Maximizing Electrical Safety and Compliance in Mining
Electrical hazards are one of the top five major causes of fatality in mining. This can occur from exposed wiring and cables in wet / damp climates, dust and gases generating fires or explosions, inadequate lockout / tagout, system failure components, and arc flash, as well as other sources.
While there isn’t one perfect solution to minimize these fatal risks, there are tools to help keep efficiency high while minimizing electrical hazards and prioritizing the safety of miners. For example, MELTRIC, a company that designs durable plugs and receptacles for the safety of its end users is a beneficial tool to help minimize risks like an electrical shock in a mining environment while maintaining compliance.
Grounding mining equipment
Grounding electrical equipment in mining is crucial for the safety of anyone coming in contact with it. As outlined in Standard M421-16 – Use of Electricity in Mines, equipment is grounded so that in the case of any present overvoltage it should dissipate to ground and, if this isn’t happening, the voltage can build up, which can be as dangerous and deadly as touching a live wire.
Typically, mining equipment is grounded and monitored with Mining G-GC circuitry; a composite cable with a ground check conductor is used to accomplish this, running a voltage potential of zero to ensure the ground remains constant and no ground interference is happening.
There are limited alternate solutions to maintain the safety of the Mining G-GC circuitry – hard-wiring, running two connectors together, and a plug and receptacle with auxiliary contacts that mimic a ground check conductor. The safest option is using MELTRIC plugs and receptacles with auxiliary contacts which adjust for the additional conductors required in the Mining G-GC circuitry.
The integral pilot contacts in these devices allow users the convenience and flexibility of controlling auxiliary equipment, monitoring parameters (such as motor temperature), and / or communicating alarms through the same plug and receptacle used to supply power to the equipment. Because the pilot contacts are integral, they also facilitate the rapid change-out or reconfiguration of equipment by eliminating the need for hardwiring or multiple plug connections and saving both time and effort for monitoring and replacement of equipment.
Test requirements and ratings comparison
Most mining applications require electrical connections that can handle frequent connection / disconnection with reliable conducting power and proper safety ratings. Standard brass pin and sleeve plugs and receptacles work but they do not last very long due to high initial contact resistance and negative effects of oxidation on the brass material used.
Unlike ordinary pin and sleeve devices, MELTRIC Switch-Rated devices use solid silver-nickel material as the contact surface for superior conductivity with spring-loaded butt contacts for thousands of consistent and reliable connections all while prioritizing operator safety.
MELTRIC Switch-Rated plugs and receptacles achieve UL 2682 switch ratings. They have passed tests that far exceed those of ordinary plugs and receptacles. These tests include horsepower / locked rotor overload tests from the UL 508 standard for Industrial Control Equipment and electrical endurance and short-circuit make-and-withstand testing from the UL 98 standard for Enclosed and Dead-front Switches.
To illustrate how the electrical and mechanical endurance of MELTRIC Switch-Rated plugs and receptacles far exceeds standard plugs, the following chart compares the test requirements for achieving a Switch-Rated plug & receptacle listing with those required for a standard pin and sleeve plug and receptacle listing.
Eliminating arc flash exposure
Accounting for arc flash can complicate the efficiency of safely connecting and disconnecting mining, quarrying, and aggregate electrical equipment. Drawing an arc during plug removal is an inherent hazard with traditional pin and sleeve and twist-type devices. By contrast, MELTRIC Switch-Rated devices isolate the making and breaking of the contacts in an enclosed arc chamber. The plug contacts are de-energized and isolated from live parts before the plug can be physically removed.
When the receptacle’s OFF button is pushed, its spring-loaded operating mechanism instantly opens the contacts to break the circuit and ejects the plug to its OFF position. The quick (15 milliseconds) breaking of the contacts minimizes arcing, and any arcing that does occur is safely contained within the internal and enclosed arc chamber.
In the OFF position, the plug contacts are dead and separated from live parts by a safe distance. Isolated and inaccessible to users, all contacts are fully contained within an enclosure formed by the plug’s skirted casing and the receptacle’s casing.
The rotation of the plug required prior to its removal from the receptacle automatically closes and locks the safety shutter. This ensures that potential arc paths and access to live parts are blocked before the plug can be removed. There is no possibility of drawing an arc and the hazard is eliminated.
Designed for safety
The technology behind MELTRIC Switch-Rated devices was specifically developed to address the shortcomings and safety hazards that occur with the use of traditional plugs and receptacles. For an industry as dangerous as mining, these plugs and receptacles make the dangerous environments much safer without much additional effort.