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Earth Bond Test, Question.

PostPosted: Thu Jan 22, 2015 10:21 am
by Ford Prefect
I wonder if anyone can help.
We have a piece of equipment that I (more properly the Apollo 600 ) have failed on the earth bond test.
When it went for repair/re-wire the person who was going to repair it also tested it and passed it! I have found out he was basing his pass on a 0.2 Ohm base before allowing for cable, however according to the CoP it should be (0.1 + R) Ohm, as the unit is fed from a timer box via a 5 core cable would the 0.2 be more correct?
Any input would be greatly appreciated.

Re: Earth Bond Test, Question.

PostPosted: Fri Jan 23, 2015 3:28 pm
by Stephen Armstrong
Thank you for your enquiry

Please get your copy of our Guide to PAT, at the following link:

http://www.seaward.co.uk/userfiles/pat-testing-guide.php

Please see page 14 of the above guide, (0.1 + R) Ohms is the correct equation. However, you need to know the csa and multiply this by the length of the cable (page 22) to calculate the correct value of R. Then add this value to 0.1 to determine the total resistance.

And also please see:

http://www.seaward.co.uk/downloads/3584_pat_posters_2011_layout_2_v2.pdf

Kind regards
Technical Support

Re: Earth Bond Test, Question.

PostPosted: Fri Jan 23, 2015 4:45 pm
by Ford Prefect
Thanks for that.
So yes I was right as I am basing it on (0.1 + R) Ohms and adjusting (using the calculator on the 600) for csa and length as in the CoP.
The repairer (who has been PAT testing for years) was however starting at (0.2 + R) Ohms before adjusting for csa and length!
My question was as the unit is fed from a timer box via a 5 core cable would the 0.2 be more correct? meaning, was there another way of say adjusting for what must be extra circuitry in the box, as the repairer is a seasoned PAT tester I thought he might know something I don't that someone more experienced on this forum might be able to help with.

Re: Earth Bond Test, Question.

PostPosted: Mon Jan 26, 2015 1:56 pm
by Grizzly
Nah, the repairer is using the wrong pass limits, as can be shown from all the guidance literature available.
Maybe ask him to give his reasoning as to why he sets his pass limit at (0.2 + R)Ω rather than (0.1 + R)Ω.
I may be cynical, but I'll bet he does it so he has fewer failures, and so fewer issues to diagnose...

Re: Earth Bond Test, Question.

PostPosted: Mon Jan 26, 2015 2:25 pm
by Ford Prefect
Cheers Grizzly,
That was my reasoning but as I've only been doing this for just over a year and he's been doing it ages I wanted to check.The only way I worked it out I'd be able to pass it was if it was a 4m, 3A cable which it hasn't got!
Thanks Again.