Electrical Safety...General Safety Tips, Lockout/Tagout, Appropriate Electric Equipment
This article is based on a presentation by Jim Hilton, senior electrical engineer in the Repair Department at Borton LC, Hutchinson, KS (800-835-9310/www. bortonlc.com).
He spoke in August at a Safety and Regulatory Conference sponsored by the Kansas Grain and Feed Association in Salina, KS.
All grain handling facilities use a tremendous amount of electrical energy, and not every elevator has the safest, most up-to-date electrical equipment.
Take, for example, a typical 900-amp electrical system dating from the 1970s in a relatively large grain elevator.
Alternating current (AC) from the power utility is received at an entrance switch, transformed down to the working voltage and 900 amps.
The cabinet containing the main entrance switch may have a ground fault protection sensor, but don�t be fooled into thinking that this is personal protection for anyone working on the electrical boxes.
This type of sensor is intended primarily for equipment protection.
And it doesn�t take a lot of amperage (electrical current) to cause a lot of damage to the human body.
The chart on page 31, taken from a manual provided for a maintenance engineering course offered by the American Institute of Baking, Manhattan, KS (800-633-5137/www.aibonline. com), details the effects of electrical current on the body.
Because the working voltage can arc across a certain distance in the event of a short circuit or other malfunction, it�s important to keep a certain amount of empty clearance space around electrical boxes.
Article 110 of the National Electrical Code (NEC) specifies a minimum of three feet in front of an electrical box and four feet between two facing electrical boxes.
General Safety Tips
The Bakery Equipment Manufacturers Association, Wilmette, IL (847-920-1230/www.bema.org), recommends the following safety procedures and practices in routine electrical maintenance.
� All eletrical or electronic maintenance and service should be performed only by trained and authorized technicians.
� Assume at all times that power is �on.� Treat all conditions as live. This practice ensures a cautious approach that may prevent an accident or injury.
� To remove load from a circuit or equipment, open the disconnect or breaker and lock it in an open position. For maximum protection, a locked out switch in the open position, using a lock for which only one person has the key, prevents anyone from accidentally turning on the power.
� Make certain that the circuit is open by using the proper test equipment. Note: Test equipment must be checked at regular intervals.
� Give capacitors time to discharge. Otherwise, discharge them manually with care.
� There may be circumstances where troubleshooting on live equipment may be required. Under such conditions, special precautions must be taken. Make certain that your tools and body are clear of the ground. Take extra safety measures in damp areas. And be alert, and avoid any outside distractions.
� Before applying power to any equipment, make certain that all personnel are clear of the machine.
� Open control panel doors only to check out electrical equipment or wiring. After the panel door is closed, make certain that on those panels, where applicable, the disconnect handle mechanism is operating properly.
� Close all covers on junction panels before leaving any job.
Dustproof Equipment
One question that frequently arises with electrical equipment is where Class II, Group G-rated equipment must be used in a grain handling facility.
The NEC code states that less-expensive general purpose enclosed motors, dust-tight lighting, etc. may be used anywhere that the equipment does not constitute a source of ignition under normal operating conditions.
In general, general purpose enclosed motors can be allowed in areas with low dusting and good housekeeping, such as finished package warehouses.
The overriding requirement is that the surface temperatures of electrical equipment not exceed the safe levels for their group classification. Note that Group G equipment may not exceed 329 degrees surface temperature in operation.
All Class II, Group G equipment should be used indoors, installed properly (keep the globe on lighting turned downward).
Don�t use this equipment outdoors, since not all Class II, Group G equipment is rainproof.
Some definitions:
Class II locations are hazardous because of the presence of combustible dust.
Class II, Division 1 locations are anywhere enough dust is suspended in the air during normal operation to produce explosive or ignitable mixtures of dust and air, or where mechanical failure could produce such a mixture plus a spark for ignition.
Class II, Division 2 are areas where combustible dust normally isn�t in the air in enough quantities to produce explosive or ignitable mixtures. However, equipment malfunction or mishandling could put sufficient amounts of dust in these areas to be explosive, and enough dust could accumulate on equipment to interfere with the dissipation of heat.
A general rule of thumb is that anywhere you can work all day without a dust mask is a Division 2 area. If you do need a dust mask, at least part of the time, it�s Division 1.
Written by Ed Zdrojewski, editor
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