Criteria for Good Terminations
Every cable termination should be completed and checked using the following headings.
· Solid Conductors – doubled back where possible.
· Stranded and Flexible Conductors – all strands twisted neatly together in the right direction, and doubled back where possible. – all strands present and clamped.
· No damage to conductor e.g. nicked while stripping insulation.
· No damage to insulation e.g. nicked while stripping sheath or pulling in cables.
· Insulation not clamped.
· Conductor insulated right up to the metal of the terminal ( no bare copper ).
· Sufficient slack available on cable.
· Cable arranged neatly and not fouling moving parts or covers.
· No makeshift terminals used.
· Terminal screw tightened sufficiently.
Wherever possible, conductors should be doubled back in order to fill the terminal and allow two lengths of conductor share the stress imposed by the tightening of the terminal screw. If a single solid conductor is clamped under a terminal screw, the screw tends to create a reasonable indent in the conductor, thereby weakening the conductor at that point. If the terminal is large in relation to the conductor, it is also possible for the conductor to move under the screw, giving rise to a loose termination.
Stranded conductors should be terminated in such a way that all strands are twisted neatly together in the direction of the lay of the cable, and again, neatly doubled back where possible. If this is not done some of the strands will not be clamped under the screw, giving rise to a bad termination.
If a conductor is nicked or a strand is accidentally cut away, the cross sectional area of the cable is thereby reduced at that point. This results in increased resistance and overheating.
The insulation should remain in good condition right up to the metal of the terminal. Most electrical terminals are now shrouded to prevent accidental contact by even a fingertip. If too much insulation is removed when terminating conductors, leaving bare copper exposed to touch, then what is the point in shrouding terminals in the first place.
There should be a sufficient amount of slack available on every conductor and this slack should be arranged neatly and not allowed foul any moving parts or prevent any cover / lid being fitted properly.
Use of makeshift terminals particularly applies to earthing of equipment. It is not unusual to find an earth conductor, terminated under a woodscrew used to fix a metallic enclosure in position. This is entirely wrong and should NEVER be done.
Terminal screws should be tightened sufficiently. This means that they should not be too loose or too tight. The best way to ensure this is to use the correct size screwdriver. As the tip of a screwdriver changes in size, so also does the handle.
A small handle allows a low torque to be applied to a screw and a large handle allows a high torque to be applied to a screw.
It is only through practice and repeated checking of one’s own work that one can become competent in making good terminations.
Dangers of Loose Connections
( Poor electrical terminations )
· Loose connections give rise to heat.
· This heat travels from its point of origin, along the conductor in both directions.
· The insulation becomes brittle, delicate and disintegrates.
· The result is a high resistance joint.
· Possible damage to equipment.
· Possible electric shock.
· Possible fire hazard.