The entry devices of flameproof type mainly include cable entry devices, conduit sealing devices, EX blocking parts, EX threaded pipe joints and insulating sleeves. The installation threads (the threaded entry ports installed on flameproof type equipment) of these entry devices should meet the following requirements:
1. Thread type: cylindrical threads shall be metric threads, and conical threads shall be NPT.
2. The fit grade of metric threads shall be 6g/6H or above as per the relevant regulations, and the remaining wall thickness at the deepest point of any chamfer or relief groove of the internal thread shall not be less than 2 mm.
3. NPT external threads with flanges or blanking plugs shall have an effective thread length not less than dimension “L2”, and the length between the flange end face and the thread tail shall not be less than dimension “L4”.
4. NPT internal threads shall be measured with L1 plug gauge from “buried” to “2 turns”.
5. The length of the external thread section shall be at least 8 mm and shall contain at least 8 thread pitches. If the thread has a relief groove, an integral and non-compressible washer or equivalent device shall be assembled to ensure the required thread engagement length.
*NPT Ex sealing plugs shall have no flange.
# Considering the possible chamfer or relief groove when installed into the equipment inlet, the requirement of 8 thread pitches is to ensure at least 5 thread pitches engagement.
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