Safe Reliable Electrical Connections for Mining Applications
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.
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.
Test Requirements and Ratings Comparison
To achieve their UL 2682 switch ratings, MELTRIC Switch-Rated plugs and receptacles 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 & receptacle listing.
Spring-Loaded Butt Contacts
MELTRIC products feature unique spring-loaded, butt contacts. These help to improve electrical performance and user safety. Butt-style contacts ensure a consistent connection. The spring-loading of these contacts provides a high contact force that remains consistent over thousands of operations. In addition, the high contact force automatically compensates for any wear and/or deviations resulting from manufacturing variances – reducing the chance of hazard caused by wear and tear.
As the accompanying chart demonstrates, contact resistance increases as contact force is reduced. Higher contact resistance generates more heat and oxidation, both of which contribute to the deterioration of the contact. Spring-loaded butt contacts reduce this hazard with their strong contact force. Other forms of contacts present hazards because their contact force varies due to wear caused by normal use and cannot compensate for manufacturing variances.
In conjunction with the ejection springs used on many MELTRIC products, the spring-loaded contacts ensure a quick breaking of the connection. This disconnection style serves as a safety feature arresting arcs and reducing hazards independent of personnel input, simply push the red button for disconnection.
Silver-Nickel Contact Material
MELTRIC uses solid silver-nickel (85 per cent/15 per cent) contacts. The silver-nickel material has significant advantages over the brass contacts commonly used on competitive devices.
Silver has very low initial contact resistance and is not negatively affected by oxidation. This helps to give it excellent electrical properties that are maintained even at high temperatures and after tarnishing. Nickel is used to provide hardness and improve mechanical properties. The combination of silver and nickel results in a contact material that has superior electrical capabilities and excellent resistance to wear. Silver-nickel also withstands arcs very well.
By contrast, the brass material used in most competitive plug and receptacles has a much higher initial contact resistance and is negatively affected by oxidation. In an oxidized state, the contact resistance of brass is more than 20 times higher than that of silver-nickel. In addition, brass is a soft material that wears rapidly. As the oxidation and wear induced reductions in contact force occur on the brass, contact resistance increases. This increases operating temperature, which causes further oxidation and wear, perpetuating a vicious cycle of degradation. Brass is not arc resistant and is not suitable for making and breaking under load.
MELTRIC provides added safety and reliability by providing an arc, wear, and tarnish resistant silver-nickel contact that will stand up in the most demanding of environments.
DECONTACTOR™ Technology and Safety
A MELTRIC Decontactor™ is a specialized electrical connector with push-button circuit disconnection that combines the safety and functionality of a disconnect switch with the convenience of a plug and receptacle in one device. This technology allows Switch-Rated plugs and receptacles to be safely connected and disconnected under full load, up to 200A and 100 hp, in wet or dry conditions.
DECONTACTOR™ technology prioritizes user safety by ensuring that the plugs and receptacles are safe to connect and disconnect even in “overload” conditions. The plug cannot be removed from the receptacle until after the contacts are de-energized eliminating arc flash hazards. Once the plug is removed, the receptacle’s dead-front safety-shutter prevents unintended access to live parts. When a Switch-Rated plug is disconnected from the receptacle it provides visual verification of equipment de-energization. It can then be easily locked-out and tagged-out as required. Since an electrically safe work condition is ensured, any qualified technician can safely make and break electrical connections under full load. And they can do so in compliance with NFPA 70E and CSA Z462 standards without having to “suit up”.