After much technical discussion in Code-Making Panel 4 and an appeal to the NFPA Standards Council, the requirements for a new product involving photovoltaic (PV) installations was inserted into 690.11 in the 2011 National Electrical Code (NEC). This new controversial product, a PV direct-current (DC) arc-fault circuit interrupter (AFCI), did not exist in the marketplace at the time of the panel discussion or the appeal, and there was no listing standard or outline of investigation for it.
After the NEC Technical Correlating Committee and the NFPA Standards Council decided to insert the requirement into the 2011 NEC, UL developed Subject 1699B, the Outline of Investigation for Photovoltaic (PV) DC Arc-Fault Circuit Protection, and the electrical industry started designing and building the DC AFCI unit. Within the last couple of months, UL listed the first inverter with integral PV DC AFCI protection; it is available for installation. Other devices are currently under investigation for listing.
PV DC AFCIs are intended to mitigate the effects of arcing faults that may pose a risk of fire ignition under certain conditions if the arcing persists and where a PV source, such as PV modules or arrays, supplies the DC circuits. The products covered in the PV arc-fault protection outline are PV DC AFCIs, PV DC arc-fault detectors, and PV DC interrupters. Also included in the PV standards are inverters, converters and charge controllers with integral AFCI protection. So the DC AFCIs can be built into the inverters, charge controllers or converters as an integral part or can be individual devices that provide sensing for and interrupting of arcing faults.
A PV DC AFCI is intended to be installed in a solar PV energy system to interrupt power when an AFCI detects an arcing fault. This device provides arcing protection for the PV system and the wiring.
A PV DC arc-fault detector is intended to detect arcing and provide protection for the PV system and wiring by enabling a separate interruption or shorting device to stop power delivered to an arcing fault.
A PV DC interrupting device is intended for installation in a PV energy system to interrupt a detected arcing fault. This device is generally enabled by another device that detects arcing, such as an arc-fault detector.
These products are classified as Type 1 or Type 2 devices. Type 1 devices are intended to detect and interrupt series arcing faults. Type 2 devices are designed to detect and interrupt both series and parallel arcing faults.
A series arc might occur due to internal damage or breakage of a conductor within its insulation. A parallel arc fault typically involves a metal staple or other conductive object penetrating the insulation of two conductors within a cable, creating an arc from one conductor to the other.
The products will be marked “Type 1” or “Type 2” and with the manufacturer’s name, trademark or other suitable means of identification; a catalogue designation; the electrical ratings in DC voltage; the load capacity in DC amperes; and the short-circuit current rating of the device.
The text in 690.22 states that PV systems with DC source circuits (PV modules), DC output circuits (output of combiner) or both, located on a building or penetrating into a building and operating at a PV system maximum voltage of 80 volts or greater, must be protected by a listed (DC) AFCI, PV type or other system components listed to provide equivalent protection.
The PV arc-fault protection means must comply with the following requirements:
- The arc protection system must detect and interrupt arcing faults resulting from a failure in the intended continuity (a series fault) of a conductor, connection, module or other system component in the DC PV source and output circuits.
- The arc protection system must disable or disconnect either the inverter or charge controller connected to the faulted circuit when the fault is detected.
- The protection system must be able to only manually restart the disabled or disconnected equipment.
- The protection system must have an annunciator that provides a visual indication that the circuit interrupter has operated. This indication must not be reset automatically.
Section 690.11 was inserted into the 2011 NEC to ensure a PV DC AFCI device is installed in PV installations as soon as the equipment becomes available as a listed product.
ODE is a staff engineering associate at Underwriters Laboratories Inc., based in Peoria, Ariz. He can be reached at 919.949.2576 and email@example.com.