All electric wires are covered in some sort of insulation, be it in a motor, cable, transformer, and generator, switch and so on.
The wire is usually aluminium or copper in order to be a good conductor of the electric current powering equipment.
The insulation is usually the opposite of that as it needs to be able to resist the electric current and keep it on its path through the conductor.
Insulation around a conductor has a similar purpose to a pipe that carries water, with leaks in either causing serious problems.
Voltage is akin to pump pressure for electricity, making electricity flow through the copper wire.
There will be some resistance to flow, just like with a water pipe, but far less with the wire than with the insulation.
The higher the voltage, the more current there is, and if the wire’s resistance is lowered, the same voltage will give more current.
Insulation deteriorates over time, but the good news is there is usually plenty of warning of this deterioration before it reaches serious levels when regular insulation resistance tests are carried out.
How to measure insulation resistance?
Good insulation comes with high resistance, and the inverse is also true.
Factors such as moisture or temperature can make the actual resistance values lower or higher.
A good picture of the condition of your insulation can be obtained with some record-keeping and a bit of common sense, along with the use of an IR tester, also known as a megohmmeter.
There are a number of factors that can affect the readings during insulation resistance tests, and it is important to be aware of them.
Factors that can have an impact on current can include the likes of humidity, temperature and the passage of time itself.
Using the megohmmeter properly
One of the factors that can affect the readings of insulation resistance tests is improper use of the megohmmeter itself.
This makes it all the more important to make sure that you are fully aware of how to operate the IR tester in the correct manner in order to make certain that the readings you receive will be accurate ones.
Different voltage levels
If different voltage levels are used with the megohmmeter, there will likely be different insulation resistance values measured.
Generally speaking, the reading that is taken with an IR tester of higher voltage will probably be lower.
Insulation resistance is extremely sensitive to changes in temperature. An increase in temperature results in a decrease in insulation resistance and the reverse is also true.
Insulation resistance generally has a tendency to alter by a factor of two for every 10-degree change in temperature.
So readings will need to be corrected to base temperature in order to make accurate comparisons of new readings with older ones.
It is important to carry out regular insulation resistance tests with an IR tester in order to receive readings that may warn of any insulation deterioration and allow for corrective measures to be taken in plenty of time.