When plugged into a GFCI outlet, it leaks electricity to ground and
pops the GFCI breaker. The leak is substantial, I believe, however
when plugged into a regular breaker (and handled with caution
appropriate for leaks to case), it actually works and does not blow
the breaker. So, I think, the leak is limited in extent.
My question is, what is the most likely culprit and how to approach
repair of it.
My another question is, what would be a typical application of this
drill. I am trying to decide if I need it for anything.
First, get an Ohmmeter and see if you can detect continuity from the
case (or ground prong) to either of the flat plug terminals. If so,
want to work on the drill until the ohmmeter reads infinity to the same
terminal. Open up the drill, and inspect the brush holders for greasy black
deposits. Cleant that off, and clean around the commutator (carefully) for
similar gunk. Check the plug for conductance again. If that fixed it, you
got off easy. If not, check the cord, switch/speed control and anywhere
in the drill where wires run for bare contacts and something like dirt,
greasy goo that could conduct electricity. If there is nothing more to
then you either have a short in the armature or field windings. You can
disconnect things to isolate the faulty part, but other than getting a
part from B&D, it is not easy to fix, unless you want to learn the
of motor rewinding.
First step is to dissassemble and clean the drill - and with a good
ohm-meter check for shorts to ground from the field winding (quite
common) or the brush holders. It is POSSIBLE the brush holders are
just dirty - conductive brush dust etc on the surface.
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| > Ignoramus3408 wrote:
| >>I have this Black and Decker 450 RPM drill:
| >> When plugged into a GFCI outlet, it leaks electricity to ground and
| >> pops the GFCI breaker. The leak is substantial, I believe, however
| >> when plugged into a regular breaker (and handled with caution
| >> appropriate for leaks to case), it actually works and does not blow
| >> the breaker. So, I think, the leak is limited in extent.
| > Let's just say I would not want to be handling that drill nor would
| > allow an employee or family member to handle it. It is time to have it
| > repaired or replaced.
| I gotta agree with that!
| So... any idea of how to approach repairing it? I suspect that
| something very simple is wrong, like related to brushes or some such.
If you can see into the drill and there's gobs of carbon all over the
inside of the case from the brushes, rinse it all out with brake cleaner and
replace the brushes. You might be able to make the GFCI quit tripping if
you just were to rinse it out; might be worth a shot.
To trip a regular breaker, it'd have to be "leaking" 15Amps worth of
If you're leaking 15Amps worth of electricity, then the stuff it's
leaking into is being cooked with a couple thousand watts (think
several horsepower worth of power).
GFCI's trip at the few milliamp level (I forget the official number).
Currents as small as 100 microamps can cause heart fibrilation.
Although typically only a fraction of the current flowing through your
hands or feet will go to your heart (I've read a couple of medical
papers where they take fresh cadavers and run electricity through them
sideways, upways, downways, etc, measuring heart current so there must
be some interest in this number.)
Looking at the picture, grunge grease or dirt in the plug, cable, or
drill body or motor can be enough to trip the GFCI. Looks like somebody
already changed the plug, check it out and make sure they don't
cross-connect neutral with ground (this is guaranteed to trip a GFCI,
unless you've got an open ground connection... the myriad problems with
multiple failure diagnosis!)
I hear that California has been having some technical problems with
their method of execution :-).
Truly excessive dirt/dust/grunge on the brushes could do this, but if
it were that bad then probably the drill wouldn't run. On very heavily
used and abused motors you can find metallic dust from the brushes etc.
distributed over everything and this can certainly cause leakage. That
drill looks used enough that it could fall in this category.
Do check where the brushes attach for grunge as well as the insulators,
and also look over the motor windings.
Does it trip the breaker even when the drill isn't on? If so, look on
everything on the upstream side of the switch all the way to the plug
(including the switch.)
Does it only trip the breaker with the drill is on? Then you should be
looking at the windings and grunge that would cause leakage from the
brushes to the body.
These old drills with low speeds are really nice for drilling large
holes. I have a slightly newer B&D (60's?)that runs at 200 rpm. Perfect
for 1/2" holes in 3/4" bar stock (or as perfect as ANY hand drill is for
that miserable job!) That one got a new cord strain relief last fall.
You can do a quick check on the GFI issue by run an ohmmeter on the
plug: Either of the two blades to the ground pin should be up in the
100k range or better. If not, chase it down. If it consistently blows a
GFI, it probably reads in the low 000's ohms.
As for repair, this one looks like it needs a full teardown, inspect,
clean, repair as necessary. My guess would be the plug, the switch, or
the brushes. The grease in the gearbox will be grey slime. Check the
brushes to make sure they still have wear length to them. Check the
wiring, looking for thin spots in the insulation.
I bought a similar one a while back for $2. It wound up as scrap metal,
saved the chuck. Some you win, some not.
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