An Insight into Dust-Proof Motors
What are Dust Ignition Proof (DIP) motors used for?
In environments where combustible dust surrounds the motor or where dust might settle under its own weight on the motor, Dust Ignition Proof (DIP) motors are used. Cereal, animal feed, paper, wood, chemicals, plastics and coal are some of the typical applications.
Do DIP motors undergo testing and approval?
Notified Bodies are independent testing laboratories that perform tests, audit quality systems and issue reports and certificates of conformity to design and manufacture.
What do DIP motors look like?
DIP Motors will typically contain the following markings on its data plate
- CE markings are the manufacturer’s commitment to complying with the relevant directive. The Number following ‘CE’ will indicate the Notified Body responsible.
- The Ex mark is the European Commission mark for products approved for hazardous areas.
- A Motor Grouping will indicate where the motor is approved for use ( II is for surface industries and I is for mines ).
- Equipment categories show which atmosphere the motor is approved for use in. 2 is for Zone 21 or Zone 22 with conductive dust, 3 is for Zone 22 without conductive dust.
- A marking which relates to it’s certification to work around Dust (D) or Gas and Dust (G-D)
- The maximum surface temperature
Classifications of dusty atmospheres
As with hazardous environments for gas, hazardous environments for dust are divided into zones, these are shown below
- Zone 20: Combustible dust is present permanently. Motors cannot be operated here.
- Zone 21: During normal duty, combustible dust may be present. A motor can only be installed if it has been approved and certified by a Notified Body.
- Zone 22: The presence of combustible dust only occurs by accident, not during normal operations. In the presence of conductive dust, only motors approved by a Notified Body can be installed. Dusty atmospheres can be handled with motors approved by the manufacturer for use in dusty environments.
- A cloud of dust must have an ignition temperature at least 50% higher than the motor’s marking temperature: or, the marking temperature cannot exceed two-thirds of the ignition temperature of the dust. For instance, if the ignition temperature of the dust is 210°C, the motor’s marking temperature must be lower than 140°C
- A 5mm layer of dust must be ignited at 75°C above the motor’s marking temperature. When the ignition temperature is 200°C, the marking temperature must be 125°C or lower. The user must stage maintenance periods so that the dust layer does not build up above 5mm.The ignition temperatures for various types of dust can be found in commonly available reference tables
What makes Dust Ignition Proof motors different from standard motors?
For a DIP motor, the cooling fan is made of metal or another anti-static material. static electricity. The terminal board has been enhanced to ensure higher security. The temperature marked on the motor corresponds to the performance at the worst conditions allowed for the model. To prevent dust ingress, Zone 21 and Zone 22 motors are protected to IP 65, and IP 55, respectively.
What should be considered when selecting Dust Ignition Proof motor?
The motor must be approved by a Notified Body if it is intended to be used in Zone 21, i.e. in an area with the presence of explosive atmosphere during normal duty. Any motor designated as a DIP motor by its manufacturer can be used in Zone 22 unless conductive dust is present.
How can I determine if a motor complies with the relevant directive?
Motors used in potentially explosive atmospheres must comply with Directive 94/9/EC (the ATEX directive). CE marked motors are delivered with a CE Declaration of Conformity. The document identifies which Directive the CE mark refers to.
What if the atmosphere also contains gas?
When a motor is installed in an environment that contains both gas and dust, it must meet the requirements for both. As an example, EEx d motors of size 80 to 315, in temperature class T4, and modified for use as DIP motors can be installed in both atmospheres.