Monitors providing insufficient load for insulation test

[Pyrex]

We have hit a snag with PAT testing of some computer monitors in our school (class I). We have a basic battery powered Seamark PrimeTest 50 PAT tester. Earth test passes fine, but then the insulation test gets stuck on "Check Connections", which means the monitor is not providing sufficient load. The monitors do not have a physical power switch, just a button that you can press to turn them on when they have power.

Oddly some of the identical monitors in the same room do not suffer this problem. They pass the insulation resistance test without a problem.

An electrician who was doing some other work for us tested a couple of the problem monitors with his much fancier, mains-powered tester and they passed without issue.

Does anyone have any advice on how to test these? Maybe we just have to buy/borrow a better tester.

 

[Marvo]

The PAT tester you're using isn't really the best one for the type of equipment you're testing. If the load presented by the monitor is too small there's not much you can do apart from use a more appropriate tester. The problem is that the 'on/off' switch on the monitor is actually a momentary operation switch that just sends a signal to the internal electronics and the actual switching on is really done elsewhere with the monitors circuitry so without power applied you can't effectively do the tests.

 

[Pyrex]

Thank you, Marvo. So the key thing is to have a tester that provides power while it tests? Presumably plugging into the mains?

 

[Grizzly01]

Pyrex,

No, you haven't quite grasped what Marvo was explaining.
No PAT tester will provide mains power to the EUT during an insulation resistance test.

Out of interest, have you tried running the IR test with nothing plugged into your Seaward PrimeTest 50?
That would provide zero load to the tester, so it would be interesting to see if it complained about that, or passed with maximum resistance.

 

[Pyrex]

No, you haven't quite grasped what Marvo was explaining. No PAT tester will provide mains power to the EUT during an insulation resistance test.

Fair enough. I was jumping to conclusions there as Marvo said without power applied I could not effectively do the tests. What I was trying to get at is what would make a PAT tester more appropriate for the task. So what feature should I be looking for in a tester that would allow testing these monitors?

Out of interest, have you tried running the IR test with nothing plugged into your Seaward PrimeTest 50? That would provide zero load to the tester, so it would be interesting to see if it complained about that, or passed with maximum resistance.

With no connection at all it fails the earth test and will not advance to the insulation test. If I attach the probe to the earth pin of the socket so that the earth test passes without connecting anything else, then the insulation test sticks up the "Check Connections" as for the problem monitors. The same message "Check Connections" apparently comes up with kettles when they are not turned on, but they have a physical on/off switch.

 

[Grizzly01]

It does say in the PrimeTest 50 manual, on page 10, that if you get the 'Check Connections enunciator' due to low load presented (on a Class I IR test), press the Class I test key to continue.
What happens when you do that?

 

[Pyrex]

What happens when you do that?

It then succeeds, apparently by skipping the test.

I knew that was possible, but thought it was not the right thing to do as the item is the item has not been IR tested. But you are right that manual makes it sound as if that is what we are supposed to do, that skipping the test in that case is not a problem.

 

[Pyrex]

Then again, maybe I am wrong that it is skipping the test when I press the test key. Maybe it is proceeding with the test regardless of the low load. I will try it out again.

 

[Grizzly01]

I reckon that the test continues, rather than skips.
'Check Connections' is just a warning to the person doing the test, that something may not be connected/switched on/fuse blown etc.
Pressing the test button again is your way of saying 'Thanks you for your concern. However, all is in order, so do the chuffing IR test, please'.

 

[Pyrex]

I reckon that the test continues, rather than skips.
'Check Connections' is just a warning to the person doing the test, that something may not be connected/switched on/fuse blown etc.
Pressing the test button again is your way of saying 'Thanks you for your concern. However, all is in order, so do the chuffing IR test, please'.

You are correct!

I connected the positive and earth terminals of the tester (and the earth to the probe so the earth test would pass). I got the "check connections" message, pressed the class 1 button and the test failed. So it definitely carried on and performed the IR test. I got the same result if the negative terminal and the earth were connected, so it is checking both directions.

Well that is an unexpectedly easy solution. Thank you for your help, Grizzly.