Emergency Standby Diesel Generator Monthly Load Bank Testing
This log form documents the monthly load bank test procedure for emergency standby diesel generators in critical power applications. It captures pre-test conditions, step-load data, fluid thresholds, and any corrective actions required to maintain NFPA 110 compliance and manufacturer warranty requirements.
Monthly load bank testing is required to prevent wet stacking — a condition where unburned fuel and carbon accumulate in the exhaust system during prolonged low-load or no-load operation. This test applies a resistive load at 25%, 50%, 75%, and 100% of nameplate kW rating while logging voltage, frequency, oil pressure, coolant temperature, and exhaust temperature at each step. Any parameter exceeding the tolerances listed in the matrix below triggers a corrective action entry. This log serves as the auditable record for NFPA 110 Level 1 compliance, insurance inspections, and the generator manufacturer's warranty terms.
- Verify automatic transfer switch (ATS) is in 'test' position and generator breaker is closed. Apply lockout/tagout on any remote start signals from the building management system. Confirm load bank ground bond is intact and rated for full test current.
- Personal Protective Equipment: arc-rated coverall (minimum 8 cal/cm²), voltage-rated gloves (Class 0), safety glasses, hearing protection, and steel-toed boots. No loose clothing near the radiator fan or belt drive.
- Fuel supply must be at least 75% full before starting the test. Confirm day tank level, return line integrity, and that the fuel supply pump is in 'auto'. Have a Class B fire extinguisher (minimum 20 lb) within 10 metres of the generator set.
- Coolant system must be pressurized and at operating temperature (minimum 30°C) before applying load. Confirm block heater is functioning and that the radiator shutters or fan clutch cycles freely. Top off coolant if necessary — do not open pressurized cap above 50°C.
Inspection / Load Bank Test Matrix
| Status (P/F) | Inspection Item / Task | Tolerance / Threshold | Actual Reading |
|---|---|---|---|
| [ ] Pass [ ] Fail | Coolant level & freeze protection | Level within 2.5 cm of filler neck; specific gravity ≤ –35°C | _________________ |
| [ ] Pass [ ] Fail | Engine oil level & pressure (at idle, hot) | Oil at full mark on dipstick; pressure 40–55 psi @ 1800 rpm | _________________ |
| [ ] Pass [ ] Fail | Battery voltage (rest / under crank) | ≥ 12.4 V rest (12 V system); ≥ 9.6 V during cranking | _________________ |
| [ ] Pass [ ] Fail | Block heater temperature (coolant jacket) | ≥ 30°C measured at thermostat housing | _________________ |
| [ ] Pass [ ] Fail | Voltage at 25% load (L–L average) | 208/480 V ± 2% (203–212 V / 470–490 V) | _________________ |
| [ ] Pass [ ] Fail | Voltage at 50% load (L–L average) | 208/480 V ± 3% (202–214 V / 466–494 V) | _________________ |
| [ ] Pass [ ] Fail | Voltage at 75% load (L–L average) | 208/480 V ± 4% (200–216 V / 461–499 V) | _________________ |
| [ ] Pass [ ] Fail | Voltage at 100% load (L–L average) | 208/480 V ± 5% (198–218 V / 456–504 V) | _________________ |
| [ ] Pass [ ] Fail | Frequency at all load steps | 60 Hz ± 0.5 Hz (59.5–60.5 Hz) | _________________ |
| [ ] Pass [ ] Fail | Exhaust temperature (each bank, at 100% load) | 350–550°C (individual cylinder within 50°C of average) | _________________ |
| [ ] Pass [ ] Fail | Coolant temperature (at 100% load, steady-state) | 82–96°C (thermostat rated temp ± 5°C) | _________________ |
| [ ] Pass [ ] Fail | Oil temperature (at 100% load) | ≤ 120°C measured at pan drain plug | _________________ |
| [ ] Pass [ ] Fail | Cool-down period after 100% load removal | Minimum 5 minutes unloaded before shutdown | ____ min |
| [ ] Pass [ ] Fail | Post-test visual inspection (leaks, vibration, noise) | No fluid leaks, no abnormal vibration or knocking | _________________ |
Defect / Corrective Action Log
| Date / Time | Item # | Issue Identified | Corrective Action Taken | WO # |
|---|---|---|---|---|
| ___/___/_____ ___:___ | _______ | _______________________________ | _______________________________ | _______ |
| ___/___/_____ ___:___ | _______ | _______________________________ | _______________________________ | _______ |
| ___/___/_____ ___:___ | _______ | _______________________________ | _______________________________ | _______ |
| ___/___/_____ ___:___ | _______ | _______________________________ | _______________________________ | _______ |
| ___/___/_____ ___:___ | _______ | _______________________________ | _______________________________ | _______ |
By signing below, the inspector verifies that all load bank test steps have been executed in accordance with NFPA 110 Section 8.4.1 and the generator manufacturer's published service intervals. All out-of-tolerance readings have been recorded in the Corrective Action Log.