INSTALLATIONS & CONTRACTING

The object of this report is to highlight both the positive and negative factors involved in selecting aluminium cables for use in a project. Ever since the introduction of aluminium- cored electrical cable, cost savings have been the sought-after “pot of gold”. The price of copper on the LSE skyrocketed, adding fuel to the fire.

Comparison of aluminium vs copper power cables for use in industrial installations

Aluminium cables have been shunned by Robin Coombs, Bateman due to poor performance in the past. This was mainly the result of lack of knowledge. BHP Billiton has used aluminium cables very successfully in its giant aluminium smelters in Maputo and Richards Bay. The main criteria for the use of aluminium cable were the cost savings as the vast majority of cables installed were greater than 16 mm². According to SANS 10142-1:2003 Para 6.3.1. “All conductors of nominal cross sectional area less than 16 mm² shall be of annealed copper”. Para 6.3.2.1 “Conductors of nominal cross sectional area exceeding 2,5 mm² shall be stranded, except in the following cases, where solid conductors may be Fig. 1: Solid aluminium cable. Fig. 2: Stranded copper cable. used” – (e) “Aluminium conductors of nominal cross-sectional area of 16 mm² hexagonal crimping must be utilised. Example 1 or more”. For the sake of this report stranded An example using a 35 mm² 3-core Size for size, the cost of aluminium cable aluminium cable is ignored. steel wire armoured cable. is considerably lower than the cost of Cable sizing From Table 1 it can be seen that, size copper cable but there are many other for size, aluminium cable is smaller and factors to be considered. The main difference between aluminium and copper cables is the current carrying lighter than copper except for the current Aluminium cables come in either solid rating which is very much lower. This capacity and impedance. Aluminium or stranded configuration. means that a larger cable size must be cable has a lower current carrying selected if aluminium is to be used. Stranded or solid capacity and greater impedance than the Sizing of a cable is achieved through a The cost of manufacturing stranded equivalent copper conductor. Although aluminium cable in sizes smaller than process of selection based on certain cable is greater than solid so that solid base criteria. aluminium cable is used more frequently 25 mm² is available in other countries than stranded. Large solid copper cable and is used prolifically in India, The following factors must be would be almost impossible to bend and aluminium cable is only available from considered. is not allowed. Both stranded and solid size 25 mm² and up in South Africa. l The size of the drive in kW aluminium cables, larger than 16 mm² When selecting the correct size of l Starting current multiples may be used. Deep indent crimping aluminium cable the impedance must l Power factor of the motor (generally cannot be used on stranded cable so be carefully evaluated. taken at 75% of full load)

July 2010 - Vector - Page 67 Aluminium From Tables 3 and 4 it can be seen that Copper conductors conductors by using aluminium cable, the selected cable will be two sizes larger. Current rating in air 135 A 93 A Using our example if a copper cable Impedance 0,627 Ω/km 1,043 Ω/km is used, a 35 mm² is suitable whereas Cable diameter 30,5 mm 27 mm using aluminium cable, a 70 mm² is required. Cable mass 2,08 kg/m 1,4 kg/m Bending radius 305 mm 270 mm Terminations When terminating copper conductors tin Table 1: Comparison of cable characteristics plated copper lugs are crimped on to the conductor with a hexagonal crimping tool. This results in a solid copper to l Type of starter (direct on line, variable starting is assumed. System fault level copper joint that can be bolted onto the speed, soft start, etc.) is ignored. terminating copper connection. l Derating factors for altitude, ambient, Example 2 When terminating aluminium multiple cables on racks, solar conductors a different approach is radiation Motor: 90 kW required. The lug must be a special l Length of cable from the power Line voltage: 550 V 50 Hz Al-Cu type such that the aluminium source (DB/MCC) to the equipment Full load current (FLC): 120,81 A cable core is crimped into the (control panel, motor) Power factor of motor at 75% of full aluminium tube which is bonded to l Type of cable insulation load: 0,84 lagging the (bi metallic) copper spade. This l Fault level of the system Starting factor: 7,6 times FLC can now be safely connected to the For the purpose of this report only Cable insulation: PVC/SWA/PVC copper connection. balanced three phase electric motor The crimping tool for this type of lug drives fed from a central motor control Volt drop under running conditions not to exceed 5% of nominal voltage is not hexagonal but a circular deep centre are considered. Lighting and indent, two of which are required. This small power is excluded. Cable derating Volt drop under starting conditions not to indent pierces through the outer layer is ignored and only direct on line exceed 15% of nominal voltage. of aluminium thus passing through the aluminium oxide layer of the outer Current ratings in air skin. This applies to solid aluminium conductors. A hexagonal crimp can be Copper cable Aluminium cable used provided that certain precautionary 35 mm² 3 core pvc/swa/pvc 135 A 93 A steps are taken. The outer skin of 50 mm² 3 core pvc/swa/pvc - 110 A aluminium cores develops an aluminium 70 mm² 3 core pvc/swa/pvc - 145 A oxide layer that reduces electrical conductivity. Table 2: 70 mm² aluminium cable would be the smallest allowed. To allow the use of hexagonal crimping this layer must be completely Data calculated with a cable length of 100 m removed and the surface “roughed up” immediately prior to crimping. For this Volt drop Volt drop under under starting Result reason hexagonal crimping of solid running conditions conditions conductors is not recommended. Cable size using copper If an aluminium conductor is crimped conductors 35 mm², 3 core 2,15% 7,42% Cable suitable into a copper lug, two things happen. PVC/SWA/PVC/PVC/Cu l An electrolytic reaction takes place Cable size using aluminium when moisture is introduced, causing conductors: 2,37% 5,14% Cable suitable corrosion. 70 mm², 3 core PVC/SWA/PVC/PVC/Al. l The temperature coefficient between aluminium and copper is such that Table 3: Example 2. when heated, under load, the two metals expand and contract at a -6 Data calculated with a cable length of 100 m different rate. (17 x 10 for copper and 23 x 10-6 for aluminium) This Volt drop Volt drop under running causes looseness within the crimp under starting Result conditions conditions with subsequent overheating and finally failure. This can also be the Cable size using copper Cable conductors: 35 mm², 3 core, 4,30% 14,85% cause of fires. suitable PVC/SWA/PVC/PVC/Cu. Size of lugs Cable size using aluminium conductors: Cable There is a large difference between the 2,74% 10,28% 70 mm², 3 core, suitable size of copper and bi-metallic lugs. PVC/SWA/PVC/PVC/Al Using our example a standard 35 mm² Table 4: Example 2. copper lug is 37 mm long whereas a

July 2010 - Vector - Page 68 ALU300 R21 - P36 T2 AI conductor Type no for Finnish in mm2 punch and matrix temperature- Type no for when cripming class punch and matrix when performing 16 Stud size Fig. 3: All indent crimping sequence. Cu 240 - 30 70 mm² bi-metallic lug is 86 mm Cu-conductor Type no for long. in mm2 hexagonal die Thus it can be seen that, in most instances, more space is required ALU 300 - R21 - P36 T2 for terminations. This can result in See above the terminating box being too small, requiring the addition of a larger box. Fig. 4: Termination lugs and ferrules. In many instances this is not physically possible so an additional interconnection box needs to be introduced where the aluminium cable is terminated on to short bars and the smaller copper cable connecting to the motor. It would be preferable to install local isolators where this aluminium/copper transition can take place. Availability (South Africa) Both copper and aluminium cable have the same delivery periods although aluminium, as it is not as popular, cannot readily be sourced in a hurry. It is manufactured on demand whereas copper cable is kept in stock. Fig. 5: Comparative dimensions. The order quantities are the same as are the drum lengths. Copper lugs is not recommended (quote from the 12 to 15% of the cost of termination. are manufactured in SA so are readily Electrical Contractors Association). The actual installation of the cable on available. Bi-metallic lugs are imported Contrary to the above, aluminium cables to racks costs the same. but the local stockist carries a fairly large have been used successfully on the Cable support consignment. Availability in remote Mozal and Hillside aluminium smelters, locations could be a real problem. both at high humidity coastal locations, Aluminium cable is smaller and lighter where no vibration cracking or corrosion Vibration and corrosion than copper but due to the increase in have been experienced. The only failures size a slightly larger ladder support may Aluminium cable is prone to cracking experienced are where inadequate be required in some instances. and failure when subjected to vibration. measures were taken in the selection of If, as in our example, there were In nearly all electrical installations lugs or masking with corrosion-inhibiting 10 drives following the same route vibration is present. Motors and Denso putty or tape. All motors were then the size of ladder required for transformers produce vibration so the fitted with local isolators where the copper cables would be 305 mm wide use of aluminium cable will be more transition from aluminium to copper whereas for aluminium cable it would be susceptible to cracking than copper cable took place and no vibration was transmitted to the aluminium cable 330 mm wide. A 400 mm wide rack (quote from the Electrical Contractors from the motor. The 360 kA DC open would be chosen. Association). There are recorded cases aluminium bus bar system displayed no of aluminium overhead lines failing due The mass of copper cable on that symptoms of corrosion and no special rack would be 21 kg/m whereas the to Aeolian (wind generated) vibration. precautions were taken to protect it from Vibration damage is even more serious aluminium would be 20 kg/m, thus not the elements. much different. in solid aluminium conductors. Installation Aluminium has excellent corrosion Costing resistance but this is only true for aircraft The qualification of the installation electrician is the same for both copper Aluminium cables are cheaper than grade aluminium and coated aluminium copper. Using our example we get the as used in window frames etc. Aluminium and aluminium. Aluminium is more following: used for cables corrodes when installed difficult to work with so the cost of in damp conditions so is not really termination is higher. On average 35 mm² 3 core PVC/PVC/SWA/PVC/Cu suitable for damp process plants and the additional cost is in the region of cable – R 140,36/m (2007)

July 2010 - Vector - Page 70 Fig. 6: 360 000 A DC positive aluminium busbar installation. amount of large cables involved, could Cost of Cu cables greater than 16 mm² R5 203 735 present considerable cost savings. The 27% saving on above R1405 008 cost of lugs is, conversely, much greater than copper. Additional cost for junction boxes at motors R425 000 Added to this is the additional cost of Additional cost of cable from junction box to motor R169 556 labour as aluminium cable is more Mounting of junction boxes R34 000 difficult to work with. The cost of tooling Cable cost savings R776 452 is also higher but, obviously, not to the same extent. Table 5: LV cables. A typical South African process plant The biggest drawback to the use of Cost of cable R1 492 815 aluminium cables is the risk factor. project (2007) Estimated 18% savings R268 706 l Once an aluminium cable has been All cables of 25 mm² and greater from the Total savings for the use installed it cannot safely be moved. cable schedule were used to evaluate the R1 045 158 of Al cable Further, when handling aluminium possible savings by using aluminium cable cable great care must be exercised in place of copper. The following costs were Table 6: HV cables. to ensure that it is not bent too many extrapolated using the estimated saving times as this leads to cracking. percentage from this report. l The bending radius of aluminium cable is smaller than that of copper but, once bent, it cannot safely be 70mm² 3 core PVC/PVC/SWA/PVC/Al The termination labour cost of 35 mm² straightened. cable – R 98,55/m (2007) copper 3-core cable is R151,67 thus l Great care must be taken in applying terminating both ends costs R303,34. Thus for an installed length of 200 m moisture inhibiting putty or grease Termination labour of a 70 mm² l on all joints to prevent electrolytic Using 35 mm² copper cable costs aluminium 3 core cable is R225,72 thus reaction. R28 072 terminating both ends costs R451,40. l l Corrosion can be a serious risk Using 70 mm² aluminium cable Total installed cost for copper cable is costs R19 710 factor in damp conditions. R28 166,84. Providing that the associated risk is This shows a significant saving but Total installed cost for aluminium cable acceptable and the correct installation the additional cost of lugs and labour is R20 571,40. must be added. A hidden cost is the methods are strictly applied then the Saving by using aluminium cable is requirement of larger enclosures/ use of aluminium cable can result in R7595,44 per drive of 90 kW (±27%). terminal boxes that is rather difficult to approximately 27% savings for the quantify. Summary supply and installation of cables. l Cost of 35 mm² copper lugs R10,75 The use of aluminium cable is significantly Contact Robin Coombs, ea x 6 = R64,50 cheaper than copper so when used Bateman NV (retired), l Cost of 70 mm² bi metallic lugs on a project, the cable costs will be Tel 011 849-1527, R68,35 ea x 6= R410 considerably less and, depending on the [email protected]

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