Electrical machines
To ensure that a machine’s temperature does not exceed the permitted limit, the machine shall be protected against overtemperature.
As protection against overtemperature, one of the following devices may be used:
– current-dependent overload protection connected in all phases and set to no more than the machine’s rated current, e.g. a starter (motor protection circuit breaker) with overload relay. For star-connected motors connected to systems with
a non-directly earthed neutral point, however, connection in only two phases is required
– a temperature-sensing element built into the machine that actuates a suitable device for all-pole disconnection. The type-approval certificate or other documents shall show that the protection also functions effectively with a locked rotor
– other devices that provide protection equivalent to the above against impermissible temperature rise.
The making and breaking capacity of devices for switching the motor on and off shall be equal to or greater than the motor’s starting current.
Coordination between overload and short-circuit protection shall meet the highest requirements in the applicable standard.
Automatic restart after disconnection due to overtemperature, etc., shall not occur. Measuring devices may have automatic reset.
When using current-dependent overload protection for a delta-connected motor, one of the following protections shall be used:
– a current-sensing relay set to no more than the motor’s rated current (line current), combined with phase-imbalance protection so that tripping occurs with the motor unloaded and with an open circuit in one of the windings
– a current-sensing relay connected in each phase and set to 58% of the motor’s rated current.
NOTE – Normal overload protection connected only in the main circuit of a delta-connected motor does not provide sufficient protection against temperature rise in the event of a winding open circuit. Only with a fully loaded motor is sufficient imbalance obtained in the line current for normal overload protection to operate. A delta-connected motor with a winding open circuit may also be able to start if no special measures are taken.
A slip-ring motor shall, in addition to overtemperature protection as above, be protected by an instantaneous current-sensing device set to slightly above the calculated starting current, but not higher than four times the motor’s rated current.
Transformers
Power transformers should not be installed in zone E1. Transformers shall be provided with short-circuit protection on the primary side and, with the exception stated below, overload protection on the primary or secondary side. A transformer that continuously withstands the short-circuit current at rated voltage and rated frequency without impermissible temperature rise need not be provided with overload protection.
Capacitors
Power capacitors should not be installed in zone E1. Regardless of the location of the installation site, a capacitor that, even after the voltage has been disconnected, remains connected to a circuit within zone E1 shall be provided with a discharge circuit that discharges the capacitor to a value that is not hazardous for the hazardous area. If the discharge time is longer than 30 seconds the enclosure in zone E1 shall be provided with a sign stating the time that must elapse after the voltage has been disconnected before the enclosure may be opened.
Electrical switches
Electrical switches shall have the required making and breaking capacity for the load present. The enclosure of an electrical switch that can be remotely operated shall be interlocked with an isolator so that the enclosure cannot be opened when the switch is energized. Alternatively, the interlock may be replaced by a sign stating that the enclosure must not be opened when the switch is energized. Remote operation refers to control impulses that may be, for example, mechanical, electrical, electro-optical, pneumatic, acoustic, magnetic, or thermal.
Electrical switches with contacts in oil shall not be used. Electrical switches for circuits in hazardous areas shall be connected in all phase conductors. For electrical switches for electrical machines, see the heading Electrical machines.
Electric heating appliances for space heating
Electric fan heater (aerotemper)
An electric fan heater for blowing air into zone E2 or into storage rooms that are not used continuously shall be designed and arranged as follows:
The electric fan heater shall have an explosion-protected design corresponding to Swedish standard, see SS-EN 60079-14, or be designed in accordance with the applicable requirements for an electric fan heater intended for areas with increased fire risk, see section 422.3 of the Electrical Installations Rules.
NOTE – Dehumidifiers where the electric heating element is not located in the supply air duct do not need to be designed as above.
The electric fan heater shall be permanently installed outside the hazardous area. The installation location shall be separated from the hazardous area by a wall constructed to at least fire resistance class EI 30 with a surface finish of class B-s1, d0 (previously
class I) on the side facing the electric fan heater.
The air shall be taken from a location where there is no risk that it may contain explosive substances, other combustible dust, or an explosive gas mixture. The air intake shall be fitted with a metal wire mesh with a mesh size of 6–8 mm.
The air duct between the electric fan heater and the air outlet opening shall be made of non-combustible material.
The air outlet opening shall be fitted with a damper of non-combustible material that shall close automatically when the airflow stops.
The temperature of the air discharged from the electric fan heater should not be higher than 100°
Other electric heating appliance
An electric heating appliance for use in zone E2 or in storage rooms that are not used continuously shall be permanently mounted and permanently connected, and shall be dimensioned so that the temperature of touch-accessible surfaces does not
exceed 100°C. The appliance shall have built-in overtemperature protection (fail-safe protection) that, after tripping, does not automatically re-energize the appliance.
The electric heating appliance shall be positioned so that
– heat dissipation is not impeded
– it is not covered with dust or other particulate matter
– unrelated objects are not placed on it
– it is not exposed to mechanical damage, e.g. impact from vehicles.
Heating cables and similar heating devices
Heating cable shall be installed in accordance with SS 436 47 53 with the changes or additions stated here, which also apply to similar heating devices, e.g. heating tape and heating film. NOTE 1 – Additional instructions for the installation of heating cables in industry are provided in SS-EN 60079-30-2 and SS-EN 60519-10. The requirements also apply to heating cable installed outside zone E1 but intended to transfer heat to zone E1, e.g. to prevent condensation in an exhaust air duct from zone E1. Heating cable shall not be installed in zone E1, zone E3, or in storage rooms. The heating cable shall be of the self-limiting type and have a metal sheath or metal screen with or without armouring. The metal sheath or metal screen shall be protective-earthed. Any armouring present shall be connected to the equipotential bonding system, if such exists, or to the earthing electrode of the electrical installation. Self-limiting heating cable means a heating cable whose temperature does not exceed a specified maximum value, regardless of length and cooling conditions, when connected to a specified voltage. The self-limiting function generally means that heat is generated in a conductive resistive material embedded between two parallel conductors, and that the resistivity of the conductive resistive material varies with temperature in such a way that power output decreases as temperature increases. The heating cable’s metal sheath or metal screen shall be protected against corrosion. Corrosion protection may be achieved either by selecting a corrosion-resistant material for the metal sheath or metal screen, or by providing it with an outer sheath of insulating material.
NOTE 2 – An outer PVC sheath generally permits a maximum operating temperature of 90°C. At higher operating temperatures, the outer sheath may consist, for example, of Teflon. Installation and end termination Installation, jointing, and end termination shall be carried out in accordance with the heating cable manufacturer’s instructions and using accessories specified by the manufacturer. When jointing and end terminating, it shall be ensured that moisture cannot penetrate into the cable’s insulating material. The heating cable shall be installed so that it is not subjected to mechanical stress, e.g. if a pipeline may be subject to movement due to temperature changes. At pipe joints, valves, and similar points, the heating cable shall be installed so that maintenance and repair are facilitated and can be carried out without damaging the heating cable. The heating cable shall be connected so that the junction box and connection point are not exposed to harmful temperature. Electrical protection No other loads may be connected to the group circuit for the heating cable. Each group circuit shall include a residual current device (RCD) with a rated residual operating current not exceeding 300 mA. The RCD’s rated current (through current) shall be dimensioned with regard to the inrush current and the short-circuit protection. The function of the RCD shall be tested at intervals of no more than 6 months. Signs In addition to at the distribution board, a sign shall be posted at each item stating that a heating cable for power current is installed. For items of large extent, e.g. a pipeline, signs shall be provided both at pipe joints, valves and similar points, and along the item so that the distance between signs is no more than 25 m. At least one sign shall be provided in each room.
Fuses
Fuses for the fixed installation should be avoided in zone E1. Fuses in industrial machines and similar equipment located in zone E1 may be inserted and removed only when de-energized. To meet this requirement, one of the following designs may be selected:
– the enclosure in which the fuses are located shall be interlocked so that the fuses are accessible only when de-energized, and so that they become energized again only when the enclosure is correctly closed
– the enclosure in which the fuses are located shall be fitted with a sign stating that the fuses must be de-energized with an electrical switch before fuses are replaced. In this case, the electrical switch shall be located next to the enclosure. The enclosure’s sign shall clearly indicate which electrical switch is referred to.
As a first choice, fuses should be used that make replacement with a fuse of excessively high rated current more difficult. If miniature circuit breakers are not used, the fuse size shall be stated at the fuse location. Only fuses clearly marked
with rated current may be used.
Plugs and socket-outlets
Plugs and socket-outlets in zone E1 for connection of permanently installed electrical equipment fitted with an inlet are permitted only for operating currents not exceeding 1 A. They shall be provided with a mechanical lock that can be removed only with the aid of a tool and that prevents the devices from being removed unless the lock is removed. Other socket-outlets and plugs are not permitted in zone E1. Plugs and socket-outlets in zone E2 for connection of permanently installed electrical equipment fitted with an inlet shall be provided with a mechanical lock as above
Permanently installed socket-outlets in zone E2 and zone E3 protected by a fuse or equivalent overcurrent protection with a higher rated current than 16 A shall be blocked. At socket-outlets in zone E2 and zone E3, a notice shall be posted stating that the connection of appliances other than those permitted for use in the respective zone is prohibited
Luminaires, mains-connected hand lamps, signal lamps
The light source shall be protected by a cover. Where there is a risk of mechanical damage, the cover shall be made of unbreakable material or fitted with a protective guard. A hand lamp shall be fitted with a protective guard unless the cover is made of unbreakable material. The light source shall be selected with regard to the voltage, power, frequency, and lamp size for which the item is designed or marked, so that impermissible temperature rise or other risk does not occur. NOTE – It should be noted that the specified lamp power applies only to the voltage for which the item is designed.
Appliances with their own power source
Battery replacement shall take place outside zone E1. The light source in a hand lamp and headlamp shall be protected by a cover.
Portable equipment
Equipment that can be used alternately in different zones shall be approved for the zones in which it can be used.
Climate cabinets
For climate cabinets, the other sections of this standard apply with the changes or additions stated here. A climate cabinet means a movable cabinet for drying, heating, or other conditioning treatment, with an internal storage volume of no more than 1 m3. For climate equipment with a storage volume greater than 1 m3, the other sections of this standard apply. Climate cabinets shall not be placed in zone E1. However, handling of explosive goods or explosive substances in connection with the conditioning may in itself result in zone E1 in and outside the climate cabinet’s storage compartment.
The climate cabinet should preferably be permanently connected. Any inlet on the climate cabinet shall be designed in accordance with the section Plugs and socket-outlets. The connection box in the fixed installation shall be preceded by an all-pole, manually operated, mechanical electrical switch. An electrical switch shall not be present in the connection cable. On the front of the climate cabinet, or in another suitable, clearly visible location, there shall be a signal lamp indicating that voltage is applied. The climate cabinet shall provide such a temperature distribution in the storage compartment that local overheating is avoided
Temperature monitoring
The climate cabinet shall be fitted with an operating control device, e.g. an operating thermostat, that does not permit a higher setting of the working temperature than corresponds to half the ignition temperature (in °C) of the explosive substance for which the climate cabinet is intended. The operating control device shall provide a temperature setting accuracy of at least ±2 K. The climate cabinet shall have an externally easily readable thermometer indicating the temperature at the hottest point in the storage compartment. The thermometer shall not be placed on the door of the storage compartment. A temperature limiter (fail-safe protection) shall be provided that gives an alarm and automatically disconnects the heat source at no more than 15 K above the working temperature set at any given time. The temperature limiter shall, where possible, be connected in the main circuit. If the temperature limiter is placed in the control circuit, it shall actuate a separate switching device in the main circuit.
Design of control devices and control circuits
The operating control device and temperature limiter shall be protected against mechanical damage and unauthorized changes to the set value. The temperature limiter shall either be located in a space accessible only with the aid of a tool or key, be sealable, or be otherwise protected in a reliable manner. A tripped temperature limiter shall not automatically re-energize the heat source. The circuit for the temperature limiter shall be independent of the circuit for the operating control device. Control circuits may contain only switching and making devices, e.g. hermetically sealed mercury or reed contacts, that do not produce open sparks when breaking or making the circuit.
Ventilation
For climate cabinets with natural ventilation, the electric heat source shall be designed and positioned so that dust, vapour, condensate, or sublimate from explosive substances cannot be deposited on it.
For climate cabinets with mechanical ventilation, only fresh air may be used. Fresh air shall be taken from a location that cannot contain dust, vapour, condensate, or sublimate from explosive substances. The electric heat source shall only be able to be energized when the mechanical ventilation is operating.
SEK Swedish Electrotechnical Standard
