NEC Article 702 — Optional Standby Generators: ATS, Wiring, and the 200% Rule

NEC Article 702 covers optional standby systems — the standard category for residential whole-house generators (Generac, Kohler, Cummins, etc.). Different from emergency systems (Article 700) and legally-required standby (Article 701) which apply to commercial and life-safety contexts.

System scope (702.5): optional standby is for systems serving loads where outage is inconvenient but not life-threatening. Most residential whole-house gens fall here.

Capacity / Load calc (702.4): the system must be able to carry the loads served, calculated per NEC 220 just like the main service. For typical 200 A residential service backed up entirely, a 22 kW standby gen handles most homes with electric ranges, dryers, A/C, and a few EV chargers — but always run the load calc first.

Automatic Transfer Switch (ATS) (702.5(B)): the ATS must be rated to carry the full load of the section being transferred. For whole-house backup on a 200 A service, the ATS is 200 A rated. The ATS sits between the meter and the main panel.

Service-rated ATS option: ATS units rated as service equipment can REPLACE the main breaker — utility feed enters the ATS directly, and the ATS feeds the main panel. Common for new installs. Generac's RXSW200A3 is a typical 200 A service-rated whole-house ATS.

Generator conductor sizing (702.7): conductors from the generator to the ATS sized at 115% of the generator nameplate current. For a 22 kW Generac (≈92 A at 240V), conductors at 92 × 1.15 = 106 A, requiring 1/0 AL or #2 CU minimum.

Generator EGC sizes per Table 250.122 to the breaker protecting the conductor (typically a generator-side fused disconnect). For a 100 A generator breaker, EGC is #8 CU.

Bonding at the generator (250.30): if the generator is a "separately derived system" (most are), it requires its own grounding-electrode connection at the generator. Modern Generac/Kohler air-cooled units are typically NOT separately derived (they have a switched-neutral ATS), so the grounding is from the main service only.

NJ-specific notes:

• Generators must be installed per NJ UCC subcode and the manufacturer's installation manual
• Setback from the building, gas-meter clearance, and noise ordinances vary by municipality. Hoboken has a 5-ft minimum setback from any property line, for example
• PSE&G doesn't require notification for optional standby installs but does require the ATS to be utility-locked-out compatible

For generator + ATS one-line diagrams, the free Malfettone SLD Builder at /tools/single-line-diagram has a "Whole-house standby generator + ATS" template with utility input, ATS with side-entry pins, and main panel — the AHJ-format submission shape.