Gland Plate Entry - Clearance Hole or Threaded Hole 1

[NickParker]

When is a clearance hole (no threads) and Threaded hole (for example, NPT) on the Gland plate done?
For Ex d enclosures, why only threaded hole to be used?
I understand that if the thickness of the gland plate is less, threaded entry cannot be made.

 

[waross]

The principle of the labyrinth seal is used on many Ex rated enclosures.
Rather than containing an explosion, a path is provided that is intended to cool hot gas below the ignition temperature.
Often covers are fitted with wide flat flanges and lots of bolts.
Gland connectors are threaded so that expanding hot gas is forced through the cover flange rather than past the gland connectors.
When time, labour and tooling are considered, threaded holes are seldom used for non Ex rated applications.
There are exceptions.

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Ohm's law
Not just a good idea;
It's the LAW!

 

[Kiribanda]

Through threaded entries the arc has got cooled enough after passing through the labyrinths of the threads when it comes outside.