[RE-wrenches] Point of connection question

[William Miller]

Ray and August:

 

Thanks for the speedy reply.  I did confuse M250s with the M215s.  The
actual inverters to be used are the M215s.  

 

I swear I had a spec sheet for the M190 that showed 0.75 A but I can't find
it anymore.  So using 0.8A:

 

9 * 0.8A = 7.2A

10 * .9A = 9.0A

Total = 16.2

De-rate: 16.2*1.25 = 20.25.

 

Maybe that will fly.

 

The other question is:  I don't have to use the value of the three breakers
in the Solar load center to calculate my POC in the M/M/C?  The code says:
The sum of the ampere ratings of overcurrent devices feeding a busbar or
conductor shall not exceed 120% of the rating of the busbar or conductor.  I
am assuming I don't have to add the two 15s and the 20 and use that in
figuring the back feed to the M/M/C since the M/MC is fed by a 20.

 

Thanks so much for your help.  I am going to send this on to the lead
inspector for the County.  I am fortunate that he has always been willing to
review these problems and flexible where appropriate, at least in my view.

 

Sincerely,

 

William Miller

 

PS:  I update the drawing.

 

Wm

 

 

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of August Goers
Sent: Wednesday, October 09, 2013 3:40 PM
To: RE-wrenches
Subject: Re: [RE-wrenches] Point of connection question

 

William,

 

You have 9 M190s each running at 800 mA according to spec sheet. That equals
7.2 A nominal output current. Plus you have 10 M250s (if you look at your
drawing) each running at 1 A = 10 A. 7.2 A + 10 A = 17.2 A * 1.25 = 21.5 A
min breaker size. So, you'll need to round your breaker to a 25 A or 30 A
breaker in the sub. You don't have any problem in the sub panel but the
meter main is going to be a problem if it is a 100 A meter/main.

 

Your drawing and case study notes don't seem to correspond - you mention
M215s in the case study and show M250s on the drawing. If you indeed have 10
M215s then you're at 10 * 0.9 A = 9 A. 7.2 A + 9 A = 16.2 A * 1.25 = 20.25 A
min breaker size. This is where it gets tricky. My fellow engineer just
pointed out NEC 220.5(B) which allows you to drop fractions of amperes less
than 0.5. So, I think you'd be okay with a 20 A solar breaker in this case.

 

Best, August

 

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of William
Miller
Sent: Wednesday, October 09, 2013 3:07 PM
To: RE-wrenches
Subject: [RE-wrenches] Point of connection question

 

Friends:

 

At the risk of asking a question that may have been asked and answered here
in the past, I wish to pose a question about Point of Connection.

 

Rather than outline the situation here I put it all on a web page.  If any
of you have a moment to review this, I would be most appreciative.

 

http://www.millersolar.com/MillerSolar/case_studies/POC/_POC_Question.html

 

Thanks in advance,

 

William Miller

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