Can I megger this

[just the cowboy]

I want to check if a ground is breaking down.
I was called out to a production line; and the mechanic said he thought he got a slight shock from a heat tunnel. I read from machine to machine (they are on casters) and got 150vac. I thought ok I have a bad heat element and ungrounded machine.
I read resistance from machine to machine 1 ohm, they are on different circuits but from the same panel. Took a Wiggins tester (clack type) and tested and did not read any voltage. Tried a current reading on 10a scale no reading it would have to be under .01 amps (lower scales on meter needs fuse). Don?t know how I could read 150vac between two machines with 1 ohm only between them.
Came back next day and went to take a current reading with another meter and all was OK no voltage or current that should not be there.

My real question is can I Megger the grounds from machine feed to machine feed with them unplugged and not screw up anything else that is fed from this panel. I can?t think how the megger test voltage would get out to anything it should only go wire to wire and out to ground before getting to anything else. The reason for this test is to see if my ground may be weak.

 

[petersonra]

if you use a high impedance meter you can read all kinds of goofy voltages on what amounts to an open circuit.

I suspect he experienced a static electric shock.

If it makes you feel any better you can bond the two pieces of equipment together.

with only 1 Ohm between the machines that is a pretty could bond.

I would not suspect any ground problems.

 

[Cow]

When I'm testing for shock potential I'll sometimes run a piece of THHN from the panel ground bar temporarily across the ground to the equipment for testing purposes. One meter lead on the THHN and the other on the equipment. Also, if you switch your meter over to ohms after checking for voltage you could verify your existing ground wire resistance.

 

[kwired]

You have already verified continuity between the two items you want to test between - you did have some resistance - 1 ohm.

All a megger is going to do is the same test with a higher test voltage. The purpose of using a megger is to find high resistances by using a higher test voltage to push more easily measurable current through the high resistance, it is not as necessary to use a high test voltage to measure low resistances.

A better test for determining integrity of a conductive path would inject a higher test current and determine integrity based on any voltage drop in the tested circuit.

 

[ATSman]

You have already verified continuity between the two items you want to test between - you did have some resistance - 1 ohm.

All a megger is going to do is the same test with a higher test voltage. The purpose of using a megger is to find high resistances by using a higher test voltage to push more easily measurable current through the high resistance, it is not as necessary to use a high test voltage to measure low resistances.

A better test for determining integrity of a conductive path would inject a higher test current and determine integrity based on any voltage drop in the tested circuit.

I agree. In this case we use a 10A Biddle DLRO meter (Digital Low Resistance Ohmmeter)
It is portable and will measure down to 1 micro-ohm.

 

[Besoeker]

I want to check if a ground is breaking down.
I was called out to a production line; and the mechanic said he thought he got a slight shock from a heat tunnel. I read from machine to machine (they are on casters) and got 150vac. I thought ok I have a bad heat element and ungrounded machine.
I read resistance from machine to machine 1 ohm, they are on different circuits but from the same panel. Took a Wiggins tester (clack type) and tested and did not read any voltage. Tried a current reading on 10a scale no reading it would have to be under .01 amps (lower scales on meter needs fuse). Don?t know how I could read 150vac between two machines with 1 ohm only between them.
Came back next day and went to take a current reading with another meter and all was OK no voltage or current that should not be there.

My real question is can I Megger the grounds from machine feed to machine feed with them unplugged and not screw up anything else that is fed from this panel. I can?t think how the megger test voltage would get out to anything it should only go wire to wire and out to ground before getting to anything else. The reason for this test is to see if my ground may be weak.

You can megger anything.
Whether it's advisable is a different matter.

If any electronic circuit will get exposed to the test voltage it's probably not a good idea.

 

[just the cowboy]

Thanks for the help

Thanks for the help

Over the weekend I came in and tested the circuit better, here's what I found.

Removed ground from machine, and got my 150vac, changed heater element problem went away, this is just what I thought was wrong with the machine.

Ran a 3000 watt load from 240v to the ground wire of the machine, Current was all over the place.
Found a bad ground connection on the back of the 60a plug. This was the ground that was bad that I was looking for.

Thanks for all the replies

 

[glennspark]

I want to check if a ground is breaking down.
I was called out to a production line; and the mechanic said he thought he got a slight shock from a heat tunnel. I read from machine to machine (they are on casters) and got 150vac. I thought ok I have a bad heat element and ungrounded machine.
I read resistance from machine to machine 1 ohm, they are on different circuits but from the same panel. Took a Wiggins tester (clack type) and tested and did not read any voltage. Tried a current reading on 10a scale no reading it would have to be under .01 amps (lower scales on meter needs fuse). Don?t know how I could read 150vac between two machines with 1 ohm only between them.
Came back next day and went to take a current reading with another meter and all was OK no voltage or current that should not be there.

My real question is can I Megger the grounds from machine feed to machine feed with them unplugged and not screw up anything else that is fed from this panel. I can?t think how the megger test voltage would get out to anything it should only go wire to wire and out to ground before getting to anything else. The reason for this test is to see if my ground may be weak.

something in the panel thats switched/timed?...

 

[glennspark]

You can megger anything.
Whether it's advisable is a different matter.

If any electronic circuit will get exposed to the test voltage it's probably not a good idea.

are you sure?

 

[glennspark]

something in the panel thats switched/timed?...

sorry....cant edit.

 

[glennspark]

You can megger anything.
Whether it's advisable is a different matter.

If any electronic circuit will get exposed to the test voltage it's probably not a good idea.

no....and a good application of the IR tester would be to set it on a low setting (a suitably low one that doesn`t risk damage to any sensitive equipment first)...then once it comes back clear....you knock it up....if not then further investigation is required to confirm there is nothing in circuit that can be damaged..

if you test both live (hot) conductors to earth (ground)...then you wont damage any connected loads will you...(apart from PCs...and other PELV)

 

[kwired]

Originally Posted by Besoeker
You can megger anything.
Whether it's advisable is a different matter.

If any electronic circuit will get exposed to the test voltage it's probably not a good idea.

are you sure?

Yes you can megger anything, as mentioned whether it is advisable is a different matter, but you sure can make the attempt. Whether it will give you information you really need is also a different matter.

 

[glennspark]

Originally Posted by Besoeker
You can megger anything.
Whether it's advisable is a different matter.

If any electronic circuit will get exposed to the test voltage it's probably not a good idea.





Yes you can megger anything, as mentioned whether it is advisable is a different matter, but you sure can make the attempt. Whether it will give you information you really need is also a different matter.

Ok...let me put it another way...

you can megger anything....

then see if it still works?...

 

[jumper]

Ok...let me put it another way...

you can megger anything....

then see if it still works?...

Basically, yes.

Note that no one said it was a good idea..........

 

[Besoeker]

​

are you sure?

You can. Whether it's advisable, safe, permitted or whether you have suitable instruments and PPE are reasons why you wouldn't/shouldn't.