While an electrical cable may appear to be a simple component, it can have a significant effect on the safety and reliability of an entire electrical system. The decision to use a cable because of its appearance or simple load capacity can lead to issues that may not become apparent until it is put under stress. That is the reason why it is vital to know cable current carrying capacity while designing and installing the electrical systems. It is the ability of a cable to conduct current without heating or overheating. Under sized cables can result in energy loss, equipment issues, and even serious safety risks.
What Happens When a Cable Is Undersized?
An electric current always generates heat when it passes through a conductor due to the electrical resistance. A properly sized cable will conduct this heat if operating conditions are normal.
But if the cable is too small it may be required to conduct higher than its current carrying capacity. An increase in load leads to an increase in heat generation. This heat, if it is not released properly, may cause the cable’s insulation to deteriorate, which may shorten the lifetime of the cable and the risk of electrical fault.
This isn’t merely a specification, it’s an essential. It is an important factor to consider for reducing excessive thermal stress.
Cable Size Is Only Part of the Story
For many people, the thought of buying a larger conductor seems to eliminate all capacity issues. The fact is that there are a number of factors that will determine how much current a cable can safely handle.
These include:
- The type and size of the conductor used.
- Ambient temperature
- Installation method
- The length of the cables that form a bundle.The quantity of cables in a bundle.
- Breathing and cooling down.
- Insulation temperature rating
- Extended or periodic loading conditions
An example of this is that several cables placed side by side can produce and retain heat more than one single cable placed in an open, well-ventillated area. Therefore, the actual C cable current carrying capacity may be different compared to the basic rating under the Reference Conditions.
The Problem with Ignoring Derating
Derating factors may be used by electrical engineers when environmental and/or installation conditions are different from the ones used during the standard ratings of the cable.
Failure to make these adjustments could lead to a cable that looks good on paper, but is actually running at or close to thermal limits during actual installation.
This is especially critical in industrial plants, commercial structures, power distribution circuits and where several circuits are in close proximity. If the cable selection does not consider actual operating conditions, then there is a risk that this can create a weakness in an otherwise well designed electrical system.
Why Overheating Should Never Be Ignored
Sometimes, cable overheating is not noticeable right away. Insulation can continue to perform its function as it slowly undergoes thermal stress. Repeated overheating over time can cause insulation to age and can cause the risk of short circuits, damage to equipment or equipment shutdowns.
The effects can also end up being costlier as it travels throughout the electric system. A wrongly selected cable can ultimately result in equipment downtime, maintenance issues or safety accidents.
Therefore, an understanding of cable current carrying capacity is important to help engineers recognize the thermal constraint prior to becoming an operational constraint.
Making Cable Selection More Reliable
The first step in proper cable selection is to know the anticipated electrical load and then consider the actual installation conditions. Before selecting a cable, engineers should take into account the applicable standards, load type, installation methods, environmental factors, grouping factors, and allowable temperature ranges.
In addition, it is essential to ensure that current-carrying capacity is separate from other factors like voltage drop, short circuit withstand and mechanical factors. A cable meeting one criterion may require additional tests to meet other criteria.
Conclusion
A too small cable can become a secret weak link in the electrical installation. The risk is that it could fail at any time and also that it could eventually become unreliable and unsafe because of the prolonged thermal stress. When combined with installation conditions, load requirements and applicable design criteria, the cable current carrying capacity can be evaluated to make better decisions on cable selection. The correct cable is not just the cable that can carry the necessary current, it’s the cable that will do so safely and reliably under the conditions in which it will be used.