MIL-STD-1399-3008
5.1.6.3 System power factor (pf). Shipboard electric power systems are designed to operate with a pf of 0.8 lagging to 0.95 leading for 60 Hz power systems and 0.8 lagging to 0.9 leading for 400 Hz power systems.
5.2 User equipment interface requirements. User equipment shall meet the requirements specified in 5.2.1 through 5.2.13 to ensure compatibility with the electrical power system characteristics specified in Table II.
5.2.1 Compatibility. The construction of user equipment utilizing electric power shall be compatible with the electric power system characteristics as specified in 5.1.
5.2.2 User equipment voltage. Voltage preference shall be as follows (see 5.1.6.2):
a. User equipment rated above 5 kilovolt amperes (kVA) shall operate from 440 Vrms, 3-phase input power. b. User equipment rated 5 kVA or less shall operate from 440 Vrms, 3-phase input power. Where such an
input is not practical, the following shall be the order of preference: (1) 115 Vrms, 3-phase
(2) 115 Vrms, single-phase
(3) 440 Vrms, single-phase
c. Special equipment, 115/200 Vrms, 3-phase, 4-wire, grounded neutral, 400 Hz power shall be provided for servicing aircraft in hangars and on flight decks, and to avionic shops.
d. Special equipment, 230 Vrms, 60 Hz, 3-phase, ungrounded or 230 Vrms, 60 Hz, single-phase, grounded or ungrounded. This power is provided upon request only for NATO load equipment.
e. Special equipment, 120/208 Vrms, 60 Hz, single-phase, grounded neutral or 240/120 Vrms, 60 Hz, single- phase, grounded neutral. 120 Vrms, single-phase grounded neutral loads shall be limited to 5 kVA. Equipment utilizing these special distribution system voltages shall be in accordance with NAVSEA Standard Drawing
7512881 and NAVSEA Standard Drawing 7598285, respectively.
5.2.3 Emergency conditions. User equipment shall withstand without damage electric power interruptions, rapid reapplications of power (see 5.1.3) and the emergency conditions specified in Table I and testing described in
5.3.4. The PDA shall make the determination as to whether the equipment is identified as Mission Critical
Equipment (MCE) and must operate through the emergency conditions.
5.2.4 Grounding. User equipment, except for equipment on special voltage (grounded system (see 5.2.2 (c) and (d)), shall be ungrounded as related to the electric power system ground. Where power line filters are required in the user equipment, a line-to-line configuration is preferred. If a line-to-ground configuration is used for filtering, then the value of the filter capacitance shall not exceed 0.1 microfarad per line-to-ground for 60 Hz equipment and 0.02 microfarad per line-to-ground for 400 Hz equipment for all nominal user voltages. Filters shall use balanced capacitance per line-to-ground with a tolerance value not exceeding 10 percent. Line-to-ground current due to
filters, etc., shall not exceed 30 milliamperes per line-to-ground. If performance or operational needs of user equipment require an electrical ground either solidly or by means of capacitors which exceed the values stated above
or if the line-to-ground current exceeds 30 milliamperes per line-to-ground, then that equipment shall be electrically
isolated from the power system. The neutral connection to user equipment on special voltage systems shall not be grounded at the user equipment.
5.2.4.1 Human body leakage current limits for personnel safety. In order to evaluate user equipment for potential shock hazards, a test using an impedance network simulating human body impedance shall be conducted
on all equipment that requires a dedicated ground conductor or connection path to the ship's hull. The test simulates the worst case current path through the human body to a neutral point ground if the equipment ground connection is
opened. The neutral point ground can be formed aboard ship by other equipment's line-to-ground filters. Simulated
human body leakage current shall be measured from single-phase user equipment connected across one single-phase (line-to-line of a delta source or line-to-neutral of a wye source) of a three-phase transformer aboard ship, from single-phase equipment connected across two phases (line-to-line of a wye source) of a three-phase transformer aboard ship and from three-phase user equipment, using the tests in 5.3.9. Human body leakage current test limits are defined for two frequency ranges.
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