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What to know about NEC 2017

Though the ink isn’t near to being dry on the National Electrical Code 2017 edition, there are some upcoming changes that we can expect. The votes are complete for all the Code Making Panels (CMPs), and the Correlating Committee will soon vote on any further changes necessary before a second draft is published. Af­ter that there is one more chance, via certified amending motions (CAMs), to make further changes to the draft before publication. Relatively few CAMs are heard at the association meeting in June, and fewer are accepted. So at this point we have quite a good idea what the final draft will look like, and should include the follow­ing points barring any unforeseen upsets. I’ll focus on some of the work of CMP 4 that covers the PV-specific material in Ar­ticle 690.  

Large scale systems

New article 691 has been created to address large scale generating systems of 5MW or more that are not installed on buildings, have only auxiliary load, and restrict access to only qualified personnel. These systems are allowed to be designed and installed under the guidance of an independent engineer and can use non-listed or labeled equipment that is otherwise tested.

PV system disconnect location

Figure 690.1(a) has been updated and expanded to denote component locations for typical PV systems, including interactive, DC coupled multimode, AC coupled multimode, stand-alone, and AC module systems. The location of the PV system disconnect is important to note, as only those circuits connected upstream would be considered PV system circuits. This is a clear demarcation between the PV system and other systems, such as loads or energy storage systems (treated now in Article 706), and helps clarify where the disconnect requirements described in 690.13 apply.

Maximum system voltage

For DC PV system conductors not on or in buildings, a maximum of 1500V is allowed without following the requirements of Article 490, provided the equipment is listed and rated for that voltage.

Voltage and current calculations

For systems 100kW and larger, calculations by a professional electrical engineer may be used instead of the typical NEC correction factors for voltage and current. This could possibly allow for some wire savings on larger systems that won’t see 125% of rated current due to weather conditions. 

Grounding

Grounding of PV systems through a fuse or other device that can lift the connection to ground under fault conditions is clarified as being functional grounding. This type of grounding that has been common with isolated inverters (usually grounding the system through the inverter’s GFDI circuitry) is clarified in terms of personnel protection, and similar requirement to ungrounded or non-isolated systems are applied. In general, only solidly-grounded systems, which are not often used for PV circuits, will be afforded exceptions to the rules. One implication is that all PV conductors for both isolated and non-isolated inverters will require disconnection and will not be colored as a grounded conductor. One issue that has been fixed by 690.9(C) is that fusing will only be required on one pole since it protects the entire circuit from overcurrent. This has the potential to decrease BOS costs for non-isolated inverters compared to today’s practice. / Though the ink isn’t near to being dry on the National Electrical Code 2017 edition, there are some upcoming changes that we can expect. The votes are complete for all the Code Making Panels (CMPs), and the Correlating Committee will soon vote on any further changes necessary before a second draft is published. Af­ter that there is one more chance, via certified amending motions (CAMs), to make further changes to the draft before publication. Relatively few CAMs are heard at the association meeting in June, and fewer are accepted. So at this point we have quite a good idea what the final draft will look like, and should include the follow­ing points barring any unforeseen upsets. I’ll focus on some of the work of CMP 4 which covers the PV-specific material in Ar­ticle 690.

USE-2

A formerly common wire for use in exposed locations of PV systems, USE-2 is once again acceptable in addition to PV wire for both isolated and non-isolated systems.

Additional grounding electrodes

The requirement for an additional grounding electrode and grounding electrode conductor from 690.47 has been chan­ged to be permissive rather than mandatory.

Energy storage systems

Energy Storage System requirements have been moved to a different article, 706.

Arc fault protection

Requirements in 690.11 for manual restart and annunciati­on have been removed and left for the developing AFCI stan­dard to address. For PV systems not installed on buildings, an exception to the AFCI requirement is made for PV output circuits with conductors buried, in metallic raceways or in enclosed metallic cable trays . This allows the arc fault detec­tion to be limited to smaller amperage source circuits.

Rapid shutdown expansion

The most contested area of 690 revisions comes in the expansion and clarification of the rapid shutdown requirements of 690.12. Many of the concepts in this section were originally developed by the solar industry and CMP 4’s representative from the International Association of Fire Fighters. Major changes that will go into effect upon adoption of the NEC 2017 are:

1) Reduction of maximum length of conductors over 30V from 10 feet to 1 foot from the array boundary.

2) Extension of the shutdown time from 10 seconds to 30 seconds.

3) The initiation device will be one of the service disconnecting means, PV system disconnecting means, or a readily accessible switch. The initiation device for one- and two-family dwellings must be at a readily accessible location outside the building (which may not be where the service disconnect or PV system disconnect is located).

4) Equipment that performs the shutdown function must be listed and labeled to the developing rapid shutdown equipment standard.

5) Section 690.56(C) includes very specific labeling requirements for the rapid shutdown system, including which elements are shut down. The rapid shutdown switch (initiation device) has an additional label.

The more controversial requirements for within the 1 foot array boundary will not go into effect until January 1, 2019, presumably giving the industry time to develop solutions that do not exist today. There are three options for ensuring there is reduced hazard within the array:

1) A new concept of a listed and labeled or field-labeled PV array. A new standard will need to be developed to clarify how an array can be constructed to reduce the hazard.

2) Limiting conductors to 80V or less within 30 seconds.

3) Utilizing a PV array with no exposed wiring or conductive parts and installed more than 8 feet from grounded conductive parts or ground. Certain building integrated PV products available today could likely meet this requirement.

Equipment disconnection

Besides the PV system disconnect, the requirement for isola­tion or disconnection of PV system equipment is clarified in 690.15, for safe replacement or service. A connector, switch or other isolating device is required within 10 feet of modules, fuses, converters and inverters. DC combiner outputs and in­verter or charge controller inputs greater than 30A must have a load-break rated disconnect. Y-connectors or other two-string combining devices, though technically combiners, would gene­rally be under 30A and thus would not require a disconnect.

Where disconnects can be remotely-operated from within 10 feet of the associated equipment, the disconnect can be further than 10 feet away. This would allow, for example, a contactor on the roof to act as an equipment disconnect for an inverter at ground level as long as the contactor could be operated from near the inverter, which is the case for some existing rapid shutdown equipment. The contractor would still need an isolating device nearby.

Code evolution

The code continues to evolve as the solar industry grows and we are working hard to stay in front of these code changes. We attend these crucial meetings and offer our voice as a leading string inverter manufcaturer. We want to ensure our products are not only safe, but ready for these changes of tomorrow. We also want to reduce the need for external hardware, so do our best to offer products with built-in capabilities to meet these evolving code regulations.  

Click here for more details on the NEC 2017.

Written by Brian Lydic, Standards & Technology Integration Engineer, Fronius USA 

Labels: National Electrical Code 2017,arc fault,voltage,grounding,USE-2,energy storage,rapid shutdown

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