Was called by my sister to help with a situation she encountered when she moved in to a new (to her) house. She assumed that this would be a simple issue for me and I did as well,, at least at first.
House she moved in to is a 1950's era farm house. kitchen wiring appears to be original (cloth insulation, two wire, no EGC) but outlets have been updated to GFCI outlets. The house came with a propane range. She brought her refrigerator (about two years old) with her. The only outlet within reach of the refrigerator was the outlet in which the propane range was already plugged in to which is a standard NEMA 5-15 receptacle which is fed from the load side of a 5-20 GFCI receptacle on the other side of the kitchen. No EGC is supplied to the receptacle.
Propane range functioned normally prior to installing the fridge and caused no issues even when utilizing the electric ignitor. However, once the fridge was plugged in to the same receptacle the GFCI would trip, sometimes immediately, and sometimes after several minutes. This would occur regardless of whether or not the range was being actively used.
I verified that the range alone did not trip the GFCI. I then plugged in only the fridge and it alone did not trip the GFCI. Only when both were plugged in did the GFCI trip. Naturally one would assume that there was a small amount of leakage current from each device that when added together would surpass the threshold of the GFCI and cause a trip. However, upon thinking about it, I considered this unlikely since there was no EGC and the appliances sat upon a ceramic tile floor in a house built over a crawlspace.
So after staring at the situation for a while and thinking it over I realized that the propane line running to the range was uninterrupted copper pipe that ran from the range into the ground in the crawlspace and emerged from the ground near the propane tank. So now I knew that the range and the fridge were being "grounded" through the propane line that connected to the chassis of the range which was in turn bonded to the EGC in the range cord which then created a path to ground through the outlet ground for the fridge.
Based on a few hunches, I plugged the range into the receptacle normally and then used a grounding adapter to plug the fridge into the outlet as well so that the EGC in the fridge cord would no longer have continuity with the receptacle and therefore the "ground" provided through the propane line. Now the GFCI holds. I then took some measurements and this is where it really gets bizarre. The voltage between the fridge chassis and the "grounded" range chassis was 22V. I should also mention that the fridge was plugged into a 5-15 outlet (non-GFCI) at her previous house which she says she feels sure was grounded because the "grounded" LED on her surge protector she once used for the fridge used to stay lit.
Out of curiosity, I place the back of my hand on the range and touched the fridge with my elbow expecting to sense a shock. I did not feel anything. However, I did hear a very faint buzzing sound when I bridged the two appliances with my arm. I used a different multimeter to check the values from before and confirmed the 22V to ground on the fridge frame. However, this meter gave me a frequency reading (the other meter did not have that feature) of 2.4kHz !? I initially doubted that reading, but it would explain the buzzing sound and the fact that I didn't feel a shock.
So, thoughts? Ultimately, the kitchen is going to be rewired completely. But, what do you suspect is going on here? is the fridge defective? Will is trip a rewired GFCI circuit that has a EGC? Or is something going on here that is just outside my experience that maybe one of you has encountered?
House she moved in to is a 1950's era farm house. kitchen wiring appears to be original (cloth insulation, two wire, no EGC) but outlets have been updated to GFCI outlets. The house came with a propane range. She brought her refrigerator (about two years old) with her. The only outlet within reach of the refrigerator was the outlet in which the propane range was already plugged in to which is a standard NEMA 5-15 receptacle which is fed from the load side of a 5-20 GFCI receptacle on the other side of the kitchen. No EGC is supplied to the receptacle.
Propane range functioned normally prior to installing the fridge and caused no issues even when utilizing the electric ignitor. However, once the fridge was plugged in to the same receptacle the GFCI would trip, sometimes immediately, and sometimes after several minutes. This would occur regardless of whether or not the range was being actively used.
I verified that the range alone did not trip the GFCI. I then plugged in only the fridge and it alone did not trip the GFCI. Only when both were plugged in did the GFCI trip. Naturally one would assume that there was a small amount of leakage current from each device that when added together would surpass the threshold of the GFCI and cause a trip. However, upon thinking about it, I considered this unlikely since there was no EGC and the appliances sat upon a ceramic tile floor in a house built over a crawlspace.
So after staring at the situation for a while and thinking it over I realized that the propane line running to the range was uninterrupted copper pipe that ran from the range into the ground in the crawlspace and emerged from the ground near the propane tank. So now I knew that the range and the fridge were being "grounded" through the propane line that connected to the chassis of the range which was in turn bonded to the EGC in the range cord which then created a path to ground through the outlet ground for the fridge.
Based on a few hunches, I plugged the range into the receptacle normally and then used a grounding adapter to plug the fridge into the outlet as well so that the EGC in the fridge cord would no longer have continuity with the receptacle and therefore the "ground" provided through the propane line. Now the GFCI holds. I then took some measurements and this is where it really gets bizarre. The voltage between the fridge chassis and the "grounded" range chassis was 22V. I should also mention that the fridge was plugged into a 5-15 outlet (non-GFCI) at her previous house which she says she feels sure was grounded because the "grounded" LED on her surge protector she once used for the fridge used to stay lit.
Out of curiosity, I place the back of my hand on the range and touched the fridge with my elbow expecting to sense a shock. I did not feel anything. However, I did hear a very faint buzzing sound when I bridged the two appliances with my arm. I used a different multimeter to check the values from before and confirmed the 22V to ground on the fridge frame. However, this meter gave me a frequency reading (the other meter did not have that feature) of 2.4kHz !? I initially doubted that reading, but it would explain the buzzing sound and the fact that I didn't feel a shock.
So, thoughts? Ultimately, the kitchen is going to be rewired completely. But, what do you suspect is going on here? is the fridge defective? Will is trip a rewired GFCI circuit that has a EGC? Or is something going on here that is just outside my experience that maybe one of you has encountered?
