DC Load Center's [RE-wrenches]

Christopher Freitas - OutBack Power cfreitas at outbackpower.com
Wed May 1 10:23:54 PDT 2002


> Has anyone every used the Cutler-Hammer Products rated for 125/250
> VDC? Specifically PRL3a with GHB breakers.  Supposedly, it will
> allow for a main breaker of up to 800 amps and branch circuit 
> breakers of up to 400 amps.  All rated at 125/250 VDC.  By the way, > 
> just what do they mean by that? According to my local Cutler Hammer > 
> Supplier they supply CH products to a local company who makes and 
> installs Telecomm power houses and they are using them in DC 
> applications. 

Be careful with DC ratings on AC breakers - They may be approved for 
very specific applications and installation methods.  For example, the 
interruption capacity (called AIC) may not be enough for use with 
batteries or may require "back-up" fusing to be used safely with 
batteries.  In Telecom applications it is very common for a current 
limiting fuse to be installed on each string of batteries before leaving 
the battery enclosure ahead of any breakers to limit the fault current.  
This may or may not be allowed on NEC inspected systems.  

I wrote an article on DC breakers vs. fuses in 1992 in Home Power which 
is dated but still is useful - here is the link:

www.humboldt1.com/~michael.welch/hp27-26.pdf 

The article includes some real hands on testing of DC rated breakers in 
which we blew them apart and caused excessive arcing and damage.  

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

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