Generator Installation Inspection

Per NEC 702.4, the generator must be rated for the maximum load it will serve. Load calculation per NEC 220 determines minimum generator size. Typical whole-house standby: 20–26 kW. Essential circuits only: 10–16 kW. Generator must be UL 2200 listed. Power factor and starting loads (motors, HVAC compressors) must be accounted for in sizing.

1. Review load calculation — verify all essential circuits are included

2. Confirm generator kW rating exceeds calculated load by at least 20% margin

3. Account for motor starting loads (HVAC compressor can draw 3–5x running amps at startup)

4. Verify generator is UL 2200 listed (nameplate marking)

5. Check fuel type matches available supply: natural gas, propane (LP), or diesel

6. Confirm generator voltage/phase matches service: 120/240V single-phase residential

- Generator undersized — overloads cause shutdown and potential damage

- Starting loads not accounted for — HVAC compressor fails to start

- Wrong fuel type for location (natural gas not available in rural areas)

- Non-listed generator used — insurance and code compliance issues

Per NFPA 37 and manufacturer requirements, standby generators must maintain minimum clearances: 5 feet from openings (windows, doors, vents), 18 inches from the building wall, and per local setback requirements. Generator must be on a level, stable pad (concrete or composite). Must not be in a flood zone below base flood elevation.

1. Verify clearance from openings: minimum 5 feet from windows, doors, and fresh air intakes

2. Check clearance from building: minimum 18 inches (or per manufacturer)

3. Confirm generator is on a level, stable pad rated for the weight

4. Verify the location is not in a flood zone or below grade

5. Check local setback requirements from property lines

6. Verify adequate ventilation around the unit for cooling and combustion air

7. Assess noise impact — check local noise ordinance limits (typically 65–75 dB at property line)

- Too close to windows — CO exhaust enters living space (life safety hazard)

- Placed in flood-prone area — water damage destroys generator

- No concrete pad — unit sinks or shifts over time

- Noise complaints from neighbors — check ordinance before installation

Per NFPA 54 (natural gas) and NFPA 58 (LP gas), fuel line must be sized for the generator's BTU input rating plus all other connected gas appliances. A dedicated shutoff valve must be installed at the generator. Gas piping must be pressure-tested per local code (typically 3 PSI for 10 minutes). Diesel tanks must comply with NFPA 30/30A.

1. Verify gas line size is adequate for generator BTU rating (check manufacturer specs)

2. Confirm dedicated shutoff valve at generator — must be accessible and labeled

3. Check that gas line pressure test was performed and documented

4. Verify all connections are leak-tested (use combustible gas detector at every joint)

5. For LP: confirm tank size adequate for runtime (20 lb = ~5 hrs at half load for 20 kW)

6. For diesel: verify tank is properly vented, on containment pad, and meets fire code setbacks

7. Verify flexible connector used at generator connection (protects against vibration)

- Gas line undersized — generator runs but cannot reach full power

- Missing shutoff valve — cannot isolate generator for service

- Leaks at connections — fire and explosion hazard

- LP tank too small for meaningful backup runtime

Per NEC 702.5, transfer equipment must prevent interconnection of normal and standby power sources (back-feeding). An automatic transfer switch (ATS) or manual interlock must be UL 1008 listed. The transfer switch must be sized for the panel amperage (typically 200A). Manual interlock kits must be listed for the specific panel model.

1. Verify transfer switch is UL 1008 listed and properly rated for the service size

2. Confirm mechanical interlock prevents simultaneous connection of utility and generator

3. Test transfer operation: disconnect utility, verify generator starts and transfers within 10–30 seconds

4. Verify load shedding is properly configured (if partial-home system)

5. Check that transfer switch is accessible and properly mounted

6. Confirm wiring between generator and transfer switch is properly sized and protected

7. Verify retransfer: when utility returns, system transfers back and generator cools down

- Unlisted or improper interlock kit — may not prevent back-feeding (lethal to utility workers)

- Transfer switch undersized for panel — overheating under load

- Load shedding not programmed — generator overloads on transfer

- No retransfer delay — generator stops too abruptly, no cool-down

Per NEC 702.10, the wiring between the generator and transfer switch must be installed per NEC Chapter 3 wiring methods. Wire size must match generator and transfer switch ampacity. Overcurrent protection required at the generator per NEC 702.10. Connection must include an equipment grounding conductor. Separately derived system grounding per NEC 250.30 if applicable.

1. Verify wire gauge matches generator ampacity (e.g., 100A = 3 AWG copper minimum)

2. Check conduit type is appropriate: liquidtight flexible at generator, rigid/EMT to panel

3. Verify overcurrent protection at generator output (main breaker)

4. Confirm equipment grounding conductor is properly installed

5. Check separately derived system grounding requirements (NEC 250.30)

6. Verify all connections are properly torqued per manufacturer specifications

7. Check weatherproof disconnect at generator if required by AHJ

- Wire undersized for generator output — overheating hazard

- No flexible conduit at generator — vibration damages rigid connections

- Missing or improper grounding — shock hazard during generator operation

- Connections not torqued — loose terminals cause arcing and fire

Per NFPA 37 and CPSC guidelines, generator exhaust contains lethal carbon monoxide (CO). Exhaust must be directed away from all building openings. Never operate portable generators indoors, in garages, or in enclosed spaces. Standby generator exhaust must terminate per manufacturer clearances. CO detectors required in the home per NFPA 720.

1. Verify exhaust directs away from windows, doors, and air intakes

2. Confirm minimum 5-foot clearance from any building opening for exhaust termination

3. Check that CO detectors are installed on every level of the home and near sleeping areas

4. For portable generators: verify unit is at least 20 feet from any opening (CPSC recommendation)

5. Verify adequate cooling air circulation around standby unit

6. Check exhaust system for leaks at all joints and connections

- Exhaust aimed at window or air intake — CO poisoning risk (leading cause of generator deaths)

- Portable generator in garage or covered area — lethal CO accumulation

- Missing CO detectors — no warning of exhaust infiltration

- Exhaust leaks at connections — CO seeps into nearby spaces

Per NFPA 110 and manufacturer requirements, the generator must be load-tested after installation. Test must verify automatic start, transfer, running under load, retransfer, and cool-down. Voltage and frequency must be within ±5% of nominal. All protective functions (overload, overtemp, low oil) must be verified operational.

1. Simulate power outage — disconnect utility at main breaker

2. Verify generator starts automatically within programmed delay (typically 10–30 seconds)

3. Confirm automatic transfer switch engages — power restored to selected circuits

4. Check voltage under load: 240V ±5% (228–252V acceptable)

5. Check frequency: 60 Hz ±0.5 Hz

6. Measure current draw — should not exceed generator rating

7. Restore utility power — verify retransfer and generator cool-down cycle

8. Test manual start and manual transfer if applicable

- Generator starts but does not transfer — ATS configuration error

- Voltage sag under heavy load — generator undersized or governor issue

- Frequency instability — engine governor needs adjustment

- Cool-down cycle skipped — shortens engine life

Per NFPA 110 Chapter 8, standby generators require regular maintenance: weekly exercise cycle (minimum 30 minutes under load), oil change per manufacturer schedule (typically every 200 hours or annually), air filter replacement, coolant check, battery testing, and annual professional service. A maintenance log must be maintained.

1. Verify weekly exercise schedule is programmed (30 minutes minimum, with load transfer recommended)

2. Confirm oil and filter type matches manufacturer specifications

3. Review maintenance schedule: oil change, air filter, spark plugs, coolant per manual

4. Check battery condition: terminals clean, voltage 12.4V+ at rest, charger operational

5. Verify maintenance log book or digital tracking system is in place

6. Confirm fuel supply is adequate for minimum 24 hours runtime

7. Schedule annual professional inspection and load-bank test

- No exercise schedule — generator fails when needed due to stale fuel or dead battery

- Neglected oil changes — engine wear and eventual failure

- Dead battery — generator cannot start (most common failure mode)

- Stale fuel (gasoline) — add stabilizer or switch to natural gas/propane