Equipment Notes: Generators

Defining What You Need for the Jobsite

by Jeremy Martin, midwest territory sales manager, Roofmaster









(Editor’s Note: Jeremy Martin has been with Roofmaster® for the past five years. Previously, he held senior sales and marketing positions on the fall protection and safety end of the roofing industry. Martin can be reached at


All generators, from permanent home standby generators to portable generators used on jobsites in the construction trades, have two very important specifications that all generator users should understand: continuous watts and surge watts. Continuous watts, also called running watts, are power that the generator can supply all the time. Surge watts, also called starting watts, are power that the generator can supply for a few short moments upon startup.

Both specifications are given in watts or kilowatts. For example, a manufacturer might specify that a small portable generator can supply a maximum of 2000 watts, but it is rated for 1600 continuous watts. Maximum watts in this case refer to the surge watts or starting watts. Continuous watts refer to running watts. The distinction between starting vs. running watts makes a difference when choosing a generator and especially when electric motors make up part of the total electrical load the generator supplies.

When choosing a generator for purchase or determining what loads a generator can power, take both specifications into consideration. First, add up the running watts of all the tools, appliances, or equipment the generator will run. You will need a generator that can supply the total continuous power rating all the time. Next, find the appliance or tool with the highest starting watts and add the starting watts to the running watts. This is maximum surge watts, or starting watts, the generator must supply. It is logically in your best interest to obtain a power source that supplies both enough surge watts and continuous watts to power all tools or appliances you intend to use.

Since generator manufacturers are in the business to sell us their products, they usually choose starting watts as the value we first see when choosing a generator, simply because it is the higher of the two. Only after reading the actual specs will you find the wattage that a generator can continuously provide. While this trick is somewhat deceiving, since one would expect that a 4000W generator will run 4000W worth of appliances, starting watts are not a useless number, and still must be considered.

Purchase a generator that can supply the maximum watts required for a few seconds and the continuous running watts the rest of the time. Remember that small generators may have the capacity to run a load, but not enough reserve to supply the starting watts required. Choose a generator with enough power to both start and run the load required. A good rule of thumb places the load on the generator at about 90% of the generator’s rated continuous capacity or the running watts. The generator will run cooler and last longer.