For me looking at a specification sheet and understanding the statistics is second nature… after all I’ve been factory trained.  But for the average consumer reading about generators, things can become confusing and the terminology can be like reading a different language.  After awhile instead of becoming informed you just end up with more questions.  Maybe if the terminology was explained, the specifications would make sense and become more understandable.  Always remember you can email ( or call us (928-453-4494) at Norwall PowerSystems with any questions.

Almost all of the automatic standby systems Norwall PowerSystems offers operate on either natural gas or propane.  These two fuels are slightly different in their composition so for the units that can operate on both fuel types the output is also slightly different, you will see an output rating for natural gas and one for propane.  Propane is the higher rating, natural gas slightly lower.

Btu’s = Natural Gas at 1,000 Btus per cubic foot or Propane at 2,520 Btus per cubic foot. Don’t forget to have your fuel supply and fuel line installed according to local codes and mandates.

Nema = The rating for an enclosure, such as the cabinet on a transfer switch.  Nema 1 is an indoor rating, Nema 3R is an outdoor rating.  There are other Nema levels depending on the application.  These two are the most common for generators…

Normal Operating Load = When a generator is at approximately 50% load/capacity.

Rated Power = The maximum output for continuous duty operation.  This rating does not include any surge capacity.

Sound Output = The industry standard for measuring sound output levels is 23 feet (7 meters).  While the db(A) is often listed on spec sheets the distance it was measured is not always stated.

Surge Capacity = This rating is not always published by the manufacture, an authorized dealer can help your installer determine if the unit has enough surge capacity.  Surge capacity should only be considered for starting amp requirements and never relied on for continuous duty operation.

Transfer Switch = Used to safely transfer electrical loads from one power supply to another.  Almost all of the standby units use automatic transfer switches and a portable generator would use a manual transfer switch.

Source:  Generac Power Systems