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  1. #1
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    Default 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?)

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  3. #2
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    To add to your depressions and alarm.... its an American conspiracy ... as you suggest an "American thing", maybe a bit politcal, maybe "fake news" to erode their economy and exports? .

    I am sure there are actions you can take through t get an explanation from outlet (Carbatec?) your bought if from. If you don't get some satisfaction (ie not another shock) you could take it to ACCC or Choice, Electrical Energy Services Obudsman? etc. Sorry I cant answer your technical questions

    Did your hair stand on end?

    Good Post

    Euge

  4. #3
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    Euge, I meant "American thing" in that I'm aware their domestic 120v systems are wired differently to ours. I believe that they earth their neutral lines at the transformer. It may have some input as to why the scrollsaw may be wired/designed in the manner that it is. It sure does have an excessive number of earthing points internally (picture attached).

    Not sure why this is so, I'm not an electrician.

    On CT, they are right on it. They've emailed back and Ill ship it up and theyll take care of it. Yeah!

    Also, I'm not wanting revenge or anything. I'm just interested why things are not designed to avoid this kind of shenanigans to start with....

    IMG_20190429_001842.jpg

  5. #4
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    Quote Originally Posted by woodPixel View Post
    I
    --> 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?
    This is quite common provided the motor is doubly insulated.
    This usually means a plastic bodied motor. A lot of power tools and devices like hair driers are like this.
    However I am surprised this is done on a scroll saw with so much metal in the body.

    --> Is this some sort of American thing? WHY design like this?
    See previous.

    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??
    Not quite sure what you mean by "damaged"

    --> Why didn't this trip the RCD?
    Have you tested 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.
    Yes it does - it sounds like you need to test the earth - a possible reference point for earth testing is plumbed copper line.

    --> Doesn't this type of setup mean the entire earth circuit of the shed/house is potentially carrying current?
    It sounds like you might need to have your earth tested.

    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....?!!!
    EEUW - not good - We had some of that that in our 100 year old house and the first thing we did after we moved in (in 1978) was have those wires replaced.

  6. #5
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    WP - its not clear to me what the connection cord is like.

    Are you saying the cord hardwired at the machine end and has 3 pins at the plug
    OR is it a separate cord that plugs into a 3 pin socket on the machine end but the cord is only a 2 core cable.
    If its the latter then that's a CT problem.

    BTW that is not an excessive number of earth points especially if some of the machine parts are separated by plastic components. It's common to earth the motor and machine body to the same point as the incoming earth in the manner shown.

  7. #6
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    Thank's wP, looks like you are top of things and some resolution is at hand. Could be the American 120V thing in some way.
    I notice many household electrical appliances are now without an earth and have only 2 pins.

    Much of what I said was tongue-in-cheek, trying to extract some humour from you mishap (you did survive the Zaaap!)
    Sorry I could not be helpful .. you seem to have explored the cause from various angles.

    Cheers, Euge

  8. #7
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    I use something similar to this tester https://www.bunnings.com.au/deta-pow...-plug_p4420488 to occasionally check leads for defects and power point replacements.

    If you got a decent (or any) zap consider a trip to the doctor or hospital for an ECG as it can throw your ticker out of whack.

  9. #8
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    DISCLAIMER

    No liability is accepted by UBeaut or the Wood Working Forum's administrators
    or moderators for advice offered by members posting replies
    or asking questions regarding electrical work.
    We strongly advise contacting a Licensed Tradeperson for all electrical work.
    WARNING

    Information supplied within posts is not to be considered as detailed formal instructions to complete a task.
    Members following such information do so at their own risk


  10. #9
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    I love electricity. Best invention to date, other than atoms. But, I hate being on the receiving end of it

    These were not the cables supplied by Carbatec. I in *no way* blame CT. These cables were from my Cable Box... a thing of vast wonder and full of useless accumulations. They were possibly with lamps....

    Anyway, they are kettle plugs. Pictures attached and the severed remains. Clearly shows three plug end and head.... no earth. This is CRAZY.

    As soon as I plugged in a cable with an earth, no zapping.

    Attached is also a photo of the saws manual and I also note that the USA version goes to some strenuous effort to outline the type of plug needed (http://general.ca/wp-content/uploads..._21_30_ENG.pdf page 7)

    IMG_20190429_193827.jpg IMG_20190429_193713.jpg IMG_20190429_193952.jpg

  11. #10
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    Quote Originally Posted by apple8 View Post
    I use something similar to this tester https://www.bunnings.com.au/deta-pow...-plug_p4420488 to occasionally check leads for defects and power point replacements.
    While they are better than nothing unfortunately those devices don't tell you what a problem is and as it states on the label it won't tell you if there is an earth/neutral transposition.
    They also don't correctly test the insulation resistance of extension cords, to do that a megger tester is required.

    If you got a decent (or any) zap consider a trip to the doctor or hospital for an ECG as it can throw your ticker out of whack.
    Agree. A bloke I know got a shock and he had to have a sit down for a few minutes and then said he felt OK but over a period of about 10 minutes he started feeling woozy and staggered up to the house and flopped down in a chair and told his wife what had happened. Fortunately she had the sense to ring the ambo and they came around right away ad it turned out he had had heart attack. He was in hospital for a couple of weeks and it took him a log time to recover.

  12. #11
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    Quote Originally Posted by woodPixel View Post
    I love electricity. Best invention to date, other than atoms. But, I hate being on the receiving end of it

    These were not the cables supplied by Carbatec. I in *no way* blame CT. These cables were from my Cable Box... a thing of vast wonder and full of useless accumulations. They were possibly with lamps....

    Anyway, they are kettle plugs. Pictures attached and the severed remains. Clearly shows three plug end and head.... no earth. This is CRAZY.

    As soon as I plugged in a cable with an earth, no zapping.

    Attached is also a photo of the saws manual and I also note that the USA version goes to some strenuous effort to outline the type of plug needed (http://general.ca/wp-content/uploads..._21_30_ENG.pdf page 7)
    OK - if you decide to swap cables around then the onus is largely on you to know what you are doing.
    Those types of cables are very commonly supplied on things like laptop power supplies and lamps which are double insulated.
    I have a box full I got from work where instead of testing and tagging computer cables they often just replaced them as it was cheaper to do this than employ a tester.
    I agree it would be safer it two core cables and devices were restricted to using unique plugs and sockets (eg the figure 8 type) to more clearly delineate they are not earthed.

  13. #12
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    I don't think you need to worry about dangerous defects. You felt some current which means it was 1mA or more but it did not trip the RCD so less than 5mA (although it's probably a good idea to push the test button on your RCD). Any motor will have capacitance between the windings and the frame, typically tens of nanofarads. If the frame is not isolated then it will be connected to the ground lead and any current through this capacitance goes back to the ground/neutral bonding point in the power panel. Without a proper power cord you had no path for the leakage other than yourself. Your voltmeter has an input impedance of probably 10 megohm so would measure full voltage through the winding-to-frame capacitance.

    You clearly do not have a metallic connection from the hot lead to the frame of the saw or else the RCD would have tripped from the dead short to ground when you used a grounded power cord.

    Normally of course the power switch opens the hot lead so you really shouldn't have felt anything with the saw switched off. So a possible "American thing" defect might be that the wrong lead is switched, a mistake that could be caused by confusion over the difference in color codes.

  14. #13
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    I get some odd Voltages between my laptop and the mains electrical earth.

    Metal Laptop case to Mains Earth ~6VAC
    USB Plug earth shield to Mains Earth 83V AC and n a dry day it will be a tad more and give me a little bite.
    Metal Laptop case to USB Plug earth shield 2.7V AC

  15. #14
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    Quote Originally Posted by BobL View Post
    While they are better than nothing unfortunately those devices don't tell you what a problem is and as it states on the label it won't tell you if there is an earth/neutral transposition.
    They also don't correctly test the insulation resistance of extension cords, to do that a megger tester is required.
    I think they have their place, some do indicate the problem, and the average consumer doesn’t need to know anymore than there is a problem and then extension lead is replaced or they get a sparky to check the power point fault. In woodPixel’s case it wouldn’t help as the plug was an IEC fitting and his experience is a warning for all about on how you can get caught out making an (understandable) assumption that the saw was earthed via a cable with a three pin plug. By the way, that seems to be a very long kettle cord.

    I don’t think these devices pretend to do insulation tests only connection tests. Most users of electrical cables have no idea of megger testing or have access to one or what they’d be looking for in the results and there’s no requirement to do so in domestic situations, similar to house wiring after installation even if it’s many decades old. I wonder sometimes why there aren’t more incidents when you see extension leads and power boards ganged up and left for years run under carpets, strapped to fences and awnings, trapped behind lounges, beds and TVs. In industrial environments rules are in place for testing devices but in some homes anything goes.

  16. #15
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    Quote Originally Posted by apple8 View Post
    In woodPixel’s case it wouldn’t help as the plug was an IEC fitting and his experience is a warning for all about on how you can get caught out making an (understandable) assumption that the saw was earthed via a cable with a three pin plug. By the way, that seems to be a very long kettle cord..
    Indeed. I assumed the power plug being a 3 pin one and having a regular chunky end meant it was earthed. As BobL said above, why not make it two pin and an different end?

    The pictures show two 2-metre cables. I'd already chopped the ends off to confirm my suspicions... they were too thin for 3 wires....

    I'm not an electrician and have enough knowledge to be dangerous, Dunning Kruger and all that, but I do like to know what I can... but I dont do wiring, but I like to actually know my setups.

    Thank you all for your inputs and wisdoms.

    I've an old friend who is a sparky for the fire brigade. He runs a little business doing installs on his days off. I'll talk to him about swapping out all the RCD's for RCBO's and earthing the hell out of everything...

    Interestingly my RCD's dont have testing buttons. This has me worried. I'll post a picture.

    Are RCBO's the way to go?

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