ingress dust & rain water in flame proof AC & DC motors

D

Thread Starter

d.b.sharma

We are a manufacturing company and have developed a soft sealing gel which is totally resistant to water, acids, alkalies, dust with no memories and non drying properties. During a recent visit to gas sweetning plant in India we were surprised to note from an Electrical engineer that the voids and gaps in terminal box mountings are meant for possible exit of gases caused by a possible fire.
Please comment.
 
B

Bruce Durdle

An enclosure protected using the flameproof technique (marked Ex d in standard IEC terminology) will allow gases to penetrate the enclosure where it is possible they will be ignited by arcs, sparks, or hot spots. However,
the enclosure is designed so that any effects of this fire or explosion cannot reach the outside atmosphere. As part of the design, the enclosure
will have carefully tailored air-gaps that have two purposes:

1 They act as vents to allow products of combustion to escape, and so reduce the pressure rise in the enclosure in the event of a fire or
explosion.

2 The hot gases passing through the gap are cooled to below a temperature that will ignite the outside atmosphere.

Any actions that will change the characteristics of the air gap may make the enclosure no longer safe in the event of an internal explosion - this
includes either adding seals or compound to the mating faces to try and seal the gap (unless the seal is perfect, it will increase the air gap clearance and mean that the cooling effect is no longer operative) or trying to seal the joint by applying tape or other material on the outside (this will prevent gas venting and increase the internal pressure.)

Bruce.
 
B

Bob Peterson

This is how flameproof (similar to US explosion proof) enclosures work. The flames are cooled by the passage through the threads or past the flanges. The cooled gases are cool enough not to cause ignition once they reach the outside of the box.

Bob Peterson
 
Top