EX University: Explosion Proof Lift Truck Safety & Construction Techniques
An EX Enclosure is a case or housing that has been tested and approved to contain electrical components. Although the joints of EX enclosures will permit the entry of explosive vapors, the strength of the enclosures must contain any internal explosion. The enclosures of RICO EX Trucks have been hydrostatically tested by FMRC for internal explosive resistance to pressures in excess of FMRC requirements.
Protection Against Mechanical Sparks
The perimeter of the truck, including the forks and other exposed portions, must be covered in a brass, bronze, copper, or aluminum material. This requirement is intended to reduce the potential for ‘friction’ type sparks that may be generated if/when the truck comes in contact with other objects.
Mineral-insulated (MI) cable was developed to meet the needs of a noncombustible, high heat- resistant, and water-resistant cable. MI cable has from one to seven electrical conductors. These conductors are insulated in a highly compressed mineral, normally magnesium oxide, and sealed in a liquid tight, gastight metallic tube, normally made of seamless copper. RICO uses MI cables where space is constricted and flexibility is key.
Intrinsically Safe (IS) Wiring
By definition, intrinsic safety is an explosion protection technique applied to electrical equipment and wiring intended for installation in hazardous locations. The technique is based upon limiting both electrical and thermal energy to levels which are incapable of igniting a hazardous mixture which is present in its’ most easily ignitable concentration.
Static Conductive Tires
All wheels and tires shall be made of non-sparking material. At least two tires and wheels shall be made of electrically conductive material, or some other equivalent static discharge device shall be provided. Electrically conductive straps or chains may not be used to meet this requirement.
If drive belts are used as part of the vehicle design, they must be constructed from electrically conductive material. There shall be no slippage of the belt that may cause temperature rises that could ignite the explosive atmosphere.
EX Rated Battery
An EX rated battery must be used.
Prevents passage of gasses, vapors, and flames from one portion of the electrical installation to another through the conduit.
Provides a way for the burning gasses to escape from the device as they expand during an internal explosion; but only after they have been cooled off and their flames quenched.
- Some examples include the lid of an enclosure (Ground Surface Flame Path) and the entry of the conduit into an enclosure (Threaded Flame Path)
Threaded Rigid Metal Conduit
An acceptable wiring method. Conduit is made up of EX rated piping, elbows, couplers, etc. The conduit assembly must contain a seal and all connections must be wrench-tight with at least five full threads of engagement.