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Thread: un plug first. Magnetic switches do turn on by themselves.

  1. #1
    Join Date
    Feb 2012
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    central florida
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    un plug first. Magnetic switches do turn on by themselves.

    I remember hearing about this one time but never really payed it any attention. I often change blades without unplugging the machine. I never really thought it would actually turn on by itself.

    now I know better but luckily I was not hurt. The Large RAS I recently purchased has a magnetic switch box. I had to remove it to get to the wire inside. it bolts to the frame and before I put it back in its place I did a few test runs to make sure everything was ok. the box has enough wire attached to it so it can be pulled up above the frame and worked on. i set it on the frame and ran the machine a few times. it was set at an angle with one side a little higher than the other, the high side sitting on a higher piece of the frame.

    I had just turned the RAS off and it was winding down when the box slipped, causing the high side of the box to fall flat, actually a very short drop of maybe a 1/4". the blade was almost stopped and then came roaring back to life. I was amazed to say the least.

    I will always unplug before working on any machine again.

  2. #2
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    So, did your hair turn white?

    Thanks for the heads-up.

    Enjoy,

    JimB
    First of all you have to be smarter than the machine.
    VOTING MEMBER

  3. #3
    Join Date
    Nov 2010
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    Richmond, MI near Port Huron
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    Are you saying the starter/ magnetic switch was not level? I can see how it might restart if the iron core hasn't fallen it's full length. A bump could make the core close then. Also if the core is pushed up by hand the starter will close with out the button being pushed.
    Almost 40 years ago I was working around a plastic grinder with a 15 hp motor. I was cleaning it out after a color change. Because I worked in a remote part of the molding floor I had fallen in the bad habit of cleaning the grinders with out unplugging them. At the end of the day I was cleaning the grinder when 2 guys came back to hide out and BS with me. While talking one of them thought about pushing the start button. Lucky for me he checked the plug first. Had he pushed that button I'd have lost my hands to my elbows in an instant. After telling me what he almost did I learned to unplug every time.

  4. #4
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    Quote Originally Posted by Jim C Bradley View Post
    So, did your hair turn white?

    Thanks for the heads-up.

    Enjoy,

    JimB
    Quote Originally Posted by Guy Bratt View Post
    Are you saying the starter/ magnetic switch was not level? I can see how it might restart if the iron core hasn't fallen it's full length. A bump could make the core close then. Also if the core is pushed up by hand the starter will close with out the button being pushed.
    Almost 40 years ago I was working around a plastic grinder with a 15 hp motor. I was cleaning it out after a color change. Because I worked in a remote part of the molding floor I had fallen in the bad habit of cleaning the grinders with out unplugging them. At the end of the day I was cleaning the grinder when 2 guys came back to hide out and BS with me. While talking one of them thought about pushing the start button. Lucky for me he checked the plug first. Had he pushed that button I'd have lost my hands to my elbows in an instant. After telling me what he almost did I learned to unplug every time.


    jim;
    it did actually send a shudder up my spine like a ghost was in the room. Then when I realized how quick the 12" blade starts on this saw i realized how lucky I was because I was just going to take the blade off when it stopped spinning.

    Guy;
    the box the starter was in was not bolted down yet and was just sitting on its back on part of the frame. the box didn't move much at all and only made a light clink noise an instant before the saw started.

    Now this box is made of very heavy material. about 1/8" thick steel. I don't know if the box was bolted in place and something fell against the box in the right way if it would cause the same thing to happen but the rest of my machines have very flimsy boxes in comparison. I actually think that might make an accident easier. The story I had read a long time ago was about a piece of wood that fell against the starter box of a saw. At the time it seemed very unlikely to happen.

  5. #5
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    Yes always unplug before any work. Why is the cover off of that box and have you fixed the start stop on the inverter ?
    "There’s a lot of work being done today that doesn’t have any soul in it. The technique may be the utmost perfection, yet it is lifeless. It doesn’t have a soul. I hope my furniture has a soul to it." - Sam Maloof
    The Pessimist complains about the wind; The Optimist expects it to change;The Realist adjusts the sails.~ William Arthur Ward

  6. #6
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    Quote Originally Posted by Don Baer View Post
    Yes always unplug before any work. Why is the cover off of that box and have you fixed the start stop on the inverter ?
    The cover was on the box but the box was not bolted in place. I moved the box to make it easier to check voltages.

    I have not fixed the start stop on the inverter yet. I have your wiring diagram printed out but there are more wires in the start/stop box than in the diagram. I won't be able to look at the whole thing again for about a week.

  7. #7
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    I have witnessed machines turning on or cycling when they are not supposed too. It is a scary thing. I was told by some electricians "that's impossible" more than once only to see the look of shock on their faces when they saw machines doing the impossible. There is no substitute for PHYSICALLY disconnecting all power sources from a machine before working on them. Most industrial situations call for the power to be locked out. Most of our home shops don't have that capability, and most of us work by ourselves, so unplugging is the best practice.

    As redundant as this seems, it is a good idea to attempt to turn on a machine after you think you have unplugged it. Obviously you need to flip the switch to the off position after verifying it is indeed unplugged.

    One of our tradesman got both legs broken through the thighs after he climbed into a conveyor system to make repairs. The auxiliary control panel, main control panel (and if I remember correctly) the power disconnect switch was in the off position. There was a short from another machine powering the machine that was supposed to be off, which caused the conveyor to cycle when the guy inadvertently tripped a limit switch. If only he had tried to turn the machine on after "killing" power to the machine he would have realized there was a problem.

    Be safe, be well.
    I'm a certifiable tree hugger. (it's a poor mans way of determining DBH before cutting the tree down)

  8. #8
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    Shorewood, WI
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    I keep the blade wrench attached to my cord near the plug. That way I can always find it, and I'm sure I unplug the right thing. I thought this was an excessive level of caution (I was happy with that) until the switch of my older Delta saw failed by simply turning on. I was across the shop from the saw when it went on, and went over to turn it off, but the switch was still in the off position. I had to unplug to turn off the saw.

  9. #9
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    I know someone who trusts to switches for assuring a tool is in "safe" mode. I won't mention any names but, I unplug. The only exception for me seems to be the drill press when changing bits. I don't know why that one is excused but, I use a keyless chuck . . . maybe that makes me think its "safe"(?). On most machines, if I am doing anything with them besides using them as designed, they're unplugged. The best security for your computer and your tool is an "air gap". A proper lockout or disconnect device as opposed to a "switch" achieves the same result; a gap adequate to assure no circuit even under adverse or emergent situations. I don't want to lose a digit (or even have to change my pants) due to that one in a million chance when it is so easy to avoid.
    Last edited by glenn bradley; 04-15-2012 at 04:24 PM.
    Any sufficiently advanced technology is indistinguishable from magic.
    - Arthur C. Clarke

  10. #10
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    I've never even thought about the drill press before. Probably a good idea though. I've had nightmares, I mean wake up sweating nightmare, about changing a TS blade and it turning on so I unplug it unless I'm using it.

    Glad you weren't hurt Keith!
    A man is rich in proportion to the number of things he can afford to let alone. -Henry David Thoreau
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