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Thread: Test & Tag Machine Calibration
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15th May 2021, 08:29 AM #16Most Valued Member
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I'm employed in a similar role at a similar organisation.
I'm also a qualified EE. Although I've never worked in the role, I reckon if there was an incident, Worksafe would say I should have known better. I'm new in this job and my predecessors have not done a good job of the T&T process. Nearly every appliance in the place is out of test. Some by a period of several months. The record keeping is patchy to say the least. I'm now tasked with fixing the mess. That's why I had the machine calibrated. I don't believe it's been calibrated since it was bought nearly 10 years ago. It's also the reason I queried the numbers on the test report. I need to be confident this old machine is actually serviceable before I embark on testing around 700 appliances and leads.Chris
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15th May 2021, 09:22 AM #17Pink 10EE owner
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Given house holds are not required to test and tag, I wonder why we are not seeing mass electrocutions of everyone who lives in a house with electricity.
I believe now in the halls of government bureaucracy there is a never ending list of "issues". And now for decades they have been working down the list. It started off with things pretty sensible and to make sure their jobs stay relevant they just work down their list to the absurd. I think sometime in the future they will mandate some procedure businesses will have to implement in case a stray asteroid should land on their business site.
But as we have seen in the real world the workers just ignore stupidity. I read a coroners report some time back about some poor rail workers who got killed onsite. The coroner said in his report that after determining what was done he could not understand why the workers were not following the written procedure. After reading what they did and what the procedure said to do, there was a disconnect between those that write the stuff up in an air conditioned office, and those that were to do the procedure. The office workers failed to take into account human nature.Gold, the colour of choice for the discerning person.
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15th May 2021, 11:32 AM #18Most Valued Member
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The counter argument is that there is no disconnect at office level, the problem exists at shop floor level. If a company has a procedure for a task then that is the way it should be done. The human nature you speak of is nothing more than a culture of half arsed laziness, and a she’ll be right mate it’ll never happen to me attitude.
I work in resources where things like Permit to Work and Lock out Tag out have been around forever and still we find people wanting to not lock off and control an energy or pressure source that will kill them if it goes south. It’s not just in the skilled trades sector either, two weeks ago we had a plant operator hospitalised because he wasn’t driving to condition (read too fast) hit the wall the cab deformed to the point the door lock disengaged and the cab door opened. He was flung from the cab because he wasn’t wearing a seatbelt and run over by the rear wheels of the Atlas MT65 he was driving. The thing is, the MT65 has an interlock to prevent starting if the seatbelt isn’t plugged in. The operator made a conscious decision to defeat that interlock by plugging the belt in wrapped behind the seat.
So, is there a disconnect, or a poor culture on the shop floor?
Back on topic..
You may actually find it cheaper to buy a new PAT than have your old one calibrated. The bonus to that is some of the newer ones will print the tags, and log the details for you so it’s a lot quicker.
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15th May 2021, 11:50 AM #19Member: Blue and white apron brigade
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Here is my other T&T story.
When I joined our local mens shed in 2014 they were collecting a lot of old gear (ie mostly Junk!) but as they had no resident sparky to check these machines out I volunteered to work my way through them and then set them aside until a licensed sparky could come in and sign them off.
Apart from mechanical safety issues (of which there were many) some of these old machines were fitted with old bakelite domestic electric light switches, no earth connection, Broken switch housings, missing cable glands - just wires through motor terminal boxes, wires connected by being twisted together etc.
After fixing my first half dozen machines we called a sparky in and I said to him - the machines in that corner are ready for checking out, the others still need work. Anyway he so called T&T them all and gave them all an OK, even though one machine had its wiring guts hanging half out of the switch box, and one had a badly damaged power cord repaired with a couple of turns of tape. He clearly didn't do any sort of inspection so when his bill arrived we only paid him for the machines we asked to be tested, and we did not get him back
About a year later a still licensed electrical fitter joined our shed and he has been fantastic. Everything gets properly tested, on time and fixed at short notices. He's getting on a bit in years - it will be a shame when he goes.
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15th May 2021, 01:46 PM #20Most Valued Member
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Agreed. I probably should have said tested rather than calibrated. This one (Megger brand) needs to go back to the UK if it needs adjusting, so it will be cheaper to buy a new one. It prints tags and stores the records. It even generates bar codes so you only have to scan the label at the next test. It's about a $4500 machine.
Chris
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15th May 2021, 01:50 PM #21Most Valued Member
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15th May 2021, 04:48 PM #22Member: Blue and white apron brigade
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15th May 2021, 08:06 PM #23
Hi Chris, Guys,
Megger do some very good gear and training info !
https://uk.megger.com/portable-appli...ting-dvd-ptdvd
Their gear is not cheap either.
A point often overlooked is that the test machine needs testing as well ! Particularly its own test leads and extensions.
Fundamentally visual inspection is 90% of T&T ! If it doesn't look right then its a "Fail" regardless, there is no point in going on to electrical testing, yet hidden electrical issues make up 90% of the testing.Best Regards:
Baron J.
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15th May 2021, 09:41 PM #24Member: Blue and white apron brigade
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It's not a serious impedance calibration but more of an in-house on the spot resistance check.
I made myself up a resistor chain from 2 x 1MΩ resistors and 2 x 0.1MΩ resistors that I carry around with my budget level insulation tester.
The resistor chain is inside a piece of PVC tubing with one end of the chain accessible at one end of the tube and nicks in the tube at 2.0, 2.1 and 2.2 MΩ mark. The nicks are large enough for the tester probes to make contact.
The idea is I can quickly check if the tester can reliably measure the difference between these important resistances.
Rchain.jpg
How do I know that the resistors are what they claim ? - I've have checked these against the calibrated resistors (good to 1%) at my former place of employment. Which reminds me I need to recheck mine again.
I should add that this all is for my own private use - I don't go around testing stuff for others with it/
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16th May 2021, 10:33 PM #25Most Valued Member
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Returning to the test for a moment. Let's assume the uncertainty of the RCD test is actually 29% as they claim (and they should give the game away if it is). I've got two questions I hope someone can answer:
1. If the required tolerance of a PAT machine is 5%, surely there's no point in performing the test, because you could never be certain the machine is within tolerance?
2. I believe uncertainty is a plus or minus figure. They have chosen the uncertainty to be negative which brings the measured error back to within 5%. So the actual test result could be worse than they claim?
I just want to get this clear in my head in case they change their mind and come back to me wanting their $300 for the test (which they won't be getting).Chris
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16th May 2021, 11:33 PM #26Intermediate Member
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Even when buying a new machine, particularly for this type of work I would ask the supplier "Does it come with a traceable calibration certificate". If it does not then you may require them to furnish such a report as condition of sale or commission your own report.
By traceable I mean a NATA certified report or eg from the USA a NIST traceable report. Most other countries have similar calibration institutions.
It is also very important that you fully understand the information given on any certificate. If it is unclear then query the testing company. If they cant give a clear answer then I would be a bit suspicious of them.
As an aside I have heard of a piece of equipment that was sent for testing and was returned with a report. The client then used the equipment without reading the report. If they had they would have learnt that it failed.
As a NATA assessor I have seen some accredited labs that are a bit dubious.
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17th May 2021, 01:33 AM #27
Interesting concept for self checking your insulation tester Bob, but what is the voltage rating of the resistors? Typical 1/4W axial can be as low as 200V, 1/2W as low as 300V, so the power rating can become less significant than voltage rating for higher value resistors. If perchance the resistors have been overstressed in the past (yours don't appear to have been), the safe working voltage can be somewhat lower than the original voltage rating due to degradation if the substrate or insulation. Thus there is significant possibility of resistor breakdown if they are exposed to the test voltages produced by Megger style test instruments.
I used to be an engineer, I'm not an engineer any more, but on the really good days I can remember when I was.
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17th May 2021, 07:28 AM #28Most Valued Member
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17th May 2021, 09:00 AM #29Member: Blue and white apron brigade
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Good point and I have thought of this and doubt they are under much stress.
The resistors are rated at 1W.
The tester has 250, 500, 750 and 1000V test settings.
At least 2 x 1MΩ resistors in series are always in use
The highest test V setting used is 750V so using V^2/R so power would be 0.28W.
Even at 1000V, power would be 0.5W, but I don't use this to check the meter.
Like I said its not meant to be a definitive but rather an indicative test. If they were breaking down due to exposure to the tester voltages I would expect their resistance to change over time but they're still reading the same as when I first set them up. I don't use my tester all that often, maybe 6 times a year but it sure is handy to have one at home.
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17th May 2021, 10:47 AM #30Most Valued Member
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Having been around the metal trades for 30 odd years, I can confidently say that I have no confidence in the whole testing and tagging regime as it stands. One previous workplace simply "borrowed" the licence number of the motor rewinder next door and after a simple visual inspection of leads would tag them using the "borrowed" number. Another workplace got in a licenced tester and tagger who took what appeared to be a significant amount of care in going about his business, except he tagged several power tools that did not work as being a pass and physical damage was found on several leads that were tagged as passing. Every knuckle dragging man and his dog got in on the test and tag game around 10 years ago and I seriously doubt many of them are actually up to the task of carrying out a proper test regime or understanding basic electrical fundamentals.
I believe that there is an over reliance on silly little tags, particularly in workplaces such as the metal trades and site work, where physical damage can occur at any point and often does. What was tagged yesterday may not meet standard tomorrow. Your absolute best insurance is to carry out a prestart check of any lead or tool that you intend to use just before you use it, you will then identify electrical and mechanical issues as they arise.
I fully realise that test and tag is part of the WHS framework and here to stay, but I don't trust it totally, nor do I rely on it by itself as a means of maintaining electrical safety.
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