Hi there,
Does any one know what kind of insulation resistance to expect for pink fibre wall/ceiling insulation? I'm trying to figure out if the cheap insulation meter I have is actually giving me a reasonable answer.
here's a bit of background:
I have a GFCI mounted in an electrical panel for a bathroom floor heating system that keeps tripping, and it seems to be erratic - sometimes it can stay on for weeks or months, other times it can trip within minutes it's not usually instantaneous. The heating control thermostat is also GFCI protected - I know I have 2 GFCIs on the same circuit, but it's one at each end of the same cable with nothing else connected. I'm reluctant to change the panel GFCI for a breaker until I know what's going on.
So, I completely disconnected the cable from the power panel and everything at the other end - which should have left a totally isolated wire. I then measured the insulation resistance with this cheap insulation meter that I was sent by accident (I had ordered something else) and I was getting a reading of about 10-20Mohm at a purported 1KV. In principle, not particularly concerning, except I was expecting an out of range reading.
I pulled the cable from the wall I know had been involved in a renovation, thinking that maybe the guy who did the bathroom had nicked the sheathing, but it was clean. I was still getting a 20-30Mohm from the freed cable end. However, I noticed that the readings changed dramatically. depending on where I probed (one probe on the cable ground wire, the other just hunting).
I found that putting the probes into the pink glass fibre insulation actually gave me a 20Mohm reading, no cable or copper involved, just probing the insulation. When the probes were close together, I got a reading of around 5-6Mohms - separating the probes in resulted in about 20Mohm, which more or less stayed constant, even when the probes were stretched as far as I could make them. Is this what you'd expect?
I suspect that the fact that I'm actually getting a reading means that the cable has been exposed somewhere, maybe squirrels, mice or a raccoon (we've had all three at some stages in the the last 20 years), and possibly the conductors are now touching the pink insulation, but not each other. But, before I cut the cable to try and isolate the problem area, it would be useful to know if I'm fighting a phantom insulation reading from a cheap Chinese meter. Just seems odd to me that the insulation resistance doesn't seem to change dramatically with probe separation. I actually have a ROD-L M100BVS5 Hipot Tester, but I would have to repair it before I could use it - I want to avoid that route if I can.
Thanks in advance for any suggestions, or help.
Peter
Does any one know what kind of insulation resistance to expect for pink fibre wall/ceiling insulation? I'm trying to figure out if the cheap insulation meter I have is actually giving me a reasonable answer.
here's a bit of background:
I have a GFCI mounted in an electrical panel for a bathroom floor heating system that keeps tripping, and it seems to be erratic - sometimes it can stay on for weeks or months, other times it can trip within minutes it's not usually instantaneous. The heating control thermostat is also GFCI protected - I know I have 2 GFCIs on the same circuit, but it's one at each end of the same cable with nothing else connected. I'm reluctant to change the panel GFCI for a breaker until I know what's going on.
So, I completely disconnected the cable from the power panel and everything at the other end - which should have left a totally isolated wire. I then measured the insulation resistance with this cheap insulation meter that I was sent by accident (I had ordered something else) and I was getting a reading of about 10-20Mohm at a purported 1KV. In principle, not particularly concerning, except I was expecting an out of range reading.
I pulled the cable from the wall I know had been involved in a renovation, thinking that maybe the guy who did the bathroom had nicked the sheathing, but it was clean. I was still getting a 20-30Mohm from the freed cable end. However, I noticed that the readings changed dramatically. depending on where I probed (one probe on the cable ground wire, the other just hunting).
I found that putting the probes into the pink glass fibre insulation actually gave me a 20Mohm reading, no cable or copper involved, just probing the insulation. When the probes were close together, I got a reading of around 5-6Mohms - separating the probes in resulted in about 20Mohm, which more or less stayed constant, even when the probes were stretched as far as I could make them. Is this what you'd expect?
I suspect that the fact that I'm actually getting a reading means that the cable has been exposed somewhere, maybe squirrels, mice or a raccoon (we've had all three at some stages in the the last 20 years), and possibly the conductors are now touching the pink insulation, but not each other. But, before I cut the cable to try and isolate the problem area, it would be useful to know if I'm fighting a phantom insulation reading from a cheap Chinese meter. Just seems odd to me that the insulation resistance doesn't seem to change dramatically with probe separation. I actually have a ROD-L M100BVS5 Hipot Tester, but I would have to repair it before I could use it - I want to avoid that route if I can.
Thanks in advance for any suggestions, or help.
Peter