Heat tape install/testing in horse stalls

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Last one, would the horses be in any danger while I conduct megger tests in the barn? Perhaps I should make sure none are leaning on the pipes as I hit the test button?
 
When I megger with my Fluke 1507 and something tests bad, it pulls the test voltage down to almost nothing. I wouldn't worry about the horses touching a metal fence...

But, if the horses throw their heads up in the air and run from the barn, I may have been wrong.:)
 
I went to the stalls this morning and this is what I found. The first thing I learned was I must be losing my mind. Last night I prepared my megger for it's maiden voyage by wiping the dust off it's case and put batteries in it. I didn't realize I had left it at home until I got to the job, 45 minutes away, Doh! While there the install didn't seem as complex as I had originally thought. The cables, Raychem self regulating w51 series, were either 50' or 100' in length as indicated on the cable's label. They were plugged into standard GFCI's. I checked the t-stats along with the GFCI's and all worked fine. Since I was there, I did a continuity test between the grounded and ungrounded blades of the plug. (They were all three pronged aside from one, somehow the third prong was removed). Most of the cables showed a high resistance, well at least above 100 ohms. Three gave me much lower readings, a 26, a 10, and a 4, hmm. Not sure where to go from here and unsure if I want to make the trip again just for testing purposes. Raychem's site says to megger from the blades to the ground prong at 2500vdc and you should get at least 1 gig. Of course my meter only goes to 1000vdc but I'd like to think it would have showed me something.
 
I happened to be megging heat trace today so I'll post my results for you. I tested at 1000vdc and most of mine were testing 2.5-3 gigaohms and higher, the bad ones were .02-.04. There was no middle ground. I also ohmed the good ones L-N and they were anywhere from 100-800 ohms depending on length. This is Chromolux self regulating cable.
 
Cow said:
I happened to be megging heat trace today so I'll post my results for you. I tested at 1000vdc and most of mine were testing 2.5-3 gigaohms and higher, the bad ones were .02-.04. There was no middle ground. I also ohmed the good ones L-N and they were anywhere from 100-800 ohms depending on length. This is Chromolux self regulating cable.
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Perfect timing cow, let me ask you some questions. You mentioned there was no middle ground, were these cables plug in and if so, how exactly did you hook your megger up? Considering your L-N ohm readings, would you say the three low readings I came up with (26,10,4) indicated soon-to-be-faulty cables?
 
mark32 said:
Perfect timing cow, let me ask you some questions. You mentioned there was no middle ground, were these cables plug in and if so, how exactly did you hook your megger up? Considering your L-N ohm readings, would you say the three low readings I came up with (26,10,4) indicated soon-to-be-faulty cables?
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These are not plug in cables, they terminate in junction boxes on terminal strips. I only megger L-G. You can't meg L-N, it would just read 0.0.

I honestly can't tell you about your resistance tests and whether they are low or not. In the past I've only megged heat trace, I've never ohmed it before. I was thinking of this thread today when I was doing my testing and figured if I ohmed it you might have something to compare too. It seems if you know the voltage and the watts per foot you should be able to use ohms law to figure the resistance on a known length of heat trace, right? Or am I way off?
 
Cow said:
It seems if you know the voltage and the watts per foot you should be able to use ohms law to figure the resistance on a known length of heat trace, right? Or am I way off?
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Not for self regulating cable. The resistance varies with temperature, which is what makes it self regulating.
 
Curiosity got the best of me so I ran back to the stalls this morning to meg those cables. The L and N blades to the ground prong showed at least 1g @ 1000vdc for all the cables. So, the cables seem to be good, owner said he'll turn them on for a while when it gets cold to see if they heat up. Thanks for all the help.
 
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