First thing how many Generators do you have if you have 2 or more than you must have paralleling gear, if so than run your building as a load for specific times and switch loads on Generators because the load banks are not cheap. I beleive your money can be spent on haveing a tech go through them whileyou use your building as load.
Hopefully you were able to hook up with websparky, but if you did not, or for others reading the thread, I'll try to post something herein.
If you are referring to original installation acceptance, then this is spoken to in 7.13 of NFPA 110. It is also important to clarify if this is a Level 1 systen, [life safety], and Level 2, [required system but for more "elective" load types].
For a Level 1 or 2 Acceptance test, 18.104.22.168 dictates that from a "cold" start, with the emergancy load at a standard operating level, a normal source power loss shall initiate the system. At that time, a number of parameters must be recorded and must continue for a period of time as stated in table 4.1(a) of NFPA 110, dependant on the "Class" of the system.
After this test is complete, 7.13.5 states the system shall be allowed to cool for a period of 5 minutes.
After this 5 minute period, 7.13.6 and 7.13.7 state that a full load test, equal to 100% of the kW rating of the system be applied for a period of 2 hours. During that time, operating parameters must be recorded at 15 minute intervals. Part of the load may be the building load with the remainder being supplied by a load bank.
Paraphrasing 22.214.171.124, this test may be accomplished by a load bank totally, with unity power factor, such as the common resistive load bank. This is actually how we have done all of our acceptance testing.
7.13.7 speaks to the test some more or in other terms, and mentions such things as starting my be accomplished by any method that initiates the prime mover, and picks up the 100% load in 1 step.
With respect to operational tests or exercising, is spoken to in a number of sections, including 126.96.36.199 and 8.4.2. In 8.4.2 states for Level 1 & 2, that these systems be tested at least once monthly for 30 minutes minimum at a not less than 30% of namplate kW rating.
I think that this is the section you were questioning, since 188.8.131.52 states that diesel -powered emergancy power systems that do not meet the requirements of 8-4.2, [which I interpret to mean non-required systems], shall be exercised monthly with the normal connected loads, and then anually with supplemental loads of 25% of nameplate for 30 minutes, then 50% for 30 minutes, then 75% for 60 minutes, for a total of 2 hours total load test.
8.4.3 states that these tests shall commence from a cold start.
As an aside, here at the airport, many of the geneerators installed for spot loads have resistive load banks permanently connected. They have a controller that exercises with as much normal connected building load as may exist, and uses this controller to bring in as much other resistive load via the bank to get to 90-100%.
The gentleman I work with is a mechanical engineer that at one time, ran the Chicago & Northwestern Railroad's repair shops. He has guided me in working with these diesel engines. He explained that a diesel engine that does not get exposed to full loading, such as a genset spinning without load or a truck idling will "polish out" it's cylinders allowing for a problem called "wet-stacking" by which, unburned fuel gets blown up the exhaust stack.
Most generator suppliers have and can include as part of their generator quote, load bank testing.
There a a couple of links to some load bank manuacturers. They are Avtron and Simplex.