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Photovoltaic Power Systems and the National Electrical Code: Suggested Practices SAND2001-0674
Unlimited Release
Printed March 2001
Supersedes SAND96-2797
Dated December 1996
Photovoltaic Power Systems
and the
National Electrical Code:
Suggested Practices
John Wiles
Southwest Technology Development Institute
New Mexico State University
1505 Payne Street
Las Cruces, NM 88003
ABSTRACT
This suggested practices manual examines the requirements of the National Electrical Code (NEC) as they apply to
photovoltaic (PV) power systems. The design requirements for the balance of systems components in a PV system
are addressed, including conductor selection and sizing, overcurrent protection ratings and location, and disconnect
ratings and location. PV array, battery, charge controller, and inverter sizing and selection are not covered, as these
items are the responsibility of the system designer, and they in turn determine the items in this manual. Stand-alone,
hybrid, and utility-interactive PV systems are all covered. References are made to applicable sections of the NEC.
National Electrical Code
® and NEC ® are registered trademarks of the National Fire Protection Association, Inc., Quincy, Massachusetts 02269 PHOTOVOLTAIC POWER SYSTEMS and the NATIONAL ELECTRICAL CODE
SUGGESTED PRACTICES
ii
ACKNOWLEDGMENTS
Numerous persons throughout the photovoltaic industry reviewed the drafts of this manual and provided comments
which are incorporated in this version. Particular thanks go to Joel Davidson, Mike McGoey and Tim Ball, George
Peroni, Bob Nicholson, Mark Ralph and Ward Bower, Steve Willey, Tom Lundtveit, and all those who provided
useful information at seminars on the subject. Appendix E is dedicated to John Stevens and Mike Thomas at Sandia
National Laboratories. Document editing and layout by Ronald Donaghe, Southwest Technology Development
Institute.
TECHNICAL COMMENTS TO:
John C. Wiles
Southwest Technology Development Institute
New Mexico State University
P.O. Box 30001/Dept. 3 SOLAR
1505 Payne Street
Las Cruces, New Mexico 88003-0001
Request for copies to Photovoltaic Systems Assistance Center at Sandia National Laboratories
505-844-4383
PURPOSE
This document is intended to contribute to the wide-spread installation of safe, reliable PV systems that meet the
requirements of the National Electrical Code.
DISCLAIMER
This guide provides information on how the National Electrical Code (NEC) applies to photovoltaic systems. The
guide is not intended to supplant or replace the NEC; it paraphrases the NEC where it pertains to photovoltaic
systems and should be used with the full text of the NEC. Users of this guide should be thoroughly familiar with the
NEC
and know the engineering principles and hazards associated with electrical and photovoltaic power systems.
The information in this guide is the best available at the time of publication and is believed to be technically
accurate. Application of this information and results obtained are the responsibility of the user.
In most locations, all electrical wiring including photovoltaic power systems must be accomplished by a licensed
electrician and then inspected by a designated local authority. Some municipalities have additional codes that
supplement or replace the NEC. The local inspector has the final say on what is acceptable. In some areas,
compliance with codes is not required.
NATIONAL FIRE PROTECTION ASSOCIATION (NFPA) STATEMENT
The National Electrical Code including the 1999 National Electrical Code is published and updated every three
years by the National Fire Protection Association (NFPA), Batterymarch Park, Quincy, Massachusetts 02269. The
National Electrical Code
and the term NEC are registered trademarks of the National Fire Protection Association
and may not be used without their permission. Copies of the current edition of the National Electrical Code are
available from the NFPA at the above address, most electrical supply distributors, and many bookstores.
In most locations, all electrical wiring including photovoltaic power systems must be accomplished by a licensed
electrician and then inspected by a designated local authority. Some municipalities have additional codes that
supplement or replace the NEC. The local inspector has the final say on what is acceptable. In some areas,
compliance with codes is not required. PHOTOVOLTAIC POWER SYSTEMS and the NATIONAL ELECTRICAL CODE
SUGGESTED PRACTICES
iii
Table of Contents
SUGGESTED PRACTICES......................................................................................................1
Introduction................................................................................................................................1
Methods of Achieving Objectives..............................................................................................3
Scope and Purpose of the NEC ..................................................................................................4
This Guide..................................................................................................................................5
Photovoltaic Modules ................................................................................................................5
Module Marking ............................................................................................................6
Module Interconnections................................................................................................7
Tracking Modules ..........................................................................................................8
Terminals .......................................................................................................................8
Transition Wiring.........................................................................................................10
Wiring ......................................................................................................................................12
Module Connectors......................................................................................................12
Module Connection Access .........................................................................................12
Splices..........................................................................................................................12
Conductor Color Codes................................................................................................14
Battery Cables..............................................................................................................15
Ground-Fault Protection and Array Disablement....................................................................15
Ground-Faults ..............................................................................................................15
PV Array Installation and Service ...............................................................................16
Grounding ................................................................................................................................17
GroundingSystem.....................................................................................................17
Size of Grounding Electrode Conductor..........................................................17
Point of Connection .........................................................................................18
Unusual Grounding Situations.........................................................................19
Charge ControllersSystem Grounding.........................................................20
GroundingEquipment...............................................................................................20
Inverter AC Outputs.....................................................................................................21
Backup Generators.......................................................................................................21
Suggested AC Grounding ............................................................................................21
Grounding Electrode....................................................................................................22
Conductor Ampacity................................................................................................................23
Stand-Alone SystemsInverters.................................................................................25 PHOTOVOLTAIC POWER SYSTEMS and the NATIONAL ELECTRICAL CODE
SUGGESTED PRACTICES
iv
Overcurrent Protection.............................................................................................................26
Ampere Rating.............................................................................................................26
Testing and Approval...................................................................................................27
Branch Circuits ............................................................................................................29
Amperes Interrupting Rating (AIR)Short-Circuit Conditions .................................31
Fusing of PV Source Circuits.......................................................................................32
Current-Limiting FusesStand-Alone Systems ...........