UFC 3-535-01
17 November 2005
back wall to regulator and between regulators; 1.2 meters (4 feet) in front of regulator
for access.
12-1.8.7
Vault Wiring Safety
S-1 cutouts provide safety by preventing inadvertent live wires during maintenance on
field circuits. These are recommended at the output to field circuits for constant current
regulators. Install S-1 cutout in NEMA 1 enclosures. A circuit diagram for an S-1 cutout
is shown in Figure 12-1.
Figure 12-1. S-1 Cutout Circuit Diagram
CUTOUT PLUG
INSERTED
SERIES LOOP
REGULATOR
PRIMARY
SECONDARY
CUTOUT PLUG
REMOVED
REGULATOR
SERIES LOOP
PRIMARY
SECONDARY
12-1.8.8
New Installations
For new installations, install cables in conduit or enclosed wireways. The standard L-
824 airfield lighting primary series circuit cable does not comply with NEC for installation
in open trays. High voltage conductors (exceeding 600V) should be run in rigid steel
galvanized conduit or intermediate metal conduit. Low voltage feeders and control wires
may be run in rigid steel galvanized conduit or intermediate metal conduit when run
under the floor slab; in rigid steel galvanized conduit, intermediate metal conduit, or
electrical metal tubing (EMT) when run on the walls or ceiling; and in cable trays
supported from the ceiling or walls when there are many cables and the possibility of
future expansion. Do not install conduit in concrete slabs on grade. Bring primary series
cable from regulators and various other feeders out of the vault in coated rigid steel
galvanized conduit minimum 0.6 meters (2 feet) below grade.
12-1.8.9
Installation Compliance
Comply with the requirements of the NEC (NFPA 70) for the installation of power
distribution equipment and control equipment in lighting vaults. See UFC 3-520-01,
161
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