The various types of conductor clamping designs are as below :
1. Screw Clamps - Steel
2. Screw Clamps - Spring Loaded
3. Screw Clamps - Copper Alloy
4. Spring Clamps
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 atmospheric corrosion.
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.
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 clamping.
2. Screw Clamp (Spring Loaded)
For high-vibration 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 Clamp-design.
3. 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.
4. Spring Clamps
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 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.
5. Stud-and-Nut Clamping for Cable-Lugs
This conductor-clamping 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.