Emergency Stop Button





Introduction: Emergency Stop Button

Here it is. My latest.

An Emergency Stop Button. What's it for? Any power tool/lighting/heater etc that may required to be stopped in a hurry.

I mainly made this for using with my handheld Angle Grinder, as they have a lock on switch, after it kicked back whilst cutting a bolt, jumped out of my hands, cut into one of my hands, and dropped onto the floor and continued to run, making it hard to get to the power cord to cut the power, and being on a long lead, the mains switch was a distance away.

It all could have gone a lot worse. Thankfully it didn't. Lessons learned. Other than a strong grip and clamp your work down, which I did, was, A- wear gloves, and B - get a safety switch for portable power tools.

As my hardware store did not stock Emergency Stop switches for hand held power tools, I decided to make one. There may be some out there that I do not yet know off, but none like this I am sure!

On with it then.

Step 1: The Parts

The parts list is very basic.

A Cutout Switch that could be operated by being stomped/smashed/hammered down upon, work and still survive, and easily reset. Also I wanted a basic circuit. Less to go wrong. So, a mechanical switch, which is reset by rotating the button top itself.

A box big enough to put all the parts in and take the abuse and be electrically safe.

A power cord.

Retaining clips to hold the power cord in the box.

And thats it!

Parts List:

Large Jiffy Box ABS Plastic (15.5cm x 9.5cm x 5.2cm)

Yes I know it should be measured in millimeters, but hey, smaller numbers :) !

Mains Power Lead extension type

Cable Restraint Collets

Emergency Cutout Switch

Heat Shrink Tube

Step 2: Getting Started

The first thing is to gather your parts and tools. Durr!

Here, we are going to use a Power Drill and various bits, Soldering Iron, Heat Gun (or lighter if you don't have one), Wire Cutters, Hemostats (surgical clamp. well worth getting some), Screwdrivers - Standard and Philips head, a Nail or some other sharp pointy thing to mark the box for drilling holes, and last but not least, Pointy Nose Pliers.

I think that is all the tools, other than myself! that I need.

First off, I started by disassembling the Safety Switch. This allowed me to get the correct size for the hole we are going to drill to fit it, and to position the switch on the box, in the most central position.

Here you can see I used the yellow face plate to best find the layout. Putting it in closest to the centre of the box will give the switch the most stable position when using this device.

Getting it close to centre visually is good enough here.

Step 3: First Cut Is the Hardest.

I started by drilling a smaller guide hole on the top of the box, the bottom plate or lid will be the base, and then we go up a few bit sizes to a bigger bit. It is always best to start off smaller then go up in size. One, this reduces the chance of cracking the plastic, and two, you have a guide hole for the large drill bit, stopping it from slipping and drilling off course.

As I used an electric hand drill, the hole was not perfect, but for our purposes, it will do nicely.

Next I checked the fit, with the switch. All looks good so far.

Step 4: More Holes Than One

Putting the switch fully together, we can check the fit and operation. The tightened button holds nicely in the box.

Now, to take it all apart again. More holes to drill.

We need to drill holes in each end of the box for the power cord. The holes will be measured off the collet size. One hole in each opposite end. Simple!

The type of Collets I used, tighten by screwing in.

As you can see, I have also knotted the cable, as well as use a collet restraint. Over time, the collets may loosen and lose grip, so the knot is an extra safety measure. Crude, but effective.

Step 5: Striping Is Good

Now we are onto striping the wires, soldering, putting on the heatshrink and then wiring the switch.

Some of the wires are going to be directly joined together, and the others put on the switch. In both cases, I have used solder on the wire.

Before doing so, note that the mains lead is cut in two, with one end being shorter than the other. I made the outlet side about 1.2 meters or 120cm long, and the wall plug end cable with the remaining length.

You want a short length where you plug your tools into, so the switch is close to you. The short length is long enough in use to allow the tools to be use above your head height and have the Safety Switch close by your feet, ready to be used if needed.

The wired that go on the switch are soldered, but not soldered onto the switch. They are held down by the retaining screws on the switch assembly. The solder on the wire provided mechanical strength and keeps the wires together when the screw is tightened down. Plus, when you bend the wire into a curved shape it retains it better. A bonus.

Next is joining the some of the wires together.

The basic circuit diagram shows which wires go on the switch and which ones are joined together.

Step 6: Shrink Rays to Full

Heat Shrink Tubes are great. Just thought that I would put that out there. They are fantastic. Not only can you use them for electrical products, but for other hobbies projects too.

I have bought lots of tubes, in different sizes and colours. They only cost a few buckaroos, and kept in an organiser case, they will make your life easier. Here they are doing an important role of insulating the bare wires in this project.

I could have gone and bought electrical joiners, but wanted to use what I already had, and plus, heatshrink works well, it's neat and tidy, and if done right, electrically safe. (stops the electrons from escaping the wires to harm you!)

Because we are using mains power, I have used double tubing. Using two different size tubes, sliding one over the over, to provide a better electrical insulation.

When I soldered the wires, I used a hemostat to hold the wires side by side, and then soldered them together. I pre-tinned the wires before I joined them. You could use pliers to hold the wires as you soldered them, but hemostats have a locking ratchet when you clamp them in place. Plus, they are stainless steel, so the solder wont stick to them, and they draw the heat away, cooling the solder quickly, and preventing the heatshrink from shrinking before we get it into place.

Love my hemostats!

Step 7: Finishing It

Here the wiring is completed. The wires are joined. The the active wired (brown) is attached to the switch.

On the Switch the Red Tab is the Normally Closed contacts (N/C) and the Green Tab is the Normally Open contacts (N/O).

We are putting the Brown (Active) wire onto the N/C contact points. These allow the power to flow till we hit or stomp on the big red switch button, then cutting the power flow.

To reset the switch back to the On position, we simply rotate the red button in the indicated direction of the arrows on top. Such a simple and very useful device!

When screwing in the bottom plate of the Jiffy Box, there are usually included small rubber feet, which go in the screw holes on the bottom. Put these in to make a neater looking box, and they are non-slip also.

You will notice a bit of empty mains power lead tube sitting on the switch. I did this to prevent the box from breaking when you hit the switch. This tube sits firmly between the bottom plate and switch.

Step 8: Ta Da!

Here it is. The finished product.

I thought I might need to add something to make the switch sit flat on the ground when I was using it. In use, the switch box and cable are enough to hold the switch flat on the ground.

A few questions.

Why not a safety electrical cutout switch that detects shorts?

Well, that sort of switch will not stop a running power tool that you dropped, unless it shorts the power out. What we want to do here is stop the device from running, quickly!

Nearly all industry machines, the good ones, have a safety cutout switch. Here you can have a simple one too.

Why not built into the tool you are using?

Well, if it is on the power tool, how can you safely turn it off?? Hence the switch! :)

Why use those type of parts?

Because I am cheap! Well, no actually, oh, ok, I am. But I wanted to build something that works well, is simple to build and use, and is cheap. If it cost more, I still would have built it. But cheap and effective is better.

Why have you written so many steps and so many photos?

Most people complain that I do not have enough. Maybe I need more? Hoping to cover all my bases! :D

Hope you like it! Thanks for reading.

Step 9: A Version With a Relay.

Some one suggested adding a relay for a heavy current load to prevent possible switch burnout.

So, here is a quick and easy relay added in, to the switch design.

The relay would allow for large loads to be used without switch burnout possibly occurring. As the original design was for normal load conditions, ie handheld power tools etc, and it was run in Normally Closed mode to, and activated to the Open position to the kill power, it would not likely be an issue.

But, for heavy power use, as suggested, a relay would be a good idea, you can get ones that can handle a heavier power load, greater than the 10 amps rating of the switch, thus preventing a possible switch burnout.

For bigger tools, or multi-load use, this is a good idea.

As per the diagram, I have made a circuit that, when the Cutout Switch is activated, powers up the Relay Coil, thus removing the power from the output.

Rather than having the Relay powered all the time, leading to a different other possible burnout of the Relay, we activate it only in an Emergency situation, in this design.

The idea is to remove power in an emergency, not to control the on/off power of your load. So, this circuit, like the other, will do the job easily also.

*Note: I have not bothered to switch the Neutral Line, as we want to remove power to stop a load ie a drill or grinder from running, quickly. This is not a short circuit safety switch. This is an Emergency Stop Switch.

You should always plug into a power outlet which is wired into one, or have a portable Earth Leakage Detector Cutout, when using power tools. Most houses now days have these wired into the mains board. If not, you can buy a portable powerboard with this built in, from most hardware stores.

Step 10: Ideas for Emergency Stop Switch Mark II

After a few suggestions, it seems likely that I will be designing a Version 2.0 of this project.

So, stay tuned if you will, as I design and gather more materials to make an extended version of this Emergency Stop Switch.

Same size, same look, but with added features and new improved taste, as suggested by you the viewer!

It will be awhile till I get to it, as I am currently doing 4 other projects at the moment. The Instructables for some of them will appear on this site later.

Once again, thank you for your suggestions. Some of them will make it into Ver. 2.0, and hopefully I can still see your comments and credit you for your ideas.

Laters. :)



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    I had need of just such a switch inline with a big ole 1/2 inch drill motor I was using to mix some stucco I had the drill lock on and the dam thing slipped from my hand continued spinning and wound up the power cord and broke it. all I could do was stand and watch.

    never thought of one of these before thanks for posting it. I will add one to my kit in the near future.

    I did make something a little bit similar for working on electronic equipment during trouble shooting. I got tired of having to keep plugging and unplugging the power cord so a put a single through double throw switch on a power chord to switch hot and neutral I left the ground pass through.

    always like good ideas!

    uncle frogy

    You absolutely did the right thing by "NOT" brake the, (actually it is allso called here in Europa for "Protecting earth"), earth. Here in Finland after a installation of electrical wirings in a house, they especially "check" for the grounding, (the protective earth), NOT to be broken enyware, "hazardious", "leathal", "suicidel"

    The main idea is o.k., (make this whils't having 10 fingers left :=). Theres only one or two things i wonder? To solder the stranded wire isn't necessary a good thing. When them strands be tightened in the terminal, they don't "fan" out like them unsoldered. That results in a smaller contact area for them strands to the terminal, only them soldered part surface comes in direct contact to the terminal surface, and the tinned area doesnt conduct as well as pure copper. Rather use crimp endings. Within "boating-elecricity" it is highly recommended NOT TO to solder terminatings, that is:

    1. In a boat you have to concider the wibrations that wery quickly breaks your connection

    2. The oxidation of lead is way faster than copper

    3. The solder, (I don't know the expression??), conductivity?, starts decreasing right on after soldering and after some time you have only 60% left of the conductivity.

    4. To tie a knot in the cord? to get a strain relief Hmmm... Don't do that. If you aren't got a deacent strain reliefer, you rather use a wrap-tie or two, works fine.

    In some industries, (me be'ing an electrician there), they often use in them emergency brakers, (some like yours,) to cut off BOTH "Live" and "Neutral". This is a precaution for a "worst case situation", that is, if something breaks down, there's a possibility that the "Live" get's in connection with some other parts that still are "Hot", and or gets in a touch with the "Neutral", thus not enough to blow the fuse, and this could result the "Hot" coming back through the "neutral".

    Firstly, thanks for looking at my Instructable.

    I put solder on the wires for a few very good reasons. One, as stated in the steps, is that it helps in holding a curved shape. The other reasons are; mechanical strength, which is a good reason to use solder; when you tighten down the screw on the terminal it will flatten the soldered wire out some what, increasing the contact area. As to oxidization, solder is not made of pure lead, so the level and rate of oxidization is low, and with good contact will actually keep the copper from oxidizing, as copper requires little pressure to break the oxidation and have a low resistance connection.

    Also, once again, the mechanical nature of a solder connection means it is less likely to move, when the switch is moved. As there is not going to be a vibration issue in using this switch, I see this as a non-issue.

    I never like to use cable ties to anchor mains cables, as I have seen too many times, repeatedly, the cuts caused to the insulation when used as an anchor, causing the cable to be damaged and/or break, not to mention a cable tie is not the most reliable thing as a backup anchor. I have been using a simple knot like that for over 30 years now, and have seen others do so, as a back retainer, without an issue. It is a backup for if/when the retaining grommets loosen off. As a backup measure, it is simple and effective. Otherwise, use one on the basic soft plastic loop and screw anchors.

    Yes, the can be an issue with live feeding back into neutral in some circumstances, but this is a simple cutout switch to remove the live rail. If you have live feeding back into the neutral line, your are having more than a "stop that device" problem. A good RCD should kill the power in this case. As most houses have these installed, they will do the job. If not, get and use a portable one, as I told some one earlier.

    When using power tools, use an RCD, but if you need to stop the power in a hurry, not due to a short to earth or neutral, use my cutout switch!

    Though you are right in that having both lines cut would be a better idea. One simply could added another N/C switch on the bottom of the switch body, as these a modular units. But, as it stands, the switch does it's simple job as designed.

    Once again, thank you for the comments, and hope you enjoyed my Instructable.

    In my experience, solder gives way or flows under pressure so that screw or clamp terminals don't stay tight. It's better to put a ring or fork or ferrule terminal on the wire, as appropriate. If that's not practical, then just solder the very tip of the wire to prevent fraying.

    100% agree - wire ferrules are the way to go if the wire is pressed (by a screw) as tin will flow away over time. In EU it's even forbidden to tin wire ends that are pressed by screws --> VDE 0100-520 (11.10.2)

    Gee, I so agree, ( me a FIN & a electrician for 40years, now retired), didn't know that of forbidden use of tinned endings to connectors. During the time beeing an electrician, (both in industries & private), I've NEVER ewer seen a terminating of a wire to be tinned. That is "just so, period".

    People: DO NOT never ewer tin the wires to be be terminated to a screw / spring / ..... loaded terminal.

    Ooh, need to add, forgot. I've seen a couple of them tinned endings making problems. And the corse to the poblems has been a "brake" between the soldered end of the wire and the wire itself. These faults are "extreamly" hard to find => no visible harm?? but inside the core, Ta-Daa, the strands have given way to oxidation just in the part of going "ower" from pure copper to "tinned copper".

    The elementary electricity psychics says that: "the poor donates to the more rich" thus making a "glitch" between them thus making aka a brakeage

    Ok. Thanks for the suggestion. :)

    C'om sí c'om sá. I think we both are "right" in a way or other :) . About that using a wrap-tie.... I suggested to use it "only" if you don't have a proper... that of them teeths eating the isolation: No way, them ordinary reliefers use the same method = having them teeths to grab the isolation, is there any other way to achive the strain reliefe? Oooh.. there is, sorry, them to chasiss "cable trough" plugs having a "O"-ring inside and in betveen the cap and the standing part. After having the cable through you tighten the "cap" and the "O"-ring expands inside the plug, thus tightening it around the cable. Unfortunally these plugs are a bit expensive.

    You are right about connecting the soldered end to the terminal, as long as the terminal have "only" the screw against the lead. But if you have a spring-loaded terminal, then it's better with non-soldered end allowing it to "fan-out"

    "Making that knot" for 30 years" you say? OK. but...

    1.It "looks wee...ry" amateur'ish.

    2. By the time the copper inside the core oxidates and becomes "hard and fragile" and it brakes at first in where its the most bended, and that would be the knot, (during my time as an electrician for decades, I've found these brakes in bends to be them most "annoying" and hardest faults to find). If I've made a knot on a cable in my job, (in industies, now me ritered), i would have been kicked out of my job "instantly".

    Still, Your Instr. has a wery good point's of having a "emergency circuit-braker". Ewerybody should have one. :)