Power infrastructure
With a monthly exercise under real load, an annual run at higher load when the monthly runs fall short, and a preventive visit that covers the engine, the fuel and the controls. NFPA 110 sets the US benchmark of 30 minutes at not less than 30 percent of nameplate each month; in Canada, CSA C282 governs emergency generators. The UPS is part of the same test: it has to accept the generator and hand the load to it.
A run of at least 30 minutes under enough load to bring the engine up to temperature. NFPA 110, as reprinted by Cummins, requires generator sets in service to be exercised at least once monthly for a minimum of 30 minutes, either at a load that keeps the exhaust gas temperature at the maker's minimum or at not less than 30 percent of the nameplate kW rating. Starting the engine and letting it idle does not meet either test. The run also proves the start sequence, the batteries that crank the engine, and the transfer switch, which NFPA 110 requires to be operated monthly.
Then an annual run with supplemental load makes up the difference. Under NFPA 110 as reprinted by Cummins, a diesel installation that cannot meet the monthly requirement is exercised monthly with the load it has, and annually with supplemental load at not less than 50 percent of nameplate for 30 continuous minutes and not less than 75 percent for 1 continuous hour, a total of at least 1.5 hours. In data centres the gap is common. Kohler notes that generators were historically greatly oversized for the usual load, and that because operators do not want to move the IT load onto the generator for a test, the monthly exercise uses a load bank. How that test is connected and run is covered in generator load bank testing; this guide does not repeat it.
Unburned fuel collecting in the exhaust of a diesel that runs too lightly. Kohler explains that when generators run at less than 30% of capacity for long periods, the engine cannot reach the temperature needed to burn fuel completely. Generac describes the result: liquid diesel passes into the exhaust, seen as black smoke and oily residue in the stack, and puts the exhaust temperature needed for aftertreatment at a minimum of about 536°F (280°C), reached at roughly 30% load as a rule of thumb. Cummins' NFPA 110 summary gives the practical rule: minimize operation below 30% load. Light monthly runs are the usual cause, which is why the annual load run exists.
The intervals for each item come from the engine maker and from the standard that applies to the site. NFPA 110 also sets a longer test for Level 1 systems: at least once within every 36 months, for the assigned class duration, with the test allowed to stop at 4 hours where the class is longer.
CSA C282 for emergency generators. CSA describes C282 as covering the design, installation, operation, maintenance and testing of generator sets and associated equipment supplying emergency power where the National Building Code of Canada requires it, and its current edition sets the minimum load for monthly testing at 30%. C282 does not cover emergency power from storage batteries or a UPS, so the UPS is maintained under its maker's instructions and the switchgear standards. Many data-centre generators are standby rather than code-required emergency supply; even then, C282 and NFPA 110 are the usual benchmarks for the test programme.
By transferring real load and watching the UPS accept the generator. Cummins notes that without a UPS the load is lost for approximately 10 seconds while the generator starts and the transfer switch moves; with a UPS, the battery covers that gap, and the question becomes whether the UPS accepts the generator's voltage and frequency.
Eaton warns that a generator whose frequency swings outside the UPS input window can leave the UPS on battery until the battery runs out. Cummins recommends using a UPS's generator mode if it has one, and notes that a UPS with walk-in lets the battery take the load first and ramps it onto the generator. A periodic integrated test, with the IT load protected, proves the whole chain, and a meter on the UPS input during the run shows how the two interact (see power quality and harmonics); the UPS and generator compatibility guide covers the settings.
Often several. Kohler notes that a typical data-centre facility uses between five and ten generators, and that load bank exercising for all of them adds up to a significant time commitment for operations staff. That is why generator maintenance is planned as a programme rather than one visit at a time, with the monthly runs, the annual load runs and the integrated tests on one calendar alongside the UPS maintenance for data centres.
Yes. Generator service is delivered through specialist partners and quoted alongside the UPS and transfer switch work, so the monthly runs, the annual load bank run and the integrated test are on one plan. Send the generator make, rating and fuel type through the quote request form.
At least once a month for at least 30 minutes, at not less than 30 percent of nameplate kW or at the maker's minimum exhaust temperature, under NFPA 110 as reprinted by Cummins.
A run with supplemental load at not less than 50 percent of nameplate for 30 minutes and 75 percent for 1 hour, for sites whose monthly runs do not reach the required load.
Unburned diesel collecting in the exhaust of an engine run too lightly; Kohler ties it to long periods below 30% of capacity.
No. CSA C282 covers generator sets supplying emergency power and does not cover emergency power from storage batteries or a UPS.
Sources, checked 2026-10-04:
Tell us the site, the UPS and the timing. We reply and quote within 4 business hours, or call 1 (438) 800-0382
Brand names are trademarks of their owners and are used only to identify the equipment we service. We are not the manufacturer and are not affiliated with it.