How important is it to perform an insulation resistance test on 600 V, 4 #4/0 AWG copper THHN cables after they were hand pulled through a 2.5-inch EMT, roughly 50 feet with only one 90-degree bend? I heard that megger test of a cable actually harms cable insulation. Any advice?
Insulation resistance test of 600 V rated cables
- Thread starter takakimf
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oliver100
Guest
Re: Insulation resistance test of 600 V rated cables
No harm at all with a 500 volts megger.
No harm at all with a 500 volts megger.
zog
Senior Member
- Location
- Charlotte, NC
Re: Insulation resistance test of 600 V rated cables
The IEEE requires 1000V IR test on 600V cables. An insulation resistance test will not harm a 600V cable, recent studies have shown DC overpotential testing (Hipot) will danage MV cables.
How important is it? Well do you want to find out the insulation was damaged from the pull when you close that breaker for the first time? Not me! Plus it is important to establish some baseline data for insulation rtesistance to compare to for future testing.
The IEEE requires 1000V IR test on 600V cables. An insulation resistance test will not harm a 600V cable, recent studies have shown DC overpotential testing (Hipot) will danage MV cables.
How important is it? Well do you want to find out the insulation was damaged from the pull when you close that breaker for the first time? Not me! Plus it is important to establish some baseline data for insulation rtesistance to compare to for future testing.
Re: Insulation resistance test of 600 V rated cables
There's some information on the
Slaughter web site (they make hipot and insulation resistance testers.)
There's some information on the
Slaughter web site (they make hipot and insulation resistance testers.)
zog
Senior Member
- Location
- Charlotte, NC
Re: Insulation resistance test of 600 V rated cables
The NETA ATS minimum value is 100 Megohms for 600V cable tested at 1000V.
The NETA ATS minimum value is 100 Megohms for 600V cable tested at 1000V.
friebel
Senior Member
- Location
- Pennsville, N.J.
Re: Insulation resistance test of 600 V rated cables
To: takaimf, Megger check of Cables, and what are acceptable readings. I am going to respond to the original person that started this question.
The question was, "How important is it to check the conductors after an installation." And I am going to add some more helpful information.
No. 1. After any pull of large cables, it is always recommended to have a starting base-line of the Meg-Ohm readings of the cables. Also, you should set a minimum of what is the acceptable readings that you will accept.
No. 2. What is an acceptable reading? I have two manuals from the Company that use to be the Biddle Megger Company, and then they were AVO company, but I do believe that they are called the Megger Company now.
The names of the manuals are: "Stitch in Time" The Compete Guide to Electrical Insulation Testing. Featuring Megger Insulation Testers.
The name of the other manual is "Getting Down To Earth".
On page 14 of the manual,"Stitch In Time" it states the following: INSULATION RESISTANCE SHOULD BE APPROXIMATELY ONE-MEGOHM FOR EACH 1000 VOLTS OF OPERATING VOLTAGE, WITH A MINIMUM VALUE OF ONE-MEGOHM. FOR EXAMPLE: A MOTOR RATED AT 2400 VOLTS SHOULD HAVE A MINIMUM INSULATION RESISTANCE OF 2.4 MEG-OHMS.
I am going to give you my opinion of this reading of 2.4 Meg-Ohms. That would not be acceptable to me on a original installation. I would want to see Infinity or a reading of 200 Meg-Ohms plus.
Also, on page 20 of this manual they recommend the following DC Test Voltage for AC Equipment.
For example, Equipment AC Rating of 440 to 550 Volts, you would use a DC Test Voltage of 500 to 1000 Volts.
I have never had a megger destroy cable with the proper testing voltage, but I have seen the Hy-Pot testing destroy the cable or equipment.
If anyone would like to receive the two manuals that I have just mentioned, please contact me via a private message and I will put you in contact with the Applications Engineer at the Megger Company and hopefully he would sent the two manuals to you.
To: takaimf, Megger check of Cables, and what are acceptable readings. I am going to respond to the original person that started this question.
The question was, "How important is it to check the conductors after an installation." And I am going to add some more helpful information.
No. 1. After any pull of large cables, it is always recommended to have a starting base-line of the Meg-Ohm readings of the cables. Also, you should set a minimum of what is the acceptable readings that you will accept.
No. 2. What is an acceptable reading? I have two manuals from the Company that use to be the Biddle Megger Company, and then they were AVO company, but I do believe that they are called the Megger Company now.
The names of the manuals are: "Stitch in Time" The Compete Guide to Electrical Insulation Testing. Featuring Megger Insulation Testers.
The name of the other manual is "Getting Down To Earth".
On page 14 of the manual,"Stitch In Time" it states the following: INSULATION RESISTANCE SHOULD BE APPROXIMATELY ONE-MEGOHM FOR EACH 1000 VOLTS OF OPERATING VOLTAGE, WITH A MINIMUM VALUE OF ONE-MEGOHM. FOR EXAMPLE: A MOTOR RATED AT 2400 VOLTS SHOULD HAVE A MINIMUM INSULATION RESISTANCE OF 2.4 MEG-OHMS.
I am going to give you my opinion of this reading of 2.4 Meg-Ohms. That would not be acceptable to me on a original installation. I would want to see Infinity or a reading of 200 Meg-Ohms plus.
Also, on page 20 of this manual they recommend the following DC Test Voltage for AC Equipment.
For example, Equipment AC Rating of 440 to 550 Volts, you would use a DC Test Voltage of 500 to 1000 Volts.
I have never had a megger destroy cable with the proper testing voltage, but I have seen the Hy-Pot testing destroy the cable or equipment.
If anyone would like to receive the two manuals that I have just mentioned, please contact me via a private message and I will put you in contact with the Applications Engineer at the Megger Company and hopefully he would sent the two manuals to you.
zog
Senior Member
- Location
- Charlotte, NC
Re: Insulation resistance test of 600 V rated cables
I agree, the "Stich in time" paper is a good basic guide for IR testing, you can download it from the megger website. I also agree that the 2.4 Meg reading in the stated example is too low for a new installation.
I will disagree with the "infinite" reading, there is no such thing, I would make my tech go back out with the right test equipment and get an actual reading. The most important thing about IR tests is not so much the reading you get but how that reading compares to previous readings for predictive maintance (Or trend analysis) purposes.
I agree, the "Stich in time" paper is a good basic guide for IR testing, you can download it from the megger website. I also agree that the 2.4 Meg reading in the stated example is too low for a new installation.
I will disagree with the "infinite" reading, there is no such thing, I would make my tech go back out with the right test equipment and get an actual reading. The most important thing about IR tests is not so much the reading you get but how that reading compares to previous readings for predictive maintance (Or trend analysis) purposes.
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