Cooler cables cut energy consumption

Paul Courson, UK Managing Director of Cablofil, discusses the independent tests carried out to demonstrate the relative cooling and energy efficiency benefits of varying types of cable containment.

It’s a hard fact of any commercial environment that our energy consumption has increased to meet the demands of the electronic age However, the commercial need to remain competitive by embracing technology must be balanced by an environmental responsibility to manage energy consumption as effectively as possible; in short to ensure that the energy we consume is useful energy rather than wasted. Switching off or powering down systems that are not in use can help, but specification of electrical and data installations also has a significant role to play in reducing consumption of wasted energy.

A hot topic

When it comes to cable containment, the open structure of steel wire systems provides increased natural ventilation. This is essential because copper or aluminium cable cores heat up when an electrical current is running. The heat given off is known as the Joule effect and this is caused by the resistivity of the material; more simply, the ability of the material to resist the passage of an electrical current. The resistance of a conductor is proportional to the resistivity so, as resistivity increases with temperature, any cables that are confined within a non-ventilating containment system give off heat that cannot escape, thereby increasing the ambient temperature, which causes an increase in both resistivity and resistance. In this situation, more power is required to enable the current to flow and this causes energy to be wasted unnecessarily.

To quantify the importance of effective ventilation of the cables, Cablofil commissioned tests from the world-renowned, independent laboratory, Bureau Veritas: LCIE, which proved that the Cablofil* system helped to prevent energy wastage due to the Joule effect, ensuring that the energy used in the cables is useful energy, and reducing energy consumption by as much as 37%.

Controlled conditions

Bureau Veritas: LCIE tested seven containment configurations using containment widths of both 100mm and 300mm. The systems tested were:

• Cablofil CF54 steel wire tray (a medium duty steel wire basket with a depth of 54mm)

• Perforated steel tray

• Cablofil CF54 with a cover

• Perforated steel tray with a cover

• Metallic trunking

• Plastic trunking

• Metallic conduit

All the cables used in the tests were of an identical type and equal length and the room temperature was maintained at a constant 20ºC. The intensity of the power delivered to the system was also constant at 257A. Temperature within the systems was regulated for 30 minutes prior to commencement of the tests and the conductor’s core temperature was measured continuously to map the rise in temperature during the test and record the peak temperature. The resistance of the cables in each configuration was then measured using an ohmmeter (a digital device designed to measure resistance to electrical current) and the amount of electrical energy consumed was calculated using the equation P=R.I² (Power = Resistance x Intensity of current² ).

For the test rigs using 100mm widths of steel basket (with and without cover), perforated steel tray (with and without cover) and conduit or trunking, seven cables were used in a four on the lower layer/three above configuration to create 21 metres of cables in a series circuit, and this provided a containment filling rate of 40%. Meanwhile, the 300mm width test rigs used a total of 27 cables, with 13 on the upper layer and 14 below, giving a containment filling rate of 60% and creating a series circuit 81 metres long. In every test, the rig was created using standard 3m lengths of basket, tray, conduit or trunking.

Clear results

The 100mm wide, seven cable rigs clearly demonstrated that the Cablofil system retained the lowest temperature at 69.2ºC and the lowest resistance at 5.0m?, followed by perforated steel tray which scored a temperature of 80.6ºC and a resistance measurement of 5.1m?. As predicted, both the temperature and the resistance values of these two containment methods rose when a cover was added to the test rig, however, the Cablofil steel wire tray system still demonstrated clear advantages over perforated steel tray. With a cover, the temperature of the core on the Cablofil rig was recorded at 81.7ºC and the resistance was measured as 5.1m?. Both the temperature and the resistance values for the perforated tray + cover rig were considerably higher, with a temperature measurement of 119.0ºC and a resistance measurement of 5.7m?. As anticipated, the figures recorded for both temperature and resistance were significantly higher for plastic trunking, metallic trunking and metallic conduit where temperature values of 130.2ºC, 155.9ºC and 119.6ºC respectively were recorded. The resistance performance of plastic and metallic trunking was equal at 6.0m? and for metallic conduit was 6.4m?.

Steel wire tray also demonstrated clear advantages over alternative systems in the 300mm containment tests. Here, the temperature of the core on the Cablofil rig was recorded as 68.5ºC without a cover and 101.2ºC with a cover, as compared to 93.3ºC (without cover) and 167.0ºC (with cover) for perforated steel tray. The temperatures recorded for plastic trunking and metallic conduit were 171.1ºC and 157.3ºC respectively with the cables in the metallic trunking test reaching a staggering 228.0ºC before the test was abandoned because the cables had been destroyed. Similarly, the resistance of cables in the test using Cablofil steel wire tray with no cover was lower than the result for any other method of containment at just 19.5m?. What’s more, even with the addition of a cover, only uncovered perforated steel tray demonstrated lower resistance.

Significant implications

It is important to view these test results not simply as numbers but also in the context of the cable standard which is 90ºC. Cablofil was the only system used that remained below this temperature during the 100mm ‘with cover’ test. What’s more, in the 300mm width tests, Cablofil was the only system that respected the cable standard even without a cover – and by some considerable margin, recording a temperature 25ºC lower than perforated steel tray, its nearest rival.

What the results provide is a clear picture of how much wasted energy the use of any one of the containment systems included in the tests involves – Cablofil steel wire tray was the best performer that could be regarded as an ‘A’ energy rating, followed by a sliding scale all the way through to metallic trunking and metallic conduit with a ‘G’ energy performance rating

As commercial properties (both new build and re-fit) seek to push the boundaries of energy efficiency and improve their green credentials, being able to demonstrate the energy savings of the containment system is vital. With its reduced use of raw materials, speed of installation and flexibility, steel wire cable containment already demonstrates clear advantages over other types of containment and now it can add proven reduced energy wastage to that list.

*The tests described were carried out using Cablofil steel wire tray. Not all steel wire tray systems are the same and the results cannot, therefore, be applied to similar products

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