MIL-STD-1399-300 Electric Power, Alternating CurrentThis military standard section establishes electrical interface characteristics for shipboard equipment utilizing AC electric power to ensure compatibility between user equipment and the electric power system. Characteristics of the electric power system are defined and tolerances are established, as well as requirements and test methods for ensuring compatibility of shipboard user equipment with the power system. The policies and procedures established by MIL-STD-1399 are mandatory. This section and the basic standard are to be viewed as an integral single document for use in the design and testing of electric power systems and user equipment.

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MIL-STD-1399-3008

FIGURE 31. Metering circuits for high and low frequency simulated human body leakage current tests.

5.3.10 Equipment insulation resistance test. User equipment to be installed on ships shall be subjected to an insulation resistance test. User equipment to be installed on ships with an active ground detector shall also be subjected to an active ground detector test.

5.3.10.1 Insulation resistance test. With the power disconnected, use a megohmmeter insulation tester (megger) to conduct an insulation resistance test at a 500 VDC level. The test shall be conducted between each power conductor and ground for a minimum period of 60 seconds for each conductor. Ensure sensitive electronic components are disconnected from line-to-ground during this test. The user equipment shall tolerate the 500 VDC level without equipment damage, arc-over or degradation. The resistance to ground level as measured with the megohmmeter shall be equal to or greater than 10 Mohms (see 5.2.11).

5.3.10.2 Active ground detector (AGD) test. This test is conducted to determine the equipment tolerance to

150 VDC superimposed from line to ground on the 440 Vrms system or 50 VDC superimposed from line to ground on systems less than 440 Vrms. For three-phase user equipment, the UUT shall be connected to an isolated,

ungrounded, three-phase transformer secondary source. For single-phase user equipment, the UUT shall be

connected to an isolated, ungrounded, single phase transformer secondary source. With the UUT energized, the active ground detector test DC voltage shall be applied from one input line to ground for a minimum period of 3 minutes. Including worst case and added tolerance, for 150 VDC on 440 Vrms AGD systems, the test voltage shall be 440 Vrms x 1.414 x 1.200 + 155 VDC = 902 V; for 50 VDC on 115 Vrms AGD systems, the test voltage shall be

115 Vrms x 1.414 x 1.200 + 55 VDC = 250 V. The user equipment shall tolerate the combined AC and DC voltage stress without equipment damage, arc-over or degradation during this period. No abnormal operation of the user equipment during or after the test shall be permitted (see 5.2.12). For legacy AGDs, refer to 6.7.