Note: The requirements outlined in this article are based on the 2011 edition of the NEC.
We concluded Part 1 of this topic with the requirements for the service disconnects of solar photovoltaic (PV) systems. As we continue to discuss Part III of Art. 690 (Disconnecting Means), we come to the topic of requirements for the equipment disconnects.
Equipment disconnects are for such things as inverters, batteries, and charge controllers. These disconnects must disconnect equipment from all ungrounded conductors of all sources. If the equipment is energized from more than one source, such as an inverter, the disconnecting means for all sources must be grouped and identified [690.15].
It’s necessary to provide a means to disconnect a fuse from all sources of supply, if energized from both directions. The fuse must be capable of being disconnected independently of fuses in other PV source circuits [690.16(A)]. Using disconnects with pull-out fuses is one method to disconnect a fuse from all sources of energy.
Disconnects for fuses must be installed for PV output circuits where fuses that must be serviced can’t be isolated from energized circuits. The disconnect must be:
If the disconnect is more than 6 ft from the fuse, then you must install a directory showing the location of the fuse disconnect at the fuse location. Non-load-break rated disconnects must be marked “Do not open under load.”
A disconnect for PV systems — direct current (DC) and alternating current (AC) — must be a manually operable switch or circuit breaker complying with all of the following (Fig. 1):
Where all terminals of a disconnect may be energized when the switch is open, a warning sign must be placed on (or adjacent to) the disconnect.
Part IV of Art. 690 covers wiring methods, and begins by stating that NEC Chapter 3 wiring methods and other wiring systems specifically identified for use on PV systems are allowed to be used [690.31(A)]. However, PV source and output circuits above 30V must be installed in a raceway if the conductors are readily accessible.
Single-conductor Type USE-2 or listed and labeled PV wire can be run exposed at outdoor locations for PV source circuits. But if the circuit is more than 30V, single-conductor Type USE-2 or listed and labeled PV wires must not be accessible from a readily accessible location [690.31(B) and Ex].
If you run DC input PV system conductors and AC inverter output conductors inside a building or structure, run them in metal raceway, Type MC cable, or metal enclosure [690.31(E)]. Additional installation requirements apply, which were added in the 2011 NEC to 690.31(E), including:
To limit the voltage induced by lightning, one conductor of a 2-wire PV system operating at more than 50V must be solidly grounded (connected to the earth) per 250.4(A)(1) [690.41]. The grounding connection can be at any single point on the grounded conductor of the PV DC output circuit [690.42]. PV systems with ground-fault protection that incorporates the system grounding connection must not have an additional grounding connection [690.42 Ex].
Connect all exposed metal parts of PV module frames, electrical equipment, raceways, and enclosures to an equipment grounding conductor (EGC) of a type permitted in 250.118 [250.134 and 690.43(A)], as shown in Fig. 2. You must install an EGC between the PV array and associated equipment [690.43(B)]. Devices listed and identified for grounding the metallic frames of PV modules and associated equipment can be used to bond the exposed metal surfaces of modules and equipment to the metal racks [690.43(C)].
Metallic mounting racks used as an EGC must be identified as an EGC or have identified bonding jumpers/devices connected between the separate metallic racks and be connected to an EGC as required by 690.43(A). Devices and systems used for securing PV modules to metal mounting racks that serve as an EGC must be identified for such purposes [690.43(D)]. Devices identified and listed for bonding the metallic frames of PV modules can be used to bond the metallic frames of PV modules to the metallic frames of adjacent PV modules [690.43(E)]. All conductors of a circuit, including the EGC, must be installed in the same raceway or cable, or otherwise run with the PV array circuit conductors when they leave the vicinity of the PV array [690.43(F)].
For PV circuits having overcurrent protection, size the EGC to the rating of the PV circuit overcurrent protective device (OCPD) per Table 250.122 [690.45(A)]. Where no overcurrent protection is provided for the PV DC circuit, as permitted in 690.9 Ex., size the EGC to the PV circuit short circuit current rating per Table 250.122 [690.45(A)].
If installing a DC system, provide a grounding electrode system per 250.166 with a grounding electrode conductor per 250.64. A common DC grounding-electrode conductor can serve multiple inverters with the common grounding electrode and the tap conductors sized per 250.166. A splice or joint is not allowed in the common grounding electrode conductor [250.47(B)].
PV systems with DC modules having no direct connection between the DC grounded conductor and the AC grounded conductor must be bonded to the AC grounding system by one of the
methods listed in 690.47(C)(1), (2), or (3). This set of requirements is new, with the 2011 NEC:
Install bonding jumpers around equipment so that you maintain the bonding continuity if the equipment is removed [690.48 and 690.49]. This applies to exposed conducting surfaces of PV equipment and to the PV system grounded conductor.
Apply a permanent label at the PV DC disconnect indicating [690.53]:
For interactive systems, the point of interconnection of the PV system power source to other sources must be marked at an accessible location at the disconnect as a power source and with the rated AC output current and nominal operating AC voltage [690.54].
Any building or structure with a standalone PV system not connected to a utility service source must have a permanent plaque on the exterior of the building or structure, at a readily visible location. It must indicate the location of the standalone PV system disconnect and that the structure contains a standalone electrical power system [690.56(A)].
Any structure containing both utility service and a PV system must have a permanent plaque identifying the location of the service disconnect and PV system AC disconnect (if they are not at the same location) [690.56(B)].
For interactive systems, use only inverters and AC PV modules listed as interactive [690.60]. An inverter or an AC module in an interactive PV system must automatically de-energize its output to the electrical distribution system upon loss of voltage. It must remain de-energized until the electrical distribution system voltage has been restored [690.61].
Article 705 of the NEC covers interconnected electric power production sources. There are requirements in Art. 705 that apply to solar voltaic systems.
Install storage batteries per Art. 480 [690.71(A)]. Additionally:
The production of power from solar resources is not a new concept, but it is an area of ever-changing technology and strong growth. The NEC requirements for these systems have also changed; therefore, the solar installer must keep current with the Code requirements.