Managing cables in moving lighting, sound or set applications

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Moving lighting, sound or set almost always require cables for power, data and signals. Elinore Mackay caught up with Justin Leonard, energy chain director at igus, to find out the issues around cable management in theatres and on stages and movie sets

With the increasingly advanced technology for modern lighting, sound and effects, the complexity and required flexibility grows. So does the number of moving cables needed for power, data and control systems. Conventional cable reelers are often used for these applications; they are reliable and have served the industry very well but they do have their limitations. These are becoming more and more obvious as we enter this multimedia age with high speed data and digital services. 

In your experience what is the main limitation of a conventional reeler?

The slip ring is at the core of a cable reeler, and that has its limitations. In some ways these limitations have to do with reliability due to the effects of corrosion or debris getting into the system, which is generally not a common problem in the theatre or studio but it can become an issue for outdoor venues.

However, the biggest issue is that the slip ring can limit the number of services that can be managed. It also becomes quite complicated when trying to move bus systems and power systems together; this either requires the use of separate reelers or a composite cable, which will invariably be very expensive and nearly always be of a bespoke design. 

 

Are there any other situations where there may be in issue?

Yes. If the management of fluids or fibre optic cables is required, it becomes almost impossible using slip ring cable reelers. If it is possible, it is incredibly expensive. 

One of the key backdrops to this is the ever increasing need for faster Ethernet data rates…the next step will be to move from copper cables to fibre optics, which can handle much higher data rates. Additional benefits are that fibre optic cables are physically easier to handle as they are much lighter than their copper counterparts and can handle multiple channels of data. 

All these points combined mean that the traditional cable reeler is starting to struggle as a concept to keep up with these demands and some of the bespoke requirements of venue type applications for moving cables and hoses.

What is the alternative to a cable reeler?

Taking a new approach to solve some of these problems, the e-spool system dispenses with the slip ring by using a rotating conical energy chain – called twisterband – that enables a continuous end-to-end connection. Also, instead of using a bespoke composite cable, which is expensive, e-spool can accommodate multiple cables, as well as provide physical guidance and protection. 

An additional benefit of using this system is that different cables can be added into the energy chain; this means that instead of having a large, quite stiff composite cable, single cables for the different functions lie side-by-side.  Indeed, any combination of data, control, power and fibre optic cables can be accommodated, as well as hoses for air and water or whatever is needed for the particular application. 

Offering even more flexibility, the e-spool can be fully extended and cables can be added or replaced easily without the need to develop a new composite cable or the time for carrying out re-rigging. For example, if the installation is being upgraded from Cat5e to a higher speed Ethernet or even moving to fibre optic technology, it is a relatively simple cable replacement.

 

So tell me more about twisterband – how does it work?

The conical twisting chain, called twisterband, enables a true end-to-end connection for the cables. The system wraps around and rotates in two orientations – one around the core and the second a conical helix of chain that rolls around. This allows up to 7000 degrees of rotation, or just over 19 complete turns. twisterband is available in a range of sizes and, importantly, different types of media to be combined together, whether it is data, control, power or fibre optic cables, or even hoses for air and water. The link-by-link construction of the twisterchain allows cables and hoses to be added or changed easily. 

 

What are the capabilities of e-spool?

We have a fairly mature family of e-spool types. The e-spool mini is a 2m extension that holds 3 or 4 small cables and is approximately a 300mm cube in size with spring retraction. 

The e-spool manual system handles a single cable or hose length of 5m. It has a ratchet on it so the cable can be pulled out, locked into position and attached to something and then pulled to release the locking system and retracted. Typical applications for this manual system is for charging or a temporary connection where the cable needs to be completely moved away when not being used. 

The e-spool standard range is available in three extension lengths of 4m, 7m and 14m, with a single- or double-sided feed. If more cable capacity is required, a second twisterband is added on the opposite side of the drum to feed 2 sets of cables into the reel. The energy chain on the reel, which manages the cable down or up, is wider than the single feed system to accommodate the additional cables. In terms of size, the largest 14m e-spool unit is roughly a 900mm cube. The spring retraction system is housed in an external cartridge, which is replaceable, and the tension is tuneable to suit the particular application. 

For lengths beyond 14m, the loads involved for retracting the cables particularly in the vertical plain start to become too high for spring mechanisms, instead, an electric motor is used with a closed loop control system. Standard e-spool power units with extensions of 25m are available, though longer lengths are possible.

 

Are there any common rules or general guidance for using e-spools?

The most important rule is to segregate the cables and hoses correctly in the twisterband and energy chain, this is to ensure that they remain untwisted and prolongs the lifetime of the system. Appropriate separation components are provided with the chosen e-spool unit. 

The second point to remember is that the cables can only be stacked in the twisterband and then at a maximum of 2 high. In the chain of the reel this is not advised - if there were cables in the inner and outer sides of the chain, the outer side would have a longer path length as the reel coils and uncoils, which would mean that there’s relative motion between the two path runs, reducing cable life.

Both ends of the cables, at the twisterband infeed and the end of the energy chain, need to have strain relief, ensuring that they are properly tied down. This is particularly important in vertical installations to overcome the forces of gravity, which can pull the cables through the system.

The maximum cable diameter for use in e-spools in 17mm. If a cable with a large number of cores is required, this can be split up. For example, a 36 core power cable at 2.5mm2 would be split into 3 cables of 12 cores each. In theory, larger cable diameters could be used but in practise, when the cables are bigger than 17mm, they are stiffer and therefore difficult to move.

Another point to bear in mind is that the maximum extraction and retraction speed is 1m/s. This assures that the tension of the spring or speed of the motor is harmonised with the speed of the e-spool thereby avoiding slack within the system.

The last point to consider is the cables themselves; for reeling systems, it is strongly advised to use a good dynamic cable. The complex twisting involved in the e-spool will shorten the lifetime of a standard static cable considerably - even with a low duty cycle, the non-linear effect can destroy the cable within a short time frame.

Are there any other points to consider?

When using e-spool for the first time, our engineers are at hand to offer support and guidance throughout the system design and installation.