Joints and terminations

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1 CABLES AND CONDUCTORS joints and terminations

Transcript of Joints and terminations

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CABLES AND CONDUCTORS joints and terminations

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joints and accessories IEE regulations on joints and terminations Types of terminals Types of joints Cable soldering methods

CONTENT

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Joint The connection of two lengths of conductors by a method which ensures a

continuous path for the unimpeded flow of an electrical current Termination Applied t o the end of a conductor prepared in such a way that it is suitable for

connection to the terminal to which it is to be connected by mechanical means Basic electrical and mechanical requirements for joints and terminations I. There must be sufficient contact area between the two current carrying

surfaces (e.g. between wire and terminal) this is ensures that heat is not generated on such surfaces on account of increased resistance

II. There must be adequate mechanical strength this will avoid cables form being pulled apart

III. Should be easy to connect and disconnect electrical joints are made permanent by crimping or soldering

JOINTS AND TERMINATION

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IEE REGULATIONS ON JOINTS &TERMINATIONS

1. - All joints must be durable, adequate for their purpose, and mechanically strong.

2. - They must be constructed to take account of the conductor material and insulation, as well as temperature: e.g., a soldered joint must not be used where the temperature may cause the solder to melt or to weaken. Very large expansion forces are not uncommon in terminal boxes situated at the end of straight runs of large cables when subjected to overload or to fault currents.

3. - All joints and connections must be made in an enclosure complying with the appropriate British Standard.

4. - Where sheathed cables are used, the sheath must be continuous into the joint enclosure

5. - All joints must be accessible for inspection and testing unless they are buried in compound or encapsulated, are between the cold tail and element of a heater such as a pipe tracer or under floor heating system, or are made by soldering, welding, brazing or compression.

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JOINTS AND TERMINATION Joint Making Methods The many methods use to join conductors may be reduced to two

definite groups The first group involves the use of heat to fuse together the

surfaces o the joints (e.g. soldering and welding) The second group uses pressure and mechanical means to hold the

surfaces together (e.g. soldering and welding ) Soldering soldering is defined as "the joining of metals by a fusion of alloys

which have relatively low melting points. Consider that soldering is more like gluing with molten metal

The metal used for joining copper surfaces is Solder, which is an alloy of tin and lead. It melts at comparatively low temperatures.

The disadvantage of soldering joints it makes them non separable Soldered joints in bus bars must be reinforced by bolts and clamps

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JOINTS AND TERMINATION WELDING Welding is the joining of two metal surfaces by melting adjacent

portions so that their is definite fusion between them to an appropriate depth. The heat supplied is from an electric arc or a gas torch

The welded joint is a non separable contact This process is sometimes used for large sections conductors

such as busbars . CLAMPING A clamped joint is easy to make no particular preparation being

required. The effective cross-sectional area of the conductor is not affected though the extra mass of metal round the joint of termination makes a larger bulk. However the joint or termination is cooler in operation. This method provides a separable contact. Surfaces must be clean and in definite mechanical contact. Precautions must be taken to make sure that the bolts and nuts are locked tight.

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JOINTS AND TERMINATION BOLTING This method involves drilling or punching holes in materials

and more suitable for busbars. The holes tend to reduce the effective area of the material. Contact pressure also tends be less uniformly distributed in a bolted joint than in one held together by clamps. Bolted joints can be dismantled easily.

RIVETING If well-made riveted joints make good connection. There is the

disadvantage that they cannot be easily be undone or tightened in service

CRIMPING Joints his is a mechanical method for conductor joints, a closely

fitting sleeve is placed over the conductors to be joined together and crimped together or squeezed together by a hydraulic or pneumatically – operated crimping tool. Crimped lugs are also available for conductor terminations

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TYPES OF TERMINALS There is a wide variety of conductor terminals typical methods include

1. Pillar terminal a pillar terminal is a brass

pillar with a hole through its side which the conductor is inserted and secured with a screw

If the conductor is small in relation to the hole it should be doubled back

When two or more conductors are to to go through the same hole they should be twisted together

Care should be taken not to damage the conductor by excessive tightening

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TYPES OF TERMINALS 2. Eyelet terminal Using round nosed pliers

form conductors end into an eye slightly larger than the screw shank but smaller than the outer diameter of the screw head nut or washer.

The eye should be placed in such a way that rotation of the screw head or nut tends to close the joint in the eye

Claw washers Claw washers are used to

get a better connection. Lay the looped conductor in the

pressing Place a plain washer on top

of the loop and squeeze the metal flat using the right tool

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TYPES OF TERMINALS 3. Strip Connectors Conductors are clamped by

brass grab screws in the connectors mounted in a molded insulated block.

The conductors should be inserted as far as possible into connector so that pinch screw clamps the conductor.

A good clean, tight termination is essential in order to avoid high resistance contacts resulting in overheating of the joint.

4. Lugs Lugs are made from tinned

solid copper or aluminum.

Used extensively in electrical contracting industry for terminating cables

They are fastened to cable ends by crimping

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TYPES OF JOINTS Scarf joint This is one of the simplest joints to make and is used where

the wires are not under any tensile stress and also where the joint is to be small as possible. Though generally used with solid conductors, it can be used on stranded conductors provided they are soldered solid before hand

MethodI. The end of each conductor is chamfered by carefully filling

for 40mmII. Clean the ends tin them and fit them together so that the

joint length diameter is the same as the un cut conductor III. Hold the conductors together and bind the joint with tinned

binding wire over a distance of 65mmIV. Solder the joint. Wipe off any excess solder with a fluxed

cloth pad

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DIAGRAM OF SCARF JOINT

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TYPES OF JOINTS Britannia joint This joint is used for single overhead copper conductors which

are not under tension Method I. Thoroughly clean the ends of the conductors II. Tin the ends for a distance of about 75mmIII. Bend 6mm of each end over at right angles. This prevents the

joint from pulling out when in useIV. Bring the two wires together side by side over a distance of

about 50mm. the ends should face opposite directions V. Hold the joints in a small vice or with pliers VI.Bind both conductors together 1.00mm2 tinned copper binding

wire the binding should be carried about 6mm (about five turns past each conductor end)

VII.Solder the joint (the whole length of the binding) Wipe off any excess solder with a fluxed cloth pad

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BRITANNIA JOINT

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TYPES OF JOINTS Bell hangers joint / western union This joint at times is also called straight twist joint it is not a strong

type and so it is used where more tensile stress is placed on the conductors which are usually solid core and insulated

Method I. Remove the insulation from each conductor and for a distance of

about 75mmII. Clean the ends III. If VRI cable strip off the braiding and tape for a further 12mm on each

conductor IV. Lay the conductors together about 50mm from the ends. Twist them

tightly round each other in opposite directions. Each turn of a conductor should fit closely to the next turn. Pliers can be used to grip the crossed the conductors. Each twist should contain about six turns

V. Cut off surplus conductor ends on the bevel with side cutters smooth over with pliers

VI. Wipe off any excess solder with a fluxed cloth pad make good the removed insulation

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TYPES OF JOINTS Bell hangers/ straight twist joint

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TELEGRAPH JOINT

Telegraph joint This joint is not strong and is generally used for single core insulated

conductors MethodI. Remove the insulation from each end for a distance of about 100mmII. Clean and tin the ends III. If VRI cable, strip off the braiding and a tape for a further 12mm on each

conductor IV. Cross the conductors about 30mm from the insulation keeping the left-

hand conductor in frontV. Using pliers grip the crossed conductors together VI. Twist the left hand end and the right hand main portion together. This

turns need not to be sharp VII.Twist the right-hand end and the left hand main portion together VIII.Cut off surplus conductor ends on the bevel with side cutter smooth over

with pliers IX. Solder the joint. Wipe off any excess solder with a fluxed cloth padX. Make good the insulation removed

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TYPES OF JOINTS Telegraph / American twist joint

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TEE TWIST JOINT Tee Twist Joint This is a branch or TEE joint made with single core conductors Method I. Remove insulation from through piece a distance of 50mm in the center.

This wire must not be cut II. If VRI cable, strip off the braiding and tape for a further 12mm at each sideIII. Remove the insulation from the tee piece for a distance of about 75mm

from the end IV. If VRI cable strip off the braiding and tape for a further 12mmV. Clean the bare conductors if necessaryVI. Place the tee piece at right angles to the left hand side of the bared

through piece and tightly bind round the through conductor from left to right

VII.Cut off surplus conductor end on the bevel with side cutters and smooth over with pliers

VIII.Solder the joint leaving two or three turns free for flexibility IX. Wipe off any excess solder with a fluxed cloth padX. Make good the insulation removed

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TEE TWIST JOINTTee Twist Joint / Aerial Tap

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TYPES OF JOINTS Straight Married joint The married joint is made with stranded conductors When made correctly it forms a very strong and satisfactory joint Method (three stranded conductors )I. Remove insulation for about 75mm from each conductor II. If VRI strip of and tape a further 12mm on each conductor III. Twist the strands of each conductor firmly in the direction of lay for 25mm

leaving 50mm splayed out IV. Untwist the splayed strands and straighten them V. Interleave the strands and butt the twisted portions together. Each strand of the

conductor should lie should lie between two conductors of the other conductor VI. Hold down the strands of the right hand conductor over the left hand conductor

neatly around the right hand conductor half a turn at a time keep the strands tight and close together

VII. Wrap the strands of the right hand conductor round the left hand conductor as in step VI

VIII. Cut off surplus strands on the bevel with side cutters smooth over with pliersIX. Solder the joint. Wipe off any excess solder with a fluxed cloth padX. Make good the insulation removed

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STRAIGHT MARRIED JOINT Method seven stranded conductors

I. Remove insulation for about 75mm from each conductor II. If VRI strip of and tape a further 12mm on each conductor III. Twist the strands of each conductor firmly in the direction of lay for 25mm

leaving 50mm splayed out IV. Untwist the splayed strands and straighten them V. Cut off the center strand from each conductor VI. Inter leave the strands and butt the twisted portions together. Each strand of

one conductor should lie between two strands of the other conductor VII. Lightly bind the strands on the right hand side round the twisted strands VIII. Tightly bind the strands on the left hand side round twisted strands against

the lay of the conductorIX. Untwist and straighten the strands on the right-hand side. Bind tightly

round the twisted strands X. Cut off surplus strands on the bevel with side cutters smooth over with pliersXI. Solder the joint. Wipe off any excess solder with a fluxed cloth padXII. Make good the insulation removed

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STRAIGHT MARRIED JOINT

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TYPES OF JOINTS Tee married joint Method (three stranded conductor) I. Remove the insulation from the through piece for a distance of about

50mm in the center this wire must first be cut II. If VRI cable strip off the braiding 12mm at each sideIII. Remove the insulation of the tee piece a distance of about 75mm from

the endIV. If VRI strip off the braiding and tape a further 12mm V. Twist the strands of the through piece VI. Twist the tee piece in the direction of lay for about 25mm from the

insulation VII.Untwist the remainder of the length of the piece and straighten

strands VIII.Offer the tee piece to the through conductor so that so the strands are

made to go round the left hand side of the through piece and the strand round the right hand side of through piece

IX. Tighten the stands in their respective direction X. Cut off surplus strands on the bevel with side cutters smooth over

with pliersXI. Solder the joint. Wipe off any excess solder with a fluxed cloth padXII. Make good the insulation removed

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TYPES OF JOINTS Method (seven stranded conductor) I. Remove the insulation from the through piece for a distance of about

50mm in the center this wire must first be cut II. If VRI cable strip off the braiding 12mm at each sideIII. Remove the insulation of the tee piece a distance of about 75mm from

the endIV. If VRI strip off the braiding and tape a further 12mm V. Twist the strands of the through piece VI. Twist the tee piece in the direction of lay for about 25mm from the

insulation VII.Untwist the remainder of the length of the piece and straighten strands

divide into 4 & 3 VIII.Offer tee piece to through conductor so that four strands are on one

side and three on the other side of the through conductor IX. Tighten the stands in their respective direction X. Cut off surplus strands on the bevel with side cutters smooth over with

pliersXI. Solder the joint. Wipe off any excess solder with a fluxed cloth padXII. Make good the insulation removed

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TYPES OF JOINTS

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TYPES OF JOINTS Rat tail joint / Pig Tail. This kind of joint is commonly used to join two or more

conductors inside the junction box. It is suitable for service where there is no mechanical stress when wires are to be connected in an outlet box, switch, or conduit fitting

MethodI. Strip the wire insulator at the ends of the conductor to be

joined at about 50 mm.II. Clean both wires to be joined place the two ends of bare

wire in crossed positionIII. Then, twist the bare conductors about five to seven

times.

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CABLE SOLDERING METHODS solder

There are two types of solder used in electrical workFine solder(tin mans solder) Plumbers metal I. Tin mans solder It has 60% tin and 40% lead Has a low melting point due to high amount of tin Commonly used in electrical joints I. Plumbers metal It has 30% tin and 70% lead Is used for plumbing joints in armored cables as it

remains in a plastic shape allowing it to be shaped longer than fine solder

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SOLDERING BIT Soldering Bit In this method the

conductors to be joined are first smeared with resinous flux. The tinned bit is then applied under the joint until the heat penetrates it The stick of solder is then applied to the joint until solder flows through it freely

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BLOW LAMP Stick Method(blow

Lamp) In this method the joint

is first heated with a blow lamp, flux being applied. The solder is then applied by pressing the stick of solder against the heated joint until it penetrates the joint . Care should be taken to protect insulation

against blow lamp flame

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POT AND LADLE Pot And Ladle This method is commonly

used by jointers when jointing heavy conductors. A solder pot is heated until the solder is running freely. The solder should not be overheated as this will burn the tin and form a dross on the surface of the solder. When the solder has reached working temperature it is taken from the pot with a ladle. The solder is then poured over the prepared joint and is

caught with another ladle placed under the joint. This action is repeated until the solder penetrates the joint

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