By Garth Stevens, PE

It’s a warm sunny day, and your facility is at full capacity, with everything humming along just right. Suddenly, the utility power drops out, and everything goes dark. You’re not worried, though, because you have a well-maintained generator that backs up your critical loads. Within seconds, the generator is up and running, and the loads transfer to the backup power.

Since you are conscientious about maintenance, you head out to the generator building to check the load on the generator. All the backed-up loads are up and running, and you want to make sure the generator is not overloaded, especially since it’s a warm day. Expecting to see a high load on the generator, you are surprised to see that the amp draw is less than 30% of the generator capacity. Why is your generator so oversized? Did the engineer who designed the facility get a kickback from the generator supplier for selecting a big and expensive unit?

The good news is there is no conspiracy to make generators bigger and more expensive than they need to be. Instead, there are several reasons that generators do end up being sized larger than what initially seems necessary.