Locking devices
Ark-Gard ENP, ENR, ENC explosion-proof NEMA locking devices
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Ark-Gard ENP, ENR, ENC explosion-proof NEMA locking devices

Ark-Gard explosion-proof NEMA receptacles, connectors and plugs make it safe and easy to bring power wherever it is needed.

Ark-Gard receptacles incorporate three spring-loaded slide keys that prevent the receptacle face plate from being rotated until the ENP plug is fully inserted into the receptacle.  To make the connection, the ENP plug is fully inserted, and the receptacle face is moved inward by pushing the plug forward.  The plug is then rotated, closing the circuit.  As rotation begins, the plug becomes locked in the receptacle and cannot be accidentally disengaged.  In making or breaking the circuit, any resulting electrical arc is confined in the factory sealed chamber.

Ark-Gard devices are used with portable or fixed electrical equipment such as motor generator units, welders, pumps, compressors, heating and cooling units, cellular relay stations, conveyors, lighting systems and similar equipment.  Approved for use in Class I and Class II areas made hazardous by the presence of flammable vapours and gases or combustible dust.

Commonly used during standard maintenance or plant turnarounds with equipment with power requirements that do not exceed 20 amperes.

Certifications and compliances

ENR receptacles (M3 and M4 models) and ENP plugs:

  • Class I, Divisions 1 & 2, Groups B†, C, D
  • Class II, Divisions 1 & 2, Groups F, G
  • Class III
  • ANSI/UL standard: 1010
  • NEMA/EEMAC 3, 3R (M4 only), 7BCD, 9FG

†Receptacle units alone (i.e. ENR5201) are not suitable  for Class I, Group B.

ENC connectors:

  • CSA certified CSA C22.2 No. 159M
  • Class I, Groups B, C, D
  • Class II, Group G, Coal Dust
  • Class III
  • NEMA 3R, weatherproof
  • NEC Article 501.140 compliance

Design features

  • Factory sealed chamber in receptacle and connector encloses the potential arcing components between two explosion-proof threaded joints; these threads are specially coated to guarantee freedom of movement, which ensures on-off action; no additional seals are required
  • One-piece moulded gasket seals cover plate and ENP plug when plug is inserted, providing full environmental protection at the receptacle face

ENR M4 premier receptacles:

  • Gasketed screw cap cover design offers superior protection from harsh environments for increased product life
  • Spring-loaded sliding key increases safety by rejecting standard NEMA/EEMAC configuration plugs that could cause an arc in a hazardous area
  • Saddle clamp terminals are easy to wire, reducing installation costs and effort
  • Lockout/tagout hole complies with OSHA lockout/tagout requirements

ENR M3 value receptacles:

  • Top-hinged cover design with 45° downward angle provides superior protection in damp, wet, and dirty locations

ENP plugs:

  • Captive set screw design assures ease of installation and reduces likelihood of losing critical components in the field
  • Insulator and contact components are now a single-piece assembly
  • ENP plugs can be used in non-hazardous areas with standard U-ground NEMA/EEMAC configuration 5 and 6 receptacles, eliminating the need for two separately equipped portable units of the same type; the ENR receptacle will not accept standard NEMA/EEMAC configuration plugs
  • Plug body is designed with an internal cord strain relief mechanism and a cable sealing grommet which will accept various cable diameters

ENC connectors:

  • Uni-Shell handle body provides a smooth, durable external surface that prevents the connector from getting snagged on equipment or other cables
  • Spring-loaded sliding key increases safety by rejecting standard NEMA/EEMAC configuration plugs that could cause an arc in a hazardous area
  • Increased environmental reliability with hinged locking cover that provides weather protection in damp, wet and dirty locations; cover stays closed until connection with ENP plug is required
  • Improved safety with integral lockout/tagout eliminates risk of operator or contractor plugging in process equipment when conditions are unsafe
  • Saddle clamp terminals provide increased safety with easy-to-terminate connection points for reliable conductor terminations
  • Increased safety with captive Tri-Lock design: three points of contact prevent pinching of cables that could damage internal conductors or cable jacket; captive screws prevent critical components from getting lost during installation
  • Snap-in internal insulator increases safety of personnel with intermediate insulator between conductors and metallic outer shell

Standard materials


  • Receptacle housing and spring door – copper-free aluminium
  • Receptacle interior – Krydon fibreglass-reinforced polyester
  • Receptacle contacts – brass
  • Receptacle cover hinge pin and spring – stainless steel
  • Receptacle gasket – neoprene


  • Plug interior – nylon
  • Plug contacts – brass
  • Plug bushing – Neoprene


  • Connector body – copper-free aluminium
  • Connector insulation – fibreglass-reinforced polyester
  • Connector contacts – brass

Drawings and design support