Shocking dryer revelation

The following is info that may help others in the future.

Complaint:

HO getting shocks, not static, from gas dryer (electric motor). It's plugged into a relatively new GFCI receptacle. GFCI never trips. The floor is tile.

The wiring has 'iffy' grounding. You may have a ground wire, but no actual ground. That's probably from scabbing from a 2 wire circuit with a three wire cable.

Test 1:

Place stainless steel bowl on dry floor near dryer. Measured 105 volts w/ high impedance meter from bowl to dryer door hinge.

At first, I suspected a fault in the dryer, but my instincts were leaning toward not.

Test 2: Run extension cord from GFCI receptacle into kitchen and check voltages from cord to water pipe. Found hot and neutral reversed.

Test 3: Found j-box w/ 3 three wire NMS cables. One old, two newer for the addition we were in. All the colors were connected right. There was even a ground wire there! No ground. Just a wire. Found that the old NMS was connected at the other end somewhere with black as neutral, white as hot.

Test 4: My Greenlee tick tracer is GREAT at locating hot vs. neutral if you know how to do it. I turned it on and it would indicate anywhere near the dryer. It would also indicate the proper hot wire. I was impressed.

The fix: Remarked and reversed the old NMS.

Verification: 1 volt from dish on floor to dryer hinge. Test at cord to H2O pipe showed correct polarity. Apprehensive HO No longer gets shocked, even barefoot. Tick tracer no longer indicates, even actually touching the dryer.

So, here is what I learned.

GFCI receptacles DO NOT prevent shocks. They may prevent bad ones, but not 'hefty' ones as the HO described.

My Greenlee tick tracer is the quickest way to check for hot/neutral rev. where there is no electrical ground close by. Much easier than dragging an extension cord to the nearest metal pipe or back to the service.

A stainless steel bowl makes a good test contact point and isn't as messy as water.
 
Last edited:

StarCat

Industrial Engineering Tech
Location
Moab, UT USA
Occupation
Brewery Engineering Plant Technician - HVACR Electrical and Mechanical Systems
Excellent

Excellent

Great information.

SC
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
...
GFCI receptacles DO NOT prevent shocks. They may prevent bad ones, but not 'hefty' ones as the HO described.
...
The shock has to occur before the GFCI can react...The GFCI can only limit the duration of the shock.

There is a time to trip curve that for the GFCI, and while most GFCIs trip much before the maximum permitted time, the UL standard would permit the GFCI to take ~2.7 seconds before tripping on a 10mA ground fault.
 

growler

Senior Member
Location
Atlanta,GA
GFCI receptacles DO NOT prevent shocks. They may prevent bad ones, but not 'hefty' ones as the HO described.
This one wasn't opening anything! It never tripped. I tested with test button and it checked out OK.

So you had reversed polarity and customer was getting shocked.

Most of the new GFCIs won't even work with the polarity reversed. I have seen some of the older/cheaper one's that would feed through like a regular receptacle if polarity was reversed and wouldn't trip.

I would change out the GFCI to a newer and better quality one.
 

growler

Senior Member
Location
Atlanta,GA
Place stainless steel bowl on dry floor near dryer. Measured 105 volts w/ high impedance meter from bowl to dryer door hinge.
The shock has to occur before the GFCI can react...The GFCI can only limit the duration of the shock.

For him to measure 105 volts from a tile floor (bowl) to the dryer door the tile must have been damp and grounded.

With the hot connected directly to the frame of the dryer ( had to be ) this should have been enough to trip a functioning GFCI.

I would have checked by shorting the frame of the dryer to a know good ground useing an extension cord. That should have tripped the GFCI.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
For him to measure 105 volts from a tile floor (bowl) to the dryer door the tile must have been damp and grounded.
Bus since a high impedance meter was used we have no idea of how much current could flow.
With the hot connected directly to the frame of the dryer ( had to be ) this should have been enough to trip a functioning GFCI.
It didn't so I would expect that the leveling feet on the bottom of the dryer provided isolation, many have non-conductive pad on the bottom of the feet.
I would have checked by shorting the frame of the dryer to a know good ground useing an extension cord. That should have tripped the GFCI.
That would not be a good idea if you think the hot is connected to the dryer frame. The use of a test lamp or solenoid type voltage tester would be a better choice for that test. Those items would limit the current, but still get you the information you are looking for.
 

mbrooke

Batteries Not Included
Location
United States
Occupation
*
This one wasn't opening anything! It never tripped. I tested with test button and it checked out OK.
I know, but point Im trying to make, if one was to bootleg a ground from a neutral in a j box, and that neutral was to open, and even if the GFI did trip, the metal frame would remain energized. Not exactly your case, but just another example of what a GFCI wont stop, and why its dangerous to boot leg grounds in old buildings.
 

growler

Senior Member
Location
Atlanta,GA
HO getting shocks, not static, from gas dryer (electric motor).

The wiring has 'iffy' grounding. You may have a ground wire, but no actual ground.
I know, but point Im trying to make, if one was to bootleg a ground from a neutral in a j box, and that neutral was to open, and even if the GFI did trip, the metal frame would remain energized. Not exactly your case, but just another example of what a GFCI wont stop, and why its dangerous to boot leg grounds in old buildings.

You have to wonder how the frame of the dryer was energized even with the reversed polarity. Was the cord pinched on the neutral at the connector? Was the neutral and ground bonded in the machine?

If the frame wasn't energized how did the customer keep getting shocked? If it was static then then without a ground there wouldn't have been a path to bleed off the static charge. Don's right the feet may have been insulated. Dryers do produce a lot of static electricty.
 

mbrooke

Batteries Not Included
Location
United States
Occupation
*
You have to wonder how the frame of the dryer was energized even with the reversed polarity. Was the cord pinched on the neutral at the connector? Was the neutral and ground bonded in the machine?

If the frame wasn't energized how did the customer keep getting shocked? If it was static then then without a ground there wouldn't have been a path to bleed off the static charge. Don's right the feet may have been insulated. Dryers do produce a lot of static electricty.

That's what Im thinking. First scenario that comes to mind is the ground is bootlegged at the GFI and the neutral was reversed up stream like mentioned.

Normally even a large appliance like a fridge or dryer doent shock even with the ground wire disconnected. Dryer could have an electronic dryness control with a shorted resistor leaking to the chassis? Its a random guess but who knows. Other than that an internal neutral to ground fault which would then require serving the dryer and would imagine trips the GFI one connected to ground.


Believe it or not if one was to fully isolate a large appliance from ground with a fault in it the GFCI wouldn't disconnect.

I remember Mike Holt even bring up that if a hair dryer was dropped in a fully insulated swimming pool a gradient potential would exist around it but no ground path to show a current difference at the GFCI.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Yes, just as you could be fatally shocked if you put yourself in series with either a grounded or ungrounded conductor or bridged yourself from hot to neutral.
Nothing there for the GFCI to see, move along now.

Tapatalk!
 
Hello,

I would agree on replacing the GFCI receptacle. Class "A" GFCI are required to trip at >5-6 mA if I remember correctly. If that is not the right amount: someone, please, clarify.


I noticed everyone is concerned with the voltage, GFCIs do not trip because of voltage...They trip because of the current difference between the hot and neutral conductors. There is no load so there is no current draw.







The following is info that may help others in the future.

Complaint:

HO getting shocks, not static, from gas dryer (electric motor). It's plugged into a relatively new GFCI receptacle. GFCI never trips. The floor is tile.

The wiring has 'iffy' grounding. You may have a ground wire, but no actual ground. That's probably from scabbing from a 2 wire circuit with a three wire cable.

Test 1:

Place stainless steel bowl on dry floor near dryer. Measured 105 volts w/ high impedance meter from bowl to dryer door hinge.

At first, I suspected a fault in the dryer, but my instincts were leaning toward not.

Test 2: Run extension cord from GFCI receptacle into kitchen and check voltages from cord to water pipe. Found hot and neutral reversed.

Test 3: Found j-box w/ 3 three wire NMS cables. One old, two newer for the addition we were in. All the colors were connected right. There was even a ground wire there! No ground. Just a wire. Found that the old NMS was connected at the other end somewhere with black as neutral, white as hot.

Test 4: My Greenlee tick tracer is GREAT at locating hot vs. neutral if you know how to do it. I turned it on and it would indicate anywhere near the dryer. It would also indicate the proper hot wire. I was impressed.

The fix: Remarked and reversed the old NMS.

Verification: 1 volt from dish on floor to dryer hinge. Test at cord to H2O pipe showed correct polarity. Apprehensive HO No longer gets shocked, even barefoot. Tick tracer no longer indicates, even actually touching the dryer.

So, here is what I learned.

GFCI receptacles DO NOT prevent shocks. They may prevent bad ones, but not 'hefty' ones as the HO described.

My Greenlee tick tracer is the quickest way to check for hot/neutral rev. where there is no electrical ground close by. Much easier than dragging an extension cord to the nearest metal pipe or back to the service.

A stainless steel bowl makes a good test contact point and isn't as messy as water.
 

kwired

Electron manager
Location
NE Nebraska
That's what Im thinking. First scenario that comes to mind is the ground is bootlegged at the GFI and the neutral was reversed up stream like mentioned.

Normally even a large appliance like a fridge or dryer doent shock even with the ground wire disconnected. Dryer could have an electronic dryness control with a shorted resistor leaking to the chassis? Its a random guess but who knows. Other than that an internal neutral to ground fault which would then require serving the dryer and would imagine trips the GFI one connected to ground.


Believe it or not if one was to fully isolate a large appliance from ground with a fault in it the GFCI wouldn't disconnect.

I remember Mike Holt even bring up that if a hair dryer was dropped in a fully insulated swimming pool a gradient potential would exist around it but no ground path to show a current difference at the GFCI.
A bootlegged neutral does sound like a good possibility, that would put any voltage drop on the neutral on the appliance frame, or full voltage on the frame if polarity is reversed, and neither would be a fault the GFCI is designed to detect. Someone mentioned new GFCI's will detect polarity reversal, I don't see how that is possible unless they monitored the EGC somehow, they are designed to not reset if "line" and "load" conductors are reversed though, but will stay set if line and load become reversed. It has to trip first and then will not reset if power is not supplied to the Line terminals.

Hello,

I would agree on replacing the GFCI receptacle. Class "A" GFCI are required to trip at >5-6 mA if I remember correctly. If that is not the right amount: someone, please, clarify.


I noticed everyone is concerned with the voltage, GFCIs do not trip because of voltage...They trip because of the current difference between the hot and neutral conductors. There is no load so there is no current draw.
Trip level is 4-6 mA, you are correct they do not care about voltage or actual load current, they need voltage to operate the logic circuits, not sure what the minimum voltage may need to be, but otherwise are only looking for current on conductor "hot" to be within 4-6 mA of the current on conductor "N" of a basic 2 pole GFCI device.
 

steve66

Senior Member
So you had reversed polarity and customer was getting shocked.

Most of the new GFCIs won't even work with the polarity reversed. I have seen some of the older/cheaper one's that would feed through like a regular receptacle if polarity was reversed and wouldn't trip.

I would change out the GFCI to a newer and better quality one.
But it sounds like the ground was unconnected at the dryer, and probably at the receptacle too.

Without a ground, the receptacle would have no way to tell the difference between the line and the neutral. So it didn't know it was reverse wired.

Maybe they should start making GFCI's for grounded systems that won't work without a good ground connection. Then they would have to make different GFCI's for use where there isn't a ground wire.

Or maybe they should add a "ground test" button that tells you if the ground wire is actually connected to the neutral at some point.
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
I noticed everyone is concerned with the voltage, GFCIs do not trip because of voltage...They trip because of the current difference between the hot and neutral conductors. There is no load so there is no current draw.
The voltage was noted as read with a high impedance meter to show that it is more likely a polarity reversal on a supposedly grounding wire than simple capacitive leakage (which would more likely read in the neighborhood of 60 volts on a 120V circuit.
The concern about the GFCI not tripping related to the moments when the owner felt a shock. At those times there was a load, but we do not know the current associated with it.
 

kwired

Electron manager
Location
NE Nebraska
But it sounds like the ground was unconnected at the dryer, and probably at the receptacle too.

Without a ground, the receptacle would have no way to tell the difference between the line and the neutral. So it didn't know it was reverse wired.

Maybe they should start making GFCI's for grounded systems that won't work without a good ground connection. Then they would have to make different GFCI's for use where there isn't a ground wire.

Or maybe they should add a "ground test" button that tells you if the ground wire is actually connected to the neutral at some point.
No GFCI that I am aware of has a reference to an equipment grounding conductor and none of them care what voltage is from either protected conductor to equipment ground. That is not what they are designed to do. They only monitor for balanced current between hot and neutral, or in the case of a 120/240 GFCI breaker they monitor for balance between all three load conductors. Anything that goes out one conductor has to come back on another protected conductor (within 4-6 mA max lost) or it will trip. Does not matter what is grounded, what is not grounded or if there is any ground period in the particular system it is connected to. You not only can have a trip from current of the protected circuit being lost, you can also have a trip if some foreign circuit somehow introduces current into the protected circuit - like mixing up protected and non protected neutral (or hot) conductors at a junction box into the same splicing device.

Levington makes a GFCI that will not reset if line and load are reversed or the internal GFCI circuitry is broken.
I believe that is a UL standard (for about 4-5 years now) and all GFCI receptacles will not reset if line and load are reversed. Thing is you can reset the device, then power it down, reverse the line and load conductors and it will continue to operate - until it is tripped- then it will not reset until line and load conductors are properly connected. They protect you when new because they leave the factory in a tripped state, but connect one that had been reset and this protection only kicks in once it has tripped.

The voltage was noted as read with a high impedance meter to show that it is more likely a polarity reversal on a supposedly grounding wire than simple capacitive leakage (which would more likely read in the neighborhood of 60 volts on a 120V circuit.
The concern about the GFCI not tripping related to the moments when the owner felt a shock. At those times there was a load, but we do not know the current associated with it.
Chances are the current was outside the protection that the GFCI can provide, like the incoming EGC was somehow connected to an ungrounded conductor somewhere, the GFCI will not monitor the EGC at all.

Even if the "shock" current was passing through a properly functioning GFCI it must be beyond the trip curve of the GFCI before it will trip. 5 mA may not trip it, but a person will definitely feel 5 mA and it will be more than a little tingle. If you want to play with this then plug a GFCI tester into a receptacle with a missing/malfunctioning EGC and a metallic WP cover or something similar that you will easily be touching while testing, and then press the test button on your testing device - unless you are well insulated it very likely will knock you on your behind.
 
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