TJB has been making Permissible (MSHA certified) couplers for over 40 years. Over that time the basic design has remained the same but many small changes have added up to a much better coupler since they first went in to production. Permissible couplers are rated 1KV or 5KV but have been designed and tested for up to 8KV in the event that the permissible voltage at the face is raised above its current level. Couplers are available with a PTFE insulator and since a no-thread connection can't be used on an Permissible coupler, a four pitch single start thread is used on all versions. Permissible couplers feature a special compression seal cable entrance for sizes up to and including 500MCM.
ADVANTAGES OF PTFE- PTFE while more expensive up front can save a substantial amount over the life of the coupler. PTFE is hydrophobic and non-stick preventing dirt build up and allowing for easier cleaning which reduces maintenance costs. Tracking which is caused by the slow breakdown of an insulator from high voltage stresses does not occur with PTFE and it is also is not impacted by most caustic chemicals resulting in most couplers with PTFE insulators being taken out of service due to job completion or mechanical damage.
PERMISSIBLE HOUSING- The single start thread on the permissible housing provides a long flame path for the MSHA rating while still being large enough that cross threading and thread roll over are not an issue. The nut design combined with both a hard coating and a permanent dry lubricant allows for easy coupling and prevents galling after repeated couplings. Keying to prevent the mating of different voltages is provided by the insulators allowing for standardized housings on all permissible couplers.
CABLE ENTRANCE- The standard TJB cable entrance can not be used in a permissible coupler, instead a compression seal is used. Two steel rings compress a rubber disk forcing it against the cable. This type of seal is very effective but requires precise sizing, making it imperative that accurate cable sizes are given at the time of order. Strain relief is provided by the same mechanism as on our other couplers. Two aluminum clamps sized to your cable, provide even pressure on the cable jacket. Flared ends on the cable side of the clamps reduce the risk of cable damage and mitigate binding that can occur with other types of strain relief.