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.
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.
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.
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.
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?
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.
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.
[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.
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.
Some cars are more reliable than others, but even the vehicles at the bottom of this year’s Consumer Reports reliability survey are vastly better than those of 20 years ago in the key areas of powertrain and hardware, experts said this week.
Many of the materials in this slideshow are resins or elastomers, plus reinforced materials, styrenics, and PLA masterbatches. Applications range from automotive and aerospace to industrial, consumer electronics and wearables, consumer goods, medical and healthcare, as well as sporting goods, and materials for protecting food and beverages.
While many larger companies are still reluctant to rely on wireless networks to transmit important information in industrial settings, there is an increasing acceptance rate of the newer, more robust wireless options that are now available.
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.