Date Published:Apr. 07. 2016

IPX7 Waterproof Evaluation of Sealing Washers

About IPX7

IPX7 is one of the protection classes for the enclosure of electrical machinery and equipment specified in JIS C 0920, and it indicates the protection class of enclosures that protect electric equipment against harmful environments caused by temporary submersion.

Summary of IPX7: Protects equipment so that it is not affected by water penetration.
Definition of IPX7: When the enclosure is temporarily submerged in water at the
                            prescribed pressure and time, there shall not be penetration of water in amounts
                            that produce harmful effects.

Test Method and Test Conditions

Test Method

Attach the screws and nuts so that the metal part of the sealing washer [SWS] comes into contact with the waterproof box, submerge in a 1 m deep water tank for 30 minutes, then check the penetration of water into the waterproof box.

Test Conditions

  • Test subject:Sealing washer [SWS] (sealing material: NBR) All sizes
  • Number of n:3 pcs per size
  • Screw:SUSXM7 hex socket head cap screws with A2-70 strength rating (JIS B 1176)
  • Nut:1 type of SUS304 hex nut (JIS B 1181)
  • Mounting hole and chamfer dimensions:Class 2 of JIS B 1001. Refer to the table below for details on the dimensions and tightening torque.
 Diameter of Thread   Mounting Hole(mm)   Chamfering(mm)   Tightening Torque(N・m) 
 M3  3.4  0.3  0.5
 M4  4.5  0.4  1.4
 M5  5.5  0.4  2.5
 M6  6.6  0.4  7.5
 M8  9  0.6  17
 M10  11  0.6  30
 M12  13.5  1.1  50
 M16  17.5  1.1  65

Test Results

In all the tests, there was no penetration of water into the waterproof box.


  • The mounting hole size, chamfer dimensions, and tightening torque above are reference values only.
  • The sealing effect varies depending on the operating environment. Also, since the sealing effect becomes weaker as the mounting hole and chamfer dimensions become larger, we recommend that the mounting hole and chamfer dimensions be as small as possible.
  • Since the metal part of the sealing washer may reach the allowable torque of the screw before it comes into contact with the counterpart material, be sure to pay attention to the torque while tightening.

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