Protection methods

ATEX Protection methods for electrical equipment 

 

Electrical equipment often contains multiple sources of ignition. Special measures are needed to ensure these cannot take effect, i.e., that an explosive atmosphere or a dust layer cannot ignite. These are known as methods to prevent ignition, most of them have been used successfully for decades. 

The various methods of protection are based on five basic principles:

Energy limitation:       gas or dust cannot ignite because there is too little energy present in the electrical circuit (Ex i);

Exclusion:                  gas or dust cannot reach the source of ignition (Ex m, Ex o, Ex p, Ex t, Ex nR);

Avoidance:                there is no effective ignition source present in the device (Ex e, Ex nA).

Dilution:                    Any gas that may be present is diluted with air below LEL level (Ex p);

Containment:            the explosion is confined to the inside of the device (Ex d) or is prevented at an early stage (Ex q).

Preventive methods suitable for use in gas environments:

• Flameproof enclosure, Ex db. Ex dc;
• Increased safety, Ex eb, Ex ec;
• Intrinsic safety, Ex ia, Ex ib, Ex ic;
• Internal pressurization, Ex px, Ex py, Ex pz;
• Molding, Ex ma, Ex mb, Ex mc.
• Quartzfilling, Ex q;
• Oil immersion, Ex o;
• Non-sparking equipment, Ex nA, Ex nC, Ex nR.

Protection methods suitable for use in dust environments: 

• Intrinsic safety, Ex ia, Ex ib, Ex ic;
• Internal overpressure, Ex p.
• Molding, Ex ma, Ex mb, Ex mc;
• Protection by enclosure, Ex ta, Ex tb, Ex tc.

 

Ex d Protection - Flameproof enclosure

Ex d principle

The enclosure of the equipment is so strong it can withstand the pressure of an internal explosion without damage. In addition, it has been constructed so that hot gases and particles emitted by an explosion are cooled to such an extent they can no longer ignite an explosive mixture present on the outside.

The emitted hot gases still have a temperature far above the ignition temperature of any explosive mixture that may be present outside; 1000 ºC is no exception. The fact that ignition does not occur is due to the rapid and violent exposure of the hot gases to the cold environment, making the contact time between the hot gas and the explosive mixture too short to transfer sufficient energy.

Ex d enclosures with only a "U" component certificate (i.e., only the empty enclosure is certified) may not be used. Only fully certified enclosures are allowed. The contents of these have been assessed and approved during certification.

Escaping hot gases

The contents of a certified Ex d enclosure may not be modified. Modification may affect the explosion pressure or the temperature management inside the enclosure. An enclosure that has been modified anyway must be presented for certification anew.

An enclosure certified for use with a particular gas (e.g., IIB + H₂) must be installed in accordance with the requirements for its gas group. In the case of H₂ (hydrogen), it must be installed according to the gas group IIC requirements. 

Around an Ex d enclosure with flat gaps a clear space must be maintained, because leaking hot gases must be able to mix well with the surrounding (cold) atmosphere. Obstacles present may cause insufficient mixing and the gas will not cool down enough. As a result, an explosive mixture present can be ignited by leaking hot gases.

The table below indicates how much free space must be maintained.

Zone gas group	Minimum distance (mm)
IIA	10
IIB	30
IIC	40

Table 8.1 Gas group and distance from the Ex d protection enclosure

The gaps of a flameproof housing may not be painted, of course the enclosure itself may. The flange surfaces can be greased to prevent penetration of paint as much as possible.

If the manufacturer does not prescribe protection of the pressure-resistant gap, only non-hardening grease or an anti-corrosion agent free of volatile solvents may be used. Silicone-based grease is often most suitable. However, it should not be applied to gas detectors due to possible "poisoning" of the chemical sensor.

The cable gland is the most critical part of a flameproof housing. If the cable gland is not mounted correctly or the wrong cable is used, there is no effective Ex protection. An internal explosion can then propagate to the outside unhindered! 

A cable gland of an Ex d enclosure must also be Ex d certified. Increased safety (Ex e) cable entries should never be used as they are unable to withstand the pressure of an internal explosion.

Cable glands

 

A cable gland must be suitable for the type of cable. Pay attention to cable diameter and the type of cable (armored or unarmored).

Cable glands marked with "X" have a limited ambient temperature range or may only be used when strain relief is applied near the cable entry. This does not necessarily apply to all types in the same range. Details can be found in the certificate and operating manual of the cable glands.

The Ex d protection method can only be guaranteed if the gland is screwed in deep enough:

• At least 5 threads or 8 mm screw-in depth for parallel thread types;
• For conical thread types (NPT), the connection itself must be screwed down using

In some cases, a cable gland is supplied with the Ex d device, but usually a suitable gland must be selectedseparately. According to the installation standard EN  60079-14: 2014, a combination cable and gland can be selected from:

• Cable glands sealed up to the conductors with a casting compound;
• When using a cable gland without casting compound, the cable should be:
• at least 3 meters long;
• sheathed by either thermoplastic, thermosetting or elastomeric material;
• round and compact;
• bedding and sheathing must be extruded, the filling material not-

Ex d equipment has a very robust appearance. This quickly suggests few requirements in terms of inspection and maintenance. The opposite is true: the protection method only lasts when maintenance is carried out properly. A small deviation from the certified construction can already cause the protection method to fail.

When assembling Ex d enclosures, e.g., after repair or inspection, all Ex d gaps must be clean and lightly greased with an anti-corrosion agent!

Flameproof "Ex d protection" enclosure with window

The figure shows an Ex d enclosure with tempered glass window. When new, such a window can withstand a pressure of 60 bar or more. When a metal ball hits the window, not causing any visible damage, the window may break at a pressure as low as 35 bar. Visible damage will result in an even weaker glass so that the Ex d protection method can no longer be guaranteed. In that case the glass must be replaced

Ex e Protection - Increased safety

Ex e principle

Increased safety equipment does not generate sparks or hot surfaces under normal operating conditions and when foreseeablemalfunctions occur. In addition, the enclosure offers sufficiently high mechanical protection and a sufficient degree of protection (usually IP54) against penetration of dirt and moisture; this prevents the insulation between the parts from becoming contaminated under tension, which makes insulation distances smaller and can cause short circuits. 

Ex e enclosures with a component or "U" certificate may not be used because only the empty enclosure is certified. Only fully certified enclosures are allowed. The contents of these have also been assessed and approved during certification. 

The contents of a certified Ex e enclosure should not be modified because the this mayaffect temperature management inside. Any modified enclosure shouldbe submitted for certification anew.

A cable entry must be Ex e certified. Ex d cable entries can also be used because they comply with Ex e requirements. Use them only when there is no other option; In general, Ex e cable glands are much easier to use. 

A cable entry must be suitable for the type of cable (cable diameter and type). Cable glands marked with an “X” have a limited ambient temperature range or should only be used when strain relief is used close to the cable entry. Details can be found in the cable gland certificate and user manual.

Ex e protection terminal blocks

The Ex e protection method only lasts if maintenance is carried out properly. Although Ex e is used in a wide variety of constructions, maintenance should always focus on the following points:

• Make sure that seals are not damaged so that the IP rating lasts, preventing dirt and moisture from affecting insulation distances;
• Ensure that all electrical connections are properly made to prevent sparks.

Ex i Protection - Intrinsic safety

Ex i principle

The equipment is inherently (= intrinsically) safe. This means that the electrical circuit does not generate sparks powerful enough to ignite an explosive mixture both under normal operating conditions and under malfunctions and faults assumed for Ex i. Furthermore, the electrical circuit will not cause hot surfaces under the circumstances mentioned. 

Hardly any requirements are put on Ex i equipment housing, unless a specific application requires them. An example of this would be, for example, a portable gas detector that still needs to be sufficiently intact even after a fall, or when ingress of moisture or dirt can affect the protectionmethod.

One very important aspect is the separation between Ex i and non-Ex i circuits: it must be strictly enforced. The fact is that influx of energy from a non-Ex i circuit into an Ex-i circuit completely destroys intrinsic safety.

Ex i has three different safety levels:

• Ex ia is still explosion-safe under 2 concurrent error conditions. This makes it safe enough to be used in zones 0 and 20 (category 1);
• Ex ib is safe under 1 error condition. This makes it sufficiently safe to be used in zones 1 and 21 (category 2);
• Finally, Ex ic is only explosion-safe under normal operating conditions. Therefore, it may only be used in zones 2 and 22 (category 3).

The contents of an Ex i housing may not be changed; this may affect temperature management inside. A housing that has been modified anyway must be reassessed. The standard protection rate for enclosures is IP20. For functional reasons it is often higher.

Ex i cabling is always recognizable as such and can be marked as follows:

• The cabling itself is light blue;
• The cabling is in a light blue cable tray;
• The cabling is of a different color and at regular intervals clearly marked, e.g., by light blue tape or the text “Ex i”;

A combination of these markings is allowed, as long as it is clear that it indicates Ex i cabling.

The essence of an intrinsically safe circuit is to limit energy. To achieve this, the current and voltage are limited to certain maximum values, taking into account the error situations assumed for Ex i. The voltage is always relative to earth, which is why grounding plays a major role in Ex i circuits. Alternatively, complete isolation from earth (galvanic isolation) can be used. In that case the circuit must have a minimum transient voltage of 500 V to ground.

Junction box with Ex i terminals

When installing Ex i equipment, special attention must be paid to the following:

• The earth connection must be properly secured;
• The core thickness of the earth connection must be sufficient;
• There can only be one of connection to earth;
• When using galvanic isolation there can be no connection to earth; isolation must be at least 500 V;
• The separation between Ex i and non-Ex i circuits must be maintained in a terminal box as well (at least 50 mm separation between the terminals of Ex i and non-Ex i circuits).

During inspection and maintenance special attention must be paid to the following:

• Unauthorized modifications to the Ex i circuit;
• The separation between Ex i and non-Ex i circuits;
• The grounding of the equipment should be correct;
• The galvanic isolation must be present.

Ex p Protection - Pressurized apparatus

Ex p principle

The housing of the Ex p equipment is continuously at a slight overpressure (a few millibar) relative to the environment. This pressure is due to a supply of air or an inert gas. This makes it impossible for a potential explosive atmosphere to penetrate the housing and reach an ignition source inside.

This presence of overpressure is crucial for Ex p. If the pressure becomes too low or drops entirely, the equipment, depending on the zone in which the Ex p housing is placed, must be either disconnected (e.g.,zone 1) or an alarm must be given, to which the user must respond adequately (e.g., zone 2). 

The overpressure is continuously monitored by a suitably protected control unit. The equipment may only be switched on again when it is certain that no explosive atmosphere is present inside the housing. This is achieved by first flushing it with air or an inert gas for a few minutes.

Ex p controller

For gas environments, there are three types of Ex p systems: Ex px, Ex py and Ex pz, which are defined as follows: 

• Ex px: the overpressure system ensures the interior of the housing is classified as non-hazardous instead of class 1. The equipment and components inside the housing are therefore located in a non-explosive area and do not need to be explosion-safe. Ex px marked equipment may therefore be placed in a zone 1 environment.
• Ex py: the pressure relief system ensures that the interior of the housing is classified as zone 2 instead of class 1. The zone 2 classification means the equipment and components inside the housing should not spark or become too hot under normal operating conditions. Ex py marked equipment may be placed in a zone 1 environment;
  • Ex pz: the overpressure system ensures that the interior of the housing is classified as non-hazardous instead of zone 2. The equipment and components in the cabinet are therefore located in a non-explosive area and therefore do not need to be explosion-safe. Ex pz marked equipment may only be placed in a zone 2 

The following must be taken into account during installation: 

• All instructions in the manufacturer's manual and as stated in the certificate must be followed;
• On the exhaust a spark arrester is mandatory unless it is located in a zone 2 area and no dangerous sparks or particles are released inside the cabinet during normal operation;

During inspection and maintenance particular attention must be paid to the following:

• Holes, cracks and other leaks in the Ex p housing, and the supply and potential discharge pipes of the protective gas;
• Plastic parts, such as windows, may only be cleaned using non-aggressive agents;
• The quality of the protective gas (no impurities, moisture or dirt);
• The pressure and flow in the Ex p system must comply with specifications;
• The pressure and/or flow indicators, alarms and interlocks must function properly;
• Flushing time should not be shorter than the minimum specified;
• Spark arrestors must either function properly or else be replaced.

Ex m protection - Encapsulated devices

Electrical equipment, in most cases electronics, is completely cast with a suitable casting compound. The casting mass serves to separate the ignition sources present in the electrical equipment (sparks, hot components) from the potentially present explosive atmosphere. This prevents ignition provided that the casting mass works properly. Ex m therefore places very high demands on the casting mass used. A detailed description of the molding procedure is part of the certification assessment of the equipment.

Ex m principle

Installing Ex m equipment must be done according to the manufacturer's instructions. If these are missing, follow the installation instructions and “special conditions for safe use" as stated in the certificate or on the type plate present on the equipment.

Ex m provides three different safety levels:

• Ex ma is still explosion-safe during two simultaneously occurring fault conditions in the encapsulated electronics and is therefore safe enough to be used in zones 0 and 20 (category 1);
• Ex mb is safe during a single fault condition occurring in the electronics and is therefore sufficiently safe to be used in zones 1 and 21 (category 2);
• Finally, Ex mc is only explosion-safe under normal conditions and may therefore only be used in zone 2 (category 3).

In order to ensure the Ex m protection method, the following conditions must always be met:

• Supply voltage must not exceed the value indicated on the type plate;
• If the instructions prescribe a fuse, it must meet the requirements stated;
• The maximum short-circuit current, which could be supplied by the power connected to the Ex m equipment must not exceed 1500 A or the value marked on the type plate. If the maximum short-circuit current is too high, the electronics in the casting mass can become too hot and can damage the casting mass. As a result, the casting mass will no longer provide protection against the ingress of gas.

The casting mass of the Ex m equipment is not tested for chemical resistance during type-examination. It is therefore necessary that, when purchasing Ex m equipment, it is determined the material of the casting mass is suitable for the ambient conditions.

Ex m molded electronics

Once Ex m equipment is installed, it must be checked regularly for deterioration of the casting mass, if possible, by visual inspection. Should inspection reveal cracks, blisters, holes, discoloration or other irregularities at the surface of the casting mass, the Ex m method of protection is no longer guaranteed and the equipment must be replaced.

Ex Q Protection - Powder (quartz) filled equipment

Ex q protection principle

Electrical equipment, in most cases electronics, is completely surrounded by a finely powdered quartz. The gas can penetrate, reach a source of ignition and ignite. However, a startingexplosion cannot develop any further because insufficient gas and air can be supplied through the narrow spaces between the grains of quartz. Ex q places high demands on the filling used. In addition, the housing of Ex q equipment is always sealed to prevent leaks.

Ex q equipment can hardly or not be serviced because it cannot and may not be opened. During inspection, it must always be checked for any leakage of the quartz filling. If this is the case, there is no longer any Ex protection and the equipment must be replaced.

Ex O Protection - Oil-filled equipment

Ex o Protection principle

Ex o is mainly used in heavy switching equipment such as:

• Large swivels with electrical sliding contacts;
• Large transformers where other protection methods such as Ex d or Ex e cannot be applied due to dimensions and weight of the equipment.

The electrical circuit (transformer, slip rings) of Ex o equipment is completely immersed in oil. Gas maypenetrate into the enclosure, but it cannot reach the ignition source. The oil acts as a barrier.

Oil-filled transformer

Ex o places high demands on the oil used. In addition, the enclosure of Ex o equipment is usually sealed to prevent oil leaks.

Ex o equipment requires little maintenance. During inspection, it is always necessary to check for oil leaks; when these occur, there is no Ex protection and the leaking enclosure must be repaired. The oil itself must be checked regularly for contamination and replaced in time. Of course, the oil level must be high enough to keep the entire electrical circuit submerged at all times.

Ex N Protection - Non-sparking equipment

Ex n is in fact a weakened form of Ex e and is suitable for use in zone 2. Under normal operating conditions, Ex n equipment does not contain sources of ignition such as sparks or hot surfaces. Ex n is used for a wide variety of equipment such as lighting, motors, electronics, etc. and has a number of sub-protection modes: 

Ex nA:     non-sparking equipment, e.g., cage motor or electronics;

Ex nC:     sparking equipment where contacts are protected, e.g. hermetically sealed relays protected against gas ingress;

Ex nR:     equipment with a limited breathing enclosure (gas can hardly penetrate);

Ex nL:      equipment with limited energy; this mode of protection has been replaced by the protection mode Ex ic (spark energy is limited in such a way that no ignition can take place).

In general, Ex n equipment is installed in the same way as non-Ex equipment. However, depending on the type of Ex n equipment, there are a number of things that need extra attention during installation:

Ex nA:     no special requirements, except that often an IP54 protection rate is required. Make sure that seals and gaskets are installed correctly. Sometimes the manufacturer prescribes the connected (power supply) voltage must be protected against (too) high voltage peaks (overvoltage protection);

Ex nC:     no special requirements;

Ex nR:     the seal is the only protection. It must be correctly fitted during installation and must be intact;

Ex nL:      must be used within the correct specifications (current, voltage, power).

Check in particular (depending on the type of Ex n equipment):

• Seals for wear and damage;
• Unauthorized modifications;
• Correct grounding.

Ex T Protection - Protection by enclosures for dust environments

Ex t was recently introduced as the designation for equipment suitable for explosive dust atmospheres (older equipment may still be marked with the code Ex tD). The protection consists of the enclosure, which must be dust-tight to prevent dust from penetrating and thus coming into contact with a source of ignition (spark, hot surface) within the enclosure.

The required protection level of the enclosure depends on the dust environment.

Protection level	Group IIIA	Group IIIB	Group IIIC
ta	IP 6x	IP 6x	IP 6x
tb	IP 5x	IP 6x	IP 6x
tc	IP 5x	IP 5x	IP 6x

Table 8.2 Protection level, dust group and IP rating

During inspection and maintenance, the most important thing to check for:

• seals for wear and damage;
• unauthorized modifications;
• correct grounding.

Protection methods non-electrical equipment

Gear unit with angular gearbox

Mechanical equipment may contain ignition sources, e.g., due to friction (plain bearings, seals) or sparks from contact between metal parts.

In most devices friction is already prevented as much as possible during design, as this leads to wear and tear and therefore to a reduced lifespan. Shock or impact loads are also avoided because they lead to fatigue of metal parts, which results in a shorter lifespan. As a result, development and standardization of ignition protection methods for non-electrical equipment has had a low priority for a long time.

The following types of protection are suitable for non-electrical equipment:

• flow-limiting enclosure, Ex fr;
• flameproof enclosure, Ex d;
• constructive safety, Ex c;
• monitoring of ignition sources, Ex b;
• liquid immersion, Ex k.

Ex FR Protection - Flow-limiting enclosure

The enclosure of the device is sufficiently sealed (flow restricted) to prevent rapid penetration by an explosive mixture. This solution is similar to the Ex nR protection method (limited breathability) for electrical devices. A flow limiting enclosure meets the requirements for category 3 may therefore be used in zone 2. Ex fr may not be combined with other types of protection.

Ex D Protection - Flameproof enclosure

Screw cover Ex d IIC enclosure

The enclosure of the equipment is so strong it can withstand the pressure of an internal explosion without damage. In addition, construction is such that hot combustion gases and particles expelled by the explosion are cooled down to such an extent that they are unable to ignite any surrounding explosive mixture.

The robust appearance of flameproof equipment suggests it requires littleinspection and maintenance. The opposite is true; the protection method will only last if inspections and maintenance are carried out properly. A small deviation or damage to the construction can already lead to the protection method failing.

Flameproof enclosures are not widely used for the protection of mechanical constructions because in many cases other protection methods are more practical and cheaper to use.

Ex C Protection - Constructional safety

The protection method called constructional safety is widely used because it closely matches the design requirements that are normally already imposed on equipment. Think of the right choice of materials (strength) and material combinations (friction, wear, sparks). Application of Ex c is found in many well-known mechanical devices and systems such as: 

• drives;
• couplings;
• bearings;
• braking systems;
• shock absorbers;
• conveyor belts;

 During normal operation, there can be no ignition sources present within the unit. Depending on the measures taken, the unit meets the requirements for category 1 and thus it can be used in zone 0. The protection type Ex c may be combined with other protection methods.

Important points of attention when applying constructive safety are: 

• material combinations must be chosen in such a way as to prevent wear and tear (e.g., in the case of plain bearings, clutches, brakes);
• seals of moving parts must still meet the required IP rating even after foreseeable wear and tear;
• lubricants and coolants must have an ignition temperature at least 50 °C above the maximum surface temperature;
• in case of conveyor belts, there is a risk of electrostatic charging; the correct choice of electrically conductive materials can reduce this risk to an acceptable level.

Always follow the manufacturer's instructions for inspection and maintenance. If the manufacturer has not provided these, inspection and maintenance can be based on the requirements for Ex e. Pay attention to the following:

• sufficient lubrication of "wet" seals;
• wear and tear of moving parts, unwanted vibrations and maintaining the distances to non-moving parts (avoid contact);
• bearings must be state-of-the-art and regularly inspected and/or monitored in order to reduce the risks of ignition (overheating).

Ex B Protection - Monitoring of ignition sources

Due to circumstances mechanical constructions can overheat. Think of plain bearings running hot when the lubrication system fails or the load is too high. In such cases monitoring the potential source of ignition can provide protection against ignition.

The monitoring system consists of a combination of one or more sensors and a disconnect circuit. The sensors are built into the device and measure certain quantities (temperature, pressure, level, vibrations) thus detecting any unusual or undesirable behavior. When pre-set limits are exceeded, the device is switched off by the disconnect circuit, before potential ignition sources can become active. The combination of sensors and disconnect circuit is called the Ignition Prevention System (IPS).

Protection by monitoring places high demands on the sensors and the switching circuit. Selecting the correct sensors and limit values is essential for the explosion safety of the device.

The reliability of this security mechanism is indicated by the Ignition Prevention Level (IPL). There are two levels of security, IPL 1 and IPL 2, where IPL 2 is the higher of the two. This sometimes leads to confusion because in the ATEX category system, category 1 is higher (safer) than categories 2 and 3.

The following table indicates which IPL level is required to monitor a potential ignition source depending on the situation and category required.

Presence of a potential ignition source:	Category 3	Category 2	Category 1
During normal operation	IPL 1	IPL 2	-
During unforeseeable error conditions	Not applicable	IPL 1	IPL 2
During rare error conditions	Not applicable	Not applicable	IPL 1

 

Table 9.1 Required IPL level

Monitoring systems do not provide sufficient safety to adequately protect equipment used in zone 0/20 (category 1) that contains a potential ignition source during normal operation. 

In addition to electrical solutions, there are also fully mechanical Ignition Protection Systems. Some well-known examples include:

• Thermostatically controlled valves that close when the temperature threatens to become too high or open to allow the influx of additional coolant;
• Pressure relief valves that open before the pressure becomes too high.

Examples of combined mechanical / electrical Ignition Protection Systems are:

• Pressure, temperature or flow sensors which, at a certain value, control a valve decreasing energy supply or, on the contrary, increase the quantity of coolant supplied. Thesesensors are usually Ex i for category 2 equipment or Ex n for category 3 equipment;
• Force transducers mounted on a conveyor system, detecting friction between the actuator and the conveyor belt, that trigger an alarm if values become too high. These high values may be caused, for example, by insufficient belt tension.

Important points to consider when applying monitoring of ignition sources are:

• the Ignition Protection System must operate independently of normal control;
• the limit values must be chosen correctly (correct safety factor);
• selection of the sensors (suitable for the environment / correct category);
• the ignition prevention level IPL 1 or IPL 2 must be established correctly

Ex K Protection - Liquid immersion

By immersing the ignition source, it can be separated from the surrounding explosive atmosphere. In case of partial immersion, a thin layer of liquid (film) ensures separation. Usually process fluid or the lubricant used acts a protective fluid.

Examples of applications in hazardous areas:

• pumps;
• gearboxes, gear transmissions;
• hydraulic systems.

For pumps and gearboxes, protection by liquid immersion is often combinedwith constructive safety measures. Often hot surfaces and sparking parts are already unacceptable for functional reasons and this has been taken account during design. This equipment needs few modifications (sometimes none at all) to be made explosion-protected at safety level category 2. When it is to be used in zone 0 or zone 20 achieving a safety level category 1 can be difficult to realize.

Gearbox

The main concerns when using the protection method liquid immersion are:

• the specifications of the protective liquid must be known and the liquid must be suitable for the application;
• the limits for (minimum) liquid level, working angle and viscosity must not be exceeded;
• the construction must prevent leakage of the protective liquid. 

For Ex k the following checks and maintenance must be done:

• check the liquid level;
• check and possible replace of contaminated liquid;
• check for leakage of the liquid.

Gear unit nameplate

Type plate of an Ex ck gear unit, suitable for use in gas and dust environments. Of course, sufficient protective liquid must be present. In this case 0.7 liters of the “Schmierstoff CLP HC 220 Synth. Öl”.