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1 Electrical Safety 2 Introduction •Each year, about 9% of the fatalities in the American workforce is by electrocution while working around electricity. Many other workers are injured. Note: Based on Bureau of Labor and Statistics 3 Electrical Safety •This course is designed to present safe electrical work practices. Since electricity is the most widely used form of energy in most facilities, it is imperative that safe work practices are followed. 4 Introduction • The Federal government, through OSHA, has set a number of rules and regulations for working with electricity. These rules are in the 29 CFR 1910. • Michigan Rules: Part 39-Design Safety Standards for Electrical Systems Part 40-Electrical Safety-Related Work Practices 5 Voltages •The safety precautions in this presentation will be used for voltages between 50 volts and 600 volts. Most hospital equipment is set up for 115 (120) volts for most plug-in devices. 6 The “Code” •It is important to remember that this is an overview. The national and local electric “Code” will take precedence over any material in this presentation. •Maintenance will follow the Code. 7 Electrical Hazards •29 CFR 1910.303(b)(1) requires that ”Electrical equipment shall be free from recognized hazards that are likely to cause death or serious physical harm to employees” •Michigan has adapted the appropriate OSHA regulations 8 Electrocution •There are many sources of information. However, the accepted information states that a level of current between 70 and 200 milliamperes, if passed through the heart, can cause ventricular fibrillation. A milliamperes is 1/1000 of an ampere. 9 Ventricular Fibrillation Ventricular fibrillation means the heart loses meaningful pumping action thus causing death in a short period of time. This happens when a small current passes either (a) from head to foot, or (b) from hand to foot and thru the heart. About 100 milliamperes can do it 10 Electrocution •A typical household receptacle has about 15 Amperes •15 Ampere x 1000 = 15,000 milliamperes •It only takes ~ 100 mA to cause ventricular fibrillation. 11 Voltage Voltage: is the amount of electrical force (electromotive force). This is the difference of electron and proton potential. This measurement is between two points. This can be between “hot” and neutral, or between other charged items. Voltage is measured in volts (E). 12 VOLTS RMS Hot Neutral VOLTS One Cycle 13 Voltage 120 V 0V 120 V 220 V 100 V 120 V 100 Volts difference 14 Nominal Nominal: is the term used for the stated voltage for a given line. Example a 115 volt circuit may actually be 120 volts, but is called 115 volts nominal. 15 Current •There are two different types of current: AC-Alternating current DC-Direct current 16 Current Current: is the amount of electricity that flows in a circuit. Current is measured in amperes (I) (Amps). 17 AC to DC Rectified RMS Even flow of current 12V 18 AC and DC •Most existing equipment run on AC and DC 19 Resistance Resistance: opposes (uses) the flow of current measured in Ohms (R). This is caused either by the nature of the material or work done. Example: A toaster wires get hot due to resistance. 20 Volts and Amperes Resistance Voltage but no amps Force Voltage & Current Given point Force and movement 21 Ground Ground: Is the process of achieving earth neutral. This can be achieved by strategically placed earth grounds, or through a combination water main and earth ground. This ground should supply the system with a ground wire and neutral potential. 22 Ground •This is the symbol for ground. •May be on the back panels of equipment. 23 GFCI •Ground Fault Circuit Interrupter Prevents electrocution by detecting a ground fault and opening the circuit up. Activates at 5 mA 61 mA and 1/25 of a second fault. Note:Other sources have indicated between 4-7 mA and 1/40 of a second. 24 Ground Fault A fault between Hot and Ground 25 GCFI-Receptacle 26 GFCI •Are used in wet areas Bathrooms Kitchens Outside work Maintenance 27 Overcurrent •Overcurrent is the extra amount of current that passes through a circuit and an overcurrent protection device that usually opens the circuit. •These devices are usually circuit breakers or fuses. The fuses and breaker are on the load side of the disconnects. 28 Overcurrent Protection •A fuse or breaker usually works on the principle that the extra amount of amperage will cause a conductor to get hot and either “blow” or move to open an overloaded circuit. •You have fuses or breakers in your house and car. 29 Short Circuit •A short circuit is when there is a direct contact between “hot” and “neutral”. 30 Parallel Circuit •Even with one open circuit branch, the system is still hot. •Don't become part of this 120 volts circuit! 31 Static Electricity •Static electricity is the buildup of the difference of potential between materials. Positive Negative 32 Static Electricity • Static electricity is the buildup of the difference of potential between materials. • Static electricity is high in voltage but low in amperage (in most cases). • This is why you feel the static release charge, but usually it does not do physical bodily damage. • This spark can ignite flammable vapors and dust. 33 Static charges are caused by friction. 34 Clearance distance around panel boxes Normal voltage to ground Clearance distance 0-150 3 feet 151-600 3 ½ feet 35 Safety Distance 36 Disconnect Identification 3 1 2 37 Plugs 38 Receptacle Return neutral side Hot side 39 Extension Cords • 1910.305(g)(1)(iii) does not allow flexible cords to be used: As a substitute for fixed wiring Running through holes Running through doorways, windows, etc. Attached to building surface Behind walls, ceiling, or floors 40 Extension Cords •Additional material covered in 1910.305(g)(2)(ii-iii) requires that most flexible cords will not be used with splices, and will have a stress relief fitting or device to prevent the cord from pulling on the terminal screws. 41 Temporary wiring: •1910 305(a)(2) requires that temporary wiring be used for that purpose and not take the place of permanent wiring, and only be in place for a maximum of 90 days for decoration and like items. 42 Grounded Equipment •Never use a plug with a missing ground prong. •Always check before plugging into a receptacle. 43 Three Prong Cords 44 Three Prong Cords •Never use a plug with the ground prong missing. •Inspect all plugs for missing or bent blades or prongs. 45 End 46