What Generator Load Bank Testing Involves
Generator load bank testing runs a standby generator against an artificial electrical load for a set time, so the engine and alternator are proven at a meaningful share of their rated output. A load bank is a bank of resistive elements, sometimes with reactive elements, that turns the generator’s output into heat. It is either a portable unit brought to site on a trailer or a permanently installed bank with its own connection point.
A typical test runs like this:
- Pre-test inspection. The provider checks fuel level, oil, coolant, belts, hoses, battery and charger, and looks for leaks, so the test does not run a unit that is already in poor condition.
- Connection. Cables are run from the load bank to the generator output, usually at a breaker or a dedicated load bank connection cabinet. Live parts are de-energized and locked or tagged out before anyone works on them.
- Warm-up. The engine is started and brought to operating temperature before the timed load steps begin.
- Stepped load. Load is added in steps up to the target percentage of the generator’s nameplate kW rating and held for the required duration.
- Readings. At set intervals the provider records kW, voltage, amperage, frequency, oil pressure, coolant temperature and, where fitted, exhaust temperature.
- Cool-down and close out. Load is removed, the engine runs unloaded to cool, the controls are returned to automatic, and the results and photos are attached to the work order.
In many installations the building can stay on utility power during the test, because the load bank supplies the load. The provider confirms this from the site’s electrical arrangement before the test is scheduled.
NFPA 110 Requirements for Load Bank Testing
NFPA 110, the Standard for Emergency and Standby Power Systems, sets testing requirements for generators that serve emergency and standby power systems where the standard applies. The details below are taken from the 2010 edition as summarized by the Minnesota Department of Health in its guidance for health care facilities. Editions and adoption differ by jurisdiction, so the authority having jurisdiction decides which edition and which sections apply to a given site.
- Monthly exercise. Generators are exercised under load at least monthly (Section 8.4.1). A diesel unit runs for at least 30 minutes either at a load that maintains the minimum exhaust gas temperature recommended by the manufacturer, or at operating temperature and not less than 30 percent of the nameplate kW rating (Section 8.4.2). Warm-up and cool-down time does not count toward the 30 minutes.
- Annual load bank test. A diesel unit that cannot meet the monthly load requirement with the building’s available load is exercised monthly with the available load and annually with supplemental load: steps at 50 percent of the nameplate kW rating and then not less than 75 percent for 60 minutes, for a total test duration of 1.5 continuous hours (Section 8.4.2.3).
- 36-month test. Level 1 systems are tested at least once every 36 months, continuously for the system’s assigned class but not more than 4 hours, at not less than 30 percent of the standby nameplate kW rating for diesel units (Section 8.4.9). Supplemental load may be added to reach it.
- Combined test. The 36-month test can be combined with one of the monthly tests. Where it is combined with the annual load bank test, the first 3 hours are at not less than the 36-month minimum load and the final hour at not less than 75 percent of the standby nameplate kW rating.
- Transfer switches. Transfer switches are operated monthly from the normal to the alternate position and back (Section 8.4.6).
- Records. A written record of inspections, tests, exercising, operation and repairs is kept on the premises (Section 8.3.4).
Air permits and run hours. Under the federal rules for stationary engines at 40 CFR 63.6640(f), there is no time limit on running an emergency engine in an emergency, but operation for maintenance checks and readiness testing is limited to 100 hours per calendar year. The testing must be recommended by a federal, state or local government, the manufacturer, the vendor, a regional transmission organization or balancing authority, or the insurer. Load bank tests are maintenance and readiness testing, so their hours are logged against that allowance, and state air permits can add their own conditions.
Electrical safety. OSHA requires live parts to be de-energized before employees work on or near them, unless that adds hazards or is infeasible (29 CFR 1910.333(a)(1)), with circuits isolated by locks, tags or both (29 CFR 1910.333(b)(2)).
Preventive Maintenance Schedule for Generator Load Bank Testing
A load bank test is one item in a wider generator schedule. Planned testing finds weak components under controlled conditions instead of during an outage, spreads cost across the year, and produces the records that fire code officials, insurers and air permit regulators ask for.
| Task | Recommended frequency | Basis |
|---|---|---|
| Visual inspection of fuel, oil, coolant, exhaust, battery and charger | Weekly | NFPA 110 (2010 edition), Section 8.4.1, as summarized by the Minnesota Department of Health, where NFPA 110 applies; Facility First default, elsewhere |
| Exercise under load for at least 30 minutes, at not less than 30 percent of nameplate kW or the manufacturer’s minimum exhaust temperature (diesel) | Monthly | NFPA 110 (2010 edition), Section 8.4.2 |
| Operate the automatic transfer switch to the alternate position and back | Monthly | NFPA 110 (2010 edition), Section 8.4.6 |
| Load bank test with supplemental load, 1.5 continuous hours, where monthly runs do not reach the required load | Annually | NFPA 110 (2010 edition), Section 8.4.2.3 |
| Extended test of up to 4 hours for Level 1 systems | At least every 36 months | NFPA 110 (2010 edition), Section 8.4.9 |
| Infrared scan of transfer switch connections | Annually | Recommended, not required, in Minnesota Department of Health guidance |
| Load bank test after major engine or alternator repair | After the repair | Facility First default |
| Log run hours for testing and maintenance against the annual allowance | At every run | 40 CFR 63.6640(f) |
Facility First default is the starting interval in each program, adjusted for each site.
The authority having jurisdiction, the manufacturer and the property’s insurer can require more frequent service, and each location’s schedule is set in its program and recorded on every visit.
Signs a Generator Needs a Load Bank Test
- Monthly test logs show load below 30 percent of nameplate kW, or exhaust temperature below the manufacturer’s minimum
- The building load on the generator has dropped after a remodel or equipment change
- The generator has had major engine, cooling or alternator repair
- Unsatisfactory conditions in past test records have not been closed out
- The insurer or authority having jurisdiction has asked for proof of performance at load
Records to Keep
- Generator identification, install date, nameplate kW and the kW value equal to 30 percent of nameplate
- Fuel type and normal operating temperature
- Test date, load steps, duration and readings at each interval
- Transfer switch used, transfer time and cool-down time
- Names of the people providing the service, the tester’s signature or initials, and any unsatisfactory conditions found
- Corrective actions taken and parts replaced
- Run hours for testing and maintenance in the calendar year
The Minnesota Department of Health recommends keeping generator logs on site for at least three years and making sure at least two staff members know where they are kept.
How Facility First Runs Generator Load Bank Testing Across a Portfolio
- Request. Testing is scheduled in the location’s program, or requested through the platform or by phone.
- Triage. Facility First confirms the unit’s nameplate rating, connection point, test type (annual or 36-month), access for a portable load bank and any notice the landlord or tenants need.
- Dispatch. A vetted generator provider in the location’s market receives the work order and the unit’s history.
- Completion. The provider runs the test, records readings at each step and closes out with photos and the test report.
- Verification and invoice. Results are checked against the required load and duration, deficiencies are opened as follow-up work orders, and the job is invoiced in one format.
Tests within the client’s approval limit proceed on schedule; repairs found during the test above that limit are quoted first.
What Affects the Cost of Generator Load Bank Testing
- Generator size in kW and output voltage
- Portable load bank versus a permanently installed bank or connection cabinet
- Distance and access from the trailer position to the connection point
- Test type: annual 1.5 hour test or a combined 36-month test
- Fuel used during the test and any refill afterward
- After-hours or weekend scheduling
- Repairs found during the test
Approval limits set by the client decide what proceeds automatically and what is quoted first.
Generator Load Bank Testing for Retail Stores, Restaurants and Offices
- Retail stores and grocery. Generators often back up refrigeration, lighting and point of sale. Tests are timed outside trading hours where the portable load bank or cables would occupy parking or loading areas.
- Restaurants. Load bank exhaust and engine exhaust are kept away from outdoor seating and kitchen air intakes, and tests are scheduled outside meal periods.
- Offices and multi-tenant buildings. Landlords may require notice before a test, and the transfer switch test is coordinated with building management because it moves building systems to generator power.
Frequently Asked Questions
What Is a Generator Load Bank Test?
It is a test that runs a generator against an artificial electrical load so it is proven at a set share of its rated output. It shows whether the unit can carry a load it may not see during routine monthly runs.
How Often Should a Generator Load Bank Test Be Done?
Where NFPA 110 applies, a diesel unit that cannot reach the monthly load requirement with the building load is load bank tested annually, and Level 1 systems also have an extended test at least every 36 months. The authority having jurisdiction, the manufacturer and the insurer can set other intervals.
How Long Does a Load Bank Test Take?
Under the NFPA 110 edition summarized in this page’s sources, the annual supplemental load test runs for 1.5 continuous hours, and the 36-month test runs continuously for the system’s assigned class, up to 4 hours. Set-up, warm-up and cool-down add to the time on site.
Does a Load Bank Test Interrupt Power to the Building?
Often not, because the load bank supplies the load. The monthly transfer switch test does move building systems to generator power, so it is coordinated separately.
Do Load Bank Tests Count Toward EPA Run-Hour Limits?
For emergency engines covered by the federal stationary engine rules, yes. Under 40 CFR 63.6640(f), operation for maintenance checks and readiness testing is limited to 100 hours per calendar year, so test hours are logged against that allowance.
Sources
- Minnesota Department of Health: Inspection and Testing of Emergency Generators (rev. June 2024), citing NFPA 110 (2010 edition)
- Minnesota Department of Health: Fire and Life Safety Code Documentation Guide
- NFPA: NFPA 110, Standard for Emergency and Standby Power Systems
- Legal Information Institute: 40 CFR 63.6640, Continuous compliance with emission limitations
- OSHA: 29 CFR 1910.333, Selection and use of work practices