Dispelling the myths of aluminium busbar trunking
Following years of copper being the material of choice for high power busbar trunking in the UK, yet aluminium reigning supreme in the rest of the world, Schneider Electric takes a look at the case for aluminium over copper busbar trunking at a time when cost of materials is having a significant impact on specification choices.
The company addresses industry misperceptions and sheds light on some of the common arguments against its widespread use including performance, weight, expansion and cost.
When it comes to performance and resistance many designers consider copper to offer a higher performance than aluminium for the same rated bar. However, the differences are marginal as Lee Jones from Schneider Electric explains: “Tests show that in a 1400A load through 30 metres of 1600A of Canalis busbar trunking, the voltage drop for aluminium was just 0.32 per cent compared to 0.30 per cent for copper. This equates to a difference of only 5mV.
“On longer runs, we calculated a 250 metre run of Canalis 32000A aluminium busbar trunking at 2700A and at this level we found that the system had a volt drop percentage of 3.2%. According to the wiring regulations the maximum volt drop on power circuits on a privately owned supply is 8%. As a guide, 40% of this 8% is lost in the sub-distribution and the balance in the final circuit wiring. With a cable system, it’s standard practice with designers to increase the size of cable to overcome volt drop issues. However, it seems with busbar trunking the preferred choice is to use a copper conductor. In the calculations we then utilised a 4000A aluminium system and compared this to a 3200A copper system.”
Tests showed that on a 250 metre length where the load is 2,700A, the voltage drop on a 4,000A aluminium trunking is 2.70%, which is minimal when compared to a voltage drop of 2.53% on 3,200A copper trunking – equating to a difference of just 675mV or 0.17%.
Lee adds: “These examples at 250 metres were taking the product to the maximum volt drop in sub-distribution. They were extremely long runs but indicated the length of the runs where volt drop may become a concern.”
Following on from this point, Lee continues: “Installing aluminium busbar trunking with an equivalent performance means that it is typically between 16% and 25% larger in volume than copper busbar trunking. However, it is 40% lighter, offering contractors a trade-off as it’s easier to handle, more manageable, requires less people to install it, offers a faster installation and could eliminate the need for special lifting equipment – all saving time and money for the contractor and the customer. In addition, the use of aluminium trunking over copper means the building’s electrical support structures can be lighter.”
In response to the view that aluminium expands more than copper, Schneider Electric highlights that an allowance for expansion and contraction has to be made at the point of manufacture to ensure a reliable connection. For example, with Schneider Electric’s Canalis range, the joints between each length feature an ‘elastic connection joint’ that automatically compensates for expansion.
In addition, the joints on Schneider Electric’s busbar trunking range are silver plated not tin plated as commonly used by other manufacturers. This metal offers the best electrical conduction and resistance to abrasion when the bar is moving along the joint, providing longevity of the installation. In fact ASEFA tests show that silver plating is 12 times better performing than tin. In addition, copper and aluminium busbar trunking are both tested to BS EN 60439-2, so there is no discrepancy in the standards used.
The final argument relates to cost. Even going to a higher rated aluminium trunking over copper, it still offers financial savings. In cost comparisons between 3,200A copper versus 4,000A aluminium, there is a saving of 23%. This increases to 35% when comparing a 3,200A rating like for like in material.
Lee Jones comments: “There are many benefits for choosing aluminium busbar trunking, which means designers and contractors shouldn’t be put off from using it. On shorter runs the performance difference between the two materials is marginal and on longer runs where volt drop may be an issue, then designers can choose a higher rated aluminium bar. In addition, no special tap-offs are required on our range because of the use of silver on the joints. So, as busbar trunking can be used as an alternative to traditional cable and is gradually becoming more widespread in today’s building market, contractors can reap the benefits of faster installation times, while offering customers a system that can be upgraded and reused as the building use changes over time.”
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