* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download intake structures uptake 316(b) regulations
Telecommunications engineering wikipedia , lookup
Electric power system wikipedia , lookup
War of the currents wikipedia , lookup
Electric machine wikipedia , lookup
Electromagnetic compatibility wikipedia , lookup
History of electromagnetic theory wikipedia , lookup
Electrification wikipedia , lookup
Skin effect wikipedia , lookup
Mechanical-electrical analogies wikipedia , lookup
Mercury-arc valve wikipedia , lookup
Electrical ballast wikipedia , lookup
Resistive opto-isolator wikipedia , lookup
Ground loop (electricity) wikipedia , lookup
Three-phase electric power wikipedia , lookup
Electronic engineering wikipedia , lookup
Opto-isolator wikipedia , lookup
Buck converter wikipedia , lookup
Current source wikipedia , lookup
Switched-mode power supply wikipedia , lookup
Portable appliance testing wikipedia , lookup
Circuit breaker wikipedia , lookup
Voltage optimisation wikipedia , lookup
Electrical engineering wikipedia , lookup
History of electric power transmission wikipedia , lookup
Electrical substation wikipedia , lookup
Power engineering wikipedia , lookup
Rectiverter wikipedia , lookup
Electrician wikipedia , lookup
Surge protector wikipedia , lookup
Ground (electricity) wikipedia , lookup
National Electrical Code wikipedia , lookup
Earthing system wikipedia , lookup
Stray voltage wikipedia , lookup
Alternating current wikipedia , lookup
KTR Associates, LLC 2917 Windmill Rd Suite 2, Sinking Spring, PA 19608 Tele. 610-670-6061 Fax 610-670-6068 Engineering Solutions ELECTRICAL HAZARD AWARENESS Current Kills…Not Voltage Many electrical workers have heard the expression, “It’s not the voltage that will kill you, it’s the current”. This is a true statement. It’s important to understand how much, or in reality, how little current it takes to affect the human body. Approximately, 10% of occupational deaths each year are the result of electrical “contacts”. Many of these electrocutions are the result of electrical feedback where unknowing electrical workers work on electrical equipment that they believe is deenergized. Many individuals believe that normal household current cannot kill but just presents a nuisance tingling due to the low voltage (120 volts). Documented cases at voltage levels as low as 17 volts have caused electrocutions. Working with faulty electrical wires and/or equipment have caused both internal injuries as well as death. One example of electrical injuries occurs through arc flashing. Electrical arcs have caused heatrelated flash burns to the eyes, skin, and internal organs. Arc flashing is dangerous because if your clothing catches fire, depending on your clothing’s material (natural fibers versus manmade), it may burn your entire body and cause additional damage. Effects of Electrical Current on the Human Body Electrical current follows the path of least resistance. Human bodies offer resistance to electrical current. The amount of current passing through a human body is determined by where it enters the body and where it exits. Once electrical current enters the body it will follow many paths to exit the body. Page 2 of 3 The table below estimates the affect of electrical current on the body: Amps < 1 mA Barely perceptible 5 - 10 mA Tingling sensation (annoying) 10 - 20 mA “Let Go” threshold (discomfort, cramps) 20 – 50 mA Painful, cannot “Let Go” 50 - 100 mA Ventricular fibrillation Amps > 100 mA Cardiac arrest Electric current greater than the “Let Go” threshold ( current > 20 mA) contracts the human body’s muscles. Individuals unable to “Let Go” an energized line face life threatening damage to their bodies. If this current level continues for an extended period of time, respiratory paralysis is possible. Ventricular fibrillation (uneven pumping of the heart) causes death to lack of oxygen to the brain. Why Didn’t the Circuit Breaker Operate? Typical voltages entering heavy industrial plants range from 4.8 kV to 115 kV. An “electrical contact” with these voltages can rupture the skin, greatly reducing the resistance of the human body, allowing more current to flow through a victim. The resistance of the human is approximately 500 to 1000 ohms when the skin is broken. An example of the current flowing through a human body for a 13.2 kV system is 7620 volts (phase to ground) / 1000 ohms = 7.62 amps (remembering OHM’s Law). Assume a 15 kV circuit breaker with both phase and ground relay protection (residual connection) in the example above is the protective device for the relevant circuit. If the circuit breaker inside the switchgear is programmed for 480 amp phase setting and 120 amp ground setting, the circuit breaker will not operate. Electrical workers should not assume circuit breakers are part of their personal protection. Page 3 of 3 Conclusions Again, it’s not the voltage that kills you, it’s the current. Remember to follow all safety precautions when working in the vicinity of energized equipment. Treat all equipment as energized unless you positively know equipment has been properly deenergized and grounded. Equipment should be grounded on both sides of working area if the possibility for feedback exists. KTR Associates, LLC understands power systems. KTR has many years of experience with protective relay coordination, power system analysis and has “Expert Witness” experience. KTR’s power system engineers specialize in designing safe power systems while insuring compliance with NFPA 70E standards. For additional information on power system protection requirements, please contact the following: Joseph Deane, PE 610 670 6061 EXT: 101