# 10 CFR § 429.47 - Distribution transformers.

§ 429.47 Distribution transformers.

(a) Sampling plan for selection of units for testing.

(1) The requirements of § 429.11 are applicable to distribution transformers; and

(2) For each basic model of distribution transformer, efficiency must be determined either by testing, in accordance with § 431.193 and the provisions of this section, or by application of an AEDM that meets the requirements of § 429.70 and the provisions of this section.

(i) For each basic model selected for testing:

(A) If the manufacturer produces five or fewer units of a basic model over 6 months, each unit must be tested. A manufacturer may not use a basic model with a sample size of fewer than five units to substantiate an AEDM pursuant to § 429.70.

(B) If the manufacturer produces more than five units over 6 months, a sample of at least five units must be selected and tested.

(ii) Any represented value of efficiency of a basic model must satisfy the condition:

$\begin{array}{c}RE\le \frac{100}{1+\left(\frac{100-\stackrel{—}{x}}{\stackrel{—}{x}}\right)\left(\frac{\sqrt{n}}{\sqrt{n}+.08}\right)}\\ \mathrm{where}\phantom{\rule{0ex}{0ex}}\stackrel{—}{x}\phantom{\rule{0ex}{0ex}}\text{is the average efficiency of the sample}\phantom{\rule{0ex}{0ex}}\end{array}$

(b) Certification reports.

(1) The requirements of § 429.12 are applicable to distribution transformers except that required information in paragraph (b) of this section may be reported by kVA grouping instead of by basic model and paragraph (b)(6) of this section does not apply; and

(2) Pursuant to § 429.12(b)(13), a certification report shall include the following public product-specific information: For the most and least efficient basic models within each “kVA grouping” for which part 431 prescribes an efficiency standard, the kVA rating, the insulation type (i.e., low-voltage dry-type, medium-voltage dry-type or liquid-immersed), the number of phases (i.e., single-phase or three-phase), and the basic impulse insulation level (BIL) group rating (for medium-voltage dry-types).

(c) Alternative methods for determining efficiency or energy use for distribution transformers can be found in § 429.70 of this subpart.

(d) Kilovolt ampere (kVA) grouping. As used in this section, a “kVA grouping” is a group of basic models which all have the same kVA rating, have the same insulation type (i.e., low-voltage dry-type, medium-voltage dry-type or liquid-immersed), have the same number of phases (i.e., single-phase or three-phase), and, for medium-voltage dry-types, have the same BIL group rating (i.e., 20-45 kV BIL, 46-95 kV BIL or greater than or equal to96 kV BIL).