Electric shock happens to more people than they care to admit. In almost every NFPA 70E / electrical safety training class that I conduct, I ask the group “how many of you have NEVER experienced an electric shock.” I have yet to see a hand go up. In today’s “Modern World” electricity is part of daily life and as a consequence, an electric shock can happen to anyone – Including Me!
#@&%!! I can’t believe I just did that. While trimming the hedge at home one afternoon, I moved the orange extension cord around one of the bushes. Simple enough – being a very safety conscious person, I wanted to make sure I did not accidentally cut it. As I grabbed the cord, I felt an unexpected surprise. The painful buzz in my hand said it all. I just received an electric shock – This wasn’t supposed to happen to me – I teach people how not to get shocked.
This was a not so subtle reminder of just how easy this potentially deadly event can occur. Puzzled about why it happened, it became apparent when I looked at the cord – something I should have done first. Sure enough, there was a minor nick in the orange insulation revealing a very small shiny spot – the exposed conductor!
I began to wonder how many others have experienced a shock. I recalled a statistic found in NFPA 70E Informational Annex K.2 Electric Shock that states “Approximately 30,000 nonfatal electrical shock accidents occur each year.” This always seemed like a large number and now I know why.
Digging a little deeper, I decided to ask a survey question to a group involved with electrical power systems and electrical safety. The question was: “Have you ever received an electric shock?” I assumed based on NPFA’s number, there would be a relatively high percentage of people that had. However, the results were more surprising. Out of a group of around 100 people, every one of the respondents indicated they have been shocked before – 100 percent. A follow up question was asked: How many times have you been shocked?” Over half said “More than I can Remember”. Even though electrical safety practices have greatly improved over the years, the potentially deadly electric shock still happens.
Much or what is known today about the effects of electric shock on the human body can be traced back to research conducted by people such as Charles Dalziel. His work in the late 1940’s and early 1950’s as well as his landmark 1961 paper “Deleterious Effects of Electric Shock” helped define current levels that can produce certain physiological responses in the body. This helped pave the way for the development of the Ground Fault Circuit Interrupter (GFCI) which is used protect people from the electric shock hazards.
A GFCI device is designed to operate when it senses an imbalance in the current flowing on the phase and neutral conductors of an electrical circuit. Both of these conductors pass through a sensing transformer and if more current flows through one conductor than the other, it is likely because the “missing current” is taking an alternate path – perhaps though a person. The device responds by tripping instantaneously to interrupt the potentially deadly circuit.
According to the National Electrical Code a GFCI is defined as “A device intended for the protection for personnel that functions to de-energize a circuit or portion thereof within an established period of time when a current to ground exceeds the values established for a Class A device. In an informational Note, the Class A GFCI is required to trip when the current to ground is 6 milliampers (mA) or higher and should not trip when the current is less than 4 mA.
The first mention of GFCI Protection in the National Electrical code came with the 1968 Edition. Over the years the requirements for GFCI protection have expanded in almost every revision of the NEC since then. The requirement for GFCI protection of garage receptacles was first introduced in the 1978 Edition (a few years after my house was built.)
The 2012 Edition of NFPA 70E was expanded to include additional language about GFCI protection. Sections 110.4(C) (1) and (2) were added which require the use of GFCI protection where required by applicable state, federal, or local codes and standards. In addition, GFCI protection shall be provided when an employee is outdoors and operating or using cord and plug-connected equipment supplied by 125-volt 15, 20 or 30 amp circuits. As always, each new edition of NFPA 70E brings with it continually improving electrical safety practices.
It’s a common saying – you don’t always get a second chance when making mistakes around electricity. Although my “mistake” was minor, it quickly lead to buying a new extension cord and adding GFCI protection to the garage circuit – I am not going to count on having a third chance.
By Jim Phillips | Brainfiller, Inc. | ArcFlashForum.com
Originally Published: September 2012 | Electrical Contractor Magazine