Generate Clean Jobsite Power

All generators look relatively the same, but don?t assume this makes them interchangeable. Carefully examine the ratings and compare the voltage regulation and frequency tolerances.

Start by choosing the most appropriate size. ?When determining adequate power for a task, it is important to know how many pieces of equipment you are trying to power, how many amps are required and what voltage is required,? says David Spears, product manager, power products, Terex.

Consider how you plan to use the generator on the jobsite. ?Just get an understanding of what you are going to be hooking up to it and do a rough calculation of how many amps each of those items draws, either by looking at the data plate on the item or looking in the manual that came with it,? suggests Todd Howe, generator product marketing manager, Doosan Infracore Portable Power. ?Then make sure the total number of amps for everything you are connecting to the machine doesn?t exceed the continuous rating.?

It?s important to understand several key parameters. ?Using generators to supply loads requires knowledge of what the continuous non-motor load is and the horsepower (and resulting starting kVA) of all the motor loads,? says Dave Dahlstrom, marketing and business development, Shindaiwa Construction Products.

Determine how the motors will be started and the maximum voltage drop allowed during motor starting. ?Will they be started across the line, with a variable-speed controller, or reduced voltage?? Dahlstrom asks. ?You also need to know what sequence the motors will be started in, and whether or not more than one motor will be started at any given time. With this knowledge of the actual loads, you can then size the generator properly for the job.?

Differences in power ratings

One of the most important considerations is the continuous power rating. ?Continuous power is the maximum amount of power that a generator can run at for an indefinite period of time without degradation or damage,? says Spears. ?The standby rating represents the maximum amount of power the generator can produce for short periods of time without overheating or causing damage. It is important to note that extended use at the standby rating output can cause damage and reduce the useful life of the generator.?

Generator rating terminology differs between small portable models and towable units. ?Typically, in smaller generator models (less than 10,000 watts), the model number reflects a maximum power rating,? says Rick Bernier, national product specialist, sales application engineering, Wacker Neuson. ?This is the temporary amount of power a generator can deliver for about 30 minutes in a six-hour period.?

Beyond that time frame, the generator must be run at a lighter load or be turned off for six hours to allow it to cool down before it can carry this load size again. ?It is recommended you choose a generator that is at least 10% larger than your continuous power needs, so you have extra capacity for unexpected load requirements,? Bernier advises.

Towables have a slightly different nomenclature. ?Typically, a towable unit is rated in prime power, then it has a 10% overload rating that will get it to what is called the standby rating,? notes Howe. ?This is the maximum amount of power you can pull out of the generator. If you operate it there, you would have a reduced lifespan.?

Units used in emergency applications are typically sized according to the standby rating, because they are not going to run very much and therefore will have a useful service life. ?A mobile application for rental and construction, keeping it at the prime power rating, will ensure the unit will live to maybe a 10,000-hour lifespan,? says Howe.

Do the math

The math to determine the required size for a single-phase generator is rather straightforward.