I am really not sure about calibrating a meter, the idea is that if it fails then anything tested with it would need retesting, and in a year that would be a lot of testing, so I would test the same socket every day, so if the meter goes out, hopefully only one days work to redo. OK if only used a few times a week then yes the test period can be extended, the calibration one would hope corrects any drift and high lights errors.
However bitter experience has shown me not worth the paper written on. I started a new job and was presented with what looked like a brand new historic PAT testing machine, it had a series of lights, no meter reading, just go/no go lights.
I voiced the opinion that it would be a good move to computerise the records, which should mean in the future I would be told by the computer what needed testing that week. So a program was sent for, however it asked for readings, which I did not have, so rang up the program supplier.
Answer was easy, look at the calibration certificate and write down what it said was pass level, however this was not on the certificate so program sent back and I used Excel instead, all I needed to do was use the same word for each reading, and once we got the values, use the replace command.
So it was a traceable record so contacted firm who had it calibrated, this was our main supplier, but it seems they contracted the work out to a calibration house. Each time I saw the rep, it was where is my certificate, in the end I threatened to stop putting business there way until sorted, getting to 4 months at this point.
So next was can I give them the PAT tester so it can be retested, it seems they could not trace the traceable records! So it went back, next it seems this historic machine was made when the pass level was lower than it is now, and it could not be calibrated to the new pass levels, so by this time I had 6 months of PAT testing not worth the hard drive space it was held on. The firm was very apologetic, and gave us a very good deal on a new top of range Robin, and sent their guys to PAT test office which would help me catch up.
However after that, I have to ask, why bother? I could have sent for one MΩ resistors etc and tested my own equipment, I would at least then be able to actually trace the traceable records and know it was correct, OK some things I can't test, tripping times for a RCD for example, however two testers both testing the same RCD at regular intervals would mean very unlikely that anything goes wrong without my knowledge, and it would not take 6 months to find the meter was faulty.
In real terms if we follow the rules, even if we don't test regularly we should soon know, as we should be given the previous test results so we can see if the installation is degrading, so if reading don't match it rings alarm bells, and we retest the test set. However some people seem to think we would not test things if we had old results, so retain them. As if!!!!!
And regulation says continuity needs to use at least 200 mA, some of my meters actually use 25A, this is not a fail, yet you sheet shows there is an upper limit as well as lower limit so would worry a little about that calibration house.
