While we may like to view the modern world as a wireless haven, cables remain to be an important element of almost all electrical systems. Therefore, it is important for engineers to know how to test cables effectively to ensure they are fit for purpose. Here, we explain a few things that engineers should look out for when testing electrical cabling.
In the early 20th Century, renowned inventor and electrical engineer, Nikola Tesla, first created a wireless power transmission. Tesla described it as being “the motive power and thought transmitter of the near future”. Over a hundred years have gone by, but wireless power transmission hasn’t quite lived up to Tesla’s promise. Instead, much of our electrical equipment still requires the use of cables to receive power. However, this is only possible if the cable is in the right condition and fit for purpose. A cable that is damaged or compromised is unsafe and ineffective.
Why Testing Cables is Important
Therefore, it is essential for engineers to understand what it is they should be looking for when inspecting and testing cables. This week, we shall discuss the ways in which you can test your cables as thoroughly as possible to ensure that they are safe for use.
The first and most obvious step is to look for any visual signs of damage to the insulation of the cable, the plug and the socket connectors. For temporary applications, you will usually see signs such as slashed, shredded, crushed and cracked connectors.
However, not all types of damage are so easy to spot. Though it may be easy to identify a slashed cable, many engineers may view things such as dirtiness as little more than a problem of aesthetics. The truth is that something like a cable covered in mud may be a sign of water in the cable run. This can pose a serious health and safety risk.
Electrical Continuity Testing
After a cable has passed the visual inspection, it must go through a selection of dead tests to be tested for electrical continuity. This includes tasks such as de-energising the cable by connecting an electrical tester end to end. This will determine if a complete circuit can be made.
This step is essential. By testing the continuity of phases and earthing in the cable, you can ensure that the internal elements of the cabling are wired as they should be. If a cable fails this test, it is not reliable to be used in a live application. As a result, it must be removed from a service, rewired and then retested.
Fit for Purpose
Finally, you should test the cable to ensure it is fit for purpose. This can be done with both Insulation Resistance and a live test. An Insulation Resistance test, also known as a megger, is crucial for ensuring the cable is fit for purpose. This tests the current leakage through the conductor’s insulation material. In doing so, the tests are compliant with BS 7671 wiring regulations.
Begin by connecting an Insulation Resistance tester to the cable. Then, select the test voltage and you will be given an electrical reading. A high reading is a pass and a low reading indicates a problem. This could be water, loose connection or damaged cable.
Despite the fact that cabling in outdoor applications should be properly IP-rated to protect against water ingress, this could change with use. If an IP-rated cable runs through a muddy field for a range of events over time, it may find itself experiencing some level of ingress.
After the dead tests have been carried out and you have recorded all the results, only then will it be safe to connect the cable to a known live supply and carry out the live test. The cable is energised, and a phase rotation meter should be connected to the one end of the cable. Then, check that the phase rotation metre is displaying the correct sequence of neon lights. This will indicate that the test is now correct and complete. Only then can it be marked as “ready for hire”.
While Tesla may have been correct about many things, wireless power transfer still has a long way to go before that can be one of them. Until that day, engineers must continue to make sure that cables are fit for purpose and safe for use.
Training with ECTA
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