[RE-wrenches] 120% rule for hybrid inverters

billbrooks7 at sbcglobal.net billbrooks7 at sbcglobal.net
Fri Aug 12 10:24:57 PDT 2016


All,

 

The 2011 NEC reference for stand-alone systems is 705.12(D)(2) Exception:

 

Exception: Where the photovoltaic system has an energy storage device to allow stand-alone operation of loads, the value used in the calculation of bus or conductor loading shall be 125 percent of the rated utility-interactive current from the inverter instead of the rating of the overcurrent device between the inverter and the bus or conductor.

 

The 2014 NEC made this the rules of the road for all inverter output circuits connected to other sources.

 

Bill.

 

 

From: RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Howie Michaelson
Sent: Friday, August 12, 2016 8:39 AM
To: RE-wrenches <re-wrenches at lists.re-wrenches.org>
Subject: Re: [RE-wrenches] 120% rule for hybrid inverters

 

Mark,  I read that section as stating that both must be true, which I would take to mean if one is using a 20 amp breaker to protect the output from a 3 kW inverter, you need to count it as 20 amps toward the 120% rule, not the 15.63 amps the 125% calculation would infer.  I know that 2014 was changed to allow for larger breakers to feed hybrid inverters, but I can't recite the code that allows that (unless I am misreading the intent of the section you quoted). Can you clarify this for me?

Thanks,

Howie




Howie Michaelson
NABCEP Certified Solar PV Installer™
Sun Catcher, LLC
Renewable Energy Systems Sales and Service
VT Solar Electric Incentive Partner
802-272-0004

 

On Fri, Aug 12, 2016 at 9:39 AM, Mark Westbrock <westbrock at positiveenergysolar.com <mailto:westbrock at positiveenergysolar.com> > wrote:

Hi Mac,

 

The wording changed because in the 2011 NEC 705.12(D) you had to use the size of your backfeed breaker in calculating the busbar loading, but in 2014, 705.12(D)(2)(3)(b) now says "125 percent of the inverter output circuit current and the rating of the OCPD protecting the busbar shall not exceed 120%".  

 

So, the 2014 wording basically allows all inverters to follow the exception that used to be there for hybrid inverters.  I hope that helps.

 

Cheers,

 

Mark




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On Fri, Aug 12, 2016 at 7:26 AM, Mac Lewis <maclewis1 at gmail.com <mailto:maclewis1 at gmail.com> > wrote:

Hello wrenches,

 

I am looking for the exception to the 120% rule in the 2014 code that allowed for compliance to the 120% rule to be based on the utility-interactive current as opposed to the backfeed breaker size for hybrid inverter.  I hope this still exists, but I'm having a hard time finding it in the 2014 code.  In 2011 it was 705.12(D)2 Exception.  That was nice clear language that all inspectors accepted, I'm hoping the same exists for the 2014 code.

 

Thanks in advance code experts

 




 

-- 

 

 

 

Mac Lewis

"Yo solo sé que no sé nada." -Sócrates


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