Just an update:
My local Lowe's was out of the Greenlee detectors but they had a couple
Fluke 1AC-A IIs in stock so I grabbed one. It's interesting that
lowes.com did not show this meter. I like that it uses AAA batteries
instead of expensive LR-44s...
Initial tests of the Fluke left me with a mixed opinion. Sensitivity is much
lower than my GE detector which is both good and bad. It was fine on 2- and
3-conductor flat cords but very sporatic on round power cords where
the inner wires are twisted. At 120V, the tip needs to be within a couple mm
of the conductor so I'm guessing it'll do poorly if the insulation is thick.
So the upshot is if you can identify individual wires, the Fluke can probably
reliably tell you which one is hot (assuming insulation isn't too thick). But
if you have a bundle or a round cable and need to know if it contains a hot
wire and can't get close to the individual wires, this Fluke isn't the right
tool.
By contrast, the GE detector's sensitivity is off the scale. The specs claim
70V-440V but it chirps when held 4 inches from a wire carrying 5VAC (of course,
it chips when held an inch from my kitchen countertop, too, so it's probably
too sensitive). The result is lots of false positives. I wish it had a meter,
or perhaps a color-changing LED, to indicate the strength of the E-M field it's
detecting.
Okay. So on to the strange readings that prompted my original post. The Fluke
meter doesn't register anything in any of these locations so this is no doubt
an artifact of the super-sensitivity of the GE detector.
Then it occurred to me that I have another way to double-check the results:
a big honkin 22" CRT that's destined for the recycling center. If there's an
E-M field near those walls, it should distort the CRT. Plugged it into
the UPS and my laptop and wheeled it around the room on a chair. Sure enough,
the CRT showed the tell-tale jitter in several spots. Almost as if there
was an induction motor nearby (there isn't). One of these days when I feel
like doing some drywalling, I'll knock a hole in that wall to see what's
in the attic behind it.
JM
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