NEC 445 Generators for Apprentices: Conductor Sizing at 115%, Disconnects, Portable GFCI and Standby Transfer Equipment

Tsai Electro is an independent learning site. Not affiliated with TDLR, PSI or NFPA. We explain the ideas in our own words and do not reproduce NEC text. Check every rule and table value in your own 2026 NEC, follow the generator manufacturer’s instructions, and follow your supervisor and the local inspector.

Where generator rules live

Question	Where to look
The generator itself: marking, overcurrent protection, conductor size, disconnect, portable generator GFCI	Article 445
A generator that backs up loads by choice, such as a home standby unit	Article 702, Optional Standby Systems
Systems required by law or by the building code	Articles 700 (emergency) and 701 (legally required standby)
Sizing the conductors once you know the minimum ampacity	Table 310.16 and the terminal temperature rules in 110.14

Article 445 tells you how to connect the machine. The standby articles tell you how the generator and the normal supply share the building’s wiring. Most exam questions on home and small commercial standby units touch both.

Conductors from the generator terminals: 115%

The conductors that run from the generator output terminals to the first distribution device containing overcurrent protection generally need an ampacity of at least 115% of the nameplate current (NEC 445.13). The code also allows 100% where the design and operation of the generator prevent it from being overloaded, so confirm that condition before you size down. The 115% figure is a minimum ampacity; terminal temperature, correction and adjustment still apply.

Two details trip people up:

• Find the nameplate current, not just the kW. Use the nameplate current whenever it is listed. If you only have kVA and voltage, divide VA by volts for single-phase, or by (volts × 1.732) for three-phase. If you only have kW, you also need the power factor; do not assume kW equals kVA. Use the rating for the voltage and configuration you are actually connecting.
• The 115% sets a minimum ampacity, then the terminal rules still apply. After you have the minimum ampacity, pick a conductor from the column that matches the lowest terminal temperature rating in the circuit, usually 75°C for equipment terminals rated for it.

The disconnect and overcurrent protection

A generator needs a disconnecting means that can disconnect the generator and its protective devices and control equipment from the circuits it supplies (NEC 445.18). Many packaged generators include a breaker that can serve as that disconnect when it meets the requirements, so check the listing and the manufacturer’s instructions. The generator must also be protected from overload, either by inherent design, by circuit breakers, by fuses or by other identified means (NEC 445.12). An outdoor generator set used for a standby system has its own disconnect location rules in the standby article (NEC 702.12).

Portable generators and GFCI

Portable generators rated 15 kW or smaller need GFCI protection for certain receptacle outlets (NEC 445.20). The protection can be built into the generator or provided at the receptacles, and the section has conditions and exceptions, including for generators manufactured before the rule took effect. Read which receptacle ratings it covers in your 2026 NEC before you answer a question on it.

Standby systems: transfer equipment, capacity and signs

When a generator backs up building loads, the job is to keep the generator and the utility from ever being connected together by accident.

• Transfer equipment. An optional standby system needs transfer equipment that prevents inadvertent interconnection of the normal and standby sources (NEC 702.5). A cord plugged into a dryer receptacle with no transfer equipment, sometimes called a suicide cord, can back-feed the utility transformer and put the line crew at risk.
• Capacity. With manual transfer, the generator needs enough capacity for the loads you intend to run at the same time. With automatic transfer, the generator generally has to carry the full calculated load that can be transferred, unless a load management system limits what it can pick up (NEC 702.4). Load calculations are in Article 120 in the 2026 NEC.
• Signs. The sign rules differ by building type. In commercial and industrial buildings, a sign at the service equipment shows the type and location of each on-site standby source. In one- and two-family dwellings, the sign shows where each permanently installed standby source can be disconnected or shut down. Check the exact placement in your NEC (NEC 702.7).
• Neutral and grounding. A transfer switch that switches the neutral commonly makes the generator a separately derived system; one that does not usually does not. That decides where the neutral-to-ground bond belongs, so confirm it from the actual connections. Check the generator’s configuration and the transfer switch before you land the neutral.

For sizing the generator to the house, try our backup generator sizing calculator.

Worked example: conductors from a 22 kW standby generator

A home standby generator is rated 22 kW at 240 V, single-phase. For this example, assume a power factor of 1.0, no nameplate current is given, the 100% exception does not apply, all terminals are rated 75°C, and no ampacity correction or adjustment is needed. Size the copper conductors from the generator terminals to the first overcurrent device.

1. Current at the assumed power factor of 1.0: 22,000 W ÷ 240 V = 91.7 A.
2. Minimum ampacity at 115%: 91.7 × 1.15 = 105.4 A.
3. From the 75°C copper column of Table 310.16: 3 AWG is 100 A, which is less than 105.4 A. 2 AWG is 115 A, which meets it. Use 2 AWG copper, then apply any correction or adjustment factors your installation needs.
4. Check: 115 A ÷ 91.7 A = 1.25, which is more than 1.15. If you had picked 3 AWG, 100 A ÷ 91.7 A = 1.09, which is less than 1.15.

If the nameplate lists a current of its own, use that value instead of the kW division.

Check yourself

1. Conductors run from the generator terminals to the first overcurrent device. What minimum ampacity applies, unless the exception applies? 115% of the nameplate current.
2. Which standby article covers a homeowner’s backup generator chosen by the owner, not required by code? Article 702, Optional Standby Systems.
3. What equipment keeps a standby generator from back-feeding the utility? Transfer equipment that prevents inadvertent interconnection of the normal and standby sources.

FAQ

Sources checked October 2026

• PSI Candidate Information Bulletin, Texas electrician examinations (updated September 15, 2026): https://test-takers.psiexams.com/api/content/bulletin/1682
• NFPA 70, National Electrical Code, 2026 Edition, Articles 445 and 702