Nowadays, we take electricity for granted and have very little idea about what’s actually going on behind the walls. Cable systems are quite complex, and the average Joe knows very little about them. Fortunately, the internet has become an easily accessible source of information, so anyone looking to learn has an easy way to do so. If you’re interested in figuring out what factors matter in choosing a cable and ensuring it works properly, you’ve come to the right place.
Improper cable installation is one of the most common causes of equipment malfunction, electrical issues and other hazards. For that reason, it’s important to have a good understanding of the conditions the cable is installed in. Once a cable is installed properly, routine testing, maintenance and inspection should be performed to ensure the cable isn’t deteriorating and that the cable system is in proper working condition. There are a couple of different types of cables, and which one you choose will depend on the application. For example, an IEC 7 cable is perfect for installing lighting products, whereas IEC 13 cables are used for connecting monitors and computers.
The application a cable is suited for will depend on its construction. Cables are made up of conductors, wire arrangements, insulation and covers (jackets). The conductors are typically made from copper or aluminium, and which one you choose will depend on the environmental condition and maintenance requirements.
There are single and three-conductor cables, and both have their own distinct pros and cons. Single conductors are easier to install and enable the formation of multi-cable circuits. However, they have a higher reactance and are prone to mechanical stresses. It’s important for the cable to feature a ground wire. Some cables, such as the IEC 7 cable include a grounding wire, while others don’t, so you might need to buy a separate grounding wire.
As far as cable covers and insulation go, your choice will depend on the type of installation, service conditions, type of load and ambient operating temperature. In industrial applications, conditions such as high ambient temperatures, rodent and insect hazards, presence of ozone, oil and solvents will impact the ideal cable cover for the job. In some events, multiple conditions may be present, making selection even more difficult.
The insulation of the cable should be sufficient enough to withstand the voltage stresses that occur during normal and abnormal working conditions. That being said, you should select a cable based on the applicable phase-to-phase voltage. Typically, cable insulation is categorised as 100%, 133% and 173%.
Choosing the right cable size comes down to the needed current carrying capacity, short circuit rating and voltage regulation. A lot of people overlook the voltage regulation and short circuit ratings, which can result in unwanted damage to the cable, as well as to personnel and property.
The current carrying capacity of the cable refers to its thermal heating capabilities. You can learn more about the current carrying capacity of cables here. Additionally, you can learn about the current ratings of different types of installation and insulation on ICEA’s page.
As briefly aforementioned, the voltage regulation of cables is an often-overlooked factor. This is mainly due to the fact that in properly designed and installed systems, it’s typically not a problem. However, the voltage drops for long runs at low voltage should still be inspected to ensure the load voltage is right.
Lastly, the cable’s ability to withstand short circuits should be based on the circuit’s opening time for short circuit conditions. Simply put, the cable should be capable of withholding thermal damage until the circuit breaker shuts the power down.
Cables can be either shielded or non-shielded. Your choice will come down to the type of environment the cable is going to be used in. Some of the things to consider when deciding whether the cable needs shielding or not is the type of insulation system, whether the system is grounded or ungrounded, and the reliability and safety requirements of the cabling system. Systems without any shielding or metallic covering, the electric field is present in the air and in the insulation system. If the electric field is significant, such as in medium and high voltage applications, surface discharges may occur and ionise the air particles. This, in turn, will cause ozone generation, deteriorating the cable’s finish covering and insulation.
In duct-tape installations where non-metallic, unshielded cables are used, the external electric eld can be high and pose a threat to personnel. It’s similar when using cable assemblies, portable cables and exposed overhead cable installations. That being said, shielding is highly recommended, especially when working in conditions with damp conduits, connections to aerial wires, dry soil, dirt environments that contain contaminants, when transitioning from conducting to non-conducting environments, where radio interference is present and where safety to personnel should be of utmost importance.