# service entrance with solar



## jtrichard (Jan 30, 2017)

A customer of mine had solar installed HAD 200 amp 240 3 wire service with 2/O CU ....Solar company MADE him, have them change out the main to 175 amp I call BS am I correct or are they correct


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## cabletie (Feb 12, 2011)

The solar company was right. They reduced the size of the main to stay within the 125% rule of 705.12(b). 


705.12
(B)Load Side.
The output of an interconnected electric power source shall be permitted to be connected to the load side of the service disconnecting means of the other source(s) at any distribution equipment on the premises. Where distribution equipment, includ(1)Dedicated Overcurrent and Disconnect.
Each source interconnection of one or more power sources installed in one system shall be made at a dedicated circuit breaker or fusible disconnecting means.
(2)Bus or Conductor Ampere Rating.
One hundred twenty-five percent of the power source output circuit current shall be used in ampacity calculations for the following:
(1)Feeders. Where the power source output connection is made to a feeder at a location other than the opposite end of the feeder from the primary source overcurrent device, that portion of the feeder on the load side of the power source output connection shall be protected ing switchgear, switchboards, or panelboards, is fed simultaneously by a primary source(s) of electricity and one or more other power source(s), and where this distribution equipment is capable of supplying multiple branch circuits or feeders, or both, the interconnecting provisions for other power sources shall comply with 705.12(B)(1) through (B)(5).
by one of the following:
a.The feeder ampacity shall be not less than the sum of the primary source overcurrent device and 125 percent of the power source output circuit current.
b.An overcurrent device on the load side of the power source connection shall be rated not greater than the ampacity of the feeder.
(2)Taps. In systems where power source output connections are made at feeders, any taps shall be sized based on the sum of 125 percent of the power source(s) output circuit current and the rating of the overcurrent device protecting the feeder conductors as calculated in 240.21(B).
(3)Busbars. One of the methods that follows shall be used to determine the ratings of busbars in panelboards.
(a) The sum of 125 percent of the power source(s) output circuit current and the rating of the overcurrent device protecting the busbar shall not exceed the ampacity of the busbar.
Informational Note: This general rule assumes no limitation in the number of the loads or sources applied to busbars or their locations.
(b) Where two sources, one a primary power source and the other another power source, are located at opposite ends of a busbar that contains loads, the sum of 125 percent of the power source(s) output circuit current and the rating of the overcurrent device protecting the busbar shall not exceed 120 percent of the ampacity of the busbar. The busbar shall be sized for the loads connected in accordance with Article 220. A permanent warning label shall be applied to the distribution equipment adjacent to the back-fed breaker from the power source that displays the following or equivalent wording:
WARNING:
POWER SOURCE OUTPUT CONNECTION — DO NOT RELOCATE THIS OVERCURRENT DEVICE.


Welcome to the forum.


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## backstay (Feb 3, 2011)

Cabletie is right and he's wrong. He edited out both (c) and (d). But I'm told in CA you can't use 705.12(c). But the NEC says there are 4 ways to size the buss bar. You didn't say where the solar feeder landed in the panel, so an answer is not possible. The 120% rule is only if the breaker is at the opposite end of the buss from the main.


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## jtrichard (Jan 30, 2017)

When reading the first reply I realized that I did not say what the sub breakers are for the panels I will look today and post panel breaker sizes for the 2 arrays


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## jtrichard (Jan 30, 2017)

OK 2 Arrays one is breaker-ed at 20 amp other at 35 amp


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## backstay (Feb 3, 2011)

jtrichard said:


> OK 2 Arrays one is breaker-ed at 20 amp other at 35 amp


It's 125% of the inverter(s) not the breaker size. If the backfeed breakers are located opposite the main, you can go to 120% of the buss rating. If they are anywhere else, you can't go over 100% So you can keep the main if the inverter output plus 25% is less than 40 amps(in CA) Read 705.12, like I said, there are four ways to figure it. Apparently your state only allows two. Maybe they allow the forth too. I don't know.


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## chicken steve (Mar 22, 2011)

We just has a 'solar guy' walk onto one of our jobs here as well.

The job is a larger house/attached garage . The poco meter/main is on the garage, pipework goes down into the basement of the house, main panel is there.

The solar guy wants to place the inverter beside our panel & make into it, but wants his 'net meter' on the house, total opposite end from the poco meter

So how would the poco (or any spark) working on that end be aware of another power source? 

I thought that, at least, all disco's should be grouped.....am i close?

~CS~


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## cabletie (Feb 12, 2011)

705.10 Directory.
A permanent plaque or directory denoting the location of all electric power source disconnecting means on or in the premises shall be installed at each service equipment location and at the location(s) of the system disconnect(s) for all electric power production sources capable of being interconnected. The marking shall comply with 110.21(B).
Exception: Installations with large numbers of power production sources shall be permitted to be designated by groups.

There is also a rapid shut down switch. My utility required a disconnect next to the meter before the rapid shutdown was in the code. 

The utility meter is all that needs to be read by the utility. Here the other meter is the SREC meter. They don't trust the watthour meter on the inverter for determining SREC credits. That meter could go next to my bed for all they care.


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