Lars wrote:
On Wed 27 Apr 2005 23:35:40, Jeff Wisnia wrote:
The two questions I haven't noticed anyone asking you directly
are these:
What are you standing or sitting on and/or touching when you
feel that tingle?
I am standing on a carpet on the third floor of a building. The
carpet is 80% wool and presumably the 20% is polyester.
And, what is the "cold end" of the "screwdriver" mains tester
connected to when you see it lighting?
I myself am touching the "cold end" of the screwdriver mains tester
with my finger.
If you can reasonably feel that your body is well insulated from
ground when you feel that tingle, like you are standing on dry
carpeting on a wooden floor inside a house, then I'll put my
chips in with the folks who say you are probably just feeling a
capacitivly coupled ac current flowing between the hot lead in
the lamp and the lamp's metal body which is then charging and
discharging your body's capacitance.
How about trying this? connect a wire to a known ground, get the
smallest wattage 240 volt bulb you can find, unplug the lamp and
connect that bulb beween the metal lamp body and the grounded
wire. Then plug the lamp back in.
Does the bulb light, with the lamp either off or on? If it
doesn't, then the current flow (in amps) is less than the
wattage of the bulb divided by 240.
If it does light, you DO have a dangerous condition of
deteriorated insulation or some other conductive path within the
lamp, STOP and get it fixed.
If the test bulb doesn't light, replace it with an ac ammeter
set to a range higher than that bulb would draw at 240 volts and
then switch to lower ranges until you can measure the "leakage"
current. I'm betting you'll find it will be less than a
milliampre, and is likely capacitively coupled.
Could I not use an ammeter inthe first place rather than a test bulb
given that a fully-lit 100 W bulb would have a current flow of approx
0.4 A (= 100 watts/240 volts).
The reason I suggested using a small bulb rather than a meter is this.
Just in case you DO have a dead short between the "hot" side of your 240
volt supply and the metal body of the lamp, then connecting that
grounded wire I suggested directly to the lamp body through an ammeter
would cause one heck of a lot more current than the 0.4 A you mention,
possibly enough to damage the meter before the fuse or breaker opened,
unless the meter was set to something like a 400 amp range. Capiche?
While it's nice to hear that all metal bodied lamps ought to
have a direct connection from their metal parts to ground
through a three wire cord and appropriate plugs and recepticals,
that is certainly the exception rather than the rule for
household use in the USA. I've got all sorts of metal bodied
lamps in my home, all of them purchased new, some as recently as
last year, and not one of them came equipped with a three wire
cord.
My experience is the same as yours in that I have many 2-core only
appliances with metal bodies which seem designed specifically to be
2-core. Often their label refers to "double insulated" - whatever
that may be.
And I've recently read that common consumer "pop-up" toasters don't have
three wire cords and grounded cases because people often stick tableware
in them trying to remove a stuck piece of bread. If those metal
implements shorted a toaster element to a grounded case, the element
could burn out.
They rely instead on the presence of GFCI protected outlets to keep
foolish people from electrocuting themselves while doing that. GFCIs
have been required by code for kitchen outlets in the US for many years now.
In fact, I've installed capacitive "touch switch" multi level
dimmers in four of those lamps, using their bodies as the
sensing elements. I couldn't do that if we had to ground the
lamp bodies.
Let us know what you find,
Jeff
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