might reconsider, but I’d probably use a breaker instead.

The only time I will use them is for larger parallel battery banks, but this is for the protection of the battery side, not the main conductors really.

my 2c.

jay

peltz power

> On Oct 23, 2015, at 7:30 AM, Dan Fink <danbob88 at gmail.com> wrote:
> 
> Esteemed Wrenches;
> This creeps me out too and sometimes causes lack of sleep.
> The Midnite Solar power panel install manual shows no OCPD on in DC + main from battery bank to power panel. Easy to wire the main DC breaker to control those conductors, but then you have a "self destruct" switch if system shutdown and restart is not done in the proper order, IE PV and wind turbine shut down first before battery bank.
> For a class T fuse on the battery bank, it's a big $ ordeal because it has to be outside the battery box in an enclosure per NEC. 
> So, recently I've just been making sure the conduit from DC battery mains is sound up to the power panel. The only issue I can see is mice chewing 2/0 cable inside the battery box -- which means the box wasn't designed right to exclude rodents, or the owner has a lazy cat.
> I'd feel much  better if there was an OCPD NEC legal to attach right to the main battery DC + and wire from there to power panel, but I don't think that exists.
> 
> 
> 
> 
> Dan Fink
> Adjunct Professor, Ecotech Institute
> IREC Certified Instructor™ for: 
> ~ PV Installation Professional
> ~ Small Wind Installer
> Executive Director, Buckville Energy
> NABCEP / IREC / ISPQ Accredited Continuing Education Providers™
> 970.672.4342 <tel:970.672.4342>
>  
> 
> On Thu, Oct 22, 2015 at 11:26 PM, Mbalchowsky <max at seesolar.com <mailto:max at seesolar.com>> wrote:
> It's ALWAYS good practice to install a current limiting fuse at the battery bank, if fact it's very poor practice not to. We're working with a lot of larger lithium ion phosphate manganese systems and I would not install them without it. As far as working on someone else's install, make your  contract very clear as to what the customer can expect as far as your liability when working on an existing system. The more detail, the better.....
> 
> Sent from my iPhone
> 
> On Oct 22, 2015, at 7:25 PM, Jerry Shafer <jerrysgarage01 at gmail.com <mailto:jerrysgarage01 at gmail.com>> wrote:
> 
>> I agree, fuse it
>> 
>> Jerry
>> 
>> On Oct 22, 2015 3:26 PM, "Tom Ruscitti" <truscitti at taitem.com <mailto:truscitti at taitem.com>> 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
>> 
>> -- 
>> Tom Ruscitti
>> Senior Engineer
>> 
>> Taitem Engineering, PC
>> 110 S. Albany Street, Ithaca, NY 14850
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