breaker size

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cowboyjwc

Moderator
Staff member
Location
Simi Valley, CA
I am doing a plan check and I have a issue. They are showing a 100 amp panel with no main breaker and a 35 amp solar breaker. I'm saying that you can still only install at 120% of the bus rating whether a main breaker is installed or not. Am I correct? Code section?
 

augie47

Moderator
Staff member
Location
Tennessee
Occupation
State Electrical Inspector (Retired)
I may not be visualizing it correctly, but would the panel not require a main integral with or ahead of if per 408.36 ?
If so, it seems 705.12(D)(2) would come into play.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
If it's a 100A MLO service panel, then it's not subject to the 120% rule because it's a line-side tap.
True, but many AHJ's will not allow you to mount a solar breaker in a MLO panel with no OCPD ahead of it.
 

Smart $

Esteemed Member
Location
Ohio
True, but many AHJ's will not allow you to mount a solar breaker in a MLO panel with no OCPD ahead of it.
I recall you telling us this several to many times. That should require a Code amendment by the AHJ. The only non-amendment way is through denial of service by POCO under the auspices of the PUC. But I do understand some AHJ's get away with enforcing errant interpretations of Code.

BTW, cowboyjwc is a representative of his AHJ. I think he would have mentioned it if that was the case in his jurisdiction. :slaphead:
 

iwire

Moderator
Staff member
Location
Massachusetts
I recall you telling us this several to many times. That should require a Code amendment by the AHJ. The only non-amendment way is through denial of service by POCO under the auspices of the PUC. But I do understand some AHJ's get away with enforcing errant interpretations of Code.

In your personal opinion.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
I recall you telling us this several to many times. That should require a Code amendment by the AHJ. The only non-amendment way is through denial of service by POCO under the auspices of the PUC. But I do understand some AHJ's get away with enforcing errant interpretations of Code.

AHJ's are not bound to enforce only the NEC. They can (and do) make policies that add restrictions to (or remove them from) those dictated by the NEC. An example is color coding of conductors; San Antonio and Austin both have conductor color coding rules, and they are not the same as each other. Another: Austin has adopted the 2014 NEC but does not enforce 690.12 (rapid shutdown), although they will begin enforcing it later this month (January 2016). SATX does enforce 690.12.

My company installs a lot of residential PV in San Antonio, and the majority of residential services we encounter there are MLO panels. In those cases we must either upgrade the MDP to one with a main breaker and electrical space under the 120% rule, or we must install a tap box for a supply side interconnection. It is the same in Austin except that Austin allows tapping via insulation piercing connectors inside the MDP while SATX does not. Neither AHJ will allow landing a backfed breaker in an MLO panel with no OCPD ahead of it.

It makes no difference whether or not this is "legal". Do it their way or fail your inspection and your customer cannot turn his system on.
 

Smart $

Esteemed Member
Location
Ohio
AHJ's are not bound to enforce only the NEC. They can (and do) make policies that add restrictions to (or remove them from) those dictated by the NEC. An example is color coding of conductors; San Antonio and Austin both have conductor color coding rules, and they are not the same as each other. Another: Austin has adopted the 2014 NEC but does not enforce 690.12 (rapid shutdown), although they will begin enforcing it later this month (January 2016). SATX does enforce 690.12.

My company installs a lot of residential PV in San Antonio, and the majority of residential services we encounter there are MLO panels. In those cases we must either upgrade the MDP to one with a main breaker and electrical space under the 120% rule, or we must install a tap box for a supply side interconnection. It is the same in Austin except that Austin allows tapping via insulation piercing connectors inside the MDP while SATX does not. Neither AHJ will allow landing a backfed breaker in an MLO panel with no OCPD ahead of it.

It makes no difference whether or not this is "legal". Do it their way or fail your inspection and your customer cannot turn his system on.
From what you describe, they don't outright deny 705.12(A) implementation, but their policy controls the implementation and they are using 110.2 to do it. That sort of legality is hard to fight. Other than the unaware implementing a violation of their policy and having to pay for the revision themselves, any elevation in cost is ultimately absorbed by the consumer.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
My company installs a lot of residential PV in San Antonio, and the majority of residential services we encounter there are MLO panels. In those cases we must either upgrade the MDP to one with a main breaker and electrical space under the 120% rule, or we must install a tap box for a supply side interconnection. It is the same in Austin except that Austin allows tapping via insulation piercing connectors inside the MDP while SATX does not. Neither AHJ will allow landing a backfed breaker in an MLO panel with no OCPD ahead of it.

It makes no difference whether or not this is "legal". Do it their way or fail your inspection and your customer cannot turn his system on.
That doesn't mean that I don't argue points of code with inspectors. I do and I even win sometimes. I lost this one.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
From what you describe, they don't outright deny 705.12(A) implementation, but their policy controls the implementation and they are using 110.2 to do it.
And I guess it's possible that they put that much thought into it. :D
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
Is it really 'many'? I think you've mentioned Austin before. How many others have you run into? I have never run into such a one.
Not that many, but they all had the same rule. They were all in Texas; maybe that has something to do with it.

But point taken; change "many" to "some".
 
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