sunMAX - From End-Run to Main Panel (Branch Circuit Wiring for North America)

Overview


Understanding the electrical components and terminology used by PV installers can pose a difficult barrier-to-entry for WISPs and DIY-ers. One objective of the sunMAX product line is to provide a straightforward, turn-key solution for PV installers.

The purpose of this Knowledge Base article will be to provide an overview of sunMAX system integration to help installers communicate effectively with industry professionals (electricians, AHJs, inspectors, etc) in each phase of a sunMAX install.

Note: This article does not cover interconnection in depth. See Help Center article sunMAX - Interconnection for more information regarding proper interconnection methods and scenarios.

Lessons 2 and 7 of the Ubiquiti Residential Solar Specialist Online Course also cover many subjects in this article.

Table of Contents


  1. Electrical Terminology
    1. Branch Circuit
    2. Microinverter
    3. End-Run Connector
    4. Main Electrical Panel
    5. Subpanel
    6. Solar Load Center
    7. Main Breaker
    8. Main Disconnect
    9. Photovoltaic AC Disconnect
    10. Conductor
    11. Circuit Breaker
    12. Irreversible Splice
    13. Interconnection
    14. Load-Side Connection
    15. Supply-Side Connection
  2. Frequently Asked Questions
    1. Which Conductors are in a Branch Circuit Home Run?
    2. How do I properly ground a sunMAX array?
    3. Must the Branch Circuit Home Run always be run inside a conduit?
    4. What is a Junction Box?
    5. When should I perform a Rooftop Penetration vs run conduit externally?
  3. Example Scenarios
  4. Related Articles

What electrical terminology do I need to know?


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Branch Circuit


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A Branch Circuit, in the traditional sense, refers to a utilization circuit disseminating from a circuit breaker panel for the supply of one or more loads (lighting, receptacles, appliance, etc).  In a sunMAX PV system, a branch circuit refers to the circuit that delivers the power output of one to fifteen parallel-connected sunMAX microinverters (in the solar industry, this is often referred to as a "Home Run").  A sunMAX PV system can comprised of more than one branch circuit when there are more than 15 panels or when panels are separated physically.


Microinverter


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The Microinverter is the device on each PV panel that converts DC from the PV panel to an AC output. The sunMAX Microinverter optimizes power output for each panel and synchronizes the output to the grid frequency and voltage. Microinverters are connected in AC “strings” with Y-Cables (see below) and Jumper Cables (longer cables used for inter-row connections) Each string of y-cables is terminated with an End-Run Connector.  

 


End-Run Connector


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The End-Run Connector (or more commonly “End-Run”) is the sunMAX component where AC output of the PV array is first made available for connection to existing premises wiring. sunMAX End Run Connectors accept 10-12 AWG (2.05-2.59mm) copper wires, and can handle up to 15 sunMAX microinverters per End-Run.

The sunMAX Design Team uses a Conductor Schedule when determining the NEC-compliant minimum conductor size and breaker size for a branch circuit home run. The conductor schedule calculation requires inputs such as: one-way circuit length, ASHRAE temperature ratings, and array size.  


Main Electrical Panel


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A Main Electrical Panel is the Site’s primary breaker box connected to the electric meter provided by the utility. It also is called many different names,including Distribution Board, Load Center, etc. The Electrical Panel should contain circuit breakers for different loads, including perhaps, circuit breakers that connect to other Electrical Subpanels (see below). The Panel’s busbar rating determines the maximum power limit for all sources of power reaching the breaker box. The sunMAX system can interconnect to the Main Panel if the Main Panel meets NEC requirements for busbar rating, overcurrent protection, and inverter breaker location. See NEC Article 705.12 for a thorough discussion of where and how a PV system can interconnect to existing premises wiring.


Subpanel


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A Subpanel is a local breaker box that Main Panel, meant for the supply of a subset of house loads.  Typically these are used to expand the premises electrical capacity when the main panel is fully used with existing circuits. The sunMAX system can interconnect to a sub-panel if the sub-panel and Main Panel meet NEC requirements for busbar rating, overcurrent protection, and inverter breaker location. See NEC Article 705.12 and the sunMAX Interconnection Knowledge Base article for a thorough discussion of where and how a PV system can interconnect to existing premises wiring. 


Solar Lead Center


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A Solar Load Center is a dedicated-use circuit breaker panel that has only PV circuit breakers and no load circuit breakers installed. The solar load center collects the output of microinverter branch circuits and combines the PV system output to a single circuit for interconnection to wiring at the premises (such as a Subpanel).


Main Breaker


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Main Breaker refers to the breaker within some breaker boxes that will disconnect the breaker box from upstream supply. Not all breaker panels include a main breaker. If a house Main Panel includes six or fewer branch circuit breakers, a Main Breaker is not required by the NEC. 

 


Main Disconnect


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Main Disconnect refers to a circuit breaker or fused disconnect switch that will disconnect and shut down a house’s entire electrical system. If not located in the house Main Panel, the Main Disconnect will be located at the house’s utility meter. In most houses, the Main Panel Main Breaker is the Main Disconnect for the house’s entire electrical system. However, a premises having six or fewer breakers or switches located in a panel at the meter does not require a Main Disconnect.


Photovoltaic AC Disconnect


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A Photovoltaic AC Disconnect refers to a disconnect switch that will disconnect all PV arrays from the house’s electrical system.  AC disconnects are sometime required by the local power company or the AHJ.  sunMAX requires a 2 pole 240V disconnect with an amperage rating greater than or equal the solar CB rating.   For load-side connections, an unfused AC disconnect is generally used, and for a line-side connection a fused AC disconnect is required. 

 


Conductor


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A Conductor is a wire made of copper or aluminum and can be covered with a coat of insulation. In the US, all conductors are sized according to the American Wire Gauge (AWG) scale. The sunMAX End-Run Connector accepts 10-12 AWG (2.05-2.59mm) copper conductors. However, these wires can be spliced to a larger home run conductor to minimize the voltage drop and power loss. Many AHJ’s will require engineering plans to call out conductor sizes.

The type of insulation used on the wire is important.  Typically for solar and outdoor installations, THWN-2 wire is required which is rated at 90°C for wet or dry locations.  THWN stands for Thermoplastic Heat and Water-resistant Nylon-coated.  The wire rating is usually printed on the jacket of the wire.  Many times wire is dual rated for many different rating types.

In the US, the wires should typically be colored as follows:

Line 1 Black
Neutral White
Line 2 Red
Grouds Green or green-yellow

When using 4 AWG or larger wire the ends of the wire can be colored with electrical tape of the proper color instead.

It is important when using aluminum conductors that you follow the manufacturer's installation instructions and use only devices rated for aluminum wire usage.


Circuit Breaker


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A Circuit Breaker is an overcurrent protection device that connects the microinverter branch circuit home run to a Main Panel, Sub-Panel or Photovoltaic Load Center. There are two types of circuit breakers commonly used in the US: One-pole Circuit Breakers accept one current carrying conductor (120V). One pole breakers are commonly used for smaller household appliances. Whereas, two pole breakers accept two current carrying conductors (240V) and connects across both bus bars in the breaker panel. Both poles are connected so both will trip if too much current is detected.  The sunMAX system requires a 2 pole breakers to be used for microinverter branch circuit protection and Solar Load Center protection.

Note that the larger the array, the higher current rating will be required for the resulting circuit breaker (e.g. a 15A 2-pole breaker can protect up to 11 panels and a 20A 2-pole breaker is required for 12-15 panels). 


Frequently Asked Questions


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Which Conductors are in a Branch Circuit Home Run?


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In the US,  there are four wires per microinverter branch circuit where it originates at the sunMAX End Run Connector. There are three current-carrying conductors called Line 1, Neutral, and Line 2 denoted by black, white and red wires, respectively. Each microinverter branch circuit also includes a green Equipment Grounding Conductor (EGC), and the branch circuit home run includes an EGC when it originates at the End Run. The NEC allows the combination of several EGCs into a single EGC when multiple home run circuits occupy a common conduit.

 


How do I properly ground a sunMAX array?


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In addition to the four wires that connect to a sunMAX End-Run, a Grounding Electrode Conductor (a minimum AWG #6 copper wire, green insulated or bare) must be run continuously (or with irreversible splices) from a house’s grounding rod to an external Grounding Lug on a sunMAX Panel Connector at each physically separated subarray (up to 60 panels). A single GEC can ground more than one microinverter branch circuit, as long as the different branch circuits comprise a single physically connected array (up to 60 panels). Where more than one physical subarray exists, a GEC/GEC tap in compliance with NEC 690.47(B) must be run to each physical subarray.  In situations with multiple individual arrays, multiple GEC’s can be spliced together using an irreversible splice.

Depending on which version of the NEC is being used, and where the sunMAX system is being interconnected to the premises wiring, the EGC and GEC may or may not be combined (spliced) in the vicinity of the array. The termination point of the GEC at the premises wiring system also depends on which NEC version is being used, and where the sunMAX system interconnects to the premises wiring. NEC article 690.47 provides the requirements for GEC termination and combination (or not) with the EGC.


Irreversible Splice


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An Irreversible Splice is the electrical conjoinment of two or more conductors that cannot be undone. Under NEC 250.64(C), a Grounding Electrode Conductor (GEC) must be continuously run from a houses grounding rod (or interconnection panel busbar, depending on applicable NEC version) to the grounding point (Panel Connector grounding lug on each physically separate PV array. Any GEC taps to the main continuous GEC, as allowed under NEC 690.47(B), must be made using connectors listed as grounding and bonding equipment (Panduit CTAPF series compression lugs, for example).

Note: The sunMAX system GEC(s) must transition from external wiring on the roof to conduit, either for penetration through the roof, or for external conduit routing to the Photovoltaic Load Center.


Must the Branch Circuit Home Run always be run inside a conduit?


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Except for certain conductor types such as Type PV or Type USE, the NEC requires all single conductors to be installed in conduit. Different AHJ’s have different requirements specially about which type of conduit that is acceptable (EMT, PVC, flex, etc.) Consult your local AHJ to determine their specific requirements.

The figure below shows an example of the conduit used to protect the exposed run of wires from the End Run to a commercially available rooftop pass-through enclosure.


What is a Junction Box?


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A Junction Box (commonly referred to as a “JB” or “Combiner Box”) is any enclosed box installed in the electrical circuit.  Junction boxes can be used to combine multiple end run conductors into a single conductor before running to a house’s main panel. This wire splicing declutters the conduit and allows smaller/less conduit to be used to minimize the installation labor.

Junctions boxes can be either metal or plastic depending on AHJ requirements. Note that metal enclosures will need to be grounded. Outdoor located junction boxes typically need to be a minimum of NEMA 3R rated.

See the figure below for an example of a junction box that is used to join two smaller arrays into a single circuit running to a sub panel.


When should I perform a Rooftop Penetration vs run conduit externally?


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The choice between penetrating the roof and running wire through the attic vs running it external comes down to the preference of the installer and installation constraints. For instance, some houses do not have adequate attic spaces to properly access the roof penetration from the inside in certain locations. In situations like these you either need to run conduit across the roof to a better location or run the externally down an exterior wall.    

It is important to note that whenever you penetrate the roof surface that the penetration needs to be sealed and flashed to meet building codes.  Many commercially available flashings exist to run conduit through any type of roofing surface.

The requirements for supporting PVC conduit are given in NEC Article 352.

PVC conduit must be supported within 3' of any box or enclosure. PVC conduit 1" and smaller must be supported at intervals not greater than 3' throughout the conduit run. PVC conduit from 1-1/4" through 2" size must be supported at intervals not greater than 5' throughout the conduit run.

The requirements for supporting EMT conduit are given in NEC Article 358. EMT conduit must be supported within 3' of any box or enclosure. EMT conduit shall be securely fastened in place at intervals not greater than 10' throughout the conduit run.

Note that an extra solar roof mount, such as the SM-RM-C and/or SM-RM-T, can be used as a conduit support if needed.

Generally speaking it is good practice to locate the End Run(s) closest to the potential penetration or the main panel.  This minimizes the length of the wiring required and the subsequent cost of the installation.




Interconnection


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Our sunMAX is an on-grid solar solution, meaning that, in order for it to produce energy, it must first receive power from the grid. A connection to the grid can be performed in two ways; a load-side or line-side (also called supply-side) connection.

Load-Side Connection

In a Load-Side Connection the PV array is connected via circuit breaker(s) or fused disconnect  at some point on the load side of the premises main utility disconnect. Load-side connections are preferred for PV installs and require no utility intervention before working on the premises wiring. In cases where there are not enough circuit breaker spaces on the house’s main panel, a new sub-panel can to be installed and fed into the house’s main panel.

Supply-Side Connection

In a Supply-Side Connection the PV is interconnected (using a fused disconnect) on the utility “supply” side of the premises main utility disconnect. Supply-side connections are used when the existing load side equipment does not meet NEC size requirements for interconnection.  Supply-side connections (also referred to as “line-side” connections) are less common, must meet additional  NEC requirements, and undergo greater scrutiny by the AHJ. Always be sure to work with a licensed Electrician when installing a supply-side connection.  Note that some AHJs do not permit line-side taps to busbars, so check with your local AHJ first.  

For more information on Load-Side and Supply-Side Connections, refer to NEC Article 705.12.


Example Scenarios


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Below are five feasible home run methods.

1. 8-Panel array terminating at a single breaker.

2. Two separate 8-panel arrays terminating at separate breakers. Since there are 16 panels total, this design requires two end run connectors and two separate branch circuits.

Note: two inverter breakers are permitted by the NEC only in a Solar Load Center, or in a premises panel meeting the requirements of NEC Article 705.12(D)(2)(3)(c) and NEC Article 705.12(D)(1).

3. Two separate 8-panel systems joined by a junction box and terminating at one breaker. Multiple branch circuits can be combined in JB to minimize breaker space.

4. Two 4-panel arrays on separate rooftops connected by a junction box and terminating to one breaker. In designs where multiple arrays are physically separate, a junction box can be conveniently placed on the rooftop, on the house exterior, or near the house’s main panel to combine branch circuits and conserve breaker space.

 

 

 

5. Two 4-panel arrays in close proximity connected by two ½ Jumper Cables and a conduit run; terminating to a single breaker. A sunMAX Jumper Cable can be spliced and used with conductors to electrically connect multiple arrays in close proximity.

 

Have additional questions regarding electrical contracting procedures? The sunMAX Design Team is available via chat support or by phone at (801) 618-0488.


Related Articles


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sunMAX - Interconnection

 

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