HOME  |  NEWS  |  BLOGS  |  MESSAGES  |  FEATURES  |  VIDEOS  |  WEBINARS  |  INDUSTRIES  |  FOCUS ON FUNDAMENTALS
  |  REGISTER  |  LOGIN  |  HELP
Blogs
Sherlock Ohms

Broken Switch Shocks Engineer

View Comments: Oldest First|Newest First|Threaded View
<<  <  Page 2/3  >  >>
dmorgan
User Rank
Iron
Re: Oh yeah!!
dmorgan   3/29/2012 9:24:37 AM
NO RATINGS
I'm afraid that the "tech" and I would have discussed this further, maybe outside around back...

Bob Salter
User Rank
Iron
Re: Circuit Tester
Bob Salter   3/29/2012 9:48:07 AM
NO RATINGS
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.

IQ Process Control
User Rank
Iron
Re: Beware of the broken switch
IQ Process Control   3/29/2012 9:52:39 AM
NO RATINGS
Yes sir, kf2qd has hit the nail on the head, any professional electrician will tell you this is exactly the right proceedure. And if you are not a professional electrician, get one! :)


OLD_CURMUDGEON
User Rank
Platinum
LETHAL VOLTAGE PRESENT ...
OLD_CURMUDGEON   3/29/2012 10:32:24 AM
NO RATINGS
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!

Leer
User Rank
Iron
Re: ground it all
Leer   3/29/2012 10:42:02 AM
NO RATINGS
Always a good idea to groung everything. An isolated motor with a spinning pully and a rubber belt makes a great Van de Graaff generator. The kind in science museums that through sparks several feet.

Leer
User Rank
Iron
Re: Oh yeah!!
Leer   3/29/2012 10:46:17 AM
NO RATINGS
I've met engineers that had zerro sense  and some tech's that put engineers to shame. Too bad there isn't a better way to "certify" skills.

rrietz
User Rank
Iron
Even More Lessons...
rrietz   3/29/2012 11:40:24 AM
NO RATINGS
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.

Rob Spiegel
User Rank
Blogger
Re: Oh yeah!!
Rob Spiegel   3/29/2012 12:24:31 PM
NO RATINGS
You're right Gsmith120. He asked the technician to turn off the switch. So there is no excuse when the technician later says the switch is broken. It's really unfathomable.

William K.
User Rank
Platinum
Broken switch leads to shock for engineer
William K.   3/29/2012 4:38:13 PM
NO RATINGS
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.

bdcst
User Rank
Platinum
Re: Broken switch leads to shock for engineer
bdcst   3/29/2012 5:20:20 PM
NO RATINGS
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.

<<  <  Page 2/3  >  >>
Partner Zone
More Blogs from Sherlock Ohms
Sherlock Ohms highlights stories told by engineers who have used their deductive reasoning and technical prowess to troubleshoot and solve the most perplexing engineering mysteries.
Sherlock Ohms highlights stories told by engineers who have used their deductive reasoning and technical prowess to troubleshoot and solve the most perplexing engineering mysteries.
Sherlock Ohms highlights stories told by engineers who have used their deductive reasoning and technical prowess to troubleshoot and solve the most perplexing engineering mysteries.
Sherlock Ohms highlights stories told by engineers who have used their deductive reasoning and technical prowess to troubleshoot and solve the most perplexing engineering mysteries.
Sherlock Ohms highlights stories told by engineers who have used their deductive reasoning and technical prowess to troubleshoot and solve the most perplexing engineering mysteries.
Design News Webinar Series
7/23/2014 11:00 a.m. California / 2:00 p.m. New York
7/17/2014 11:00 a.m. California / 2:00 p.m. New York
6/25/2014 11:00 a.m. California / 2:00 p.m. New York
5/13/2014 10:00 a.m. California / 1:00 p.m. New York / 6:00 p.m. London
Quick Poll
The Continuing Education Center offers engineers an entirely new way to get the education they need to formulate next-generation solutions.
Aug 4 - 8, Introduction to Linux Device Drivers
SEMESTERS: 1  |  2  |  3  |  4  |  5  |  6


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.
Next Class: August 12 - 14
Sponsored by igus
Learn More   |   Login   |   Archived Classes
Twitter Feed
Design News Twitter Feed
Like Us on Facebook

Sponsored Content

Technology Marketplace

Copyright © 2014 UBM Canon, A UBM company, All rights reserved. Privacy Policy | Terms of Service