Section 12 Customer’s Electrical Equipment
12.1 General Comments
The Department offers the following suggestions as an aid in maintaining reasonably uniform voltage and continuous service. The type, size and mode of operation of equipment frequently affects the voltage and the quality of service received. Three wire, single phase and all multiphase circuits should be arranged to maintain load balance on the individual circuits and the main service within 10%. Many of these details can be best resolved when the wiring is in the design stage.
The Department recommends that the Customer’s wiring be designed so that the voltage drop between the disconnecting means or service entrance switch, and the farthest outlet be limited to not more than 2% at full load. A Customer shall not cause the voltage on the primary side of a distribution transformer to sag more than 4% of the nominal voltage by the operation of the Customer’s facilities.
Equipment such as computers and other sensitive electronic devices may be adversely affected by minor voltage variations. It is the Customer’s responsibility to provide any uninterruptable power supplies, voltage regulating equipment or other protective apparatus for these sensitive devices and equipment.
12.2 Radio and Television Interference
Some types of utilization equipment, including certain types of motors, equipment depending for its operation upon frequent making and breaking of the circuit, X-ray machines and other devices, may cause unsatisfactory operation of television, radios and other electronic equipment unless especially designed or equipped to prevent such interference. In purchasing utilization equipment, the Customer should inquire regarding such interference characteristics and select non-interfering types. Where interference is experienced from utilization equipment, it can often be eliminated or minimized by equipping the interfering device with an U. L. approved interference suppresser. These suppressers are available through many retail stores.
12.3 Electric Heating
Large heating appliances should be connected to 120/240, 120/208, or 277/480 volt circuits and arranged to operate 240, 208, or 480 volts on high heat so far as practicable.
12.4 Motor – Voltage Rating
Single phase motors manufactured under American National Standard Institute (ANSI) Standard C84.1-1970 have 115 or 230 volt nameplates and, if three phase, have 208, 230, 460, 2,300, 4,000, or 13,200 volt nameplates. These are nominal voltage ratings and do not imply that the motors shall be operated at the exact voltages supplied. Motors may be supplied with nominal voltages as listed below:
Table 12.4-4. Nominal Voltage Rating of Motors
| Type of Service | Nominal Supply Voltage | Motor Voltage Rating (Nameplate) |
| Single Phase | 120 | 115 |
| Single Phase | 240 | 230 |
| Three Phase | 208 | 208 |
| Three Phase | 240 | 230 |
| Three Phase | 480 | 460 |
| Three Phase | 2,400 | 2,300 |
| Three Phase | 4160 | 4,000 |
| Three Phase | 13,800 | 13,200 |
All motors should have a manufacturer’s nameplate indicating the voltage, current rating, speed and horsepower rating for continuous or intermittent use as the case may be. This nameplate should also carry the NEMA “code letter” designation of the motor. When a motor is rewound to produce a change in its original design, a new nameplate should be attached indicating the new characteristics and the name of the firm or person making the change.
12.5 Motor Starting
12.5.1 General Comments
Most motors, when starting at rated voltage, draw current much in excess of full load running current. Also, the power factor of this starting current is usually low. This causes, for a brief period, a voltage drop or lighting flicker. It is essential that the Customer’s equipment have good starting characteristics to assure against objectionable effects to the Customer’s equipment and to service to other Customers. Soft-start motor load controllers must be used. The Department finds it necessary to establish certain limitations for the maximum allowable starting currents of motors to be connected to its lines. Frequency of starting is also a factor.
Considerable latitude in the amount of starting current is permissible under certain conditions, especially where the motors are started not more than two or three times per day. It is necessary that the Customer consult with the Department as to the acceptability of the proposed installation in this respect. The Department, however, can give no warranty, expressed or implied, that particular conditions may not require change, unless starting currents are within the limits in the following sections.
12.5.2 Single Phase Motors
12.5.2.1 Horsepower Rated
Single phase motors rated in horsepower may be started “across the line”, that is, at full rated voltage by merely closing a switch. It is recommended that single
phase motors larger than 1/2 hp be operated at 240 volts. Locked rotor motors specified in Table 13.5-5, will be permitted under the following conditions only:
- When such motors are provided with proper current limiting starting equipment; or
- When the locked rotor current of each motor in an installation is less than that of the largest motor permitted in the installation; or
- When the total locked rotor currents of two or more smaller motors which may be started simultaneously are less than the allowable locked rotor current of the largest motor in said installation.
Table 12.5-5. Allowable Starting Currents For Single Phase
Motors Rated in Horsepower
| Equipment Rated | Locked Rotor Current |
| 115 volts | |
| All Sizes | 50 amps |
| 230 volts | |
| 2 hp. or less | 60 amps |
| 3 hp. | 80 amps |
| 5 hp. | 120 amps |
| 6-1/2 hp. | 150 amps |
| Over 6 1/2 hp. | Consult the Department |
The NEC contains specific information for motor characteristics.
12.5.2.2 Btu/h Rated
Years of development have resulted in single phase, hermetically sealed air conditioning and heat pump units that, from the Customer’s stand point, are as efficient and trouble-free as three phase units up through units sized with a nominal 60,000 Btu/h (5 ton) rating. All hermetically sealed motors in this category will be served single phase provided they do not exceed the locked rotor current values of Table 13.5-6.
Table 12.5-6. Single Phase Air Conditioning and Heat Pump
Equipment Rated In BTU Per Hour
| Equipment Rated | Locked Rotor Current |
| 115 volts | |
| All sizes | 50 amps |
| 230 volts | |
| 20,000 BTU/H or less | 60 amps |
| 20,000 Btu/h to 60,000 Btu/h | 60 amps plus 3 amps per 1,000 Btu/h in excess of 20,000 Btu/h |
| 60,000 BTU/H | 150 amps |
| Over 60,000 Btu/h | Consult the Department |
For larger homes requiring heating and cooling capacity in excess of a nominal 60,000 Btu/h, (5 tons), the Customer should consult the Department to determine the type of service that will be supplied. The Customer should not overlook the possibility of using two or more independent units which can provide better zone control.
12.5.3 Three Phase Motors
12.5.3.1 Horsepower Rated
Because conditions vary widely at different points on the system, no specific rule can be written as to the size of polyphase motors which may be connected, either for ” across-the-line” starting or with starting equipment to limit the starting current. Therefore, it will be necessary to consult the Department for motors of 10 hp size and larger to determine the maximum value of starting current permissible at a given location. Refer to Section 14.9, Converters – Operation of Three Phase Motors from Single Phase Electric Supply, for phase converter operations.
12.5.3.2 Btu/h Rated
Where it has been determined that three-phase service will be rendered, motor starting currents shall not exceed the following values: 159 amps if the service voltage is 208V, 150 amps if the service voltage is 230 V, or 75 amps if the service voltage is 460 V. For motors exceeding these values and for units greater than 120,000 Btu/h, (10 tons), it will be necessary to provide facilities to limit the starting current to values specified by the Department for the location involved.
12.5.4 Motor Starting and Control Equipment
All motors and motor control equipment shall be installed in accordance with the NEC Article 430 and any other referenced code.
Auxiliary starting devices must be used on all motors which cannot be safely subjected to full voltage while starting. They must also be used on all motors which, if started at 100% voltage, would draw currents in excess of those discussed in 13.5.2.1 (Single Phase Motors) Horsepower Rated, 13.5.2.2 (Single Phase Motors) Btu/h Rated, and 13.5.3.2 (Three Phase Motors) Btu/h Rated. The auxiliary starting device must limit the starting current such that the values in the previous sections are not exceeded. The auxiliary starting device should be designed in such a way that the motor can be thrown into the running position before the motor has reached rated running speed in the starting position.
Typically, electric irrigation motors above 60 hp served at three phase, 480 volts will be started with reduced voltage starting equipment. The Department may specify the particular voltage tap setting to be used.
Motor Starters/Controllers of the Silicon Controlled Rectifier (SCR) type as well as other similar devices can create harmonic disturbances that may have detrimental effects on the Department’s electric system and/or service to the Customers. Disturbances of this nature attributable to the use of these type devices must be corrected without undo delay, at the Customer’s expense, to the satisfaction of the Department. Consult the Department for information.
12.6 Critical Service Motor Operation
Where continuous operation of a motor is essential, the no-voltage release should have a time delay relay, which will prevent the opening of the circuit in the event of momentary voltage fluctuation. The Department will assist the Customer in selection of an automatic starting device and any other device to hold motors on line during voltage disturbances.
12.7 Motor Protection
12.7.1 Phase Reversal Protection
Reverse phase relays are required on three phase elevator services (NEC Article 620) and it is strongly recommended that they be installed by the Customer where accidental reversal of motor rotation would cause serious inconvenience, damage, or delay. The Department shall not be responsible for any damages caused by phase reversal.
12.7.2 Over Current Protection
The NEC requires that adequate over current protection be provided in each phase on all motor installations. The Customer must ensure complete protection against “single-phasing” on all three phase motors. Over current protection in two phases is not adequate protection for this condition. Single phasing on the distribution system is necessary at times for fault clearing and switching and occurs occasionally due to unforeseen circumstances. Motor protection is the responsibility of the Customer.
12.7.3 Partial or Complete Loss of One or More Phases
It is recommended that all polyphase motor installations be equipped with an automatic disconnecting device as part of the Customer’s installation, which would disconnect the motor from the supply voltage in the event of partial or complete loss of one or more phases. Partial or complete loss of one or more phases may be caused by failure of the Customer’s conductors, circuit breakers, fuses, connectors, etc., or by partial or complete loss of one or more phases from the Department’s electric distribution facilities. The Department shall not be held responsible or liable for damage to the Customer’s installation due to such causes. Motor protection is the sole responsibility of the Customer.