For the rubber packing between case and cover, the overall- surface packing method is adopted; hence perfect air-tightness is maintained, and even in the case of repeated tension due to push-button operations, no deterioration will occur.

The case cover is made of premixed resin, which has outstanding corrosion-proofing as compared with ordinary steel or cast-iron plates. Further, since stain-less steel is used for cover-fixing screws and padlock-locking plate, there is no need to worry about corrosion.

For the OFF push-button, the locking unit using a padlock plate is a standard type; hence by padlocking, it is conformed to Article 107 (2) of the Labor Safety and Hygiene Regulation.