Metrel OmegaPAT MI2141

[D J Sheridan]

Hi all,
New to the site so bear with me.
I have a little problem with the above machine in-as-much it keeps giving me the following message before it tries to do the Insulation Test on a water cooler:-

L-N RESISTANCE TOO HIGH (>30 kohms)
CHECK FUSE OR SWITCH
Do you wish to PROCEED
(Y/N)

Yes I have in the past realised I'd forgot to switch the switch on the appliance to ON but always remember this now.
Now yes I have checked the fuse (the appliance does work okay) and I checked the switch (which was on).

I have come across this on other machines recently and just selected Y to proceed but now found out that the test might not be valid as it only powers up and/or checks the mains cord to switch and not the whole appliance.

What to do? Any help much appreciated in as Layman terms as possible...

 

[D J Sheridan]

I need to BUMP this one as I require some help on this...

I've now tested a UV Light Unit that is Class 1, only 28W power with a 3amp fuse in it.
now it is used for detecting germs on people's hands and we need it installed within the next few weeks.
It is not a handheld appliance and I don't feel it comes under heating/cooking either.

Now this L-N RESISTANCE TOO HIGH... malarkey happens on this too even though the switch is on and the fuse is okay (plugged into the mains and switched it on to check it).

So why does it do this?

Results for UV Light are as follows:-

Earthbond:
Output: 10A
Limit: 0.10ohm
Result: 0.07ohm

Insulation:
Output: 500v
Limit: 1.00mohm
Result: >200mohm

Leakage:
Output: 230v
Limit: 3.50mA
Result: 0.01mA

Now all passed but due to the Insulation test saying "L-N RESISTANCE..." I know that only the lead to switch will have been checked and not the whole unit...

Can please someone help in this as I'm not wanting to pass the unit even though I'm sure it IS okay?

 

[amckay]

Not sure on that one mate. Maybe download user manual, usually a free PDF format. Alternatively when it needs calibrating take it to whoever did it last and ask them?

 

[Richard Burns]

When the piece of equipment has an electronic power conversion system inside it then the tester will be attempting to measure the resistance of the electronics which could well be practically infinite resistance. Effectively, until powered up from a main supply, there is limited connection to the internal electronics.
However when you are PAT testing you can consider that the internal electronics will not present a danger as they will not be at an unsafe voltage and so you are testing to see if the 230V incoming can present a danger.
It is only when the internal workings of equipment are also at 230V that you need to get past the main switch.

 

[D J Sheridan]

Not sure on that one mate. Maybe download user manual, usually a free PDF format. Alternatively when it needs calibrating take it to whoever did it last and ask them?

Hi,
Thanks for your reply.
But I have the manual but it doesn't really say much about it. It only gives you the warnings but doesn't explain them.
I've even downloaded the updated manual and that's the same.

 

[D J Sheridan]

When the piece of equipment has an electronic power conversion system inside it then the tester will be attempting to measure the resistance of the electronics which could well be practically infinite resistance. Effectively, until powered up from a main supply, there is limited connection to the internal electronics.
However when you are PAT testing you can consider that the internal electronics will not present a danger as they will not be at an unsafe voltage and so you are testing to see if the 230V incoming can present a danger.
It is only when the internal workings of equipment are also at 230V that you need to get past the main switch.

Hi Richard,
I see what you mean, but I'm worried due to the case of the equipment being metal although black powder coated.
The unit works fine and I've touched all external screws that go into the chassis and nothing wrong...
I feel there ought to be better clarification on why these things happen...

I suppose I'm really wanting peace of mind that if the above readings (sans the Insulation one) are okay does this mean the unit is fit for use?
Yes it should be Earth Bond, then Insulation, then Leakage but what if the readings on the Insulation are over the limit?

 

[Richard Burns]

The results you have shown there all demonstrate that the equipment is safe to use, obviously assuming the tests were carried out correctly and that the rest of the inspection was OK.

The warning is there to ensure you have actually got the appliance connected, although electronic power supplies will confuse the issue.

For the particular appliance so long as the insulation resistance from the incoming supply to the casing is high enough then there should be no problem.
If the appliance is class I then the casing should be connected to earth and the test will confirm everything is OK.
If the appliance is class II then the casing should be insulated from both earth and the supply, the testing you do will have confirmed that this is the case.

If the insulation resistance test shows a value lower than the permitted level then this would be a fail, if the insulation resistance test shows a reading that is above the maximum measurement for the instrument (as in your >200MΩ) then this is a very satisfactory reading and a pass.

The leakage test is an alternative to the insulation resistance test and only needs to be done where the IR cannot be done.

 

[D J Sheridan]

The warning is there to ensure you have actually got the appliance connected, although electronic power supplies will confuse the issue.

Yes the switch was on and the fuse is okay... The warning only comes up when the switch is off or the fuse has gone. But it seems to come up when on certain appliances...

For the particular appliance so long as the insulation resistance from the incoming supply to the casing is high enough then there should be no problem.
If the appliance is class I then the casing should be connected to earth and the test will confirm everything is OK.
If the appliance is class II then the casing should be insulated from both earth and the supply, the testing you do will have confirmed that this is the case.

It was a Class 1

If the insulation resistance test shows a value lower than the permitted level then this would be a fail, if the insulation resistance test shows a reading that is above the maximum measurement for the instrument (as in your >200MΩ) then this is a very satisfactory reading and a pass.

As stated on this:-
Insulation:
Output: 500v
Limit: 1.00mohm
Result: >200mohm

Surely the limit here is 1mohm but the test result was >200mohm... so wouldn't this indicate a fail?

The leakage test is an alternative to the insulation resistance test and only needs to be done where the IR cannot be done.

So I'm still at a loss if this was okay on the insulation test... re the limit and result.

 

[Engineer54]

Surely the limit here is 1mohm but the test result was >200mohm... so wouldn't this indicate a fail?

Limit in this case meaning ''minimum'' (1 Mohm) !! Anyway, why on earth would you think that an insulation test with a value of inexess (eg ''>'') of 200 Mohm would indicate a fail?? There isn't much out there, that would require an insulation test to be over 200 million ohms!! lol!!

 

[D J Sheridan]

Limit in this case meaning ''minimum'' (1 Mohm) !! Anyway, why on earth would you think that an insulation test with a value of inexess (eg ''>'') of 200 Mohm would indicate a fail?? There isn't much out there, that would require an insulation test to be over 200 million ohms!! lol!!

I do see what you mean but I was referring to the limits posed on the PAT machine.

The other results...

Earthbond:
Output: 10A
Limit: 0.10ohm
Result: 0.07ohm

Insulation:
Output: 500v
Limit: 1.00mohm
Result: >200mohm

Leakage:
Output: 230v
Limit: 3.50mA
Result: 0.01mA

... show accordingly they were not over their limits tested - but the Insulation test does show over (limit 1.00mohm and result >200mohm).
It's this differential I can't make out...

Re:
L-N RESISTANCE TOO HIGH (>30 kohms)
CHECK FUSE OR SWITCH
Do you wish to PROCEED
(Y/N)

Slap me silly!

 

[Richard Burns]

This is very very very basic understanding of what you are measuring and why.

For insulation resistance you are measuring to ensure that the resistance between two conductors, that should not be connected, is sufficiently high to ensure that there is no danger.
So the higher the result the better, the limit is a minimum limit.

For the earth bond test you are measuring the resistance of the connection to earth from the equipment, this resistance should be as low as possible for safe connection and so the limit is a maximum limit.

For the leakage test you are measuring the amount of current that might leak from the appliance (and so through anyone touching it) the lower the leakage current the safer the equipment is. The limit is a maximum limit.

 

[D J Sheridan]

This is very very very basic understanding of what you are measuring and why.

For insulation resistance you are measuring to ensure that the resistance between two conductors, that should not be connected, is sufficiently high to ensure that there is no danger.
So the higher the result the better, the limit is a minimum limit.

For the earth bond test you are measuring the resistance of the connection to earth from the equipment, this resistance should be as low as possible for safe connection and so the limit is a maximum limit.

For the leakage test you are measuring the amount of current that might leak from the appliance (and so through anyone touching it) the lower the leakage current the safer the equipment is. The limit is a maximum limit.

Consider me slapped!
I did think that was the case (insulation) but was going by too much resistance (as in switch not on and fuse blown - would indicate unlimited resistance) was a fail.

What I really need now is to find out why it occurs on certain appliances. As mentioned earlier it is possibly down to the internal electronics... but would like clarification as such... so might try contacting Metrel and see what's what.

A HUGE THANKS to all here.