[RE-wrenches] NEC 705.12 Point of Connection - 120% rule for center-fed panelboards

billbrooks7 at sbcglobal.net billbrooks7 at sbcglobal.net
Thu Mar 3 12:45:30 PST 2016


Howie,

 

To clarify what the 2017 NEC states, it allows for either end of the bus. There is some value to having loads in between the PV breaker and the main breaker. Also, by putting the PV breaker as far away from the main as possible, the heat of both breakers are likely to affect each other. 

 

The 2005 and earlier NEC did not stipulate anything about location on the bus.

 

Bill.

 

From: RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Howie Michaelson
Sent: Thursday, March 03, 2016 12:11 PM
To: RE-wrenches <re-wrenches at lists.re-wrenches.org>
Subject: Re: [RE-wrenches] NEC 705.12 Point of Connection - 120% rule for center-fed panelboards

 

Bill,

Did I understand your earlier post to infer that there never was an intent to apply the "opposite end of the buss" rule to the 120% backfeed allowance in residential applications?  And that you have been working to rewrite a solar backfeed breaker in a residential setting to land anywhere on the buss?

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 Thu, Mar 3, 2016 at 12:07 PM, <billbrooks7 at sbcglobal.net <mailto:billbrooks7 at sbcglobal.net> > wrote:

Phil,

 

I think you already understand how to apply the “120% rule.” All this is saying is that the breaker can go at either end of a center-fed panel for dwellings. Do you understand now?

 

To summarize—a 200A center-fed panel would allow a 40-amp PV breaker to be installed at either end to meet the 120% rule.

 

Bill.

 

From: RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org <mailto:re-wrenches-bounces at lists.re-wrenches.org> ] On Behalf Of Philip Lawes Insoltech
Sent: Thursday, March 03, 2016 8:26 AM
To: 'RE-wrenches' <re-wrenches at lists.re-wrenches.org <mailto:re-wrenches at lists.re-wrenches.org> >
Subject: Re: [RE-wrenches] NEC 705.12 Point of Connection - 120% rule for center-fed panelboards

 

Bill,

Could you please provide an example of this showing calculations?

Thanks so much,

Phil

 

From: RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of billbrooks7 at sbcglobal.net <mailto:billbrooks7 at sbcglobal.net> 
Sent: Wednesday, March 2, 2016 11:24 AM
To: 'RE-wrenches' <re-wrenches at lists.re-wrenches.org <mailto:re-wrenches at lists.re-wrenches.org> >
Subject: Re: [RE-wrenches] NEC 705.12 Point of Connection - 120% rule for center-fed panelboards

 

All,

 

Here is the new language that has been approved for the 2017 NEC (more authoritative than JW).

 

705.12(B)(3)(d)

 

(d) A connection at either end, but not both ends, of a center-fed panelboard in dwellings shall be permitted where the sum of 125 percent of the power source(s) output circuit current and the rating of the overcurrent device protecting the busbar does not exceed 120 percent of the current rating of the busbar.

 

This clarifies that it was never the intent of the NEC to limit the 120% rule to the opposite end of the busbar for dwellings (it was allowed from 2005 back to 1987). I was able to convince the panel that centerfed panels did not need the opposite end stipulation. Several large jurisdictions in California or considering making an official policy accepting the language of the 2017 NEC on this item. Please share this with your own jurisdiction.

 

Bill.

 

 

From: RE-wrenches [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Glenn Burt
Sent: Wednesday, March 02, 2016 10:54 AM
To: RE-wrenches <re-wrenches at lists.re-wrenches.org <mailto:re-wrenches at lists.re-wrenches.org> >
Subject: Re: [RE-wrenches] NEC 705.12 Point of Connection - 120% rule for center-fed panelboards

 

I believe that John Wiles has stated this in a couple of places in print, therefore you may have a tough time justifying a way around the rule to an AHJ.

Supply side connections are very popular in this situation.

  _____  

From: August Goers <mailto:august at luminalt.com> 
Sent: ‎3/‎2/‎2016 11:32
To: RE-wrenches <mailto:re-wrenches at lists.re-wrenches.org> 
Subject: [RE-wrenches] NEC 705.12 Point of Connection - 120% rule for center-fed panelboards

All –

 

We are seeing more AHJs not allowing us to use the NEC 7015.12(D)(2)(3)(b) 120% rule on center-fed panelboards. For example, if we have a 100 A meter/main combo with a center fed 100 A breaker we cannot apply the 120% rule at all and need to do a panel swap. What are other wrenches doing in this case?

 

Best,

 

August

Luminalt


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