If it only pops the GFI with the switch on, means the plug is good. Zip
tie the switch closed and proceed with trouble shooting. Expect to see
serious dirt and crud in the brushes area and the switch area. Blow
everything out, rinse with electical contact cleaner (flamable!)
They're also wonderful for large diameter/long wood bits (eg: drilling
for 3/4" hardware thru fence posts), driving lag screws, large hole saws (esp.
thru steel), and sometimes large carbide bits thru masonry.
I have a similar vintage one. I don't use it often, but there
are things it does that none of my others can. Yours is similar to
more standard 1/4" and 3/8" drills, with a D-shaped push handle. Mine
is somewhat beefier - the D handle is rotated 90 degrees, and there's
yet a third handle that can either be attached opposite the handle
with the trigger (like a jackhammer) or come out the side (like a bolt
action on the side of a rifle).
Put the ohmmeter on the plug in various combinations (_not_ plugged
into the wall) and pull the trigger. If you see conductivity, it's
probably a dirt/wiring problem on the motor side of the switch. If you
don't, it's probably something to do with the motor windings - eg: a worn
spot that peridiodically contacts some rust or grit on the armature
or something like that.
A very thorough cleaning will likely solve it. If the windings are shot,
it's not worth repairing. Cannibalize it - looks like a good chuck.
Chris Lewis, Una confibula non set est
It\'s not just anyone who gets a Starship Cruiser class named after them.
That's a nice rugged drill, to replace it with an equivalent new model
of the same durability would be expensive.
As has been recommended, a thorough cleaning may completely solve the
current leakage problem.
Conductive dust (from the brushes or other external sources) can create
a leakage path for 120VAC.
After normal cleaning, a flush with an appropriate solvent should
remove all traces of any conductive contamination.
An ohm meter may not indicate the leakage path, since the applied
voltage from the meter is much lower than the breakdown path voltage.
The most commonly known tester for insulation breakdown is the Megger..
it applies a high voltage to various components to allow the user to
locate the insulation leakage, by indicating the leakage reading in
megohms, or mA, or uA. There are many other ways to perform the same
tests with other equipment.
Leakage testing on live equipment should only be done when the
equipment being tested is powered thru an islolation transformer.
The actual fault could be something as simple as a pinched, but not
shorted, wire (lowering the voltage breakdown level of the wire's
insulation) or oily dust accumulation on the field or armature
windings, or around the normally-isolated brush holders previously
discussed. Moist dirt is more conductive than dry dirt (sawdust, for
As you already know, the fault is a high resistance path to the metal
case. It would be wise to make certain that the ground lead is
undamaged, and securely attached to the drill case, and at the plug
GFCI protectors basically react to an imbalance between the line and
neutral conductors, and will protect the user even when the appliance
cord is only a 2-wire cord (hair dryers, for example).
Most appliances with metal housings definitely need to have a 3rd lead
to be earth grounded. In other metal-cased appliances, the design and
insulation meet requirements for safe operation, but the insulative
characteristics can be compromised by infiltration of contaminants,
abuse or damage. Maybe the most common contaminant would be water or
moisture. Even very humid air can cause insulation leakage, excessively
in high voltage circuits.
What a great post. To me, low amount of leakage indicates that the
problem is crud related and fixable. I'll see. I appreciate the time
you spent writing your post, it is pretty much on target. I have a
megger, but, I think, will start with disassembly and good cleaning.
I found just such a problem in a 1/2 horse motor I use for my tool bit
grinder. It ran fine, but showed voltage from the housing to ground.
Grounding the housing eliminated the problem, but when I dismantled the
motor to replace bearings, I found the source a wire that had been crushed
between two members. Insulation was intact, but there was a high resistance
leak. Taped the crushed portion and the problem went away.
On Wed, 22 Feb 2006 21:13:39 -0800, "Harold and Susan Vordos"
Harold, I had one like that last year, only it was the power wiring to
a 460 V. 15 Hp. motor crushed in the motor junction box cover.
Luckily, the AB Powerflex 700 VFD was smart enough to instantly trip,
so no light show. This was on a new installation.
I would like to know the reasoning behind your opinion (that if I have
to ask how to fix it, I should throw it away). My experience with
repairing various things (spa, compressor, a diesel generator are some
examples) suggests that asking intelligent people nicely results in
good suggestions and finally in good results.
You apparently think otherwise and I would like to know why.
"Ignoramus15109"wrote: (clip) I would like to know the reasoning behind
your opinion (that if I have to ask how to fix it, I should throw it away
I will answer for Mike. There was something about the tone of your original
post that could be mistaken for naivity. In following the rest of the
thread, including your various responses, I have concluded that expressions
like, "leaks electricity to the case" and "what would be a typical
application for this drill" were not indicative of your non-newbie status.
Clearly, to anyone who read the whole thread, it should be clear that you
not only know what a *megger* is, but you have one, and you know a little
something about the whole subject.
Maybe Mike jumped in and posted without reading the whole thread.
PLEASE don't throw that rugged old drill away. If necessary, use it on a
non-GFI circuit and wear a pair of rubber gloves. It just occurred to
me--maybe this whole thing was just an excuse for you to gloat over the
possession of such a fine old drill. ;-)
I believe that you have an extra "not" (or "non") somewhere above.
Otherwise, yes, I think that Mike made some assumptions that were not,
in fact, true.
I know a little bit and have done a few electrical projects. Nothing
really advanced, but somewhere at or a little above the level of
repairing an old metal cased drill.
Not really. The more I think about it, the more I realize that I
should sell it, as even my 1/2" Dewalt drill is too powerful for my
hands. I would get no benefit from this drill, it is designed for men
stronger than I am. I will likely sell it after I repair it. I first
though to keep it, and then realized that it is too strong for me,
torque wise. As it often happens, I may change my mind.
Leo wrote: (clip) not indicative of your non-newbie status. (clip)
Igor-amp-us wrote: I believe that you have an extra "not" (or "non")
to which Leo responds: No. I think I have the right amount of double
negativity. The meaning I was after was, "Your writing style fooled us by
sounding like it came from an uninformed person."
In defense of Iggy: he asks some pretty basic questions when he starts a
project but seems to power his way through to some exotic questions
fairly quikly. Most of us are not up to designing inverter welder circuits.
Leo Lichtman wrote:
I under estimated your abilities and I tend to error
on the side of safety. I did not intend to be
insulting or inconsiderate. Sorry ...
That said, I would not use (or sell) that drill with
or without rubber gloves until it is properly
The most likely cause of the problem is that
carbon dust from the brushes has coated the inside
of the drill and allows a small current to leak
from the active line to earth. Take the drill
apart, clean off the dust with an alcohol dampened
rag and re-assemble it. Earth leakage devices are
very sensitive and will trip at the least bit of
current to earth.
Sounds right to me. Which leads me to a question:
Is the power cord two-wire, or three-wire? If three wire, there is
little danger of shock, as the ground wire will short the leakage path.
If it's two-wire, I would also rewire the drill, changing to a
three-wire cord would also change the cord to be three-wire, thus
grounding the case. Because carbon dust will re-accumulate.
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