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In Reply to: Re: ? about a Cheater plug to eliminate hum---might this configuration cause "death"? posted by StephenJK on April 6, 2007 at 17:30:20:
Two wire appliances, such as hand-held drills and other power tools, are "double-insulated", meaning they have no metal parts that can readily become energized, even if an internal hot wire becomes completely detached.Three wire plugs have a ground wire that is used on appliances with metal enclosures that CAN become energized in the event of a short circuit (i.e. frayed hot wire, hot wire come loose, component failure, etc.).
In normal operation of a three wire branch circuit, when an enclosure becomes energized, the ground wire (via the ground PIN) provides a path for the fault current to return to source. Since the breaker is on the 120V (hot), the breaker "sees" the fault current and trips very quickly. This is because the fault current magnitude is high, because typically the impedance of a short circuit is quite low. (This is why it is called a "short" - it's an abnormal path where the source voltage goes directly to ground, instead of driving the loads in the device it is intended to drive.)
If you cut the ground pin off, you do NOT have the same appliance as a typical two-prong appliance. You have an appliance that was DESIGNED to RELY upon that ground pin in the even of a short that has it's main safety feature completely disabled! When a short to the case occurs when the ground pin is removed, the enclosure remains energized, but no fault current can flow (except for a small current due to capacitive coupling which is insufficient to trip the breaker).
Touching this enclosure can result in a deadly amount of current flow in the human body - just enough to send the heart into fibrilation. This is the deadliest type of shock. Shocks less severe only cause small contact burns or discomfort. Shocks more severe will completely stop the heart, but in this case the heart can be restarted.
When a heart is in fibrillation, it spasms uselessly and cannot provide life-sustaining blood pressure.
The bad news is that only a defribulator can stop fibrilation. This is (oddly enough) a controlled shock which is actually used to stop the heart (not start it like on TV). Sometimes the heart re-starts by itself after a shock from a defibrilator, but failing that, adrenaline is administered to the heart muscle directly, or the chest is opened and the heart is massaged manually.
If you have humming equipment, you have defective equipment, branch circuits, or improper or faulty interconnects. Fix these problems - but do not remove that ground pin.
And avoid listening to misinformed laypersons that believe it's "not a big deal" to do.
Cheers,
Presto
Follow Ups:
the chances of a metal cabinet powering up, and your body's resistance to ground being low enough to cause fibrillation, are remote, but why take a chance?A personal experience highlighted this danger to me. A carpenter on a job I was on was using a skilsaw (the old metal-bodied style) while standing on a scaffold. His saw shorted out, and because his arm and hand muscles contracted from the current, he could not let go of the saw. Finally, in desperation, he jumped off the scaffold, the cord hooked on the way down, and the saw came unplugged. There was no one around at the time-if he had not been able to stop the current, his heart would have fibrillated, with potentially dire results. For me, lesson learned.
Powermatic:Did you know that falls as a result of electric shock is very common? Electricians have this addage "If the shock doesn't kill you - the fall just might!"
This guy may have made a life saving decision. When you're being shocked and you cannot let go, if you cannot throw yourself with sufficient force to either remove yourself from the device or unplug it... you're done for! Not too many people even have the presence of mind to take such action during a sudden violent shock. Others may face falling to their deaths if they attempt to jump or leap away from the source of the shock. Not a desireable situation at all.
Questions to ask:
1) Was that "old tool" a two-wire double insulated tool? With metal parts - not likely.
2) How much is a new double insulated or properly grounded skil saw?
3) Why did the carpenter wait until he was almost killed to buy the new skil saw, or at least inspect the tool to ensure it was safe?
A very sobering story. Thanks for sharing that.
The saw of choice for pros, and least on the western side of the country (easterners seem to prefer the sidewinders).This model has remained unchanged for a long, long time (sorry, don't know exact time lines, but well over 50 yrs). This is the latest iteration, but the only real difference between this and much older models is the resin pistol grip, trigger, and top handle, which were previously all metal, like many tools of the period (drills, etc) and the grounded cord. The older, all metal, no-ground type was the kind Rob was using at the time, and it definitely was not double-insulated. The change to the resin parts was done at least 20 yrs. ago. The newest models are 2-wire/w ground, with the ground presumably attached to the magnesium body.
The good/bad with the worm drive skilsaws is that they will, almost literally, last forever. The gear box is oil filled, and I've never heard of a gear failure (new parts are available, though). The brushes are user-replaceable. Armatures eventually wear out, but those are easily rebuilt. The only part that tends to need replacement is the 'foot' (base) that tends to get bent when it's dropped.
The 'bad' aspect of this equation is that there are still lots of the all-metal ones around, and who wants to give up a tool that his granddad gave to him, and still works great?. However, these can be used safely by (a) always plugging into a gfic receptacle (b)attach a 2 wire/w grnd. cord with a solid connection to the metal body (c)wrap handles with tape.
As far as safety on a job site, well, I'll just say that you would not believe some of the shit I've seen. Just skilsaw-wise, some carpenters wire the blade guard up (makes it easier to start a cut)-while many (most?) wood shake and shingle roofers remove the guard completely! It doesn't take much imagination to think about what that spinning blade would do if you accidentally hit the front of your leg as you drop the saw to your side.
The link shows current prices for skilsaws. The black-handled worm drives are the same as the red-handled, just heavier (and cheaper).
- http://www.amazon.com/s/ref=nb_ss_gw/102-2292484-5623340?url=search-alias=aps&field-keywords=skilsaw&Go.x=11&Go.y=8&Go=Go (Open in New Window)
I have not had to wield a saw all day every day but you are absolutely correct about the east vs. west difference regarding the preference of worm drives and sidewinders!My 5150 consumer grade sidewinder is at least 20 years old, well used in a DIY/handyman sort of way (including cutting concrete and cast pipe with abrasive blades).
the company is now owned by Bosch. They'd be idiots to do anything to undermine the reputation for durability that this saw has.The sidewinders have certain advantages (lighter, startup torque doesn't twist the saw), but also disadvantages (the 'line of sight' on the 77 is on the left which is perfect for right-handers, the linear motor makes it easier to cut straight lines(at least for me (-:), and the gearing gives it a bit more torque). In the end, you pick your poison, get out on the deck, and start cutting up some damn studs!
...that even the best made tools are not immune from electrical failure.Perhaps moving to a moulded handle was for electrical isolation reasons...
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