Most utility demand readings are based on a 15 or 30 minute sliding window and will not reflect the motor starting current.
This is correct. Billable peak is different from maximum draw.
Here is two definitions (because, each PoCo is different). Back in the days, it was basically giving into the capability of the meter, but with today's computerized meter, PoCo can setup its own rules in the program.
Monthly Demand: Monthly Demand is defined as the highest integrated kilowatt load during any 60-minute period occurring in the billing period for which the determination is made.
Definition of On-peak Demand: The maximum kW used by the customer in any fifteen-minute period between the hours of 10:00 a.m. and 10:00 p.m.
Let's look at the latter.
This means that during the 12 hour window shown, the highest average in any given 15 minute period will be used.
Imagine that you're driving your car. You're stuck in grid lock, then you see a clear path. You get frustrated, floor it, and get the car up to 110mph. Still, in 15 minutes you only traveled 5 miles, so the 110mph doesn't count as your peak. So, even though you got it up to 110mph, the 15min average "peak" is 20mph. (you can compare this peak with the motors coming on)
If you use an integration period of 3 seconds, you'll most likely capture the 110mph "max".
Later on in that day, you were driving on the freeway on cruise control @ 70mph and you sustained it for 30minutes. A 15 minute snap shot will show that "highest 15 minute average speed" as 70mph.
Suppose you were sizing the engine for that car. You figure that something that can get it up to 85mph based on the 15 minute average date. Nope, 110mph capability is needed. Even if this is only for one minute, if its required for one big critical piece of equipment, such as an elevator, it will fail to operate.
With electrical power, you don't necessarily want to document a very short surge, so you'd need use a peak meter with shorter
integration period that is more in line with the holding duration of the flywheel effect of generator.