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Discussion Starter · #1 ·
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.



 

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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.
always looking to learn so would you explain how a megger test will show a weak ground? I have only used them to test insulation and motor windings for faults
 

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Discussion Starter · #3 ·
always looking to learn so would you explain how a megger test will show a weak ground? I have only used them to test insulation and motor windings for faults
I'm hoping that if it is a weak ground connection it will open under the high voltage, a meter don't always put out enough to breakdown the connection.
 

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PPE Saves Fingers
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If you're 1 ohm reading from one machine to the other, then I'd say they're both grounded, and you're reading from the metal, through the bond, back to the nearest common point.

The 150 volts sounds like you have a fault in one. Depending on the nature of the machine, you'd probably be better off disconnecting the machines and measuring hot to ground on each, first with a regular meter, then megger if you don't get any readings.
 

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Discussion Starter · #5 ·
If you're 1 ohm reading from one machine to the other, then I'd say they're both grounded, and you're reading from the metal, through the bond, back to the nearest common point.

The 150 volts sounds like you have a fault in one. Depending on the nature of the machine, you'd probably be better off disconnecting the machines and measuring hot to ground on each, first with a regular meter, then megger if you don't get any readings.
All voltage reading are good to ground, Readings from all voltage sources to both grounds all equal. Yea I know one of the heater elements may be going bad but I still should not read 150 vac to ground from machine to machine, that is what I am looking to find out before I fix the heater ( machine is not being used right now so no hazard exists)
 

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If you're 1 ohm reading from one machine to the other, then I'd say they're both grounded, and you're reading from the metal, through the bond, back to the nearest common point.

The 150 volts sounds like you have a fault in one. Depending on the nature of the machine, you'd probably be better off disconnecting the machines and measuring hot to ground on each, first with a regular meter, then megger if you don't get any readings.
Or is reading phantom voltage due to the type of DMM
 

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Donuts > Fried Eggs
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Nah, something doesn't add up. Even if this was induced, you don't get phantom voltage between objects that are bonded together.

A megger is extremely low current, it's not gonna be useful for showing you if there's a high-resistance ground, on the contrary the high voltage will very likely push right through it and show it as a dead short. You need a high current source to expose that.
 

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Discussion Starter · #10 ·
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
 
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