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Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work. |
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#1
Posted to rec.crafts.metalworking,alt.home.repair
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Drill leaks electricity to case
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 example). 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 end. 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. WB .............. Ignoramus3408 wrote: I have this Black and Decker 450 RPM drill: http://igor.chudov.com/tmp/450-rpm-drill.jpg 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. i |
#2
Posted to rec.crafts.metalworking,alt.home.repair
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Drill leaks electricity to case
"Wild Bill" wrote in message oups.com... snip----- 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) 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. Harold 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 end. 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. WB ............. Ignoramus3408 wrote: I have this Black and Decker 450 RPM drill: http://igor.chudov.com/tmp/450-rpm-drill.jpg 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. i |
#3
Posted to rec.crafts.metalworking,alt.home.repair
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Drill leaks electricity to case
On Wed, 22 Feb 2006 21:13:39 -0800, "Harold and Susan Vordos"
wrote: "Wild Bill" wrote in message roups.com... snip----- 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) 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. Harold snip 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. Pete Keillor |
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