All you home improvement enthusiasts out there should take note. No matter how adept you are are understanding electrical currents, this is still always a danger with home repairs. My husband, who's not an engineer, but a pretty handy guy, has learned this lesson the hard way as I'm sure many of our readers have over the years. Broken switches and nasty shocks are definitely no fun.
Gosh, this reminds me of the Inspector Jacques Clouseau sketch from The Pink Panther Strikes Again:
Clouseau: Does your dog bite? Hotel Clerk: No. Clouseau: [bowing down to pet the dog] Nice doggie. [Dog barks and bites Clouseau in the hand] Clouseau: I thought you said your dog did not bite! Hotel Clerk: That is not my dog.
ANyone who is a tech should have learned this procedure by heart -
Turn it off, lock it out and then get your voltmeter and make sure it is really off.
Built, installed % service industrial equipment and that is the only way to avoid getting shocked. Generally the shocks don't hurt too bad, but the back of your head does tend to suffer from the reaction...
My wife and I have done this a time or two with our forays into the amatuer world of electrical experimenting. It usually ended up with a blown fuse...or two. Just remember with the switches and outlets the black wires touch the black wires and the white wires go to the white wires. Good luck.
There are some cases where if the black wires touch the black wires you will have trouble. My previous house was wired with a burglar alarm that would turn on outside flood lights. One day we came home and found the alarm had tripped (the cat bothered a motion sensor) and a breaker was tripped. The installer had wired the relay in such a way that hot from one phase of the panel was switched to another phase when the alarm relay tripped. I could have simply moved the lighting circuit to the other phase, but the install was so botched I pulled out that relay.
I was doing some wiriing and found out that somewhere along the line the black wires got hooked up to the white wires and vice versa. Not a good situation that resulted in several blown fuses before I figured out what was going on. I always say it's better to be safe than sorry, so turn off the power when working on wiring.
Seems you should have followed your own advice prior to learning the hard way! When it comes to anything above 48VAC, I check thrice!. Another lesson: I used to work for a hosiptial fixing these HUGE indistrial washers that used relay logic and stepper switches. No 5Volt logic here - all the ciruits were 120VAC and some were 208VAC. I had to check the panels hot in order to trace down the anomolly. One day my wedding ring got caught on a relay terminal just as it turned on. OUCH. From that day on, I always take off my wedding ring, watch band or anything metallic. Even with 5-Volt logic, you can draw some considerable current from these SMPS, easily frying traces and your finger. Word!
As a freshout designing high voltage circuits for military radar system, some of things I was taught was to work with one hand behind my back, no jewelry (especially if it dangled), don't reach over my circuits. There were many scary stories about carelessness that got people hurt or killed. Never got shocked never had a desire to either. I always remembered to put up my danger high voltage signs and didn't take anything for granted. While I don't design many circuit over 100K anymore I still carry and follow those rules with me today.
Oh yeah, by the way, that switch...... Did this tech go on to become an elected political official in charge of domestic financial policy? Oh yeah, by the way, the financial regulations that are supposed to prevent these economic meltdowns....
I'm telling this two-part story as it may save some reader from a nasty shock or worse. I'm a Mechanical Engineer with a very low level of electrical savvy; however, out of necessity, I have done some basic car and home wiring. When it comes to transistors, frequency generators and other such electrical components, I'm totally mystefied. 1. I have a small metal cutting lathe at home which I upgraded the 1/2 H.P. electric motor to a full 1 H.P. motor. Somehow while wiring up the new motor I realized that the motor was mounted on a pivot plate bolted to the wooden bench while the power switch was mounted to the metal lathe. This means that the motor was not grounded, and if it ever shorted to its frame and I reached over and touched the metal tensioning lever with one hand and kept my other hand on the lathe, I could receive a jolt of 110 AC volts through my chest. To rectify this, I simply ran a green grounding wire from the switchbox grounding screw through the flexible conduit to the motor frame grounding screw. 2. One month later, I read in a trade magazine that an air conditioning service man was replacing a fan motor on an industiral size unit. The existing motor was a replacement for the original put in by another serviceman and was not properly grounded. When the man reached in through the access port and touched the motor, his upper body was in contact with the metal housing and he received a fatal shock.
In my earlier years, I was a project engineer for a large radio communications equipment manufacturer. In that capacity, I designed several different r.f. amplifiers with output powers ranging from 400 watts to 10Kwatts. To achieve those outputs, required PLATE voltages from 500V DC to 5KV DC. One learns in one heck of a hurry that you not only place your weaker hand & arm behind your back, BUT you get one of your technicians to physically tie it there w/ rope designed to hold the U.S.S Forrestal @ the pier. There are NO 2nd chances w/ this level of DC power, considering that it is NOT only the voltage, but also the current. Typical plate current for a 1Kwatt transmitter is in the order of amperes. For a 10Kwatt transmitter, it's in the order of tens of amperes!
I too have been bit by my wedding ring - once. Learned to put it in my pocket when working on equipment, live or not. Capacitors can sometimes stay charged for a bit with the power off.
My other pet peeve is the way tie wraps are sometimes carelessly installed. When one is working on live equipment as a necessary part of troubleshooting, a prick on the back of your hand can cause one to instinctively back out in a hurry. If the prick is from a poorly cut off tie wrap, a nasty gash can appear on the back of your hand.
Very early in my career I learned the trick of touching things very lightly before grabbing them firmly. That way there is only a tingle when touching something that is not off. In many places I also would use a shorting probe to ground the circuits that I needed to touch, which has saved me from shocks a few times. The third trick is using one of those neon circuit testers, but holding the bulb between my fingers. That will show higher voltage AC and demonstrate the need for additional checking prior to touching.
The high voltage in transmitters is a totally different situation though, and must be dealt fith far more carefully than even the 480 volt AC circuits. After you are certain that everything is off and discharged, then use the meter and extended probe to check again!
MY guess about the tale is that there was a small bit of "attitude problem" that provoked the tech to not mention that the switch was failed. Most techs are far more decent than that.
Lock out tag out. Always find a more secure way to de-energize a device before inserting body parts and/or tools into said equipment!
And do use a "Jesus stick", grounding hook, to secure the potentially hot connections to ground potential.
I think I've written, in the past, about the common sense practice of never trusting anyone else to de-energize a circuit you're going to be working on. A faulty switch, circuit breaker or a wrong label is all it takes!
If I'm in unfamiliar territory I always use a DVM to check for voltages that should not be there. Pressing lightly with your fingers might not do you much harm at 120VAC, but not at 230 VAC. Better to use an AC voltage sniffer or DVM than your flesh. And for HV circuits, ground them with the stick! If its still hot, the flash, the bang and the words you'll utter will explain the safety device name I used in paragraph #2 above.
[Sorry of that mess. Let me try alternate paste method.]
I have three "shocking stories."
In 1965, I was a high school grad with a summer job before starting EE in the fall. My boss dispatched me to repair a motor contactor at a commercial grain elevator and I arrived on scene with a replacement solenoid for the contactor. A voltage check confirmed the bad coil: volts present but no energize. I killed power, confirmed no volts on the coil, and had began to swap the coil when I got a very nasty shock. My shaking didn't abate when my voltage tester informed me that there was 440V three-phase still present on the contactor. I felt simultaneously very stupid and vey lucky.
Another summer job, before senior year, I was again an electrician at a high school under construction. My buddy and I were trouble-shooting an inoperable lighting circuit when he informed me he'd just gotten shocked. He assured me that he was fine but he was angry that he's burned-out his new pen-light style continuity tester. An hour later at lunch, he had a heart attack and passed-out. Fortunately, he was back at work about three weeks later.
Final story is most bizarre. I was 15 or 16, working for my dad. Dad was a farmer and self-taught electrician-wizard who built his own crop dryer on-the- cheap and had a real talent for automation using relay logic. He wanted try this sort of work in preference to farming and contracted to automate a farmer's crop-drying facility.
So I found myself working atop a 60-some foot grain elevator, connecting position-sensing limit switches. A thunder storm forced me to stop for a few minutes, but I went back to continue right afterward, and remember the service-decking was still wet with rain water. I grabbed a weather-proof flex conduit with slack wire dangling that was destined for connection to a limit switch. I got shocked! I shouted down to my dad that I'd been shocked, but he expressed doubt and confirmed that none of the wires at the other end were connected to anything at all. I can't recall if I got shocked yet again, but I soon noticed one of the remaining flex conduits draped past the edge of the edge of platform. The protruding wires had thin, thready sparks leaping out into the air. I scrambled down the service ladder as fast as my shaky legs would take me. God's honest truth, every detail.
I'm still kicking almost 50 years later, so maybe I did learn some lessons.
The lock-out-tag-out group is an interesting attitude, and of course if there are no other considerations that is a good idea.
BUT I do quite a bit of work in places where there are often a lot of people who would not be able to work if I switched off the power to have a completely safe working environment. So not only do I work on live wiring, I also must be careful to not do any momentary shrts that trip the breaker and stop people from working, (making money). The precautions for working live are less convenient but there is no reason that it can't be done safely. Of course it does require full concentration and a good bit of planning ahead. It is indeed tedious, but not hard.
There is an additional benefit, which is that I very seldom find folks tinkering with the work that I do, since the wires are all live.
1)If you were to electrocute yourself so the people "making money" could continue to work, would they take a break long enough to come to your funeral?
2)If someone were hurt or killed by contacting one of your live circuits would you feel bad?
3)Do you work in some 3rd world country where there is no OSHA?
4)If the answer to # 3 is negative, how much do you suppose the fine OSHA would impose on your employer be if your work practices were discovered?
5)Would your employer be happy with your for allowing the people working (making money) to continue their activity unencumbered while exposing themselves to a lawsuit, or would they throw you under the buss if legally encumbered?
In reality it is not that difficult to work on live circuits and avoid both shocks and short circuits. Of course it does require concentration and it also requires thinking out just what I am going to do. Besides that, it does take some skill.
So I am not recommending that just anybody who can grasp a screwdriver correctly start working on live circuits. It is very clear that the safety regulations are intended to protect those who are not able to concentrate on what they are doing and who refuse to pay attention to their surroundings. I would also strongly insist that none of those individuals who are unable to focus attention ever approach a live circuit.
Aside from that, I always avoid setting myself up for injury in the event that I do contact a live circuit. This means avoiding grounds and not hanging on to grounded objects. I also use a plastic ladder to avoid grounded feet. Experienced common sense is a wondeful tool.
This approach can be utterly shocking. If you have good insurance and like to live on the edge then working on live circuits isn't such a big deal I suppose. The potential for a live circuit to generate widows and orphans is present even when the plan does not include contact with the circuit (things can and do go wrong). One slip, one distraction or one mistake is all that is required to create anything from a mild tingle to a heart stopping, flesh searing catastrophe. Being able to accomplish a task more conveniently for others is not always better and in many instances it takes longer to complete the job. I found that when I would work "HOT" (this is something I no longer do) I had to slow my pace due to the unnecessary hazards present; the additional stress of this work practice is certainly not required and is easily avoided, LOCK and TAG the energy source.
The 100% solar-powered airplane Solar Impulse 2 is prepping for its upcoming flight, becoming the first plane to fly around the world without using fuel. It's able to do so because of above-average performance by all of the technologies that go into it, especially materials.
With major product releases coming from big names like Sony, Microsoft, and Samsung, and big investments by companies like Facebook, 2015 could be the year that virtual reality (VR) and augmented reality (AR) finally pop. Here's take a look back at some of the technologies that got us here (for better and worse).
Good engineering designs are those that work in the real world; bad designs are those that don’t. If we agree to set our egos aside and let the real world be our guide, we can resolve nearly any disagreement.
Focus on Fundamentals consists of 45-minute on-line classes that cover a host of technologies. You learn without leaving the comfort of your desk. All classes are taught by subject-matter experts and all are archived. So if you can't attend live, attend at your convenience.