I have a wall in my garage which has (on the same circuit with a breaker) 4 outlets and an outdoor light with a switch. For the sake of this question and attempted schematic below, I will use the following notations:
14 gauge three strand wiresource lines into a junction / outlet box
^to denote a line leaving the box / switch (
14 gauge 4 strand wire)
+to denote a wire splice / junction box
(s) to denote a switch
PS denotes the input power from the box with circuit breakers
and single letters labeling wall outlets
PS | ---+--- ^ | | (S)-B | D -----C-------------A
So what I hope is clear from this diagram is that the line that feeds the wall in question from my garage electrical box is spliced in the attic and feeds two lines - (1) the B line which consists of an outlet (B) a switch, and a light; and (2) the A line which has three outlets, (A & C & D) chained together in series. For clarity on this question, all tests have been verified with and without an outlet - and the GFCI was removed for diagnostic clarity.
The point of this question is that outlets C & D report an open ground on using a an outlet tester. A & B are fine, and this has been verified with direct continuity testing to the circuit panel box.
- The first thing I did was to thoroughly wire the grounds in the outlet boxes of C & D.
- When this didn't work, I tested for continuity between grounds C & D --- Grounds were continuous
- So then I tested for continuity between grounds C and A --- NO GROUND CONTINUITY
- Tested for continuity between white wires in C and A --- White wires were continuous as expected as the outlet receives power
- Tested for continuity between black wires in C and A --- Black wires were continuous as expected as the outlet receives power
- Similarly - Tested for continuity between grounds C and the Circuit breaker box (PS) --- NO GROUND CONTINUITY
- Tested continuity between White and Ground wires in A - Continuous as expected.
- Traced the location of my wire using a cheap(ish) circuit tracer and know roughly where my lines are behind the finished insulated wall.
- Tried connecting the circuit tracer in various pair combinations between the white, black, and ground wires of A and C
So I see a few possibilities to explain the broken ground:
- there is a physical wire break somewhere, anywhere between A and C
- there may be a outlet box behind the drywall somewhere, which I've been unable to find with a level or magnets, and like outlets C & D did not get a properly wired ground connection
There's a few things confusing me however:
- When I apply the energized probe of the circuit tracer direct to the ground wire in A the entire wall gets energized and the probe is overwhelmed by signal. I don't expect drywall or paint to be electrical conductors so I'm truly shocked that a couple of AA batteries are energizing the wall with a field that the induction wand is picking up on so strongly (several feet away). Anyone have any thoughts or explanations?
- When I try this on the ground wire at outlet C, I can't reproduce the overwhelming positive signal. Instead the signal during testing is only ever so slightly higher than signal detected when using two insulated wires (black and white). Even in this case I have to have the probe right up against the wall. To me this makes sense as I think the two electric fields being sent down each strand of the wires connected to the tester (not continuous) are detectable with the induction wand (probe) and if one isn't insulated that signal will be a bit stronger with less insulation based field attenuation.
- Unfortunately this cheap electric field induction tester isn't precise enough to find a broken wire. I bought it hoping there would be a significant signal drop off, but this wasn't the case. Anyone know of a trick to make these scanners a little more sensitive (I've tried what I think is referred to as a remote ground, but with no noticeable difference)?
A friend has suggested that a drywall screw may have broken the ground wire and has remained in direct contact effectively bridging the ground (energized during testing) with the drywall, dust, paint, and whatnot on the wall. Anyone ever seen this before? Any good way of finding the offending screw invisible under paint and/or mud?
When I test continuity between White and Ground in A it's continuous - as expected, but for some reason this isn't enough to make the ground in C when the outlet is wired up and you'd expect continuity given that the neutral whites are continuous between A & C. Would the broken ground explain this? Or does this hint at more fundamental problems in outlet box C?
Thanks for the help!