Understanding and Troubleshooting Grid Connected PV systems

PV System Notes


This Note section generally follows the wiring diagram on the left. The drawing illustrates a 3-phase system, but a single-phase system follows the same general design.


The allowed number of series modules depends on the inverter design and local low temperature values.


PV system grounding is very important.  See the Grounding section immediately below the the PV modules on the diagram for more detail.


More than two module strings in parallel must have fuse protection per module listing. Fuses may be located in a DC combiner enclosure or in the inverter. DC disconnects may be separate, or part of the combiner or inverter.


Most inverters have the ability to display operational data and fault information on a digital display. A typical string inverter design is shown in this example. Note: There are other designs available, such as microinverters. The inverter may be marked for positive or negative ground (some PV modules perform better with a specific polarity). Note: No polarity is shown on this diagram. The inverter will likely have a fuse for detecting an array wiring ground fault. Some inverters do not ground reference either polarity of the array and use other methods to detect a ground fault.


A separate kWh meter may be included in the design to record the energy generated by the PV system.


Many electric utilities require the inclusion of a separate lockable AC disconnect switch that is readily accessible to utility crews. These disconnects typically do not have fuses, and access may be locked by an electric utility padlock. Some utilities require a separate GEC bond from the inverter to the main service ground.


The drawing shows a load side connection of the inverter circuit to the service entrance. The circuit breaker is typically required to be on the opposite end of the distribution buss from the main circuit breaker and must be marked.


Labels specifying voltage and current values are required on many components in the system.


Refer to NEC Art. 690 for additional requirements.

PV System Notes

Instructions on using this page

Safety Warning


The systems outlined in this article use high DC voltages that cannot be simply turned off. This discussion is limited to test techniques that do not require disassembly of the PV array, but there is some exposure to terminals within the equipment that will normally have high voltages. Any work on roofs requires fall protection for safety.

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Troubleshooting Help



Photovoltaic (PV) power systems are becoming very common as the cost of these systems is declining and the availability of incentives that further lower the costs.  The technology is supported by codes and standards (NEC Article 690 is the main code), Listed equipment, and training programs that should result in safe and reliable systems.  Most systems are installed and maintained by companies specializing in the technology, but other electricians are called upon to service and/or work on related wiring of these systems.


This article is intended to provide some guidance to persons who need a basic understanding of these systems in order to check out a system that may be non-performing or under-performing.  This article covers one of the basic types of PV system, string inverter based systems that use a single inverter to connect PV modules to the utility grid without any battery backup.  There are other designs such as micro-inverters (one inverter per PV module) and systems with multiple inverters or large utility scale inverters.


Basic System Design and Operation


The PV industry uses some terminology that is not common.  PV modules are the basic building block and generally consist of PV cells laminated behind glass and encapsulated with insulating materials and mounted in a frame.  There are other designs that are flexible and are adhesively mounted to metal roofs.  And assembly of modules on a mounting frame is a panel, and the complete assembly of modules/panels is an array.  An inverter is used to convert the DC power from the array into controlled AC power suitable for connection to the utility grid.  Other wiring components are involved.


The figure on the main page shows the basic 3-Line diagram of a PV system of the design generally called ‘String Inverter’ where one or more series strings of PV modules are used to generate the higher voltages (250-500VDC is typical) needed by these inverters.  The text next to the diagram describes the function of the components and some of the special considerations.


These systems function automatically and do not require any user or owner interaction.  If the utility power is interrupted or is not within the normal limits of voltage and frequency, the system will stop operating until the utility returns to stability within these limits.  The inverters are designed to detect a ground fault within the PV array and associated components and cease operation.


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