First of all, You need to understand why do we must do this test? and also when will we do this test?
The cable is composed of either a solitary core (conductor) or multi-core (conductors).
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Each conductor has its insulation, add to the cable has outer insulation surrounds all the conductors.
After pulling the cables and also before an energetic them, we should ensure no fault will take place after the energizing.
This fault can be instant after the energizing, or it will take a item of time.
It counts on the top quality of the conductors’ insulation.
So, we need to check and test the insulation’s top quality of the conductors prior to the energizing process.
Now, I will talk around how to perform the insulation test of cables, step by step.
Firstly, we will perform this test making use of a machine called one insulation tester.
This maker is a portable tool prefer an ohmmeter v a built-in generator that produces high values of DC voltages.
As every the manufacturing withstand voltage the the cable, us will select the check voltage.
Usually, the applied voltage to the short voltage cables will variety from 500 volts come 1000 volts for 60 seconds.
You need to know in plenty of projects that they will contact this test megger test, but this is no the correct name of the test, together the suitable name the this test is the insulation test.
Megger is a brand name (manufacturer) the manufactures this an equipment to examine the cable’s conductors’ resistance.
And together it was using widely in the projects, the human being used to call it megger test. However, other renowned companies are additionally manufacturing the insulation test devices, choose Fluke, kyoritsu, etc.
The insulation check of low voltage cable’s main ide is using a particular volt worth on 2 conductors of the cable because that a particular time, climate measuring the resistance in between them.
The time of the test, generally to it is in from 30 seconds up to 60 seconds.
As the device’s applied voltage is known, the device will measure the present flow’s value in the conductor and then calculation it to gain the resistance.
Usually, the analysis will it is in in values thousands of megaohm, or Giga ohms, or also can reach approximately Tera ohms.
It relies on the top quality of the insulation.
You require to understand that an excellent insulation has actually high resistance, while bad insulation, reasonably low resistance.
The actual resistance values of the cable deserve to be higher or lower,
depending upon such factors as the temperature or moisture content of the insulation (resistance reduce in temperature or moisture).
As you have the right to see in this photo, we have a multi-core cable, is composed of 4 conductors.
The color of the cable’s conductors space Red, Yellow, Blue, Black.
The preferably withstands voltage for the cable’s conductors is 1 KV= 1000v.
Note:After this value, the insulation the the cable’s conductors will begin to fail.
Before starting this test, you should care around the adhering to points:
1- You should ensure remove the cable’s terminals from any type of panel or breaker.
This is just for the cable on which you need to apply the check on.
2- You should ensure each cable has a tags or brand labeled indigenous both ends.
This is to avoid any type of mistakes, particularly if you have multiple cables are pulled in ~ the very same location.
3- You need to proceed with the continually test very first on the cable come ensure no touching between the exact same cable’s conductors.
4- There’s a separation between the cable’s conductors in ~ both ends.
5- in ~ the ar where girlfriend will use the insulation test and apply the voltage to a cable’s end, make sure the cable’s outer sheath and the conductors’ insulation are removed.
This is to allow connecting the insulation tester’s leads to the conductors for the test.
6- You need to make sure that the insulation tester is calibrated and also has a precious calibration certificate.
You require to affix this certificate v the check results throughout the investigate to the consultant.
The prestige of this calibration certificate is to ensure the readings room correct.
7- Before starting the test, you have to ensure the you changed the insulation tester for the required applied voltage and time on the cable.
Now, us will know the helpful procedure of applying the test to a short voltage cable:
A- So, let united state say us will use a dc voltage through a worth of 1000v on just two conductors Red & Yellow.
B- us will use this voltage because that 60 seconds and also then document the resistance between these 2 conductors Red and also Yellow.
C- when we record reading in a sheet, us will remove the insulation tester’s leads and also connect them come the various other two conductors.
We will follow the same procedures to examine the resistance in between the following conductors:
Red with Blue.
Red v Black.
Yellow with Blue.
Yellow with Black.
Blue with Black.
So we will document all the readings and also put castle on a table that a form that is ready-made because that this test.
You have the right to download a sample the this type from here!
After that, the quality manage will submit an inspection inquiry to the consultant to concerned the site and also physically inspect the results.
Once the consultant find the it is registered results almost identical to the results acquired during his presence, that will approve the test.
Now, friend are all set to energize the cables.
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You will certainly follow the above steps for all the short voltage cables in her project.
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