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Wiring Conduit for Solar PV Systems

Scope

During construction, add a 1 inch metal conduit from the Photovoltaic array to the designated inverter location, and add a second 1 inch metal conduit from the inverter location to the electrical service panel.

DOE Zero Energy Ready Home Notes 

The U.S. Department of Energy Zero Energy Ready Home National Program Requirements (Rev. 04) Exhibit 1, Mandatory Requirements, Item 7 Renewable Ready, that all homes must meet the requirements in the Consolidated Renewable Energy Ready Home (RERH) Checklist.

The RERH Checklist requires builders to

  • Install a 1-in. metal conduit for the DC wire run from the designated array location to the designated inverter location (cap and label both ends). (RERHPV Guide 3.2)
  • Install a 1-in. metal conduit from designated inverter location to electrical service panel (cap and label both ends). (RERHPV Guide 3.3)

See the Compliance Tab for related codes and standards requirements, and criteria to meet national programs such as DOE’s Zero Energy Ready Home program, ENERGY STAR Certified Homes, and Indoor airPLUS.

Description

A conduit is intended to protect the wiring leading from the PV array to the inverter and from the inverter to the electrical service panel.  The ends of the conduit should be clearly labeled, particularly if the intent is to install the PV system at a later date.  In areas subject to environmental concerns or hazards, the stub outs should be properly sealed and/or capped to prevent contamination.

To meet the requirements of the DOE Zero Energy Ready Home program, install a 1-inch metal conduit from the designated array location to the designated inverter location with the end of the conduit clearly labeled as a Renewable Energy Ready Home component and indicating its purpose and intended use. The conduit run should be identified on electrical and architectural diagrams to be provided to the homeowner.

Architectural diagram showing metal conduit
Figure 1. Architectural diagram showing metal conduit.

How to Install a Wiring Conduit for a Future Solar Photovoltaic System:

  1. Designate a proposed location for the solar photovoltaic system on the roof. 
  2. Install a 1-inch metal conduit from the attic to the future location of the inverter.  
    1. Begin conduit about 6 inches above the finished insulation depth directly below the designated array location in the attic. Ensure the conduit location in the attic provides at least 18-in. of space below the roof deck and is easily accessible for the future solar installer.
    2. Run the wiring conduit through the home so that the overall length of the conduit is minimized.
    3. Ensure there are three or fewer 90-degree turns from the attic to the designated 4 ftx 4 ft plywood area or provide for accessible pull boxes, as required by the National Electric Code.
    4. Terminate the conduit at the bottom edge of the 4 ft x 4 ft plywood backing for a future inverter.  (Optional) For aesthetic reasons, terminate into a flush mount junction or pull box near the bottom edge of the plywood area.
  3. Install a 1-inch metal conduit from the designated inverter location to the electrical service panel.
  4. To facilitate the wiring of the solar PV system at a later date, the builder may also want to include a pull line in the conduit, particularly if the overall conduit run is lengthy or has multiple bends.
  5. Cap and label both ends of both conduit runs so the text is visible and upright (if possible).  The label should read, “Renewable Energy Ready Home – Solar Photovoltaic Wiring Conduit.”  

Ensuring Success

Ensure adequate utility room size and location for the solar water heating and photovoltaic system components early in the house design process.  

Confirm with local code officials early in the design process what steps are needed to guarantee that installation of PV panels will meet with local codes, homeowner's association covenants, and historic district regulations. 

Protect the electrical and mechanical components of the solar photovoltaic system from bulk moisture, high temperatures, and direct sunlight.  The utility room should be properly ventilated and maintain average indoor temperatures. 

Climate

Among other things, the Consolidated Renewable Energy Ready Home (RERH) Checklist is required only under the following condition related to climate:

-    Location, based on zip code, has at least 5 kWh/m2/day average daily solar radiation based on annual solar insolation using the PVWatts online tool.

Average daily solar radiation

Training

Right and Wrong Images

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Presentations

  1. Zero Energy Ready Home Training
    Author(s): Rashkin
    Organization(s): DOE

Videos

None Available

CAD Images

None Available

Compliance

The Compliance tab contains both program and code information. Code language is excerpted and summarized below. For exact code language, refer to the applicable code, which may require purchase from the publisher. While we continually update our database, links may have changed since posting. Please contact our webmaster if you find broken links.

DOE Zero Energy Ready Home (ZERH) Program

The DOE ZERH Consolidated Renewable Energy Ready Home (RERH) Checklist states

  • Install a 1” metal conduit for the DC wire run from the designated array location to the designated inverter location (cap and label both ends). (This exact language also appears in the EPA Renewable Energy Ready Home – Photovoltaic checklist item number 3.2)
  • Install a 1” metal conduit from designated inverter location to electrical service panel (cap and label both ends). (This exact language also appears in the EPA Renewable Energy Ready Home – Photovoltaic checklist item number 3.3)

Homes that already have a solar hot water system installed do not need to meet the SHW requirements of the Consolidated RERH checklist.

DOE Zero Energy Ready Home National Program Requirements Mandatory Requirement 7 (Renewable Ready) shall be met by any home certified under the DOE Zero Energy Ready Home program, only where all of the following conditions are met:

  1. Location, based on zip code has at least 5 kWh/m2/day average daily solar radiation based on annual solar insolation using PVWatts online tool, AND;
  2. Location does not have significant natural shading (e.g., trees, tall buildings on the south-facing roof, AND;
  3. Home as designed has adequate free roof area within +/-45° of true south as noted in the table below. Note that in some cases a house may have insufficient roof area for the Solar Electric RERH checklist, but it may still have the minimum roof area for the solar thermal RERH Checklist and would therefore have to comply with the Solar Thermal RERH checklist. In other cases, the home may only have adequate south facing roof for the Solar Electric or Solar Thermal RERH Checklist, but not both. In that case the builder can decide which one of those two checklists to apply.

2009, 2012, 2015, and 2018 IECC

Section 401.3 A permanent certificate shall be posted on or near the electrical distribution panel that lists types and efficiencies of water heating, heating, and cooling equipment, as well as insulation R values, and window U and SHGC factors.

Retrofit: 2009, 2012, 2015, and 2018 IECC

Section R101.4.3 (Section R501.1.1 in 2015 and 2018 IECC). Additions, alterations, renovations, or repairs shall conform to the provisions of this code, without requiring the unaltered portions of the existing building to comply with this code. (See code for additional requirements and exceptions.)

200920122015, and 2018 IRC

M2301 Solar Energy Systems (Solar Thermal Energy Systems in 2015 and 2018 IRC)  - See requirements for solar water heating systems.

Retrofit: 2009, 2012, 2015, and 2018 IRC

Section N1101.3 (Section N1107.1.1 in 2015 and 2018 IRC). Additions, alterations, renovations, or repairs shall conform to the provisions of this code, without requiring the unaltered portions of the existing building to comply with this code. (See code for additional requirements and exceptions.)

Appendix J regulates the repair, renovation, alteration, and reconstruction of existing buildings and is intended to encourage their continued safe use.

2009, 2012, 2015, and 2018 International Mechanical Code (IMC)

Follow the requirements for solar water heating systems found in the IMC, Chapter 14, Solar Systems (Solar Thermal Systems in 2018 IMC).

2014 National Electric Code (NEC)

Follow the requirements for solar photovoltaic (PV) systems found in the 2014 National Electric Code (NEC), Article 690, PV Power Systems, and Article 110, Requirements for Electrical Installations.

More Info.

Access to some references may require purchase from the publisher. While we continually update our database, links may have changed since posting. Please contact our webmaster if you find broken links.

Case Studies

None Available

References and Resources*

  1. Author(s): Department of Energy
    Organization(s): DOE
    Publication Date: April, 2017

    Standard requirements for DOE's Zero Energy Ready Home national program certification.

  2. Author(s): Brooks, Dunlop
    Organization(s): NABCEP
    Publication Date: March, 2012
    This Photovoltaic (PV) Installer Resource Guide is an informational resource covering basic requirements for PV installations intended for individuals pursuing the Photovoltaic Installer Certification credential offered by the North American Board of Certified Energy Practitioners (NABCEP).
  3. Author(s): Building Science Corporation
    Organization(s): Building Science Corporation
    Publication Date: June, 2006

    Report aiming to "de-mistify" technology and economic considerations of residential PV systems.

  4. Author(s): U.S. Environmental Protection Agency
    Organization(s): EPA
    Publication Date: May, 2014

    Website tool intended to guide home builders in assessing whether a new home has the proper physical orientation to support a future installation of a solar energy system.

Contributors to this Guide

The following authors and organizations contributed to the content in this Guide.

Last Updated: 08/08/2014