IET
Decrease font size
Increase font size
Topic Title: Testing PC's
Topic Summary: Problems with pass levels on 200Ma continuity test
Created On: 14 January 2014 08:48 AM
Status: Read Only
Linear : Threading : Single : Branch
Search Topic Search Topic
Topic Tools Topic Tools
View similar topics View similar topics
View topic in raw text format. Print this topic.
 14 January 2014 08:48 AM
User is offline View Users Profile Print this message



PatMann

Posts: 2
Joined: 14 January 2014

Hi all, I am new to this forum and would like to ask a question about testing of Personal Computers. I have been Pat testing for about five years now and set up my own business in 2011. I now use a Megger Pat420 which is a great machine for saving time on the job. I have problems often though with the preset test for PC testing. The default pass level for the 200 Ma continuity test is set at 0.1 and I find a lot of PC's give readings in the range of 0.11 to about 0.19 and so therefor FAIL the test. I am not an electrician so I am not sure how dangerous this is. I often get asked by office managers if I can change the pass parameters in my test set. Of course, I am able to do this but I am reluctant to change any presets because I presume they are set at the levels recommended by the IEE. My question is:
Would it be dangerous to change the pass parameter to say 0.2 for the PC continuity so that I don't keep getting all these PC failures.
As a follow on to that:
How bad is it if a PC gives a reading of say 0.4+ on the continuity test?
Anyone else have this problem with testers that have preset tests and pass/fail levels?
Advice on this would be appreciated.
 15 January 2014 02:54 AM
User is offline View Users Profile Print this message



kengreen

Posts: 400
Joined: 15 April 2013

The answer to the first part of your question lies in the tolerances set by the Brains of the (now defunct) IEE ?

No tolerances ? Then your measurments and tests are meaningless.

For the second part - please say to what that 0.4+ is referenced. For example a reading of 0.4 volts is a lot of volts when measured with a f.s.d. of 1.0 volts but could be no more than parallax error when the f.s.d. is 100 volts ?

Ken Green
 24 January 2014 07:03 PM
User is offline View Users Profile Print this message



PatMann

Posts: 2
Joined: 14 January 2014

The preset tolerance in my test set for an earth continiuty test on a PC is 0.1 megaohms but I often get readings of 0.11 up to 0.16 and technically this is a fail. We are only talking about what is generally called a casual earth connection here as it is only as good as the connection made by the act of bolting all the parts together. Obviously, the only part of a PC that contains a physical earth connection is the PSU itself and the only way to get at the casing of the PSU usually is to remove a cover from the PC. I just wish that manufacturers would provide an earth stud on the rear casing so that a physical wired earth connection could be made to the exposed metal parts. Would solve all of my issues. At least then if it fails it fails lol.
 25 January 2014 10:46 AM
User is offline View Users Profile Print this message



kengreen

Posts: 400
Joined: 15 April 2013

Your reasoning won't apply to my premises here. On a valley slope we drain at 45-degrees into a small stream and any value of any direct earth depends on timing and extent of recent rain.

You must size up the situation, make your own decision and run with it.

It is not possible to make Rules that apply to ALL situations ?

Ken Green
 18 March 2014 06:52 AM
User is offline View Users Profile Print this message



Killaswfc

Posts: 1
Joined: 18 March 2014

PatMann

Posts: 2
Joined: 14 January 2014

The preset tolerance in my test set for an earth continiuty test on a PC is 0.1 megaohms but I often get readings of 0.11 up to 0.16 and technically this is a fail. We are only talking about what is generally called a casual earth connection here as it is only as good as the connection made by the act of bolting all the parts together. Obviously, the only part of a PC that contains a physical earth connection is the PSU itself and the only way to get at the casing of the PSU usually is to remove a cover from the PC. I just wish that manufacturers would provide an earth stud on the rear casing so that a physical wired earth connection could be made to the exposed metal parts. Would solve all of my issues. At least then if it fails it fails lol.

1, Your test parameter is set at 1Mohm??? Then there's a problem there, as that is 100,000 ohms!
2, The test itself depends on the length, csa, connection of the iec lead and quality of the earth connection inside the unit itself.
3, Use your own judgement! Is the iec lead well connected? Is it a bit sloppy fitting? Is the iec lead old and worn? Has your tester lead been nulled? Are the socket tubes on your tester a little worn after long time use? Is the PC old and worn? Are the earth bonds inside a little sloppy or dirty?
Don't take this as a license to pass any old tat, but I would suggest that if it isn't a brand new PC, short good quality iec lead and your tester is not perfect then I would say anything below 0.3 Ohms would be ok!
Statistics

See Also:



FuseTalk Standard Edition v3.2 - © 1999-2014 FuseTalk Inc. All rights reserved.