Previous in Forum: Use of Variable Frequency Drive in Energy Meters?   Next in Forum: Wound Rotor Motor
Close
Close
Close
9 comments
Rate Comments: Nested
Member

Join Date: Jul 2010
Posts: 7

Min Cable Insulation Value

09/25/2010 10:25 AM

I have to check the insulation for cable for 210kW (415V) motor, 3C x 185 sq.mm.

What is the minimum acceptable cable insulation after megger test with 1000V?

Register to Reply
Interested in this topic? By joining CR4 you can "subscribe" to
this discussion and receive notification when new comments are added.
Guru
United Kingdom - Member - New Member

Join Date: Aug 2010
Location: Resting under the Major Oak
Posts: 4347
Good Answers: 181
#1

Re: Min Cable Insulation Value

09/25/2010 10:54 AM

Have a look in Google or search this forum!

__________________
The reports of my death are greatly exaggerated.
Register to Reply
Guru

Join Date: Oct 2008
Posts: 42355
Good Answers: 1693
#2

Re: Min Cable Insulation Value

09/25/2010 11:23 AM

What does the specification say? You DO have a specification, right? Why else would you know that you are supposed to test? And if you know that you are supposed to test, you should know why and what the requirements are, right?

Register to Reply
Guru
Engineering Fields - Electrical Engineering - Been there, done that. Engineering Fields - Control Engineering - New Member

Join Date: Dec 2008
Location: Long Island NY
Posts: 15600
Good Answers: 981
#3
In reply to #2

Re: Min Cable Insulation Value

09/25/2010 12:46 PM

The OP wants to fail the cable. By failing this cable, he'll prove to his boss that he's a knowledgeable employee doing his job. The problem is he doesn't have a specification or requirement to show off his capabilities. That's why he came to us.

Well I'll give some numbers to suit the goal.

The minimum insulation resistance at 1000V is nothing less than 1012 ohms for a one meter length of cable. Now if you wish to really show off, you can also measure the cable's capacitance per meter which should not be more that 10-12 farads.

__________________
"Don't disturb my circles." translation of Archimedes last words
Register to Reply
Guru
Technical Fields - Technical Writing - New Member Engineering Fields - Piping Design Engineering - New Member

Join Date: May 2009
Location: Richland, WA, USA
Posts: 21017
Good Answers: 795
#4

Re: Min Cable Insulation Value

09/25/2010 5:30 PM
__________________
In vino veritas; in cervisia carmen; in aqua E. coli.
Register to Reply
Anonymous Poster
#5

Re: Min Cable Insulation Value

09/26/2010 6:31 PM

1000 ohms per volt--general rule .

Register to Reply
Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
Posts: 32175
Good Answers: 839
#6
In reply to #5

Re: Min Cable Insulation Value

09/27/2010 12:55 AM

If that were the case, then no residual current device would ever do anything other than trip! So the answer is inctredible.

__________________
"Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
Register to Reply
Anonymous Poster
#7

Re: Min Cable Insulation Value

09/27/2010 3:06 AM

Identify what type of cable your testing (should be marking on outside sheath) and, search for cable spec. or speak to the manufacturer.

Register to Reply
Power-User

Join Date: Jun 2010
Location: Kolkata, West Bengal, India
Posts: 172
Good Answers: 1
#8

Re: Min Cable Insulation Value

09/27/2010 9:05 AM

Thumb rule which is applied in field for Insulation Resistance ( IR ) testing of cable is :

Rated Voltage of cable ( in KV )* 10/ Length of cable ( in KM ) in Meg. Ohms.

__________________
Manindra
Register to Reply
Commentator

Join Date: Jun 2010
Posts: 75
#9

Re: Min Cable Insulation Value

09/29/2010 1:30 AM

As a thumb rule for for 415V motors, minimum acceptable cable insulation should be 1 Megaohm. There is a formula:

Safe Minimum IR value = Rated Voltage/ (Rated output in KVA) +100.

In your case it comes as 1.14 Mohms.

BB Raina

Register to Reply
Register to Reply 9 comments
Copy to Clipboard

Users who posted comments:

Anonymous Poster (2); BB Raina (1); lyn (1); manindra (1); PWSlack (1); redfred (1); TonyS (1); Tornado (1)

Previous in Forum: Use of Variable Frequency Drive in Energy Meters?   Next in Forum: Wound Rotor Motor

Advertisement