The standard frequency for alternating current distribution systems shall be either 60 cycles per second or 25 cycles per second. Secondary Voltages. The voltage at the utility's service terminals, as installed for each customer, shall be maintained within the Limits specified in the table below. If a utility adopts any standard voltage not included in the table, it shall advise the Commission in order that the Commission may establish appropriate voltage limits. When 3-phase service is provided, the utility shall exercise reasonable care to assure that the phase voltages are balanced. Primary Voltages. The following limits shall apply where the utility supplies service at primary voltage: Industrial Customers. For service rendered principally for industrial or power purposes, the voltage may not exceed 7-1/2 percent above or 7-1/2 percent below the standard nominal voltages as filed in the utility's rules. Sales For Resale. For service rendered to public utilities and others for resale, the nominal voltage shall be as mutually agreed upon by the parties concerned. The allowable voltage may not exceed 7-1/2 percent above or 7-1/2 percent below the agreed upon nominal voltage without the express approval of the Commission. Special Contract Exceptions. The limitations in §§B(1) and B(2), of this regulation, do not apply to special contracts in which the customer specifically agrees to accept service with unregulated voltage. Exceptions to Voltage Requirements. It will not be considered a violation when voltages outside of the prescribed limits are caused by any of the following: Action of the elements; Service interruptions; Temporary separation of parts of the system from the main system; Infrequent fluctuations not exceeding 5 minutes' duration; or Other causes beyond the control of the utility. Requirements. Each utility shall have the following voltmeters for the purposes indicated: Secondary Standard. Each utility shall have at least one secondary standard indicating voltmeter to be used in checking the accuracy of working standard voltmeters. Working Standards. Each utility shall have at least two working standard indicating voltmeters to be used in checking the voltage on the utility's electric system and in checking the accuracy of recording voltmeters. Recording Voltmeters. Each utility shall have at least two portable recording voltmeters to be used to record the voltage on the utility's electric system. Accuracy. The voltmeters shall be of sufficient quality to meet the accuracy standards prescribed below: Secondary Standard. The secondary standard indicating voltmeter shall have a stated accuracy within 0.25 percent of full scale. This instrument shall be maintained within its stated accuracy. Working Standards. The working standard indicating voltmeters shall have a stated accuracy within 0.75 percent of full scale. Recording Voltmeters. The portable recording voltmeters shall have a stated accuracy within 1.5 percent of full scale. Calibration. The accuracy of the voltmeters shall be checked as indicated below: Secondary Standard. Secondary standards shall be checked at intervals not exceeding 3 years at the National Bureau of Standards, or at a laboratory acceptable to the Commission. Working Standards. Working standards shall be checked at intervals not exceeding 3 years by comparison with a secondary standard in the utility's meter shop. Certificates. Each standard shall be accompanied at all times by a certificate or calibration card, duly signed and dated, on which are recorded the corrections required to compensate for errors found at the customary test points at the time of the last calibration test. Care In Handling. Extreme care shall be exercised in the handling of standards and other instruments to assure that their accuracy is not disturbed. Voltage Surveys. Each utility shall make voltage measurements, using recording voltmeters, in order to determine if voltages are in compliance with the requirements contained in Regulation .02. Point of Measurement. Voltage measurements shall be made at the utility's service terminals. For single phase service, the measurement shall be made between the grounded conductor and the ungrounded conductors. For 3 phase service, the measurement shall be made between the phase wires. Voltage Records. All voltmeter records obtained under §A, above, shall be retained by the utility for at least 2 years and shall be available for inspection by the Commission's representatives. Notations on each chart shall indicate the following: Location where the voltage was taken; Time and date of the test; Results of the comparison of the recording voltmeter with an indicating voltmeter. Record of Corrective Action. If action is taken to correct the voltage conditions, the chart which records the voltage subsequent to the change shall be attached to the first chart so that the conditions before and after the change may be reviewed. Endeavor to Avoid Interruptions. Each utility shall make reasonable efforts to avoid interruptions of service, but when interruptions occur, service shall be re-established within the shortest time practicable, consistent with safety. Report to Commission. Each utility shall promptly report to the Commission's Engineering Division and Consumer Affairs Division: The onset of a major outage event; A sustained interruption, to firm-service customers, initiated by the utility in response to unacceptable system voltages; and A sustained interruption, to firm-service customers, initiated by the utility in response to thermal overloads of electric plant. The utility's report required by §B(1) of this regulation shall include a general description of the areas experiencing a sustained interruption and the expected system restoration times, if available. The utility making the report required by §B(1) of this regulation shall also provide periodic updates to the Consumer Affairs Division. Planned Interruptions. Planned interruptions shall be made at a time that will not cause unreasonable inconvenience to customers and shall be preceded, if feasible, by adequate notice to those who will be affected. Record of Interruptions. Each utility shall keep records of interruptions of service on its primary distribution system and shall make an analysis of the records for the purpose of determining steps to be taken to prevent recurrence of the interruptions. The records should include the following information concerning the interruptions: Cause; Date and time; and Duration. Momentary Interruption Record. A utility shall maintain information which it collects on momentary interruptions for 5 years. Unattended Substations. The record for each unattended substation shall show interruptions which required attention to restore service, with the estimated time of interruption. Public Utilities Article, §§2-121, 5-101, and 5-303, Annotated Code of Maryland Effective date: May 22, 1942 (Order No. 38330) Chapter revised effective May 18, 1960 (Order No. 54348) Chapter revised effective June 1, 1965 (Order No. 55819) Regulation .03C amended effective June 6, 2005 (32:11 Md. R. 983) Regulation .05 amended effective April 15, 2002 (29:7 Md. R. 622) Regulation .05B amended effective May 28, 2012 (39:10 Md. R. 661) Regulation .06 adopted effective April 15, 2002 (29:7 Md. R. 622) Regulation .06 repealed effective May 28, 2012 (39:10 Md. R. 661) Regulation .07 adopted effective April 15, 2002 (29:7 Md. R. 622) Regulation .07 repealed effective May 28, 2012 (39:10 Md. R. 661)