Ignoramus15109 wrote:
Thakns to all. I fixed it. I took the cover off and blew out
accumulated carbon crud. It made a little cloud, I tried not to
breathe and walked out of the garage for a little while to let it
settle.

After that, the drill runs (as it did before), but it no longer trips
the same GFCI breaker. I tried starting and stopping it many times,
shook it while running etc, but the breaker would not break. I made
some pictures, but I doubt anyone would be interested -- just brushes
touching the rotor.

I want to say big thanks to all people who gave me good suggestions!
It was the easiest fix of my life.

I also tested hot to ground with a multimeter, no obvious leaks (I did
not use a megger, but I used the 1M setting of the multimeter).

For the record, I used rubber boots and gloves while I was trying the
drill.

Indeed, there is a big threaded hole on top of the drill, for
inserting a big handle. Maybe it is even meant to be held by 2
people with a big handle.

i

This brings to mind something I encountered a couple years ago. Someone
in a Campground tripped the Camp Group power GFCI when he plugged in his
Travel Trailer. He said it did not happen when he used it at home and
other places (that did not have GFCI).

The problem was that the Ground and Neutral wires were tied together
inside the trailer. Of course the Ground and Neutral were also tied
together in the Campground. Therefore some of his return current was
flowing in the Ground tripping the GFCI.

Same thing was happening in the drill but only a tiny bit was probably
flowing through the carbon dust but it was enough to cause the GFCI to trip.

According to Rich256 :

This brings to mind something I encountered a couple years ago. Someone
in a Campground tripped the Camp Group power GFCI when he plugged in his
Travel Trailer. He said it did not happen when he used it at home and
other places (that did not have GFCI).

The problem was that the Ground and Neutral wires were tied together
inside the trailer. Of course the Ground and Neutral were also tied
together in the Campground. Therefore some of his return current was
flowing in the Ground tripping the GFCI.

Same thing was happening in the drill but only a tiny bit was probably
flowing through the carbon dust but it was enough to cause the GFCI to trip.

A dirt/crud induced conduction path in a device that causes a GFCI to trip is not
_likely_ to be between the ground and neutral leads.

Think about it: A GFCI requires 3-5ma to trip. If the dirt/crud resistance
is 1000 ohms (it certainly won't be zero), you'd have to have at least 3 volts
between neutral and ground for it to trip. Given allowable voltage droops
due to load, that device has to be drawing a _lot_ of current before you'll
see that much ground-neutral voltage. Meanwhile, a hot leak of 1000 ohms
(100+ ma) can be quite lethal (eg: you use Igor's drill before repair
in a circuit without ground).

Secondly, assuming enough voltage between ground and neutral to trip,
provided that the device is nominally wired correctly (switching
the hot), the device will trip the GFCI without switching it on.

For the most part GFCI tripping under these sorts of circumstances will
mean that the defect is on the hot itself, or somewhere in the motor winding
(which acts as a voltage divider between hot and ground). These can
potentially be quite lethal if you use it in the wrong circumstances.

Igor: You mentioned previously that you thought that this thing had
too much torque for you, and you were going to sell it. Remember: this
class of drill is intended to be used two-handed for where you really
do need the torque. Used two-handed this drill will be fine.

[I mentioned I had a similar drill. When I got it it was missing the
extra detachable handle. So I made one. Yours has two viable handles.
It's just that mine now has three ;-)]

I don't know what sorts of work you do, and whether you need occasionally
something of this class or not, but think carefully... A drill of this type
with gears/bearings/wiring/chuck in good shape is worth quite a bit (many
hundreds to buy new), and occasionally can't be beat for work around
the home without renting something that costs a lot more per hour than
what you have invested in this thing so far.

Heck, on our property[+], you can just about auger post holes with such a
unit ;-) Great drill for making mortise and tenon log rail fencing or
slapping together timber structures (lag screws etc) or boring big holes
in concrete.

If you decide to sell it, do ask a decent price for it.

[+] fine sand.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.

On Thu, 23 Feb 2006 16:25:20 GMT, Rich256 wrote:

Ignoramus15109 wrote:
snip

This brings to mind something I encountered a couple years ago. Someone
in a Campground tripped the Camp Group power GFCI when he plugged in his
Travel Trailer. He said it did not happen when he used it at home and
other places (that did not have GFCI).

The problem was that the Ground and Neutral wires were tied together
inside the trailer. Of course the Ground and Neutral were also tied
together in the Campground. Therefore some of his return current was
flowing in the Ground tripping the GFCI.

Same thing was happening in the drill but only a tiny bit was probably
flowing through the carbon dust but it was enough to cause the GFCI to trip.

A GFCI works because in a single phase circuit that is working
properly, the current in the neutral must match the current in the hot
conductor. When both conductors are passed through a coil, the coil
won't energize because there is no current imbalance. If some of the
current has a different path to complete the circuit, then there will
be a net difference in current at the sensing coil, and it'll trigger.
That's why GFCI's work on two wire cords just as well as grounded
cords.

Pete Keillor

According to Ignoramus22178 :

Actually, a similar (but broader) statement applies to polyphase
circuits, such as three phase circuits. The sum of currents going
through hot conductors must be zero at all times.

Slight correction: through all _current_carrying_ conductors.
Eg: the hot conductor current in a 240/120V circuit (eg: stove
or dryer or "kitchen split receptacles") doesn't balance very often -
the GFCI has to sum the neutral current too.
--
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.