188.8.131.52 Working Space. The NEC defines working space as sufficient access provided
and maintained about all electric equipment to permit ready and safe operation and maintenance
of such equipment.
a. Working space in vaults has been provided in accordance with the NEC requirements
applying at the time the vault was built.
b. As with all safety aspects affecting both the public and workers, safety requirements
have, over the years, become more rigorous.
c. Although NEC current requirements do not apply to vaults built to previous NEC
editions, in line with Naval safety requirements, the NEC current requirements should be
compared by each activity with actual working space provisions.
d. Each activity should evaluate the comparisons as to their effect on workers safety and
provide SOP's as necessary to assure safe working conditions.
Ship's Electrical Power Input Safety
Ship's electrical input cables will provide an ungrounded correctly-
phased, correctly-cable-oriented system providing an adequate number of
power cables to serve the ship's load.
a. The ship's hull serves as the ground for the ship's electrical service. A ground
connection between the shore ground and the ship's ground can result in damaging circulating
b. Improper matching of phase rotation will result in the ship's motors operating in the
wrong direction. Connecting two or more power cables to a ship requires that all the same phase
cables be connected together.
c. The number of power cables should meet the ship's electrical officer's request that is
based upon the ship's activity in port. When more than one feeder cable is required, all cables will
be of the same length and size (within plus or minus 10 percent) to minimize unequal load
distribution. Low-voltage receptacles have a power supply capability of 386 kVA. (Per NEC
Table 310-17, 75 degree C for 500 kcm at 450-volts for continuous service or 620 amperes x 450
volts x 1.732 x 0.80 1,000 = 386 kVA). Medium-voltage outlets have a power supply
capability of 2075 kVA. (Minimum cable rating is 360 amperes or 360 amperes x 4,160 volts x
1.732 x 0.80 1,000 = 2,075 kVA).