Query - Zapped by my scrollsaw (!!!!) - what is happening with Earth?
I'm after some info, as I'm ignorant as to what is occurring and the "why" of it. Not a solution, but a reason.
Hoping the sages here can offer some wisdom.....
I've a Carbatec branded 21" Excalibur scrollsaw CTEX-21-CEC. It is made in USA/Canada?
It has been used, since April of 2016, exactly twice. Once the week after it was bought for a single job (which paid for it) and this weekend as I was feeling in need of something new to do.
Pulled it off the shelf, gave it a quick wipe down (trivial dust from 3 years on a shelf a metre from the benches and saws!!!), plugged it in and zzzzzaaaaapppppppp.....
Hooolleeyyy shhhiiitttttt...... :)(:)(:)(:)(:)(
(admit, my depression seems to have faded into the background today....????? Cool!)
It was plugged into a professionally wired workshop setup. Each circuit has a RCD and a fat earth. Didn't trip. Interesting.
Well, dang, said I. Pulled out the multimeter, set to Volt~, touched a probe to a bolt on the scrollsaw and the other to the top of the table saw.... 230 volts.... geez.
Detached the cord, sat down, wrote an email to Carbatec about warranty*, had a few coffees and contemplated my good+bad luck combo. (* 3 years warranty, guess what, expired on 7/4/19.... fffffffuuuuuuuu!!!!)
Went back to shed and retested everything with continuity, amps, volts and thought to run a bit of an unplugged diagnostic to see where it might be. Everything was as it should be (???).
So as a last resort, I did a continuity on the plug cord. Active yep, Neutral yep, earth nope (?what). Tried another cord, same result. I've never seen this before, so I cut the cords, they had ONLY the A/N and no E wire despite having the 3-plugs at both ends and a pin! W...T..F.... Checked every other cord I have, and all with Earth pins have continuity. Two new long cords have no earth wire! WHAT??
NOW... plug in a "good" cord. Retest the scrollsaw, no volts to the "tablesaw-top earth"! (yay!)????
NOW, the QUESTIONS!
--> WHY would a machine be deliberately rigged to potentially return current via the Earth of the socket it is plugged into? Isn't this insanely dangerous?
--> Is this some sort of American thing? WHY design like this?
My understanding is that should the Neutral get damaged somewhere in the circuit, then its going to earth 100% of the Active on the machines being turned on??
--> Why didn't this trip the RCD?
--> If I happen to earth the machine out (by say, standing in a puddle of water) and the houses earth pole is "dry", damaged/corroded or just has a ton of resistance, that I become the new earth and ...zaaaappppp???? (How is this SANE??) e.g. is it not sort of like this situation.
--> Doesn't this type of setup mean the entire earth circuit of the shed/house is potentially carrying current?
I see this as a major problem, as this house is from the 1960's and all the "earthing" is via an exposed wire run from all the powerpoints all around under the floorboards. Its all tied up like an old bush telegram under there....possibly the lights too....?!!!
Thanks in advance to any comments or advice.
I really don't understand what is going on - and frankly, I don't like that. It seems to me that I need to re-evaluate what I thought was a very safe new electrical setup, possibly adding in some sort of earth-current-detection-RCD-magic?? (are these RCBO's?)