Explosion proof fans

Mechanical part

Rosenberg fans for potentially explosive atmospheres are manufactured and tested in accordance with the state of technical knowledge. The possible contact surfaces between rotating and stationary components, in view of operating malfunctions which are typically to be expected, are manufactured using materials with a minimised ignition risk resulting from friction, grinding or impact sparks. The inlet and outlet of the fan can be fitted with guards, if required, to prevent the dropping or sucking in of foreign particles. The guards must at least meet the requirements of EN 13857.

Electrical part

The motor data for an optimally cooled motor are stamped onto the type nameplate and are part of the contents of the EC type examination certificate for zone 1 motors. Refer to the fan nameplate for the nominal fan data. In order to realise a favourable speed ratio for voltage-controlled fans with external rotor motors, motors may possibly be used which have a higher rated voltage than the fan voltage. In this case, the information on the motor differs from that on the fan in the voltage, current, power, speed and tipping time data.

Identification

As a result of the assessment of ignition risks, the fans will be marked as follows:

II 3G c IIB T3 (X) / II 2 G c IIB T3 (X)

Explosion proof operating equipment for potentially explosive areas is classified in the European Standard EN 60079-X. The individual ignition protection categories are detailed in separate standards, such as:

Ignition protection categories	Standard
General requirements	EN 60079-0
Equipment protection by flameproof enclosures "d"	EN 60079-1
Equipment protection by pressurized enclosure "e"	EN 60079-7
Classification of areas - Explosive gas atmospheres	EN 60079-10-1
Equipment protection by intrinsic safety "i"	EN 60079-11
Construction, testing and marking for Group II electrical equipment with type of protection "n"	EN 60079-15

Rosenberg external rotor motors comply with ignition protection category "nA" or "increased safety" "e".

These ignition protection categories are valid for electrical appliances in potentially explosive rooms and units, where gases or vapours can form or accumulate and produce explosive mixtures in combination with air.

The ignition protection category "Increased Safety" shows that increased safety measures are taken to prevent the possibility of inadmissibly high temperatures and the occurrence of sparks or electric arcs in the interior or on external components of electrical appliances which do not occur during normal operation (according to EN 60079-7).

Electrical equipment of ignition protection category "nA" is not able to ignite a surrounding potentially explosive atmosphere. They only can be used as category 3 (Zone 2) devices.

Zones

As a basis for determining the extent of requirements to be imposed, explosive areas are classified into zones according to the likelihood of a dangerous, explosive atmosphere or combustible dust. For combustible gases, vapours and mists, the following applies:

Zone 0

For areas where danger of an explosive atmosphere exists long-term (continuously) or frequently

Zone 1

For areas where danger of an explosive atmosphere exists during normal operation

Zone 2

For areas where danger of an explosive atmosphere seldom exists or only for short-term periods

Rosenberg ex-fans are suitable for the ventilation of explosive atmospheres in zones 1 and 2 as well as for installation in zones 1 and 2. When installing 2G fans in zone 2 or in non-potentially explosive atmospheres, or 3G fans in non-potentially explosive atmospheres, it should be taken into account that the fans are not gas-tight.

Temperature classes

Electrical appliances in potentially explosion areas are listed according to their maximum surface temperatures in temperature classes ranging from T1 to T6. The lowest temperature of ignition of the concerned potentially explosive atmosphere must be higher than the maximum surface temperature of the electrical appliance used (according to EN 60079).

Temperature classes	maximum surface temperature
T1	450 °C
T2	330 °C
T3	200 °C
T4	130 °C
T5	100 °C
T6	85 °C

Rosenberg fans in the Ex-versions are used for the temperature classes T1 to T3 (T4 on request).

Rosenberg Ex-fans are equipped with external rotor motors with a protection class IP44 as a standard, insulation class F and ignition protection category Ex e or Ex nA, or standard IEC motors with a protection class IP 55, insulation class F and ignition protection category Ex e (Ex d/Ex de available upon request). The motors were tested by the PTB (Federal Physical Technical Institute) and correspond to the European Standards series 60079-xx.

Motor protection of external rotor motors

The winding of the motors feature integrated triple PTC thermistor temperature sensors according to DIN 44082, which must be connected to a PTC thermistor tripping unit with protective labelling Ex II (2)G as motor protection. This specific thermal motor protection is capable of precisely identifying any abnormal operating conditions and external influences, and will then disconnect the motor from the mains via a contactor in the event of any conceivable malfunction. It is only permissible to install commercially available motor circuit breakers as additional safety devices, since they are not able to ensure complete motor protection under all conceivable operating conditions (e.g. operation with reduced voltage).

Speed control of external rotor motors

The design of the drive motors allows for a stable modulation of the motor speed via a voltage reduction. Only transformer controllers may be used for this purpose. Rosenberg controllers for use with explosion-proof fans already contain the mandatory essential PTC tripping device, but they must not be operated directly in a potentially explosive zone.  Refer to the tables of the accessory list for the allocation of the controllers. The permissible voltage modulation range of between 25 and 100 % of the nominal voltage meets the typical requirements of systems with a variable volumetric flow. If the system is operated in the reduced-voltage range, the operating current may exceed the nominal current. The percentage current increase in comparison to the nominal current is listed in the data tables as Delta I. Controller and control units must be designed to handle the maximum operating current. Regular external rotor motors with the ignition protection category “e” are not allowed to be used with frequency converters.

Motor protection of IEC standard motors

Standard motors have to be fitted with an upstream motor protection switch. The information provided by the motor manufacturer is to be observed. Standard motors with the PTC thermistor permit as single motor protection can also be protected with a PTC thermistor tripping unit. Refer here to information under motor protection for external rotor motors. However, an authorised motor protection device must be connected in any case.

Speed control of IEC standard motors

The speed of standard motors can be controlled by frequency converters. In this case, only motors with ignition protection categories "d" or "de" should be used.