Testing Wire Insulation
Electrical wiring is designed to resist a certain amount of voltages but the insulation ensures that the electricity is directed where it needs to. When electrical insulation breaks down it might cause electrical failure and accidents that cause damage and fatalities every year.
To continue the integrity of an electric wire’s insulation, the strength of the insulating elements need to tested on a regular basis. There is a term used to define the maximum voltage that an insulating material can take before it starts to degrade and it is known as the Dielectric strength. Dielectric tests are conducted by exposing to short burst of high voltage electricity and then taking readings of the leakage.
Types of Insulation Tests
There are three tests that you can conduct to test the integrity of the insulation on a wire:
- The first one is done to determine the amount of voltage that an insulator can resist before is degrades. It involves passing high voltage current between two points on a wire and you keep increasing the voltage until the insulation starts to give in. This is called a Dielectric Breakdown Test.
- Dielectric Withstanding Tests are used to determine whether a certain cable can resist a set amount of voltage for a required period. It involves applying voltage for a specific amount of time and watching the current that leaks by the cable. You can only hope that there is no leakage and the cable remains intact.
- This test is meant to calculate the resistance of the insulation to high voltage electricity. There is a calculation involved but the best thing to be to use an Ohm meter.
What is “hipot” testing?
There is one definitive test that is used in the industry known as the hipot testing (High possible Voltage). It is carried out by using different instruments that have different voltages from 5kV to larger testers that have an output of 400 kV or more.
You might be familiar with the continuity test that effectively tests whether there is any electrical flow between two points. The desired results of such a test is to have current flowing, with a Hipot you are checking for good isolation, you do not want the current to flow, you want it to stay in one area to test the integrity of the insulation in that single area.
The hipot test is conducted by using two conductors that are secluded and applying a very high voltage between them. Current flowing by is watched, if the test is properly done, very little current should flow.
For more complicated things, like a network of contacts where wires, connect with resistors, capacitors and other elements all the contact are connected to the hipot device and the device is grounded. Every part should be tested in isolation from the body of the rest of the device.
This test can also be used to detect defects like spacing between current-carrying conductors and the point where they have to be “earthed”. Cables are sometimes placed under environmental conditions and things like humidity, dirt, vibration, heat and contaminant can damage the insulation and create dangerous situations.
How do these “hipot” tests affect quality?
High possible voltage tests are often required in product design, especially in the quality management stages. During the design phase, one can know the maximum voltage that design specifications need to make allowances for.
These kinds of insulation tests are mostly found to be useful in basic applications. Some manufacturers will require every cable that is produced to undergo insulation testing. The hipot test can be sensitive arcs that you would find in most IDC cables.
There is always a risk involved with working with electricity. The first consideration is to use testing equipment according to the instructions by the manufacturer. To minimize the risk of danger and injury from electric shock, follow these guidelines:
• The shock you could receive should not be greater than 45 Cu
• The total hipot energy should not be greater than 350 m
• and the total current should not go beyond 5 ma peak
Those are the minimum requirements. With electricity there is no space to break the rules which method it is important that the tester you choose meets the requirements or be equipped with a safety interlock system just in case things don’t work as they should.
Other Testing Methods/ equipments
Besides the standard hipot tester, there is a test known as the Megger Test which works on the same assumption as the hipot. A Megger reads high voltage resistance in electric circuits.
It detects the slightest changes that occur in high voltage circuits. It is commonly used in high voltage industrial applications and although there are units that can be used to test your typical run of the mill insulation, the Megger in an industrial high voltage testing method.