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Recently my radon fan stopped working. I traced the line from my breaker in the basement to the unit. At one point in the basement, my voltage detector shows that the voltage stops/drops in the wire, just before it enters the wall to the outside of the house where the fan is located.

My first guess is that the copper wire in the romex broke -- but that seems odd, since the wire hasn't moved or come into contact with anything.

Is it possible that there are other reasons that the voltage would drop right at this point? I've attached pictures for reference. Thanks.

Update

I stripped the white sheathing from the cable to see if there were any breaks/punctures in the wire. I found none. However, right at the point where I lose voltage, there is oxidation (green) on the bare copper ground wire. This leads me to believe that moisture has entered from the outside into the wiring. Not good. I think the best bet is to pull new wire from the outside fan and connect via junction box in the basement. I will post a picture later. Thanks for all the comments!

Voltage

No Voltage

nobody
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shackleton
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  • What's on the run aside from the fan? – Ram Jan 10 '24 at 00:20
  • Good question - the fan is the only unit. The breaker was installed specifically for the fan. – shackleton Jan 10 '24 at 00:22
  • In that spot, I would think a wonky tester. It is possible that the wire was broken before and something happen that just moved the ends far enough apart to cause it. – crip659 Jan 10 '24 at 00:22
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    If it is a break in the wire, somehow at that location, wiggling the romex with the tester on the dead part should result in it lighting up / flashing as the broken wire makes contact. – Ram Jan 10 '24 at 00:25
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    If the wire is broken, it will be simple to add a junction box there with the extra loop of cable straighten out. – crip659 Jan 10 '24 at 00:27
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    IMO -- no power at the device, plus the test you've pictured --- that's enough evidence to do a destructive test, IE cut the cable just to the panel side of that last staple, ensure power there, then decide what to do. If the cable isn't too long end to end, replace the whole thing. Otherwise put a junction box a foot to the right of the photos and use the bit on the left to pull a new length of cable through the wall to the new box. "Too long" is defined by your appetite to pay for new cable. – jay613 Jan 10 '24 at 02:56
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    Please don't put your answer as and "Update..." edit in the question. Properly post it down below. Also be sure to up vote any and all answers that helped you and give a check mark to the one that helped the most. TBH, I'd put your "update" in a comment on Robert Chapin's answer and give him the check mark. – FreeMan Jan 10 '24 at 19:10
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    Installer in a hurry: "Oh no, I stapled through the cable!" -> pulls by the cable to remove the staple -> "Oh good, only outer insulation damaged, I'll put a new staple on it." But not realizing they've broken the conductors when pulling off the staple. – jpa Jan 11 '24 at 06:24

2 Answers2

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Based on that photo, I'd take an extremely thorough look at the staple nails. If you nailed through the cable you might have an energized nail, so be cautious.

Your tester is going to read high voltage some distance away from where the actual break is, so I'm suspecting it's closer to the staple anyway.

illustration

Robert Chapin
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    If you zoom in to the staple on the first picture it even looks like the insulation on the bottom wire is broken,, might just be a paint fleck but looks suspicious – Alan Birtles Jan 10 '24 at 08:22
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    Exactly. I bet there's 1 or 2 holes in the hot wire where the installer screwed up and then moved the staple. Looks like defective workmanship. – Robert Chapin Jan 10 '24 at 13:03
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    You are correct -- there is a break in the sheathing where the installer must have nailed through mistakenly. I've stripped it down now but the hole did not puncture the inner wire sheathing -- just the outer. So, the copper is fine. – shackleton Jan 10 '24 at 19:00
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    @shackleton if they've done it once, it's not unlikely they've done it twice, I'd guess another staple has the same problem which is what's causing your issue. Mains wiring doesn't just break on its own, there must be some external factor – Alan Birtles Jan 11 '24 at 12:30
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    Thanks all. The plan now is to replace the wire to the left of the staples and connect old to new in a junction box. – shackleton Jan 11 '24 at 15:19
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    A few more updates: I pulled everything apart. The installer had used standard 14/2 wire outside the house in the PVC conduit. The inside of the wire (paper coating around ground) was soaked in water. I'm redoing it all with UF-B cable. The fan motor was also dead. Thanks again. – shackleton Jan 13 '24 at 19:48
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I wouldn't put too much stock in what the NCVT says without additional tests to correlate. They're a "quick and dirty" or "best guess" kind of tool.

If you want to know whether the cable is interrupted or not:

  1. de-energize the cable
  2. short together two of the conductors at one end
  3. measure resistance from the other end of the cable.

If resistance between the shorted pair comes up anything more than just a few ohms then yes at least one of the conductors is damaged/open somewhere along the path. You can test the cable more thoroughly if desired by iterating through combinations of the pairs of conductors, open and shorted.

If you do find that a conductor is open then I'd say "Wow, ok, maybe the NCVT is on to something. Let's cut the cable here and test with the multimeter to confirm."

Greg Hill
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