Following years of copper being the material of choice for high power busway for some, and aluminium reigning supreme for many others, Schneider Electric takes a look at the case for aluminium over copper busway at a time when cost of materials is having a significant impact on specification choices.

When it comes to performance and resistance many designers consider copper to offer a higher performance than aluminium for the same rated bar.

However, according to Schneider Electric Power Business product marketing engineer Hersch Joshi, the differences are marginal.

“Tests show that in a 1,400A load through 30m of 1,600A of busway the voltage drop for aluminium was just 0.32% compared to 0.30% for copper. This equates to a difference of only 5mV,” Hersch says.

“Then we calculated a 250m run of 3,200A aluminium busway at 2,700A, 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 10%. As a guide, 40% of this 10% is lost in the sub-distribution and the balance in the final circuit wiring.

“With a cable system, its standard practice with designers to increase the size of cable to overcome volt drop issues. And it seems with busway the preferred choice is to use a copper conductor. In the calculations we then used a 4,000A aluminium system and compared this to a 3,200A copper system.

“Tests showed that on a 250m length where the load is 2,700A, the voltage drop on a 4,000A aluminium busway is 2.7%, which is minimal when compared to a voltage drop of 2.53% on 3,200A copper busway – equating to a difference of just 675mV, or 0.17%.”

Hersch adds: “These examples at 250m 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.

“Installing aluminium busway with an equivalent performance means that it is typically between 16% and 25% larger in volume than copper busway. 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 busway over copper means the building’s electrical support structures can be lighter.”

In response to the fact 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 busway range, the joints between each length feature an ‘elastic connection joint’ that automatically compensates for expansion.

In addition, the joints on Schneider Electric’s busway range are silver-plated not tin-plated as commonly used by other manufacturers. This metal is ideal for electrical conduction and resistance to abrasion when the bar is moving along the joint, providing longevity of the installation. In fact, tests consucted by the not-for-profit French association ASEFA show that silver plating performs up to 12 times better than tin. In addition, copper and aluminium busway are both tested to IEC 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 up to 55%. This increases up to 65% when comparing a 3,200A rating like for like in material.

“There are many benefits for choosing aluminium busway, which means designers and contractors shouldn’t be put off from using it, Hersch says.

“On shorter runs the performance difference between the two materials is marginal and on longer runs where volt drop may be an issue 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 busway 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.”