aluminium cables paper

7/24/2019 Aluminium Cables Paper

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Aluminium conductors and cables are extensively used by utilities throughout the world for both medium

and low voltage applications, whereas building and industrial cabling has been predominantly being

carried out with copper conductors. The recent (5 years) meteoric rises in copper prices have forced

manufacturers and engineers in all sphere of industry and construction work to look at alternative

materials.

This paper investigates the use of aluminium conductor for industrial and building cabling, as on an

average there is a potential of saving of around 50% of power cabling costs in a project.

1.

Aluminium as an electrical conductor

The earliest applications of aluminium as an electrical conductor were:

1895 Stranded aluminium bare conductor for overhead lines in America and France

1908 Stranded steel-reinforced aluminium bare conductor (ACSR) for overhead lines

1910 Underground lead-sheathed cable with paper-insulated aluminium conductor at Boston and

Ealing

1912 Aluminium bus-bars in a ship named AQUITANA

1917 Aluminium transformer coils

1920 Aluminium squirrel-cage rotor for induction motors

2. Properties comparison with copper

The table below shows the comparative physical properties of E-Cu copper, E-Al aluminium, and AlMgSi

aluminium alloy (used in some OH conductors and cables)

Properties UnitE-Cu

Copper

E-Al

Aluminium

AIMgSi Al

Alloy

Density kg/dm3 8.9 2.7 2.7

Tensile strength (hard annealed) N/mm2 450240 18080 310

Elongation at break (hardannealed) % 135 235 3

Modulus of elasticity kN/mm2 120 70 70

Melting point C 1083 658 658

Coef. of thermal expansion 10-6/ C 16.6 23.8 23.0

Temperature coef. of resistance @ +20C 1/ C 0.0039 0.0040 0.0036

Conductivity @ +20C IACS % 97100 6162 53

Resistivity @ +20C mm2/m 0,01786 0,02857 0,03280

Table-1: Physical properties of aluminium & copper

Use of Aluminium Cables

in Buildings & Industries

Naveed Jabbar, AMIEEEP


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With 60% of the conductivity of copper, and 30% of its density, an aluminium conductor would be 60%

larger and 50% lighter than the equivalent copper conductor (which would have the same voltage drop

and I2R losses).

Use of aluminium conductors would require larger raceways (conduits, trunking, ladders), but would be

much lighter to pull and install. The weight advantage is a major reason aluminium conductor is used in

overhead transmission (lighter poles/structures) and underground distributions.

3. Price comparison with copper

-

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

1978

1979

1980

1981

1982

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1984

1985

1986

1987

1988

1989

1990

1991

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1993

1994

1995

1996

1997

1998

1999

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2002

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2004

2005

2006

2007

2008

Ye

ar

UK

pertonne

0

0.5

1

1.5

2

2.5

3

Copper/Aluminium

Pri

ceRatioCu/Al

Cu

Al

Fig 1: Trends in LME prices of copper and aluminium

Electrical metals costs vary over time, and in recent years have shown a marked upwards trend. The graph

above shows the pattern over the past thirty years, based on London Metal Exchange prices.

4. Current-carrying capacity

The table below shows roughly equivalent

sizes of copper and aluminium cable based

on IEE Wiring Regulations current-carrying

capacity tables.

In each case, the aluminium cable size is

about 60% greater than the corresponding

copper cable size.

It will be noticed that the voltage drop / amp

/ m is approximately equal for equivalent

sizes, and, consequently, the I2R losses are

the same.

Table-2: Comparative electrical

characteristics of copper & aluminium

cables

Current

capacity

Copper

conductor

Aluminium

conductor

Amperes Size

(mm2)

Volt drop

(mV/A/m)

Size

(mm2)

Volt drop

(mV/A/m)

64 16 2.4 25 2.5

80 25 1.5 35 1.8

100 35 1.1 50 1.35

120 50 0.81 70 0.92

150 70 0.57 95 0.68

190 95 0.43 150 0.44

220 120 0.35 185 0.37

250 150 0.29 240 0.3

300 185 0.25 300 0.25

350 240 0.21 400 0.24

400 300 0.185 500 0.22


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5. Cost advantageCurrent

capacity

Copper

conductor

Aluminium

conductor

Saving

AmperesSize

(mm2)

Rate

(Rs./m)

Size

(mm2)

Rate

(Rs./m)(Rs./m)

64 16 532 25 160 372

80 25 771 35 189 582

100 35 1056 50 253

Based on Table-2 above, a

comparative is given in the table

below of approximate current prices

of equivalent copper and aluminium

cables.

803

120 50 1427 70 373 1054

150 70 2045 95 472 1573

190 95 2831 150 713 2118

220

Aluminium conductor cable costs60% less; if the cost of the larger

raceway and special terminations is

included, the price saving is still

around 50%.

120 3561 185 884 2677

250 150 4376 240 1145 3231

300 185 5479 300 1485 3994

350 240 7188 400 1810 5378

400 300 9013 500 2220 6793

In a typical office building the cost of

power cabling is around 8% to 10% of

the cost of the electrical works. By

carefully substituting aluminium

conductors in place of copper about

50% of the power cabling costs (4%

to 5% of the total electrical costs) canbe saved. In industrial projects,

depending upon their nature, this

saving can be much higher.

Table-3: Comparative prices of equivalent copper& aluminium cables

6. Additional factors

Changing over from copper to aluminium, despite the price and weight advantages, can only be done

when the following factors have been taken into account:

a)

Connectivity Issues

Three phenomena are encountered: Oxidation in the presence of moistureAll metals when exposed to air (oxygen) in the presence of moisture form metal oxides with varying

degree of severity and characteristics. Aluminium oxide is a bad conductor as compared to copper oxide.

Hence if not correctly made, any electrical connection between aluminium or other metal degrades.

Various sealant formations have been developed to provide improved electrical and mechanical

performance. These when applied immediately after scratch brushing seals the exposed surface to prevent

re-oxidation thus excluding future ingress of air and moisture.

Galvanic corrosion of dissimilar materials

Galvanic action results in corrosion when two dissimilar

materials are in contact with each other. In most situations, it is

necessary to connect aluminium conductors to copper terminalsas the majority of equipment (circuit breakers, fuse holders,

switches) has copper terminals. When using aluminium

conductors with such equipment, special bimetallic accessories

(ferrules and lugs) must be used to avoid the connection

corroding. In a (aluminium/copper) bi-metallic lug, the barrel is

aluminium into which an aluminium conductor is crimped, and

the head (or palm) is of copper. The contact between cable to bi-

metallic terminal lug is aluminium, and the contact between bi-

metallic lug to copper equipment terminal is copper. The bi-metallic lug manufacturers generally supply

these lugs filled with anti-oxidation sealant compounds.

Al

Cu

Fig-2: Bi-metallic lug


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In addition the lug crimping tools (dies) must be compatible with the lug. When crimping aluminium

ferrules or lugs, deep indent crimping is preferable in order to break the aluminium oxide layer which will

have formed on the conductor.

Looseness of contact with thermal cycling

Aluminium has a high coefficient of expansion, and with cyclic loading, a connection between two

terminals can become loose, resulting in a higher resistance connection. This is generally overcome using

appropriate spring cone washers.

Solutions to the above issues have been detailed in Annexure-1. However, point wiring is not done with

aluminium cable because terminals on switches, accessories, luminaries, etc are generally copper.

b)

Brittleness

Aluminium is more susceptible to vibration cracking than copper, especially when solid aluminium

conductors are used. Consequently, aluminium cables should not be used for final connections to motors,

transformer, generators or other equipment subject to movement.

7. Conclusion

Many utilities in world use aluminium conductor cables for MV and LV distribution, and as service drops

from overhead lines 11kV and 400/230V systems, including to meters.

Ex-WAPDA DISCOS and uses aluminium conductor cables for all of their LV cable requirements i.e.

from overhead conductor to meter, from transformer to meter, breaker, etc. The problems reported are all

at overhead joints. No appreciable complaints have been observed at connections to meter or other

locations.

Today, KESC is working on converting copper OH low-voltage distribution lines in Karachi to

aluminium bundled conductors, and expects to finance 50 - 60% of the cost from the sale of the old

copper.

Aluminium, instead of copper is also used in other areas of electrical equipment. Some examples are bus-

bar trunking, dry-type transformers, and squirrel-cage rotors.

References:

4. Electric Power Systems in Commercial Buildings, IEEE, USA.

5. Tyco Connectors & Fittings

6. Connector Theory & Application FCI Brundy Products

(Engr Roland deSouza is Principal Electrical Engineer, and Engr Naveed Jabbar is General Manager

[Electrical] with Fahim, Nanji & deSouza, a multi-disciplinary firm in the field of building services. This

paper was presented at the '23rd Multi-Topic International Symposium 2008'of the IEEEP, Karachi

Centre.)


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Annexure-1

Connectors for Aluminium

Aluminium conductors are different from copper in several ways, and these property differences should be considered in

specifying and using connectors for Aluminium conductors. The normal oxide coating on Aluminium has a relatively high

electrical resistance. Aluminium has a coefficient of thermal expansion that is greater than copper. The ultimate, the yield

strength properties, and the resistance to creep of Aluminium are different from the corresponding properties of copper.

Corrosion is possible under some conditions because Aluminium is anodic to other commonly used metals, including

copper, when electrolytes from even humid air are present.

1) Mechanical Properties and Resistance to Creep Creep has been defined as the continued deformation of material

under stress. The effect of excessive creep resulting from the use of an inadequate connector that applies excessive

stress could be the relaxation of contact pressure within the connector, and a resulting deterioration and failure of the

electrical connection. In mechanical connectors for Aluminium, as for copper, proper design can limit residual unit

bearing loads to reasonable values, with a resulting minimum plastic deformation and creep subsequent to that

initially experienced upon installation. Connectors for Aluminium wire can accommodate a range of conductor sizes,

provided that the design takes into account the residual pressure on both minimum and maximum conductors.

2) Oxide Film The surface oxide film on aluminium, though very thin and quite brittle, has a high electrical resistance

and, therefore, should be removed or penetrated to ensure a satisfactory electric joint. This film can be removed by

abrading with a wire brush, steel wool, emery cloth, or similar abrasive tool or material. A plated surface, whether on

the connector or bus, should never be abraded; it can be cleaned with a solvent or other means that will not remove

the plating. Some aluminium fittings are factory filled with a connection aid compound, usually containing particles

that aid in obtaining low contact resistance. These compounds act to seal connections against oxidation and corrosion

by preventing air and moisture from reaching contact surfaces. Connection to the inner strands of a conductor requires

deformation of these strands in the presence of the sealing compound to prevent the formation of an oxide film.

3) Thermal Expansion The linear coefficient of thermal expansion of aluminium is greater than that of copper and is

important in the design of connectors for aluminium conductors. Unless provided for in the connector, the use of

metals with coefficients of expansion that are less than that of aluminium can result in high stresses in the aluminium

during heat cycles, causing additional plastic deformation and significant creep. Stresses can be significant, not only

because of the differences in coefficients of expansion, but also because the connector may operate at an appreciably

lower temperature than the conductor. The condition will be aggravated by the use of bolts that are of a dissimilar

metal or have different thermal expansion characteristics from those of the terminal.

4) Corrosion Direct corrosion from chemical agents affects aluminium no more severely than it does copper and, in

most cases, less. However, since aluminium is more anodic than other common conductor metals, the opportunity

exists for galvanic corrosion in the presence of moisture and a more cathodic metal. For this to occur, a wetted path

should exist between external surfaces of the two metals in contact to set up an electric cell through the electrolyte

(moisture), resulting in corrosion of the more anodic of the two, which, in this instance, is the aluminium. Galvanic

corrosion can be minimized by the proper use of a joint compound to keep moisture away from the points of contact

between dissimilar metals. The use of relatively large aluminium anodic areas and masses minimizes the effects of

galvanic corrosion. Plated aluminium connectors should be protected by taping or other sealing means.

5) Types of Connectors for Aluminium Conductors UL has listed connectors approved for use on aluminium, which

have successfully withstood UL performance tests that are contained in ANSI/UL 486B-1982, Wire Connectors for

Aluminium Conductors. Both mechanical and compression connectors are available. The most satisfactory connectorsare specifically designed for aluminium conductors to prevent any possible troubles from creep, the presence of oxide

film, and the differences of coefficients of expansion between Aluminium and other metals. These connectors are

usually satisfactory for use on copper conductors in non-corrosive locations. The connection of an aluminium

connector to a copper or aluminium pad is similar to the connection of bus bars. When both the pad and the connector

are plated and the connection is made indoors, few precautions are necessary. The contact surfaces should be clean; if

not, a solvent should be used. Abrasive cleaners are undesirable since the plating may be removed. In normal

application, steel, aluminium, or copper alloy bolts, nuts, and flat washers may be used. A light film of a joint

compound is acceptable, but not mandatory. When either of the contact surfaces is not plated, the bare surface should

be cleaned by wire brushing and then coated with a joint compound. Belleville washers are suggested for heavy-duty

applications where cold flow or creep may occur, or where bare contact surfaces are involved. Flat washers should be

used wherever Belleville washers or other load concentrating elements are employed. The flat washer should be

located between the aluminium lug, pad, or bolt and the outside edge of the Belleville washer with the neck or crown

of the Belleville against the bolting nut to obtain satisfactory operation. In outdoor or corrosive atmospheres, the


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above applies with the additional requirement that the joint be protected. A non-plated aluminium -to- aluminium

connection can be protected by the liberal use of a non-oxide compound. In an aluminium -to-copper connection, a

large aluminium volume compared to the copper is important as is the placement of the aluminium above the copper.

Again, coating with a joint compound is the minimum protection; painting with a zinc chromate primer or thoroughly

sealing with a mastic or tape is even more desirable. Plated aluminium should be completely sealed against the

elements.

6) Welded Aluminium Terminals For Aluminium cables 250 kcmil and larger, which carry large currents, excellent

terminations can be made by welding special terminals to the cable. This is best done by the inert gas shielded metal

arc method. The use of inert gas eliminates the need for any flux to be used in making the weld. The welded terminal

is shorter than a compression terminal because the barrel for holding the cable can be very short. It has the advantage

of requiring less room in junction or equipment terminal boxes. Another advantage is the reduced resistance of the

connection. Each strand of the cable is bonded to the terminal, resulting in a continuous metal path for the current

from every strand of the cable to the terminal. Welding of these terminals to the conductors may also be achieved by

using the tungsten electrode type of ac welding equipment. The tungsten arc method is slower, but, for small work,

gives somewhat better control. The tongues or pads of the welded terminals, such as the large compression

connectors, are available with bolt holes to conform to NEMA Standards for terminals to be used on equipment.

7) Procedure for Connecting Aluminium Conductors.

(i) When cutting cable, avoid nicking the strands. Nicking makes

the cable subject to easy breakage.

(ii)

Contact surfaces should be cleaned. The abrasion of contact

surfaces is helpful even with new surfaces. . Do not abrade

plated surfaces.

(iii) Apply joint compound to the conductor if the connector does

not already have it.

(iv) Only use connectors specifically tested and approved for use

on aluminium conductors.

(v) On mechanical connectors, tighten the connector with a

screwdriver or wrench to the required torque. Remove excess

compound

(vi) On compression connectors, crimp the connector using the

proper tool and die. Remove excess compound.(vii) Always use a joint compound that is compatible with the

insulation and as recommended by the manufacturer. The

oxide films penetrating or removing properties of some

compounds aids in obtaining good initial conductivity. The

corrosion inhibiting and sealing properties of some

compounds help ensure the maintenance of continued good

conductivity and the prevention of corrosion.

(viii) When making an aluminium-to-copper connection that is

exposed to moisture, place the Aluminium conductor above

the copper. This prevents soluble copper salts from reaching

the aluminium conductor, which could result in corrosion. If

there is no exposure to moisture, the relative position of the

two metals is not important.(ix) When using insulated conductors outdoors, extend the

conductor insulation or covering as close to the connector as

possible to minimize weathering of the joint. Outdoors,

whenever possible, joints should be completely protected by

tape or heat-shrink insulation. When outdoor joints are

covered or protected, the protection should completely

exclude moisture, as the retention of moisture could lead tosevere corrosion.

aluminium cables paper

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