The radius of the curve will be calculated automatically. On a run of cable tray, an internal bend with the desired radius and in the proper spot can be constructed. It is not essential to perform an internal bend and secure it in the proper place. Mark the tray in the manner indicated in Figure 30. The flat surface against which you press should be smooth and free from dust. Use a piece of cardboard as a cushion when marking.
If numerous cables must travel the same path, a cable tray or rack system may be the best way to support them. The minimal internal bend radius is calculated by multiplying the cable's overall diameter by a factor of four. For example, if a cable has an outer diameter of 1/4 inch, then its inner surface should have a radius of 1/2 inch or greater for effective support.
Cable trays are available in a wide variety of shapes and sizes. The simplest type consists of a series of parallel hollow tubes for supporting cables. These can be made from aluminum or steel and are usually covered with plastic or rubber to prevent damage from weather conditions.
Cable trays can also be designed with bracing between each tube to strengthen them and provide better support for heavier loads. These are often used where space is limited such as inside walls or ceilings. Cable trays can be built into the structure of a building instead of being added after the fact using metal framing members. These pre-made cable trays are commonly seen in office buildings as they can be easily installed when the building is being constructed out of steel and other durable materials.
The last type of cable tray I'll discuss here is one that uses corrugated cardboard as the support medium. These are easy to install and remove and don't damage supported cables if removed without first disconnecting them.
The minimum bend radius is the smallest radius that the cable can be bent about. For example, while bending a medium-voltage cable with a copper tape cover, cracks in the outer jacket may emerge. The minimum bend radius should be large enough to allow for these cracks to remain within the cable's mechanical limits.
Cable manufacturers specify several factors when determining the minimum bend radius: the size of the cable itself, the distance between bends, the type of insulation, and the number and thickness of the strands in the cable. For example, an aluminum cable used as a ground wire in a circuit should be allowed to have a smaller minimum bend radius than the copper power cable because of the increased risk of damage if too much pressure is applied to the aluminum wire.
Generally, the minimum bend radius should be at least twice the diameter of the cable or loop it forms, but most electrical codes require a minimum bend radius of at least four times the cable's diameter.
For example, a 500-foot section of 2-inch aluminum cable with a 0.5-inch thick copper tape covering would have a minimum bend radius of 8 feet. If this cable were bent back on itself too closely, then it could cause the strands to pinch together, causing a short circuit.
Table 1 shows that the minimum bend radius is six times the overall diameter of the cable. The total diameter of the cable is specified in the product catalog as 2.08 inches. Therefore, the minimum bend radius is 12 inches.
Cable tolerances will affect how tightly it can be pulled into a connector. For example, if one type of cable is.5 inch in diameter and another is.75 inch, then the with-drier-cord version of the connector must be used with the smaller cable because there isn't enough room for both cables to fit through at the same time.
If you try to pull too small a cable into a connector, it will get kinked up inside the connector and not work properly.
For best results, maintain a minimum bend radius of 12 inches for all types of cable. This will ensure that no part of the cable is compressed against the wall of its housing when it's being pulled into a connector.
Also note that fiber-optic cable should never be bent without proper care. Bending fiber-optic cable increases the risk of damage occurring which could result in loss of signal strength or complete failure of the cable.
Optical fibers are very fragile and should only be handled by trained professionals.
According to 330.24 (A), the radius of the inner edge of any bend must be at least ten times the external diameter of the metallic sheath for cables no larger than 3/4 in. In external diameter. Make your voice heard! To leave a comment on this website, you must first login or register. It's quick and easy!
The minimum bending radius is required by law in some states to prevent electric shock from happening if someone were to touch both the metal sheath and the core of the cable. The warning label will also show the minimum bending radius that has been set by the manufacturer. If you want to learn more about this topic, check out our article on electrical code requirements for wiring installations.
Given the mobility of workers between the cable trays, the horizontal clearance between the attempts must be at least 500 mm. Depending on the width and cross section of the cable tray, each tray may hold an unlimited number of cables. The maximum number will depend on space availability and the severity of weather conditions where the system is located.
The distance between two cable trays needs to be at least 1.5 times the depth of a tray. This allows room for cables to be routed around or under other objects. The minimum distance between cable trays is therefore 600 mm with deep trays and 900 mm without.
Cable trays are available in a wide variety of depths and heights. The optimal tray size depends on the application but generally speaking, the deeper the tray the easier it is to clean out debris that can cause problems with signal transmission. Larger trays also allow for more cables to be held within the same amount of physical space. For example, if there are eight 50-foot cables held in one tray then the total length of cable would be 400 feet. If the same quantity of cables were held in four 100-mm trays then the total length of cable would be 200 feet.
The distance between cable trays should be long enough to prevent cables from being pinched between adjacent trays.