Class T fuse source request [RE-wrenches]

Kurt Albershardt info at es-ee.com
Wed Feb 14 23:35:03 PST 2007


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--On Wednesday, February 14, 2007 10:01 PM -0700 Ray Walters <walters at taosnet.com> wrote:
>
> I too have pondered these same issues, and would like some clarification from Outback. Left to my own devices, I've done just as you: double runs of 4/0 to feed 4 inverters. Then there is all that unprotected cable from the batteries till the breaker. In some ways the breaker only protects the inverter and its 2 ft of cable in any system. John Wiles said we needed additional protection for longer battery cable runs.... he didn't say what length or how to do it. He did say no T fuse at the 
battery terminal. I agree with that, because of the corrosion problem, but otherwise a fuse right at the terminal does protect that whole cable: battery to load center.
> I think both the NEC and manufacturers should deal with this. On sealed batteries, I happily add a secondary fuse at the terminal.

I think that this is a rather significant unaddressed issue in many battery installations (including telcos.)  Large battery banks represent *immense* sources of fault current potential and anyone who has been in this business long enough has seen graphic proof of the damage which this is capable of doing.  A failed inverter in one of our projects generated enough short circuit current to weld a pull-out fuse holder to its base--without tripping the 200A Class T fuse inside (and the 600A rated 
pullout prongs were coated with copper-doped Penetrox E.)  It also flamed out rather spectacularly and tripped the gas fire suppression system, making ancillary damage near zero--but incurred ~$11k in charges from Ansul in addition to the electrical repair work and inverter replacement (to their credit, the manufacturer sent a brand new replacement for this $10k out-of-warranty inverter as soon as they saw the photos.)



> The final question in my mind, is where is that fuse going to be located? In the load center, so that it protects a couple of feet to the breakers? at the battery?  A second enclosure adjacent to the battery box? IMHO, if your going to protect the cables, then you should also protect against a short in the cables before the breaker. Big batteries feeding a short circuit in double 4/0 cables could cause much more trouble than the slight overload you're considering from the inverters.

I'll again ask if anyone has looked into cable limiters for this application?















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