Efficiency levels are defined by the US Department of Energy (DOE).  TP1 efficiency went to effect  on January 1, 2007 with efficiency levels as defined by Energy Act of 2005 .  DOE 2016 efficiency is from the Department of Energy (DOE) 10 CFR 431.  The DOE released new efficiency standards which were put into effect January 1, 2016. These standards surpass and supersede NEMA TP1 efficiency standards. All low-voltage dry type three-phase ventilated transformers from 15 kVA through 1000kVA must be manufactured to these standards after January 1, 2016. DOE 2016 standards also apply to Harmonic Mitigating Transformers.  Transformers manufactured to DOE 2016 efficiencies must meet efficiency levels with a 35% load and temperature of 75°C. Transformers with DOE 2016 standards have grain-oriented, non-aging silicon steel cores. DOE 2016 standards do not apply to single phase, encapsulated, motor drive isolation, and auto transformers.

Below is a comparison of efficiencies between TP1 and DOE 2016.