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Unformatted text preview: Electrical hazards exist when wires or other electrical parts are exposed. Wires and parts can be exposed if a cover is removed from a wiring or breaker box. The overhead wires coming into a home may be exposed. Electrical
If you touch live electrical parts, you will be shocked. This hand-held sander has exposed wires and should not be used. Page 24 Section 5 terminals in motors, appliances, and electronic equipment may be exposed. Older equipment may have exposed electrical parts. If you contact exposed live electrical parts, you will be shocked. You need to recognize that an exposed electrical component is a hazard. Approach boundaries
The risk from exposed live parts depends on your distance from the parts. Three "boundaries" are key to protecting yourself from electric shock and one to protect you from arc flashes or blasts. These boundaries are set by the National Fire Protection Association (NFPA 70E). The limited approach boundary is the closest an unqualified person can approach, unless a qualified person accompanies you. A qualified person is someone who has received mandated training on the hazards and on the construction and operation of equipment involved in a task. The restricted approach boundary is the closest to exposed live parts that a qualified person can go without proper PPE (such as, flame-resistant clothing) and insulated tools. When you're this close, if you move the wrong way, you or your tools could touch live parts. Same for the next boundary: The prohibited approach boundary--the most serious--is the distance you must stay from exposed live parts to prevent flashover or arcing in air. Get any closer and it's like direct contact with a live part. Electric Shock Boundaries To Live Parts for 300600 Volts
Prohibited Approach Boundary 1 inch Power source Restricted Approach Boundary 1 ft. Limited Approach Boundary 3 ft. 6 in. Section 5 Page 25 S A F E T Y M O D E L S TAG E 1 -- r E C O G N I Z I N G H A Z A r D S
APPrOACH BOUNDArIES To protect against burns, there's one more boundary: The flash protection boundary is where you need PPE to prevent incurable burns, if there's an arc flash. Flash Protection Boundary For Live Parts For 300600 Volts
Flash Protection Boundary 4 ft. Power source Overhead powerlines kill many workers! Keep outside the flash protection boundary Photo from Fluke Corporation "Electrical Safety Video" by Franny Olshefski (reprinted in IBEW Local 26 Newsletter May 2005) Page 26 Section 5 Overhead powerline hazards
Most people do not realize that overhead powerlines are usually not insulated. More than half of all electrocutions are caused by direct worker contact with energized powerlines. Powerline workers must be especially aware of the dangers of overhead lines. In the past, 80% of all lineman deaths were caused by contacting a live wire with a bare hand. Due to such incidents, all linemen now wear special rubber gloves that protect them up to 36,000 volts. Today, most electrocutions involving overhead powerlines are caused by failure to maintain proper work distances. Watch out for exposed electrical wires around electronic equipment. Electrical line workers need special training and equipment to work safely. Section 5 Page 27 S A F E T Y M O D E L S TAG E 1 -- r E C O G N I Z I N G H A Z A r D S Operating a crane near overhead wires is very hazardous. Shocks and electrocutions occur where physical barriers are not in place to prevent contact with the wires. When dump trucks, cranes, work platforms, or other conductive materials (such as pipes and ladders) contact overhead wires, the equipment operator or other workers can be killed. If you do not maintain required clearance distances from powerlines, you can be shocked and killed. (The minimum distance for voltages up to 50kV is 10 feet. For voltages over 50kV, the minimum distance is 10 feet plus 4 inches for every 10 kV over 50kV.) Never store materials and equipment under or near overhead powerlines. You need to recognize that overhead powerlines are a hazard. F ive workers were constructing a chain-link fence in front of a house, directly below a 7,200-volt energized powerline. As they prepared to install 21-foot sections of metal top rail on the fence, one of the workers picked up a section of rail and held it up vertically. The rail contacted the 7,200-volt line, and the worker was electrocuted. Following inspection, OSHA determined that the employee who was killed had never received any safety training from his employer and no specific instruction on how to avoid the hazards associated with overhead powerlines. In this case, the company failed to obey these regulations: mployers must train their workers to recognize and avoid unsafe E conditions on the job. mployers must not allow their workers to work near any part of an E electrical circuit UNLESS the circuit is de-energized (shut off) and grounded, or guarded in such a way that it cannot be contacted. round-fault protection must be provided at construction sites to G guard against electrical shock. Defective insulation hazards insulation--material th...
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This document was uploaded on 03/14/2014 for the course ECE 482 at University of Tennessee.
- Spring '09