Wiring, electrical hazards

The process designer and project engineer should classify the various areas of a plant following NEPA-70, Article 50528.29 order to advise the electrical and other project team members of the degree of electrical hazards anticipated. The appropriate equipment (motors, instruments, conduit, wiring, etc.) should be specified according to NEPA-70, Article 500 and others as applicable, the ASME Code and the API Code as appropriate. See NEPA-497A and... 

Electrical Hazards— Potentially dangerous situations related to electricity (e.g., a bare wire). 

To avoid exposure to microwaves, ovens should never be operated with doors open. Wires and other objects should not be placed between the sealing surface and the door on the oven s front face. The sealing surfaces must be kept absolutely clean. To avoid electrical hazards, the oven must be grounded. If use of an extension cord is necessary, only a three-wire cord with a rating equal to or greater than that for the oven should be used. To reduce the risk of fire in the oven, samples must not be overheated. The oven must be closely watched when combustible materials are in it. Metal containers or metal-containing objects (e.g., stir bars) should not be used in the microwave, because they can cause arcing. 

At construction sites the most common electrical hazard is the grovmd fault electrical shock. A ground fault occurs when a hot electrical wire contacts a grounded enclosvu-e. In most situations, the fault will trip a circuit breaker or blow a fuse. However, if a break in the ground wire occurs, the worker would no longer be protected, unless a secondary safety measure is available. 

Eliminate electrical hazards. Check electrical cords for cracks, broken plugs, and poor connections. If you find damaged cords, replace them immediately. Never use makeshift wiring. Never overload extension cords. Too many appliances plugged into an extension cord can cause the cord to overheat and ignite the cord s insulation. 

Among the ANSI standards is the National Electrical Code (NEC) which is directed at the elimination or control of electrical hazards. It defines the classification of areas according to the degree of hazard possibly foimd in the atmosphere and prescribes wiring methods, grounding, control, etc. These factors are important in motor selection. The NEC is a product of the National Fire Protection Association (NFPA). 

The potential for electrical shock exists when removing the extruder covers, thus exposing bare wires and electrical connections. Extruder heater bands are normally 220 or 440 volts and can cause serious electrical shock. Check the wires to the heater bands on the die and adapters to assure there are no frayed, bare, or exposed wires or connections that can cause electrical shock. In some extrusion processes, watercooling baths are very close to the die, which can create additional electrical hazard. Operators unless properly trained should never remove guards exposing electrical terminals on heaters or open electrical cabinets to solve electrical problems. 

Is there any evidence of exposed wiring or electrical hazards ... 

Explosion-proof enclosures are characterized by strong metal enclosures with special close-fitting access covers and breathers that contain an ignition to the inside of the enclosure. Field wiring in the hazardous environment is enclosed in a metal conduit of the mineral-insulated-cable type. All conduit and cable connections or cable terminations are threaded and explosion-proof. Conduit seals are put into the conduit or cable system at locations defined by the National Electric Code (Article 501) to prevent gas and vapor leakage and to prevent flames from passing from one part of the conduit system to the other. 

Intrinsically Safe Equipment and wiring which is incapable of releasing sufficient electrical or thermal energy under normal or abnormal conditions to cause ignition of a specific hazardous atmospheric mixture or hazardous layer. 

These materials are developed from the polyetherimides introduced by General Electric (see also Section 18.14.2). At the time of writing one grade, Ultem Siltem STM 1500, is being offered. It is of particular interest as a material for wire and cable insulation, as it not only has excellent flame resistance coupled with low smoke generation but also avoids possible toxic and corrosion hazards of halogenated polymers. This can be of importance where there are possible escape problems in the event of a fire, such as in tunnels, aircraft and marine (particularly submarine) vessels. 

The mere fact that voltage, current, or even both, are at low levels does not guarantee a circuit to be intrinsically safe, even though intrinsically safe circuits do utilize relatively low voltage and current levels. Intrinsically safe systems employ electrical barriers to assure that the system remains intrinsically safe. The barriers limit the voltage and current combinations so as not to present an ignition hazard should a malfunction develop. Typically, devices upstream of barriers are not intrinsically safe and are installed in control rooms or other unclassified locations. All devices and wiring on the downstream side of the barriers are intrinsically safe and can be installed in classified areas. 

All wiring and electrical equipment in chemical plants should be installed in accordance with the National Electrical Code. Electrical equipment for use in hazardous locations should be recognized by Underwriters Laboratories (or other testing organizations recognized by the authority having jurisdiction) for the conditions to be encountered. 

About two-thirds of the N2 produced industrially is supplied as a gas, mainly in pipes but also in cylinders under pressure. The remaining one-third is supplied as liquid N2 since this is also a very convenient source of the dry gas. The main use is as an inert atmosphere in the iron and steel industry and in many other metallurgical and chemical processes where the presence of air would involve fire or explosion hazards or unacceptable oxidation of products. Thus, it is extensively used as a purge in petrochemical reactors and other chemical equipment, as an inert diluent for chemicals, and in the float glass process to prevent oxidation of the molten tin (p. 370). It is also used as a blanketing gas in the electronics industry, in the packaging of processed foods and pharmaceuticals, and to pressurize electric cables, telephone wires, and inflatable rubber tyres, etc. 

FPN) Hazards often occur because of overloading of wiring systems by methods or usage not in conformity with this Code. This occurs because initial wiring did not provide for increases in the use of electricity. An initial adequate installation and reasonable provisions for system changes will provide for future increases in the use of electricity. 

Scope—Articles 500 Through 505. Articles 500 through 505 cover the requirements for electrical equipment and wiring for all voltages in locations where fire or explosion hazards may exist due to flammable gas or vapors, flammable liquids, combustible dust, or ignitable fibers or flyings. 

All other applicable rules contained in this Code shall apply to electrical equipment and wiring installed in hazardous (classified) locations. 

Other inspection services available include the examination of steel structures (new and existing), electrical wiring installations, containers (to meet Statutory Instm-ment No. 1890), dangerous substances (carriage by road in road tankers or tank containers) to meet Statutory Instmment No. 1059, examination of second-hand plant prior to purchase, plant undergoing repair or modification, the Control of Industrial Major Accident Hazard Regulations (CIMAH) Statutory Instmment No. 1902 and Control of Substances Hazardous to Health (COSHH) and Pressure Systems Regulations. 

Additional Requirements. In addition to electrical and physical isolation requirements, the surface temperature of all equipment and wiring located in the hazardous environment must not exceed the values indicated in the standard. 

---