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Short Circuiting Straps
Short Circuiting Straps are used to short the positive
and negative circuits of a d.c. feeder section. In the event of an emergency
or inadvertent re-energisation of the supply, the devices cause the supply
protection to operate.
Design
Each Short Circuiting Strap consists of three J117-NSE
rail clamps fitted with suitably rated interconnecting flexible copper
leads. The clamps are ruggedly constructed from a steel fabrication which
is zinc galvanised to provide protection from site atmospheres. All other
components are suitably finished to inhibit corrosion. The body has an
insulating shield fitted to prevent welding to the rail should the clamp
be subjected to fault current.
Application
Sure location upon the foot of both 'Flat-Bottomed'
and 'Bull-Head' rail types is provided by a pointed tip above the rail
and a grooved block beneath the rail. The pointed tip fits into the operating
screw with an insulating bush to ensure the preferred contact path is
not through the screw thread. The grooved block fits directly on top of
the copper busbar ensuring low contact resistances. The busbar sits upon
a stack of disc spring washers, which should be fully compressed when
applying the clamp. These washers apply a pre-loaded pressure upon the
rail in order to maintain firm contact through atmospheric changes.
Transportation
A fluorescent orange, re-inforced pvc carrying bag
can be supplied to provide protection and ease transportation of the equipment
on site. The complete kit weighs 5.5kg (12lb. 2oz).
Standards
Short Circuiting Straps are to be used in accordance
with the requirements of Railway Group Standard GO/RT3091 and Railtrack
Working Instructions for the Drayton Park - Morgate (BR29987/9) and Working
Instructions for d.c. Electrified Lines in the Liverpool Area (BR29740).
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