PV line side connection question

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Robert Gisch

Member
Location
Chicago
How to accomplish a line side connection for a Enphase PV system? Is it acceptable to splice the service entrance conductors? If so, is it acceptable to splice service entrance conductors (to the tap conductors feeding the combiner box) inside the panel which contains the main? Is a separate tap box required? Is a back feed breaker required? Stumbled on reference which stated not acceptable to splice line side connection in panel containing the main. But now I can find it. Not sure where I saw it. Please help.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
How to accomplish a line side connection for a Enphase PV system? Is it acceptable to splice the service entrance conductors? If so, is it acceptable to splice service entrance conductors (to the tap conductors feeding the combiner box) inside the panel which contains the main? Is a separate tap box required? Is a back feed breaker required? Stumbled on reference which stated not acceptable to splice line side connection in panel containing the main. But now I can find it. Not sure where I saw it. Please help.

I don't have much experience with microinverters, but line side interconnections do not use backfed breakers. I also don't know what you mean by "tap conductors feeding the combiner box". Enphase microinverters do not use combiner boxes.

Are you sure that you need to connect to the line side of the service? What is your total PV amperage and what is the rating of the service panel busbars?
 

Robert Gisch

Member
Location
Chicago
I don't have much experience with microinverters, but line side interconnections do not use backfed breakers. I also don't know what you mean by "tap conductors feeding the combiner box". Enphase microinverters do not use combiner boxes.

Are you sure that you need to connect to the line side of the service? What is your total PV amperage and what is the rating of the service panel busbars?

I didn't phrase the question well. It was a late night and the more I thought about it, the more I was confusing myself. After a good night sleep things have clarified. After a great deal of research I have decided to pass the inspection despite may earlier concerns. The entire configuration was not what I expected to see. I have attended classes and seminars, contributed to a few installations, but this is not a common technology in my jurisdiction. I wanted to be certain I was doing my due diligence. Its just a small array, 3 source circuits, enphase microinverters, line side connection to service entrance conductors. Straight forward really. When I arrived on site, I expected to see a combiner box on the roof and a back feed breaker in the panel. When faced with a configuration I was not familiar with I began to question. And I'm glad I did, it was an opportunity to learn something. Considering the existing conditions, I can now better understand the benefits of a line side connection. Thank you for your reply.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
I didn't phrase the question well. It was a late night and the more I thought about it, the more I was confusing myself. After a good night sleep things have clarified. After a great deal of research I have decided to pass the inspection despite may earlier concerns. The entire configuration was not what I expected to see. I have attended classes and seminars, contributed to a few installations, but this is not a common technology in my jurisdiction. I wanted to be certain I was doing my due diligence. Its just a small array, 3 source circuits, enphase microinverters, line side connection to service entrance conductors. Straight forward really. When I arrived on site, I expected to see a combiner box on the roof and a back feed breaker in the panel. When faced with a configuration I was not familiar with I began to question. And I'm glad I did, it was an opportunity to learn something. Considering the existing conditions, I can now better understand the benefits of a line side connection. Thank you for your reply.
I'm glad to help, but I am curious. A "small" array generally doesn't require a line side tap. Would a backfed breaker the correct size for the array plus the rating of the main breaker have exceeded 120% of the busbar rating in the main panel?
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
As an installer I only do line side taps within the existing service enclosure if there is plenty of wire bending space. Namely, I try to meet 312.6 and 312.8, at least by my eyeball.

I think you should study your terminology and make sure not to confuse DC and AC definitions. "Combiner box" and "source circuit" are DC definitions that don't apply to wiring methods for micro-inverters. I suspect when you say there are 3 source circuits you really mean three AC branch circuits. They may be combined in a subpanel, but we usually call that an "AC combiner" or a "solar subpanel" to distinguish from DC combiner boxes.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
As an installer I only do line side taps within the existing service enclosure if there is plenty of wire bending space. Namely, I try to meet 312.6 and 312.8, at least by my eyeball.

I think you should study your terminology and make sure not to confuse DC and AC definitions. "Combiner box" and "source circuit" are DC definitions that don't apply to wiring methods for micro-inverters. I suspect when you say there are 3 source circuits you really mean three AC branch circuits. They may be combined in a subpanel, but we usually call that an "AC combiner" or a "solar subpanel" to distinguish from DC combiner boxes.

So, do you also do line side taps only when you cannot connect through a backfed breaker?
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
So, do you also do line side taps only when you cannot connect through a backfed breaker?

You mean when there's no space left? I think I've done that once. More often I just add a sub off the existing panel and move a couple circuits to it. Every job is a little different.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
The strongest reason for using a line side tap is that you cannot satisfy the 120% rule in an existing main or subpanel configuration.
And the PV disconnect for line side will also be a backfed breaker, just not a branch breaker.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
The strongest reason for using a line side tap is that you cannot satisfy the 120% rule in an existing main or subpanel configuration.
And the PV disconnect for line side will also be a backfed breaker, just not a branch breaker.
Here in Austin they do not allow a line side connection through a breaker. It must be through a fused disco.
 

SolarPro

Senior Member
Location
Austin, TX
Here in Austin they do not allow a line side connection through a breaker. It must be through a fused disco.

What about a supply-side connection made in a main distribution panel with an extra breaker or breaker space? Things could have changed, but they used to allow that.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
What about a supply-side connection made in a main distribution panel with an extra breaker or breaker space? Things could have changed, but they used to allow that.
Unless your main distribution panel is MLO with multiple parallel service disconnect handles (breakers), that would not be a supply side connection. It would be a load side connection.
 

SolarPro

Senior Member
Location
Austin, TX
This is from a UL white paper on molded case circuit breakers:

5. Line and Load Identification ? A circuit breaker may or may not be marked ?Line? and
?Load.? If it does not have this marking, it is acceptable for reverse connection. A breaker with
interchangeable trip units is marked ?Line? and ?Load,? unless there is no risk of electric shock when
changing the trip unit.

The Code also indicates that you can backfeed any breaker that is not marked "line" and "load." And most breakers don't have this marking, in my experience. (Ground-fault circuit breakers are a notable exception.)
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
Correct. But what about that MLO scenario? Why require a fused disco for a supply-side connection?
I dunno, but I had a case come up where the customer wanted me to use an enclosed breaker instead of a fused disco for a supply side interconnection because the breaker enclosure would be smaller. Austin Energy said no, it must be a disco. Their system, their rules.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
I dunno, but I had a case come up where the customer wanted me to use an enclosed breaker instead of a fused disco for a supply side interconnection because the breaker enclosure would be smaller. Austin Energy said no, it must be a disco. Their system, their rules.
Could be they were more interested in the visible break contacts than the fuse. But that may not have made it into the text of the rule.
FWIW, that would allow you to use a non-fused disco plus a breaker.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
Could be they were more interested in the visible break contacts than the fuse. But that may not have made it into the text of the rule.
FWIW, that would allow you to use a non-fused disco plus a breaker.
Maybe so, but of course that would have taken up even more space and would have cost more than a fused disco, so it's a moot point.
 
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