702
Optional Standby Systems
An optional standby system is any backup power source a homeowner or business installs by choice — the classic example is a residential whole-house generator or a portable generator connected through a manual transfer switch. Because these systems are optional, they do not require automatic transfer switches or automatic start-up like emergency or legally required standby systems do. However, Article 702 still imposes important safety rules. Section 702.5 requires transfer equipment that prevents inadvertent interconnection of the normal utility supply and the standby source — this is the anti-backfeed rule that protects utility lineworkers. For manual connections, the generator must be sized to supply all loads intended to operate at one time (702.4). For automatic connections, it must handle the full automatically-connected load or use a load management system that limits the connected load to the generator's capacity. Section 702.7 requires a permanent sign at the service entrance equipment indicating the type and location of the on-site standby power source, so firefighters and utility workers know a generator exists. Where a power inlet is used for a portable generator, a warning sign must indicate the generator type permitted. Optional standby systems are allowed to supply emergency, legally required standby, and optional standby loads from a single source, provided an automatic load management system handles selective load pickup and load shedding to prioritize critical circuits.
When You Need This
- Installing a whole-house standby generator for a residential customer — this article governs every aspect of the connection
- Wiring a manual transfer switch for a portable generator hookup with a power inlet box
- Designing a commercial backup power system that is not required by the building code but requested by the owner
- Determining whether a customer's standby system needs automatic or manual transfer equipment
- Studying for the master electrician exam — Article 702 questions often appear alongside Articles 700 and 701
Key Points
Common Mistakes
Connecting a portable generator to the panel through a standard receptacle or double-male cord (suicide cord) instead of using proper transfer equipment — this is a lethal backfeed hazard
Failing to install a sign at the service entrance indicating the type and location of the standby source — firefighters and utility workers need to know a generator exists
Oversizing the automatic transfer switch load without a load management system, causing the generator to overload and shut down during an outage
Confusing Article 702 (optional) with Article 701 (legally required) or Article 700 (emergency) — each has different requirements for transfer time, automatic start, and wiring methods
Not verifying the short-circuit current rating of the transfer equipment and field-marking it on the exterior as required
Exam Tip
Know the three backup power articles: 700 = emergency (automatic transfer within 10 seconds, separate wiring), 701 = legally required standby (automatic transfer within 60 seconds), 702 = optional standby (manual transfer is fine). The exam will test whether you know which article applies. Article 702 is the most relaxed — no automatic start, no automatic transfer, and no separate wiring required. But transfer equipment to prevent backfeed is ALWAYS required regardless of article.
Frequently Asked Questions
Yes. Unlike emergency systems (Article 700) which require automatic transfer within 10 seconds, optional standby systems under Article 702 are permitted to use manual transfer switches. The homeowner or building operator physically moves the switch from utility to generator. The transfer switch must still prevent simultaneous connection of both sources.
In most jurisdictions, yes. Generator installations involve electrical work that requires a permit and inspection. The inspector will verify proper transfer equipment, signage at the service entrance, proper grounding and bonding, fuel line compliance, and setback distances. Even portable generator hookups with a power inlet and manual transfer switch typically require a permit.
Yes, but only with an automatic load management system that provides selective load pickup and load shedding per 702.4. The system must prioritize emergency loads first (Article 700), then legally required standby loads (Article 701), then optional standby loads (Article 702). If the generator cannot handle all loads simultaneously, the load management system must shed optional loads first.
Inline Tools
Dwelling Load Calculator
Calculate residential service load per NEC 220
Related Code Sections
This is an educational summary, not the official code text. The NEC® is a registered trademark and copyright © National Fire Protection Association (NFPA). The CEC is copyright © CSA Group. For official code text, visit nfpa.org or csagroup.org. SparkShift is not affiliated with NFPA or CSA Group.