# COMAR Title 20 — Public Service Commission

## Subtitle 50 — Service Supplied by Electric Companies

### Chapter 02 — Engineering

**Authority:** Public Utilities Article, §§2-113, 2-121, 5-101, 5-303, and 7-213, Annotated Code of Maryland

**Administrative History:** Effective date: May 22, 1942 (Order No. 38330)

**Administrative History:** Chapter revised effective May 18, 1960 (Order No. 54348)

**Administrative History:** Chapter revised effective June 1, 1965 (Order No. 55819)

**Administrative History:** Regulation .02 amended effective January 23, 1981 (8:2 Md. R. 117); March 27, 2006 (33:6 Md. R. 580); June 9, 2008 (35:8 Md. R. 808); September 21, 2009 (36:19 Md. R. 1438); May 28, 2012 (39:10 Md. R. 661); October 8, 2018 (45:20 Md. R. 920); March 20, 2023 (50:5 Md. R. 183); August 21, 2023 (50:16 Md. R. 728)

**Administrative History:** Regulation .02K, L amended effective July 7, 2025 (52:13 Md. R. 657)

**Administrative History:** Regulation .02M—O adopted effective July 7, 2025 (52:13 Md. R. 657)

**Administrative History:** Regulation .04 amended effective April 15, 2002 (29:7 Md. R. 622); May 28, 2012 (39:10 Md. R. 661)

**Administrative History:** Regulation .05 adopted effective March 27, 2006 (33:6 Md. R. 580)

**Administrative History:** Regulation .05 amended effective June 9, 2008 (35:8 Md. R. 808)

**Administrative History:** Regulation .06 adopted effective September 21, 2009 (36:19 Md. R. 1438)

**Administrative History:** Regulation .06D adopted effective December 2, 2019 (46:24 Md. R. 1104)

#### Regulation .01 Good Engineering Practice.

*COMAR 20.50.02.01*

The electric plant of the utility shall be constructed, installed, maintained, and operated in accordance with accepted good engineering practice in the electric industry to assure, as far as reasonably possible, continuity of service, uniformity in the quality of service furnished, and the safety of persons and property.

#### Regulation .02 Acceptable Standards.

*COMAR 20.50.02.02*

Unless otherwise specified by the Commission, the utility shall use the applicable provisions in the latest revised version of the incorporated by reference publications listed below as standards of accepted good engineering practice in this subtitle:

A. National Electrical Safety Code, ANSI C2 — 2017;

B. National Electrical Code, ANSI/NFPA 70 — 2020;

C. American National Standard for Electric Meters — Code for Electricity Metering, ANSI C12.1 — 2014;

D. American Standard Requirements, Terminology and Test Code for Instrument Transformers, ANSI/IEEE C57.13 — 2016;

E. Standard for Interconnection and Interoperability of Distributed Energy Resources with Associated Electric Power Systems Interfaces, IEEE 1547-2018;

F. Standard for Interconnection and Interoperability of Distributed Energy Resources with Associated Electric Power Systems Interfaces, IEEE 1547-2018 Amendment 1 (IEEE Std. 1547a-2020);

G. Errata to Standard for Interconnection and Interoperability of Distributed Energy Resources with Associated Electric Power Systems Interfaces, IEEE 1547-2018;

H. IEEE 1547.1-2020, Standard Conformance Test Procedures for Equipment Interconnecting Distributed Energy Resources with Electric Power Systems and Associated Interfaces;

I. UL Standard for Inverters, Converters, Controllers and Interconnection System Equipment for Use With Distributed Energy

J. NEMA Standards Publication TP 1 — 2002;

K. Guide for Electric Power Distribution Reliability Indices, IEEE Standard 1366 — 2003, 4.5 Major event day classifications;

L. Institute of Electrical and Electronic Engineers Standard 1695 — 2016 — IEEE Guide to Understanding, Diagnosing, and Mitigating Stray and Contact Voltage;

M. Interconnection Requirements for Onboard, Grid Support Inverter Systems, SAE J3072, Revision 3, June 10, 2024;

N. Electric Vehicle Supply Equipment, UL 2594, Edition 3, December 15, 2022; and

O. Electric Vehicle Power Export Equipment (EVPE), UL 9741, September 29, 2023.

#### Regulation .03 Adequacy of Supply.

*COMAR 20.50.02.03*

The generating capacity of the utility's plant, supplemented by the electric power regularly available from other sources, shall be sufficiently large to meet all normal demands for service and provide a reasonable reserve for emergencies.

#### Regulation .04 Electric Plant Operation and Maintenance.

*COMAR 20.50.02.04*

Each utility shall adopt written operation and maintenance procedures for its electric plant in order to determine the necessity for replacement and repair. The frequency of the various procedures shall be based on the utility's experience and accepted good practice. Each utility shall keep sufficient records to give evidence of compliance with its operation and maintenance procedures.

#### Regulation .05 Specific Electric Plant Engineering Requirements.

*COMAR 20.50.02.05*

A. When the National Electrical Safety Code and the National Electric Code, which are incorporated by reference in Regulation .02 of this chapter, call for different standards or requirements for installations that are under the exclusive control of the utility and located in legally established easements or rights-of-way, or located pursuant to agreements recognized by the Commission such as a utility tariff, the utility shall use the standard or requirement of the National Electrical Safety Code.

B. Utilities shall maintain the vertical clearances of overhead electric supply lines that cross water surfaces suitable for sailboating in accordance with the values specified by Rule 232 of the National Electrical Safety Code.

#### Regulation .06 Life-Cycle Cost Analysis to Guide the Purchase of Liquid-Immersed Distribution Transformers.

*COMAR 20.50.02.06*

A. Scope. This regulation does not apply to an electric cooperative that supplies electricity to fewer than 60,000 electric meters in the State.

B. Purchase of Liquid-Immersed Distribution Transformers.

  (1) Beginning January 1, 2009, a utility shall use the life-cycle cost methodology contained in NEMA Standards Publication TP 1-2002, which is incorporated by reference under COMAR 20.50.02.02, when selecting any liquid-immersed distribution transformer for purchase.

  (2) Evaluation of Distribution Transformer Models.

    (a) Within each capacity class or type of liquid-immersed distribution transformer, a reasonable number of commercially available models shall be evaluated, and, except as provided §B(2)(b) of this regulation, a utility shall select for purchase the model in each capacity class or type with the lowest total owning costs as determined by the life-cycle cost methodology.

    (b) If a utility is soliciting bids to supply multiple capacity classes or types of liquid-immersed distribution transformers under a single contract, models offered by a supplier in more than one capacity class or type may be combined for purposes of life-cycle cost evaluation.

    (c) A utility shall select for purchase the aggregation of models offered by a supplier in the combined classes or types with the lowest total owning cost as determined by the life-cycle cost methodology in §B(2)(b) of this regulation.

    (d) Under this section, a utility shall use:

      (i) The values for load losses and no-load losses as determined by the “Uniform Test Method for Measuring the Energy Consumption of Distribution Transformers”, Appendix A to Subpart K of 10 CFR Part 431, as amended, which is incorporated by reference; and

      (ii) The estimated value of energy and capacity from the most current year available at the time of any bid solicitation.

C. This regulation does not require a utility to purchase any liquid-immersed distribution transformer that fails to meet federal energy efficiency standards specified in 10 CFR Part 431, as amended, which is incorporated by reference.

D. Each utility shall keep sufficient records to give evidence of compliance with this regulation.