12.2 Interconnected Power Sources, Energy Storage, Power-Limited Circuits, Fire Alarm & Communications (Articles 705-830)

Interconnected electric power production sources (Article 705)

Article 705 covers any power source that runs in parallel with the utility or another primary source: PV, wind, fuel cells, generators, and energy storage.

Load-side busbar options (705.12(B))

For a panelboard busbar fed by both the utility (through its main breaker) and an inverter (through a backfed breaker), one of these must be true:

1. 100 percent rule: 125 percent of the inverter output current, plus the rating of the device protecting the busbar, does not exceed the busbar ampere rating.
2. 120 percent rule: 125 percent of the inverter output current, plus the rating of the device protecting the busbar, does not exceed 120 percent of the busbar rating. The backfed breaker must be at the opposite end of the busbar from the main supply, and a permanent warning label must read "POWER SOURCE OUTPUT CONNECTION - DO NOT RELOCATE THIS OVERCURRENT DEVICE."
3. Sum rule: the sum of all overcurrent device ratings on the busbar, excluding the one protecting the busbar, does not exceed the busbar rating.

Worked example (120 percent rule): a 200 A busbar has a 200 A main breaker. The inverter output is 32 A continuous.

• Maximum allowed: 200 A x 1.20 = 240 A.
• 240 A - 200 A main = 40 A available.
• The inverter needs 32 A x 1.25 = 40 A, so a 40 A backfed breaker at the opposite end fits exactly.

Energy storage, stand-alone systems, and microgrids (Articles 706, 710, 712)

• Energy storage systems (706): must be listed. They need a disconnecting means that is readily accessible and within sight of the system, or lockable with its location marked. They also need working space, ventilation, and marking of the maximum voltage and available fault current.
• Stand-alone systems (710) and DC microgrids (712) operate without the utility and follow similar source, disconnect, and labeling rules.
• Washington requires a design review on site when these sources are interconnected or stand-alone (WAC 296-46B-705, -710).

Class 1, Class 2, and Class 3 circuits (Article 725, 2020 NEC)

Key rules:

• Class 1 overcurrent protection (725.43): based on conductor ampacity. For 18 AWG, no more than 7 A; for 16 AWG, no more than 10 A.
• Class 1 conductors may share a raceway, cable, or enclosure with power supply conductors only when they are functionally associated with the equipment those power conductors supply (725.48(B)(1)).
• Class 2 and 3 separation (725.136): Class 2 and Class 3 conductors may not be placed in any cable, cable tray, compartment, enclosure, box, or raceway with electric light, power, Class 1, or non-power-limited fire alarm conductors, unless separated by a barrier or as otherwise permitted.
• Support (725.143): Class 2 and 3 cables may not be strapped, taped, or attached to the outside of a conduit or raceway as a means of support. 300.11(C)(2) allows the exception where the raceway carries the power for the equipment the Class 2 circuit controls.
• Cable types: CL2P or CL3P (plenum), CL2R or CL3R (riser), CL2 or CL3 (general), and CL2X or CL3X (limited use). A higher-rated cable may substitute for a lower one.

The 2023 NEC reorganized this material into Articles 722, 724, and 725. The 2020 numbering above matches the exam's code edition.

Fire alarm systems (Article 760)

• Dedicated branch circuit (760.41(B), 760.121(B)):
  • The branch circuit supplying fire alarm equipment may supply no other loads.
  • The location of its overcurrent device must be permanently identified at the fire alarm control unit.
  • The circuit disconnect must have red identification, be accessible only to qualified personnel, and be marked "FIRE ALARM CIRCUIT."
  • The branch circuit may not be supplied through a GFCI or AFCI.
• Circuit identification (760.30): fire alarm circuits must be identified at terminal and junction locations so they won't be disturbed by accident during testing or servicing.
• Cable types: FPLP (plenum), FPLR (riser), and FPL (general) for power-limited fire alarm circuits.
• Washington: fire alarm device and junction boxes must be substantially red inside and outside, and power-limited fire alarm conductors must be marked in boxes (WAC 296-46B-760). A red receptacle with a red cover that supplies only a fire alarm system in a garage or unfinished basement needs no GFCI (WAC 296-46B-210).

Optical fiber (Article 770)

• Optical fiber cables are nonconductive (OFN types) or conductive (OFC types). Conductive types contain non-current-carrying metal such as a strength member or armor.
• Conductive optical fiber cable members must be bonded or grounded where they enter a building.
• Nonconductive optical fiber cables may share a raceway or enclosure with power conductors only under the conditions of 770.133.

Communications systems (Chapter 8, Articles 800-840)

In the 2020 NEC, Article 800 was added for the general requirements shared by communications systems. It is followed by 805 (communications circuits), 810 (radio and television equipment), 820 (CATV), 830 (network-powered broadband), and 840 (premises-powered broadband).

Washington telecommunications rules (WAC 296-46B-300, -800, -901):

• Telecommunications cables must be supported at intervals of no more than 5 ft.
• The demarcation point may be no more than 12 in. inside the end user's occupied space.
• A permit is required for projects of more than 10 outlets, all backbone work, and fire-barrier penetrations.