[RE-wrenches] wire sizing question

[jay peltz]

HI Drake

I don't use the FW 500 boxes, which I'm guessing you are using.  ( the FW 1000 are ok for larger wire combos) because either I'm going with a single inverter (E panel) or radian.
The other way I also run paralleled wires is with larger conduit.  
I suggest you check out midnight for some big battery cabling boxes.

jay 
peltz power


On Jan 2, 2015, at 3:17 PM, drake.chamberlin at redwoodalliance.org wrote:

> 4/0 copper is good for a 24V, 4000 W inverter. What is being used for
> multiple inverters?
> 
> I've paralleled 4/0 into outback boxes using 2, 2" PVC conduits. It gets
> pretty messy trying to put 4 sets of 4/0s into enclosures and battery
> boxes (although I have worked on such systems). Does anyone have clean
> solutions for these systems?
> 
> Thanks,
> 
> Drake
> 
> 
> 
> 
> 
>> Some other things:  If you keep the conduit less than 24" long, which is
>> recommended anyway for main battery connections, the conduit fill
>> requirements don't apply. (see exception: 310.15(B)3a2)
>> Using table 310.15(B)16 yeilds 230 amps for 4/0 at 75 C.  Then 240.6
>> lists 250 amp as the next standard size of OCPD which is allowed to be
>> used by 240.4(B)  So you can just justify 4/0.
>> Further, many manufacturers (like Midnite) use the open air ampacity
>> table: 310.15(B)17, since the cable is not "in conduit" and 4/0 cable at
>> 75 C is rated to 360 amps.
>> The Free Air interpretation is not completely substantiated in the code
>> from my read of it though.  Maybe someone more knowledgable could cite
>> the chapter and verse that defines when the free air rating can and
>> cannot be used.
>> Also remember those breakers are 100% duty cycle rated, and that the
>> inverter usually can't run any where close to 250 amps continuously.
>> Bottomline is we've been using 4/0 with 250 amp breakers for almost 20
>> years, and I've never seen or heard of a problem.
>> 
>> R.Ray Walters
>> CTO, Solarray, Inc
>> Nabcep Certified PV Installer,
>> Licensed Master Electrician
>> Solar Design Engineer
>> 303 505-8760
>