MIL-DTL-29183C
3.8.8.1 Grounding connector. A solderless pressure type ground connector shall be
provided on all distribution panels. This ground connector shall be conveniently located and of
such size for connecting a ground conductor conforming to NFPA 70 and UL 67. The ground
connector shall extend through the frame of the distribution panel enclosure to the exterior of the
enclosure.
3.8.9 Transformer. Dry type, totally enclosed, two winding (high and low voltage)
transformers with four 2-1/2 percent full capacity taps (two above and two below the nominal
input voltage) shall be furnished and installed in the type II distribution panels. The transformers
shall be furnished with suitable tap changing provisions. The dry type transformers shall have an
encapsulated 365 °F (185 °C) insulation system rated for 239 °F (115 °C) rise. The transformers
shall be in accordance with NEMA ST 20 and UL 506.
3.8.9.1 Transformer cooling. Ventilation and heat dissipation means shall be provided for
removing the heat generated by the transformer at rated load from the interior of the distribution
panel to meet the requirements of NEMA ST 20 and UL 506.
3.8.9.2 Transformer noise. For type II distribution panels containing a single transformer,
the average sound level generated by the transformer shall not exceed 34 decibels (dB) for a
transformer rated 0-9 kilovolt-amperes (kVA) and shall not exceed 42 dB for a transformer rated
10-50 kVA when measured in accordance with NEMA ST 20. For distribution panels containing
three identically rated transformers, the average combined sound level of all three transformers
shall not exceed 40 dB for the three transformers having a combined rating of 0-9 kVA, and shall
not exceed 48 dB for the three transformers with a combined rating of 10-50 kVA when measured
in accordance with NEMA ST 20.
3.8.9.3 Transformer installation. Each transformer shall be installed in such a manner
that it is rigidly fastened to, and its weight supported by, the frame. The sheet metal bottom or
sides of the distribution panel enclosure shall not be used to provide transformer support.
3.8.10 Panelboards. Panelboards shall conform to UL 67.
3.8.10.1 Ventilation. The design of the distribution panel shall provide for air circulation
through the interior of the distribution panel.
3.8.10.2 Sound level. The sound level of type II distribution panels shall not exceed the
limits specified in 3.8.9.2 for transformer generated noise. Sound limits are only imposed on
type II panels.
3.8.10.3 Power-on indicator. Power-on indicators shall be provided on the circuit breaker
panel to indicate when the main buses are energized. The indicator shall illuminate red light
when the bus is energized. For 3-phase power, an indicator shall be provided for each phase.
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