Spark Resistant VS Explosion Proof Motor

Location
Ohio
Occupation
Engineer
I am looking at some fan constructions on a manufacturers website. This manufacturer claims that explosion proof motors actually means that the fan has spark resistant construction.

I though explosion proof meant that if there was an explosion, the explosion would be contained with in the housing and conduit of the explosion proof device. For motors, is this definition different and actually implies spark resistance as well?

Here is the exact wording from the manufacturer:

"When researching equipment for potentially explosive applications and environments, it is not uncommon to hear about “explosion-proof” fans. The phrase “explosion-proof” is often used to describe fans that are designed with enclosures for electric motors and disconnect switches. The correct description is that the fan features Spark Resistant Construction (SRC)."
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
The manufacturer is making a distinction between the technical and the more common use of the term explosionproof.

Most, although not all, explosionproof motors are modified TEFC. The motor's fan is not in the explosionproof housing of the assembly; rather it is mounted on an external extension of the shaft. Various design features of the fan, such as physical distances and close tolerances, and materials of construction virtually eliminate the likelihood of the fan creating a spark.
 
Location
Ohio
Occupation
Engineer
Thank you for the response. When going through the process of identifying a motor/fan application for Class I Division 2, do you think it is necessary to be able to show the spark resistance of the fan blades? I think it is a nice to have, but if the construction of the fan make it such that a spark would only be generated in during a malfunction, i would think standard fan blades would be OK in a Class I Division 2 location..
 

rbalex

Moderator
Staff member
Location
Mission Viejo, CA
Occupation
Professional Electrical Engineer
Read all of Section 501.125(B) carefully, especially Subsection 501.125(B)(3). The NEC is pretty generous with motors in Class I, Division 2.
 

kwired

Electron manager
Location
NE Nebraska
Ferrous containing metals have more tendency to spark when rubbed across other items, especially another ferrous containing metal.

"Spark resistant" might be as simple as making a moving component out of non ferrous metal so it won't create a spark if it rubs against other component(s).
 
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