60 Volt Potential on metal case of Multi-outlet assy

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Dan coulstring

Dan coulstring

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In a manufacturing facilty-operator felt a shock.

One bench with multi-outlet assy, 2-printers,1 computer and a monitor plugged in.
With meter I had 60 V between all non-current carrying metal, including case of outlet assy- and the metal frames of surrounding equipment that was powered from a different recepatcle. I tried unplugging things one at a time and only when everything was unplugged did the 60V go away.

I took the outlet assy apart and found the EGC not attached at the entry point-none of the receptacles had an EGC or the frame. Reattached

Is this now safe and where did the 60V potential come from?
 
Dan coulstring said:
In a manufacturing facilty-operator felt a shock.

One bench with multi-outlet assy, 2-printers,1 computer and a monitor plugged in.
With meter I had 60 V between all non-current carrying metal, including case of outlet assy- and the metal frames of surrounding equipment that was powered from a different recepatcle. I tried unplugging things one at a time and only when everything was unplugged did the 60V go away.

I took the outlet assy apart and found the EGC not attached at the entry point-none of the receptacles had an EGC or the frame. Reattached

Is this now safe and where did the 60V potential come from?
Click to expand...
1.It is safe now.
2. You were seeing stray voltage, either from incidental coupling from line powered elements to ground, or more likely from filters or surge protection elements in some of the equipment. The available current should be small but noticeable.
 
Dan coulstring said:
In a manufacturing facilty-operator felt a shock.

One bench with multi-outlet assy, 2-printers,1 computer and a monitor plugged in.
With meter I had 60 V between all non-current carrying metal, including case of outlet assy- and the metal frames of surrounding equipment that was powered from a different recepatcle. I tried unplugging things one at a time and only when everything was unplugged did the 60V go away.

I took the outlet assy apart and found the EGC not attached at the entry point-none of the receptacles had an EGC or the frame. Reattached

Is this now safe and where did the 60V potential come from?
Click to expand...
I may have missed something but you didn't state type of meter that you used to measure the voltage.
 
templdl said:
I may have missed something but you didn't state type of meter that you used to measure the voltage.
Click to expand...

I used a Fluke 27 and an Extech 820.
I conducted an experiment at bench-
Took a short cord with 5-15 male/female plugs-removed grounding prong on male end -left access to grounf screw on the female end.
Basically had a floating ground? Measured from the ground screw of the female plug to the conduit feeding the receptacle the cord was plugged into. Read 27 Vac with no load- and 48 Vac with a solder iron plugged in.
 
Dan coulstring said:
I used a Fluke 27 and an Extech 820.
I conducted an experiment at bench-
Took a short cord with 5-15 male/female plugs-removed grounding prong on male end -left access to grounf screw on the female end.
Basically had a floating ground? Measured from the ground screw of the female plug to the conduit feeding the receptacle the cord was plugged into. Read 27 Vac with no load- and 48 Vac with a solder iron plugged in.
Click to expand...
These are high impedance are they? In years past portable voltmeter used to draw enough current to drain the current away which resulted in little or no voltage reading at all. The only instrument that had enough impedance that was sensitive to read a voltage was the vacuum tube volt meter or VTVM. Today we have some excellent and most are extremely high impedance and are capable of measuring a voltage across about anything. As such if you have one of those analog meters with the mechanical analog swinging needle indicator meters try that. Those meter require enough current more that likely resulting in a zero volt reading. If you do get a reading then the voltage source is more than an inductive voltage.
Also, you can take a light such as one of those small 4w-7w night incandecent light bulbs and connect it across the 2 points that you are check in with your fluke while at the same time messing the voltage. Should it be an inductive voltage the bulb will drain the voltage away resulting in a reading of zero volts.
With these thoughts in mind revisit your bench test and share the results. Sometimes the readings from the modern day digital meters can be misleading.
 
But it shocked the facility operator. So it might not be phantom or induced voltage but real voltage.
 
Sahib said:
But it shocked the facility operator. So it might not be phantom or induced voltage but real voltage.
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One can feel a shock from capacitive leakage current, it just will not be as severe as the same voltage would be without benefit of current limiting from the reactive impedance. So the issue is still in doubt.
Properly bonding the EGC removed the voltage without tripping any overcurrent devices or causing any obvious equipment malfunctions, so whatever the source it is a high enough impedance to prevent a noticeable fault current.
 
GoldDigger said:
One can feel a shock from capacitive leakage current, it just will not be as severe as the same voltage would be without benefit of current limiting from the reactive impedance. So the issue is still in doubt.
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I think several kilo-volts may be required to feel a perceptible shock from induced charges on the isolated metal in the present case.
 
Some EMI filters have caps between the output's hot to ground and neutral to ground. If the EGC is missing, these caps will form a voltage divider...
/mike
 
templdl said:
I may has missed that point in you OP. If I were to have picked up on that I would have responded differently.
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" ...felt a shock...." leaves a lot of range of possible magnitude. I would consider felt a shock to be one step lower in severity than was shocked most of the time. But we do not have the details of that.
 
GoldDigger said:
" ...felt a shock...." leaves a lot of range of possible magnitude. I would consider felt a shock to be one step lower in severity than was shocked most of the time. But we do not have the details of that.
Click to expand...

Shock which is ambiguous it could be electrostatic. Without placing a load across the two points being measure in order to see if the volage could be sustained you don't know of what the source magnitude is. By placing a load of it will provide an idea of how stuff the source of the voltage is.
 
templdl said:
Shock which is ambiguous it could be electrostatic.
Click to expand...
Since it was not reported again after the EGC was connected, we can guess that it was not electrostatic, but that is not guaranteed.
If it was electrostatic, then the measured 60VAC to ground is a coincidence unrelated to the DC potential corresponding to the electrostatic shock. :)
 
The electrostatic potential is usually in kilo-volts range for an isolated metal to give even a mild shock. But the OP has not reported any high voltage but only 60V.
 
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