Selecting the correct cable reel for an application is not as simple as picking a reel with the correct number of circuits and wire size to meet the amperage needs. Several factors must be considered in the match up of the cable to the reel starting with the application. For spring driven reels in particular there are four distinct application modes including drag, lift, retrieve and stretch.
A stretch, or stretching in general, may be good for the human body but is one of the tougher applications for a cable reel. For a stretch application the cable is suspended horizontally between the reel and the extended end of the cable. To maintain a sag in the cable of 6% (3 ft. sag in 50 ft.) or less between the reel and the extended end requires a spring tension of approximately twice the weight of the extended cable. Often in stretch applications the allowable sag is critical to prevent the cable from dragging on rough surfaces such as the floor, etc. or to provide clearance over other pieces of equipment or obstacles. Therefore, the lighter in weight the cable the less spring tension required. A lighter weight cable will also normally have a smaller diameter and will allow more cable to be wound onto a given size reel hub or possibly allow the use of a smaller overall size or series of reel. The cable weight is also a vital factor for drag, retrieve and lift applicationsbut in those cases the tension required is normally less than that required for a stretch application.
While the weight of the cable is of concern to determine the spring tension required for successful retraction, the spring in the reel actually determines the amount of tension that is applied to the cable as well as the amount of cable of any given diameter that can be successfully extended and retracted on a given reel center hub or sheave. This is because the spring has a given number of 'working turns' that will vary with the original unrolled length of the spring and diameter of the spring case or housing that the spring must operate within. Increasing the thickness of the spring material will increase the tension applied to the cable but will decrease the possible overall length of the spring and therefore the number of working turns. One goal is to provide adequate tension to the reel to allow successful retraction of the reel while avoiding operating the spring within the last 2 or 3 working turns or reel revolutions of spring lockup or maximum wind at full extension of the cable. Spring life decreases exponentially within the last few working turns of the spring.
Because UEA cable reels, using a UEA slip ring assembly, can easily be constructed with more than the traditional 3 or 4 cable reel circuits, and with various combinations of voltage and amperage ratings, it is evident that options are available to meet a variety of reeling needs. Not to be forgotten, however, are the basic requirements to match the reel size, cable and spring to the type of application. UEA engineers are always available to discuss and help configure the best reel for your needs.