[RE-wrenches] Assembly Protects Conductors?

[Ray Walters]

The 100% exception is listed in 2 places:
690.8(B)(1) which sizes the conductor, and 690.9(B) which sizes the OCD.
Article 210 doesn't apply, as that is for branch circuits, not PV source 
circuits.
690.8 basically walks you through conductor sizing.  690.8(B) requires 2 
calculations one for B(1)  which is simply  Asc x 125% ( 690.8(A)(1)  
the edge of cloud effect), and is exempted from any additional derating 
if using the 100% rated assemblies.
690.9(B)(2) then  takes Asc x 125% as well, and then applies all the 
previously mentioned adjustments and correction factors.
Which ever is larger is what you are required to use.

The 100% exemption basically means that 690.9(B)(2) will prevail, and 
you may end up with a bit less than the additional 125% (or not)
Basically, the days of multiplying  by 156% are mostly over with today's 
combiner boxes.
However, properly applying all the corrections and deratings on a roof 
is a different story, that has been covered by others more informed than I.
Check SolarPro magazine, and 310.15.

Later we can get into the debate of when to apply table 310.15(B)(17) 
ampacity ratings in free air......
Does it apply to array conductors before they transition into conduit?  
Does it apply (as some manufacturers claim) inside of enclosures, or for 
conductors run through less than24" of raceway?
Stay tuned, I'm still trying to figure that one out.  Does someone else 
want to jump in here?

R.Ray Walters
CTO, Solarray, Inc
Nabcep Certified PV Installer,
Licensed Master Electrician
Solar Design Engineer
303 505-8760

On 8/23/2014 9:41 AM, Mark Frye wrote:
> Ray,
>
> I can't follow you all the way down that path.
>
> Is an insulated wire conductor permitted to be use at 100% of it's 
> rating under continuous operation? No. The ampacity is reduced and the 
> conductor must be up-sized. Hence, for a defined load (Isc * 1.25), 
> under continious operation, the conductor must be upsized to match 
> (defined load * 1.25). I don't see how this can be changed by simply 
> changing the nature of the OCP. I think the point of this exception is 
> to allow cost savings by allow assemblies and OCP devices with lower 
> ratings. The exception does not apply to every element of the circuit 
> (the conductors) but only to the 100% rated assemblies and OCP 
> themselves.
>
> What am I missing?
>
> Thanks,
>
> Mark
>
> On 8/22/2014 6:14 PM, Ray Walters wrote:
>> Most combiner boxes, DC rated breakers, and DC rated fuses and fuse 
>> holders we use today, qualify as assemblies for the 100% exception 
>> (Outback, Midnite, etc.....) so you only have to size the OCP by 125% 
>> of short circuit current rating for edge of cloud effects.
>> Since the conductor is sized based on the overcurrent protection, you 
>> do not need to size it to 156% of the short circuit current rating, 
>> if you take advantage of 100% duty rated breakers and combiners.  
>> Also, recombiners are still basically combiner boxes, and so all the 
>> same rules apply.  The additional 125% is only for breakers that are 
>> rated at 80%  (most AC breakers for example) .
>> For DC, the only time you would size for the full 156% would be if 
>> you were using something like an old QOU breaker, and those aren't 
>> rated for high enough voltage for today's arrays anyway.   I'm not 
>> aware of any other readily available DC rated breaker that is NOT 
>> 100% duty rated.   Some RK5 fuse assemblies may also not be 100% 
>> rated. (Wrench Colleagues please correct me on this....)
>> Basically unless you are using surplus equipment from the stone age, 
>> (no offense to my fellow stone age wrenches)  you only need to 
>> oversize the conductors by 125%.  By the time you apply all the other 
>> applicable deratings for conduit fill, terminals rated at 75 C, and 
>> direct sunlight on roofs (table 310.15B3c)  and consider voltage 
>> drop, you really don't need to keep oversizing.
>>
>> R.Ray Walters
>> CTO, Solarray, Inc
>> Nabcep Certified PV Installer,
>> Licensed Master Electrician
>> Solar Design Engineer
>> 303 505-8760
>>
>> On 8/22/2014 2:34 PM, markf at berkeleysolar.com wrote:
>>> Folks,
>>>
>>> In looking at a circuit breaker based re-combiner for the first 
>>> time, I am
>>> now pondering the meaning of the Exception below:
>>>
>>> NEC 2014 690.8 (B) Conductor Ampacity. PV system currents shall be
>>> considered to be continuous. Circuit conductors shall be
>>> sized to carry not less than the larger of 690.8(B)(1) or (2).
>>>
>>> (1) One hundred and twenty-five percent of the maximum
>>> currents calculated in 690.8(A) before the application of
>>> adjustment and correction factors.
>>>
>>> Exception: Circuits containing an assembly, together with
>>> its overcurrent device(s), that is listed for continuous operation
>>> at 100 percent of its rating shall be permitted to be
>>> used at 100 percent of its rating.
>>>
>>> Just to be clear, it is only the assembly that can be used at 100 
>>> percent
>>> of its rating. (Isc*number of strings*1.25) The conductors in the 
>>> circuit
>>> still have to be sized for continuous operation (Isc*number of
>>> strings*1.25*1.25).
>>>
>>> I ask because a vendor with a 100% circuit breaker re-combiner 
>>> states in
>>> their cut sheet that use of the device "allow
>>> smaller home run cable sizes from the string combiner to the 
>>> inverter". Is
>>> anyone aware of a means by which this claim can be substantiated?
>>>
>>> Thanks,
>>>
>>> Mark Frye
>>> Berkeley Solar Electric Systems
>
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