MIL-HDBK-1038
For underrunning cranes with trolleys that transfer to another bridge or
spur track, interlocking conductors are required.
4.5.20.2 Festooned Conductor Systems. The festooned conductor type of
electrification system consists, for a runway system, of a track supported from
the building structure. Carriers ride along this track and the conductors, in
flat cables, are supported from the carriers; for conductors larger than #2 AWG,
round cable is used. The lead carrier is connected to the crane bridge and moves
with it. The other carriers are pulled by the lead carrier. When the carriers
are brought together, the cables hang down to form loops. As the carriers
separate, the cables straighten out. One end of each conductor is terminated in a
junction box mounted on the building structure; the other end of each conductor is
terminated in a junction box mounted on the crane bridge.
A bridge-to-trolley system consists of a track supported from the crane
bridge with the lead carrier being connected to the trolley and the conductors
being terminated in junction boxes mounted on the crane bridge and on the trolley.
Use of an I-beam as the track provides for a substantially constructed
system with rugged carriers which protect the cables from abrasion, kinking, or
excessive twisting. Conductors should be extra-flexible type with ethylene
propylene rubber insulation in a neoprene jacketed flat cable; type G or type W
portable power cables are used for round cable applications. It is important that
the cable loops do not extend low enough to come into contact with any
obstructions. For outdoor applications most hardware is available in stainless
steel or bronze.
4.5.20.3 Cable Reel Systems. The cable reel type of electrification system
consists, for a runway system, of a cable reel supported from the crane bridge.
As the crane moves, cable is either payed out or retracted, depending on direction
of motion. A trough is used to support the cable. The use of this type of
electrification system for bridge-to-trolley applications is infrequent.
4.5.20.4 Collector Ring Assemblies. Portal and floating cranes require collector
ring assemblies to carry power between the rotating upperworks and the portal base
of the crane or the tub on the barge. The assembly consists of a series of copper
alloy rings, stacked vertically around the crane's center of rotation, with
brushes riding on each ring. Normally, the assembly is supported from the
rotating portion of the crane and turns with it, and the brushes are fixed on the
portal base or tub. NCC policy is to require that spare rings, three of the
largest size and two of each other size and construction used, be provided on new
cranes.
Silver plated rings are utilized in communications circuits.
A thermostatically controlled anti-condensation heater is installed in
the collector ring assembly enclosure.
4.5.21
Control Panel Enclosures. NEMA Standards Publication No. 250 defines and
describes various types of enclosures. The most commonly used are Types 1, 4X,
and 12.
A Type 1 enclosure is for indoor applications; it protects against
contact with the enclosed equipment. Type 1 enclosures are available either
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