The various types of
conductor clamping designs are as below :
Clamps - Steel
Clamps - Spring Loaded
Clamps - Copper Alloy
5. Stud and
Nut Clamping for cable lugs
1 Screw Clamps (Steel)
1.1 Contact Clamp :
elmex Screw Clamp consists of a U-shaped steel part
called Contact Clamp and a washer base or cheese head screw.
The vertical arms of the
Contact Clamp are folded at the top end into lips, overlapping each other. The
lip from each arm locks into recess provided on the other arm. This double
locking is an outstanding feature of elmex screw clamp design which
allows tightening torques in excess of the values specified by the Standards.
In addition, in the event of inadvertent over-tightening, this design prevents
damage to the threads and deformation of Contact Clamp.
The bottom face of the
'U' has serrations, which grips the conductor firmly during
the tightening. The lips are drilled and threaded co-axially in a special
machine to produce rolled threads for higher mechanical strengths of threads
which can take higher tightening torque.
The Contact Clamp
undergoes Heat Treatment for increased hardness and strength. It is zinc plated
and passivated to a higher degree of plating thickness than usually adopted. elmex Screw Clamps therefore have a very good resistance to normal
Heat Treatment : elmex contact clamps are subjected to a special heat treatment process
ensuring uniformity of temperature over the entire clamp surface and consistent
results of heat treatment so that the inner threads of the clamp achieve a
uniform and strong wear resistance.
1.2 Clamping Screws :
elmex Screw Clamp uses cold-forged rolled-threaded
washer-base cheese-head screws (or Philips-head screws in specific cases). The
screws are hardened and tempered for increased strength and wear-resistance.
After first assembly they become captive in the housing due to washer base
feature (for melamine housing) and a circular ring provided in the housing for
cheese head screws. These screws are corrosion-protected by zinc plating and
passivated under controlled plating process.
The screws have a flat
bottom which creates a balanced pressure on current bar for conductor
Screw Clamp - Spring Loaded
applications elmex offers spring loaded screw clamp terminal
blocks. Although elmex standard screw clamp design is already resistant to
vibrations, it is further strengthened against vibrations by provision of
compression springs in the Terminal Block.
The springs are assembled
under the contact clamp in pre-stressed condition. When the screws are fully
tightened upto specified torque, the spring under the contact clamps provide
additional pressure between current bar and conductor, which makes the spring
loaded terminals especially suitable for high-vibration applications.
The compression springs
are made of standard spring steel. All other parts are same as for the Screw
Screw Clamp (Copper Alloy)
In the elmex design of Copper Alloy Terminal Blocks, the Steel Screw Clamp is
replaced by Copper Alloy Screw Clamp. Protection against atmospheric corrosion
of Copper Alloy is achieved by tin plating in a controlled plating process. The
tin plating has undercoat of nickel plating to prevent Zinc migration. By appropriate
selection of materials and processes, the phenomenon of stress-corrosion
cracking is taken care elmex Copper Alloy Screw Clamp.
The clamping part in elmex Screw Clamp is of special design, such that the conductor clamping
is achieved by tightening of screw, the top portion bends elastically, so that
the screw threads are gripped to prevent loosening.
elmex spring clamp consists of specially shaped
stainless steel clamp, which functions as a spring for developing necessary contact
pressure between current bar and conductor current bar is the current bar is
the current carrying part in the terminal block, and it is provided with
serrations to grip the conductor.
The spring clamp is
brought under tension by inserting a screwdriver. This creates necessary
opening in the clamp for inserting conductor after the conductor is fully
inserted the screwdriver is withdrawn. The clamp are thereby presses the
conductor firmly against current bar, by spring action of the clamp.
Stud-and-Nut Clamping for Cable-Lugs
design is especially developed for receiving Ring-type or Fork-type cable lug.
The terminal block consists of housing, Studs and nuts and the current bar. The
ring type lugs can be inserted under Nuts.
The lugged cables are
clamped to the current bar by tightening the nuts standard spanner can be sued
case of “Nut-Driver” type of stud terminals for screwdriver operated stud
terminals. For screwdriver operated stud terminals, the stud is provided with a
special long nut with a slat at the top for screwdriver. This type is
especially developed where space-limitations may not allow the use of spanner
for clamping cable-lugs.
All the metal parts in
these types of terminals are made of copper alloy and fun plated with nickel
under coat for protection against atmospheric corrosion.