energy-efficientdoeA distribution transformer provides the final voltage transformation in the electric power distribution system by reducing the high voltage current from a power line to a lower voltage for use in a building. The Department of Energy (DOE) has regulated the energy efficiency level of low-voltage dry-type distribution transformers since 2007. Beginning in 2016, there will be newly amended, federally mandated, energy efficiency standards for distribution transformers. MGM Transformer Company is at the forefront of this new standard and will be offering the new efficiencies on its products starting on January 1, 2016. This ruling applies to three phase low voltage dry-type general purpose distribution transformers manufactured starting on January 1, 2016. Transformers that meet the current efficiency requirements in the U.S. (NEMA TP-1) that are physically in the U.S. can continue to be legally sold and installed after January 1, 2016. This includes units stored at manufacturers’ warehouses, distributor stock, job sites, etc.


Comparison of various efficiency standards: NEMA TP-1, NEMA PREMIUM CSL-3 & DOE 2016

The table below lists the minimum efficiencies of low-voltage dry-type three phase distribution transformers required for their kVA rating. The standards for transformers manufactured on or after January 1, 2007 are known as NEMA TP-1 (or Energy Star labeled). On May of 2010 The NEMA CSL-3 standards were introduced with higher efficiency ratings than NEMA TP-1. The benefits of CSL-3 transformers are reduced electrical & heat losses, lower total cost of ownership (TCO), greater energy savings and green/LEED design. These features are beneficial for data centers, healthcare installations, schools & colleges, green applications, LEED buildings and government projects. The CSL-3 efficiency standard was never federally mandated. Transformers manufactured on or after January 1, 2016 are required to meet the minimum DOE 2016 efficiencies listed below. These standards will be federally mandated.

(Three Phase)
(Energy Star)
Federally Mandated
Not Federally Mandated
DOE 2016
Federally Mandated
15 kVA 97.0 97.90 97.89
30 kVA 97.5 98.25 98.23
45 kVA 97.7 98.39 98.40
75 kVA; 98.0 98.60 98.60
112.5 kVA 98.2 98.74 98.74
150 kVA 98.3 98.81 98.83
225 kVA 98.5 98.95 98.94
300 kVA 98.6 99.02 99.02
500 kVA 98.7 99.09 99.14
750 kVA 98.8 99.16 99.23
1000 kVA 98.9 99.23 99.28


* Published CSL-3 efficiency percentages may vary by manufacturers.

Note: All efficiency values are at 35 percent of nameplate-rated load, determined according to the DOE Test Method for Measuring the Energy Consumption of Distribution Transformers under Appendix A to Subpart K of 10 CFR part 431.