submitted by HCE727:

I wonder how many people actually bothered connecting the earth lead on the 2 to 3 pin adaptors supplied with these. In 1957 I imagine there would be a good proportion of 2 pin sockets in use. Of course if the 2 - 3 pin adaptor is lost, one reaches for the pliers, and miraculously the plug now fits.
Hands wrapped tightly around metal cased power tools gives me the creeps.
Does double insulated construction apply in the U.S these days? While obviously modern power tools sold in the U.S are plastic cased like the rest of the world, do they have the 'square within a square' symbol on them to indicate this, or is it only in the 220-240V countries?

I have a Sears Craftsman drill which I purchased about 15 years ago (well past the point when three-wire cords were common). This drill has a two-wire cord, and the drill states that it is "double insulated". I have yet to really understand this concept. Can anyone explain what is double insulated...the cord, the internals of the drill itself...?

Mike (mamills)

The Skill model 6355 I just saw on a lab bench does have the double insulated (class II) symbol.

I don't like the idea of metal cased cordless tools where the bit or blade could have continuity to the metal case. I am not certain the following is of this construction, as the company did not answer the question I submitted online (which was over yr ago I think - I took no answer as the answer you wouldn't want to hear):

http://www.amazon.com/Black-Decker-RD1440K-Anniversary-Cordless/dp/B00006FX9U

I can not think of a product safety (compliance) reason why a product could not have double insulation from primary parts to the enclosure, and also have a grounded metal enclosure. Though I'd think your odds of being saved from the (hopefully) rare event of a double insulation fault to the chassis might be outweighed by the odds of you getting shocked from ground potential rise.

Basically, anything and everything which could result in a short causing a metal casing to become energized. For example, where the wiring connects to the motor terminals a broken conductor moving around enough could contact the case. So the whole lot gets put under another insulating cover, hence the double insulation. It's then considered unnecessary to ground the casing since the chances of any internal short causing it to become are energized are extremely small.



A good point. If I'm going to accidentally hit an energized conductor with a drill bit, I'd much prefer the whole case to be grounded in the old style than to be "double insulated" but with continuity to the chuck.

Thanks, Paul!!

Mike (mamills)

wow, my dads got one of those 1/2 drills.
damn thing doesnt stop for anything.
weighed a million pounds too.
used to have to use it when i was like 15/16 yo.made ya appreciate it, thats for sure.

Actually,
I'd never thought of the metal bit hitting a live cable with one of these drills, although metal appliances have always required an earth (ground) wire in them here.
I owned a Wolf drill that had a metal case on it for a few years, and as KJ said above, these drills don't stop for anything, thankfully my drill never had one of them trigger lock things that most drills seem to have on them these days. I think if it got out of control on you, all you could do is run away from the thing and possibly turn it's power off somewhere.

Don't laugh guys. My old boss had one of those drills that I had to use when I was a young apprentice just starting out. As for the 3rd wire, well it didn't exist. Somewhere I beileve it was missing and never used. I remember drilling holes in a damp and wet basement. The water had seeped into my shoes and the drill had a small voltage leak. I pulled the trigger and got wacked. So what did my boss do, he gave me a cement cinder block to stand on in order to finish drilling the holes. No more shock! I can't believe how stupid, but lucky I was. It wouldn't happen like that these days.

My Dad has a whole bunch of metal power tools from the 50s and 60s, although they're all Black & Decker. He's got 3 of the "classic" drill design, plus a skilsaw, heavy-duty drill, right-angle drill, and some other things that escape me at the moment. IIRC, the "classic" designs have a grounded plug; not sure if it actually came with one, or if it's a replacement. Pretty cool collection, and they all still work just fine.

My Dad had a Craftsman 1/4" power drill from about 1951. Of course, it had the metal housing, no plastic back in those days. Anyway, the power cord on it had a regular two pronged plug, but their was a 4" pigtail that came out of the side of the plug, which was the ground. Attached to the end of the pigtail was a small "socket". Presumabily, to ground the drill, you were supposed to remove the electrical outlet cover plate screw, replace it with a special screw supplied with the drill, that when screwed back into the receptical, still stuck out about 1/4". When you plugged your shiny new electric drill into the outlet, you were supposed to also attach the pigtail fitting onto the metal screw that was holding the cover plate on. Never mind the fact that most wiring was ungrounded Romex at the time, but how many homeowners actually would limit the use of the drill in that dedicated "special" outlet with the ground attachment.

Needless to say, both Dad and I used that drill for decades without it being grounded. By the way, the drill still works and is in my parent's basement, although it hasn't been used for years. I guess what we didn't know couldn't kill us! (j/k)

I had a cousin who was electrocuted when the grounding conductor in the plug came lose and contacted the energized conductor which electrified the case. He had been working on a ladder. I was the one who found the problem while investigating the accident.

I had the circular saw which took a 7" blade. I tried a 7-1/4" and it just barely fit.
I was a bit heavy but a well built saw with good power.
She bought the farm when I dropped it and broke the aluminum casting. I hated to throw it in the garbage.

I once saw the German/Austrian version of those old drills at a flea market... it just had the classic class 0 ungrounded plug.
My grandfather owned one of those tiny DIY drills and my father says it was incredibly cheesy, undersized motor and ridiculous accessories (skil saw, sander, shoe repair tool, hedge clippers... all useless).

In the HUngarian Electrotechnical Museum I saw a picture of a 1880s(!) handheld power drill which looked surprisingly modern!

Forgot one thing... my dad owns a 1973 AEG drill though, the very first model with electronic speed control, and it's indestructible! Cost a month's wages back then (or even 2) and is still going strong.

My dad had 1 of the 1/2" drills when I was working for him 20-25 years ago. One of my tasks with this drill was to climb up on a stack of plywood and drill 4 holes through it using a 2 or 2 1/2" (can't remember for sure) paddle bit.
It caught and threw me right off of the stack.
Don't remember what the plug looked like then as we were but humble carpenters at the time.
I seem to remember it being dropped and the case being broken.

I thought about it, when I was, like, a second-year apprentice. That doesn't mean I never did anything stupid like what Harold mentioned! (Yeah, remember standing at the top of the extension ladder leaned up against a pole, resting on the truck bumper, tied off only with a piece of romex, stripping a wire I wasn't sure was dead, only because I thought my foreman would say something bad about me... Don't ever do that!!)

No, on this job, my foreman gave me a Hole Hawg with a 3.5" hole saw and told me to cut a hole for a smoke detector in a lath-and-plaster ceiling. This house had "knob and tube". I put that in scare quotes because there were no actual knobs or tubes anywhere. The conductors were lead sheathed and stapled, and I'd seen enough of the house to know they would be right between the lath. Yes, both the cord and the drill had grounding continuity. Yes, I tested the GFCI, and it was functional. Still, you ever try to hold a Hole Hawg in such a way as not to touch metal? It may be plugged in to a GFCI, but I'd bet whatever circuit I might drill into isn't. A GFCI doesn't interrupt the EGC, nor does it do anything about other circuits.

Well, I cut the hole, and there wasn't a wire there. There are always risks. It's always good to think them through beforehand.

Yes, the 'square within a square' symbol is used on North American double-insulated tools.

Electech:
Yes, it's always worth remembering that even a cordless drill can electrocute you if you drill into a live conductor. Always be aware of possible paths to ground, and stay out of them. Good point!

My dad likes to tell a story from the '50s. My grandfather was a carpenter, and my dad would help him in the summers. This was on the Texas Gulf Coast, a very humid and rainy place. After a fresh rain, you really didn't want to touch the circular saw, since you knew there was a fairly good chance of getting popped.

My grandfather's boss was one of those rare people who could not feel an electric shock. This is not exactly a good thing. The tool that no one else would touch, he would pick up and use. He would be utterly unaware of the current flowing through his body, at least until he finished the cut. That's when he would realize that he couldn't let go of the saw.

By the way, he didn't actually consider this a problem. After all, to break the circuit, all he had to do was jump up in the air!

The cheapest 1/2" drill shown in this ad is $38. See the equivalent in 2006 dollars here:
http://www.westegg.com/inflation/