Want to move to all 208V for server racks

Lamar Owen lowen at pari.edu
Mon Dec 6 16:23:38 UTC 2010


On Saturday, December 04, 2010 05:52:09 pm Kevin Oberman wrote:
> Lead-acid batteries can deliver way over 100 amps of current and a
> conductor across "safe" voltage will get hot and, if not heavy enough,
> will vaporize. 

Our smallish 540Ah -48VDC plant has a 35,000A short circuit rating; important to know when sizing the disconnect breaker, as 50,000AIC breakers are required for that.  The A and B side rectifiers are Lorrain 200A three phase units, built like tanks.

We have a secondary 12V plant at one solar location that is using six 2,320Ah cells which required two disconnects in series to meet AIC ratings, since the nearly 100,000A short circuit current makes it difficult to get small (<100A) breakers with 100,000+AIC ratings.

We're doing the solar thing for our optical telescopes, using Xantrex inverter/chargers and Outback solar charge controllers, 24VDC nominal strings.  Works great; DC input switches make it even nicer, although you then need low voltage cutoffs to prevent battery damage when there have been several days in a row of dark skies.

At the 5ESS in Buckhead/Brookhaven I recall seeing an operating A buss current of >20KA years ago; the AIC on that plant has to be huge (of course, that's been 25+ years, and that's my memory, which could be mistaken as to the exact current value).  A technician there told me he had seen an 18 inch adjustable wrench totally vaporized when it bridged from B- to ground.

Yeah, not something to play with.




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