Standby Generator Installation and Commissioning
Purpose
A standby set is not finished when it is wired or when it first starts. It is finished when it has carried the building's actual connected load through a full utility-loss cycle, retransferred, cooled down and returned to automatic, with every reading written down. The gap between those definitions is where the callbacks live: a set that ran fine on a warm afternoon and dropped out the first time the compressor called.
Scope
Covers a permanently installed engine-driven optional standby generator at a dwelling or small commercial building, 600 V or less, on natural gas or propane, feeding transfer equipment under NEC Article 702 in the edition your authority having jurisdiction has adopted.
Does not cover the transfer switch's own settings and simulated-outage verification, owned by the automatic transfer switch commissioning SOP; critical-circuit selection, owned by the critical load panel SOP; the supplemental load bank test under NFPA 110, which reaches emergency and legally required systems rather than optional standby; or gas piping sizing.
Roles and responsibilities
| Role | Owns | Hands off |
|---|---|---|
| Office | Permit, utility and gas notification, delivery | Gives the lead the plan, the adopted code edition and the gas sizing letter |
| Lead electrician | Siting, conductors, bonding, first start, commissioning outage | Hands the record and every deficiency to the office the same day |
| Gas contractor | Pipe sizing and a measured inlet pressure at full load | Signs that figure onto the record; a verbal is not accepted |
| Customer | Authorizes the outage window | Signs the record acknowledging what does and does not run |
Procedure
Reconcile the set's rating against the load it will actually carry, on paper, before delivery. Take steady-state load from the critical load panel design and the largest motor's locked-rotor amps off its nameplate, never from horsepower. Acceptance: steady load at or below the continuous rating with headroom stated in amps, and that locked-rotor figure inside the manufacturer's published motor-starting capability for the model. Wrong looks like a set sized on square footage; stop rule, a set that cannot start the largest motor needs a soft starter written into the scope now rather than discovered at step 6. Hazard: none, a desk calculation.
Site the set against listed clearances, not the convenient spot. NFPA 37, in the edition your authority having jurisdiction has adopted, sets distances from wall openings and combustible walls for a stationary engine, and a manufacturer who has tested the enclosure publishes shorter listed distances that govern for that model. Acceptance: measured clearance to wall and to any openable window, door or intake, the exhaust discharge direction, and the working space at the disconnect per NEC 110.26 in the edition your authority having jurisdiction has adopted - 30 in wide and 6.5 ft high, with depth read off the table for the nominal voltage to ground and the condition of the space, which is 3 ft for the 120/240 V and 208Y/120 V cases here. Wrong looks like a set tucked beside a bedroom window because the gas line is short there; stop rule, move the set or move the opening. Hazard: this siting is the whole carbon monoxide control for the life of the install, because exhaust terminating near an intake poisons sleeping people and a UL 2034 alarm is deliberately slow at low concentrations.
Set and anchor the pad, then land power conductors with the bonding decision settled first. Whether the set is a separately derived system turns on whether the transfer equipment switches the grounded conductor, and that decides whether a system bonding jumper and grounding electrode conductor belong at the set: NEC 250.30 in that same adopted edition, with 250.34 for portable sets. Acceptance: set level and anchored per its instructions, exactly one neutral-to-ground bond in the installation verified by opening the path and reading it, every lug torqued to its marked value. Wrong looks like a second bond at the set on a switch that does not transfer the neutral, putting normal neutral current on the equipment grounding conductor; stop rule, two bonds means deciding which is correct here, not removing one at random. Hazard: rig with rated straps at the lift points, no hand between set and pad; then open the main, lock and tag, and prove every conductor dead on a known live source immediately before and after, per NFPA 70E-2021, 120.5, with work practices at 29 CFR 1910.333(b)(2), which governs because 1910.147 excludes electrical utilization work at (a)(1)(ii)(C).
Have fuel pressure read at the set's inlet with the engine at full output and the building's other gas appliances firing. That is the worst case the set meets in January. Make and break the manometer tap with the engine off and the appliance shutoff closed. Acceptance: measured inlet pressure at or above the minimum in that set's manual, in inches water column for natural gas or as the manual states for propane, recorded beside the static reading. Wrong looks like a static reading accepted as proof; stop rule, below the manual's minimum the set is not commissioned, the pipe is upsized or the regulator changed and the reading retaken. Hazard: every joint made or broken here is leak-checked with an approved solution or an electronic detector before the engine is started, no ignition source is introduced while a joint is open, and the retest after any pipe change repeats that leak check. If gas is smelled, everyone leaves immediately, no switch is operated, no phone is used near the leak, and the call is made from outside.
Land control wiring, battery and charger, then run the manufacturer's first start at no load. Land start control conductors to the diagram terminal for terminal, connect the battery last with the controller read as OFF rather than remembered, then follow that set's start-up sequence including oil, coolant where applicable and any break-in requirement. Acceptance: charging voltage at the battery inside the manufacturer's band; no active alarm; line-to-line and line-to-neutral voltage and frequency inside the no-load band; oil pressure in range; every value written on the sheet. Wrong looks like a control pair on the wrong terminal so the set cranks when the battery lands, or a voltage that will not settle; stop rule, an unexpected crank means battery off and the diagram re-checked, and a set that cannot hold a stable no-load condition gets no load applied and becomes a warranty call before the customer sees it run. Hazard: a set with a battery on it can start without warning, so no hands, sleeves or tools near belt, fan or exhaust; once running, read from outside the guarded envelope and upwind of the exhaust discharge, with hearing protection on and a personal carbon monoxide monitor in your breathing zone.
Run the commissioning outage: open the utility, time the sequence, measure the real load. Open the service disconnect inside the agreed window and let the system complete the cycle with no hand intervention. Acceptance: start delay, crank and load pickup inside the manufacturer's stated times with elapsed seconds recorded; current on each leg read at the transfer switch load terminals; the largest motor started while on generator with no under-frequency or overload alarm logged and voltage returning to band; retransfer at the set delay and the engine stopping after cool-down. Wrong looks like a transfer that works and a set that alarms when the compressor calls; stop rule, an alarm, a dropout or a failed retransfer stops the handover and the set is left in OFF with a tag rather than in AUTO. Hazard: this step puts fuel, energy and motion back into a system a crew has been inside all day, with the family in the building, so everyone stands clear, nobody is inside the switch or panel, and deadfronts are secured first. Verify the protective functions disturbed today: generator overcurrent device closed, the switch mechanically unable to close to both sources, and a GFCI on a critical circuit tripping and resetting on its test button while on generator, since a step 3 bonding error shows up here and nowhere else.
Return the system to automatic, label it, close the record. Set the exercise timer to the day and time the customer chose, confirm AUTO on the display, install the required signs and the panel label naming the generator circuit and the switch location. Acceptance: the controller photographed showing AUTO, the exercise schedule on the record, labels installed, customer signature obtained. Wrong looks like a job closed with the set in MANUAL after the demo, which is a building with no standby power and no indication anything is wrong; stop rule, no signature, no close-out. Hazard: selecting AUTO arms an unattended start, so first confirm nobody is at the set, every guard, panel and cover is refitted, and tools and rags are clear of belt, fan and exhaust; then tell the customer in words that the set starts on its own on the exercise schedule and on any utility loss, and that the battery is disconnected before anyone works on it.
The record this produces
One commissioning record per set, filed with the permit close-out and given to the customer. The next technician reads last year's step 6 currents against this year's to see whether load on the set has grown.
Header: date, technician, make, model, serial, rated kilowatts and voltage, fuel type, switch make and model, adopted NEC and NFPA 37 editions, permit number. Body: the acceptance figures from steps 2 through 6, each named to its step, with the gas contractor's name beside the inlet pressures. Footer: exercise day and time, the AUTO photograph, every deficiency with an owner and a date, the customer's signature.
Worked pass: 22 kW air-cooled set, 200 A residential service
A 22 kW natural gas set at 240 V single phase, whole-house transfer switch with load management on two compressors. Rated current is 22,000 divided by 240, or 91.7 A.
Step 1: steady-state connected load calculates to 14.2 kW, so headroom is 22.0 minus 14.2, or 7.8 kW, 35 percent of the set's rating. The larger compressor's nameplate locked-rotor amps read 78 A at 240 V, inside this model's published motor-starting capability with the second compressor locked out by the load manager. Step 2: listed clearance for this enclosure is 18 in to the wall and 5 ft to any openable window, door or intake; the chosen spot measures 24 in and 7 ft 4 in, exhaust discharging away from the house.
Step 4 fails. Static inlet pressure reads 8.0 in. w.c. With the engine at full output and the furnace and range firing it falls to 3.6 in. w.c., a drop of 8.0 minus 3.6, or 4.4 in. w.c. The manual's minimum for this set is 5.0 in. w.c. at full load, so the remaining 3.6 sits 1.4 in. w.c. under it and the stop rule fires. The gas contractor upsizes the run from the meter and moves the set's tee upstream of the range branch. Retest reads 8.1 in. w.c. static and 6.2 in. w.c. at full load, clearing the 5.0 minimum by 1.2 in. w.c., and both figures are signed onto the record.
Steps 3 and 5 run clean: one bond, at the transfer switch, on a switch that does not transfer the neutral, which is correct here; no-load baseline 60.0 Hz, 242 V line to line, no alarms.
Step 6: utility opened at 0 seconds, start signal at 3 seconds, load picked up at 17 seconds. Current at the load terminals reads 38 A on L1 and 44 A on L2, so the set carries about (38 plus 44) times 120, or 9,840 W, roughly 9.8 kW against 22 kW, which is 45 percent. The larger compressor is then called: no under-frequency and no overload alarm logged, voltage back in band with the dip visible for under two seconds. Utility restored, retransfer delay 10 minutes, load back on utility at 10 minutes 2 seconds, cool-down 5 minutes 1 second, engine stopped at 15 minutes 3 seconds. A GFCI on a critical circuit tripped and reset on its test button while the house ran on generator, confirming the step 3 bonding decision from the load side. Exercise set for Wednesday morning, AUTO photographed, customer signed.
References
- NEC (NFPA 70) Article 702, including 702.4 capacity and 702.5 transfer equipment, plus 110.26 working space; confirm the adopted edition, because 702's capacity provisions have moved between editions
- NEC (NFPA 70) 250.30 for a separately derived system and 250.34 for portable generators, at step 3
- NFPA 37, Stationary Combustion Engines and Gas Turbines, in the edition your jurisdiction has adopted, for the step 2 clearances
- 29 CFR 1910.333(b)(2) for de-energizing and verifying, with NFPA 70E-2021, 120.5 for live-dead-live
- Manufacturer's manual for the set: clearances, inlet pressure at full load, no-load bands, motor-starting capability
- See related: the automatic transfer switch commissioning SOP and the critical load panel design SOP