Installation of circuits and Ex-proof electrical equipment in explosive hazardous areas
1.Installation of electrical circuits in explosive gas atmospheres
Installation of electrical circuits in explosive gas atmospheres can be completed by cable wiring and conduit wiring.
1.1 General requirements for wiring installation
Electrical circuits shall be applied in areas where there’s a small risk of explosion or far from the source of release, avoiding being applied in places where is susceptible to mechanical damage,vibration,corrosion,dust accumulation and dangerous temperature.If inevitable,precautions shall be taken.
Cable and conduit openings on the wall between hazardous and non-hazardous locations shall be fully sealed,for example, sealed with sand or mortar.
Cables for use in hazardous locations can’t have middle joint.When unavoidable,unless suitable for mechanical and electrical environmental condition,the connection shall use Ex junction box.
1.2 Cable wiring system
Cable system in Zone 0
Zone 0 is only allowed for the use of "ia" intrinsically safe cable system,and must be provide with additional surge current protection devices and lightning protection measures.
Cable system in Zone 1 and Zone 2 flexible cable in hazardous locations shall be:
※ Ordinary rubber sheathed flexible cable;
※ Ordinary polychloroprene sheathed flexible cable;
※ Thick rubber sheathed flexible cable;
※ The plastic sheathed flexible cable with same insulation as thick rubber sheathed cable;
※ Thick neoprene sheathed flexible cable.
Cables of fixed equipment shall be thermoplastic,thermosetting sheathed cables,synthetic rubber sheathed cables or mineral insulated metal sheathed cables.Flame retardant property of fixed wiring cables shall comply with requirements of IEC standards,unless the cable buried under the ground,powder filling conduit or prevented from flame spread by other measures.
Portable and mobile equipment shall be provided with cables of thick neoprene or other equivalent synthetic rubber sheathed cable;thick tough rubber sheathed cable or sheathed cable of the same rugged construction.The minimum cross-section of wire is 1.0mm².
Isolation measures for cable going through different regions
the following measures shall be taken for cables going through the different regions:
a) cable trench of the connection joint of two regions shall be powder filled,or filled with fire retardant blocking materials or provided with fire partition;
b) places for cables going through adjacent regions that share same walls,floors,or places susceptible to mechanical damage,shall be protected;holes shall be tightly plugged;
c) For cables with protective tubes in the area of the interface (walls,floors,ground) both ends of protective tubes must be blocked by fire retardant blocking materials,filling depth not less than the pipe inner diameter,and not less than 40mm.
1.3 Wiring system of conduit
Conduit as following can be used for wiring in explosive dangerous places:
a) Wiring conduits shall be galvanized welded steel pipes for carrying low pressure fluid.
b) Conduit associated with flameproof enclosure,shall be selected according to the following:
1) Heavy gauge threaded steel pipes,seamless steel pipes;
2) Flexible metal conduit or composite structures,such as metal conduit with plastic or synthetic rubber sleeve.
Thread must be used for connection between conduits,between conduits and accessories,or between conduits and electrical equipments.Connection between conduit and electrical equipments shall be not use the back-off.Connection between the conduit and electrical equipment shall meet the requirements of the appropriate type of Ex protection.
Thread for steel pipe connecting must be processed smoothly,and without rust,the thread shall be coated composite resin or conductive rust-proof grease.Linen or insulating tape or paint is not allowed to be applied on the thread.
Isolation seals shall be used in conduit system under the following conditions:
a) When steel pipe going through adjacent partition wall of different hazardous areas,lateral isolation seals shall be installed on either side of the wall;
b) If the steel pipe being guided to other areas through floor or ground,vertical isolation seals shall be installed above the floor or ground;
c) In normal operation,within 450mm of enclosure with ignition source;
d) Places connecting conduits of diameter over 50mm and enclosure that contains connectors,or cable end;all threaded connections shall be tightened.
e) Pipelines where’s easy to have condensate accumulated,shall be installed with drainage isolation seals beneath its vertical section,the drain shall be placed underneath.
Isolation seals shall be filled by packing,after solidification,the packing shall be impermeable,no shrinkage,no cracks,such as sealants,sealing clay,epoxy resin,or sealed fiber.Isolation seals as one part of explosion-proof electrical equipment enclosure,the entire unit shall be subject to Ex certification and comply with the appropriate type of protection.Thickness of packing inside isolation seals shall be at least equal to the pipe diameter,at least not less than 16mm.
When the conduit contains multiple wires or cables,the total cross-sectional area of wires or cables shall be not more than 40% of the cross-sectional area of the conduit.
Wires must have no joint inside of seal bushing.
When wires through the walls,floor,or ground,the distance between the seals and walls,floor,or ground shall be not more than 300mm,and keep the holes plugged.
In the conduit system,explosion-proof flexible conduit with same Ex protection type shall be installed in the following places:
※ The motor inlet;
※ where the connection between electrical equipment and conduit is difficult;
※ Expansion joint or settlement joint where the conduit going through to the building.
To meet the protection requirements of enclosure,sealing measures (such as gaskets or thread sealant) shall be provided between the enclosure and conduit,as well as sealing measures (such as,sealing accessories) between the conduit and wire.
Non-charged bare metal part of electrical equipment,such as metal enclosure,metal structures,metal wiring pipes and wiring accessories,cable protection pipes,cable metal sheath,etc,shall be grounded.
All electrical equipments in explosive hazardous areas except zone 2 light fittings shall be grounded by dedicated wires;multi-strand soft twisted wires are recommended,copper core cross-sectional area shall not be less than 4 mm2.Metal pipes,or metal enclosure of cables,etc.,can be used as an auxiliary ground wire.For neutral ungrounded system,the grounding resistance is not greater than 10Ω;for neutral grounding system, grounding resistance is notgreater than 4Ω.
For light fittings in zone 2 explosive hazardous environment,metal piping systems with reliable electrical connection can be used as ground wires,but pipeline for flammable substances is not allowed.
Ground main lines shall be grounded with the grounding body at least two places in a different direction of explosion hazardous area.
For power in explosive dangerous areas,if TN power system is used,it shall be TN-S type in dangerous places (with separate neutral line N and protection line PE),that is,in dangerous places,the neutral line and the protection line shall not be linked or combined into one wire,for any part conversion from TN-C to TN-S type,protective wires shall be connected to equipotential bonding system in a non-hazardous location.
Note:leakage monitoring between neutral line and PE protection line in dangerous places shall be considered.
If TT -type power supply system used in Zone 1 (grounding of power ground and bare conductor separated),then the power will be protected by (residual) leakage current protection device.
Note:for places of high grounding resistance,this system is not allowed to be used.
If IT -type power system used (neutral line isolated with ground or reactance ground through impedance),an insulation monitoring device shall be provided to indicate 1st ground fault.
Note:The local equipotential connection which commonly referred to as an additional equipotential bonding is necessary.
When armored cables used in electrical equipments,grounding wire cores shall be connected to the internal grounding bolts,the steel strip or metal sheath shall be connected to the external grounding bolts.
During the design and operation of electrical installation,the impact caused by static electricity,lightning effects or electromagnetic radiation shall be considered.
2.Installation of Ex-proof electrical equipment in explosive gas atmospheres
2.1 Pre-installation inspection
Type,grade,group,environmental conditions and special signs of explosion-proof electrical equipment should meet the design requirements.Nameplate,Ex-mark,warning plate of explosion-proof electrical equipments should be correct and clear,enclosure and translucent parts should be without cracks or damage.
Fastening bolts of explosion-proof electrical equipment must have locking measures,without rusting.
After the internal wiring of explosion-proof electrical equipment terminal box is fastened,between the exposed live parts and metal enclosure,the clearances and creepage distances should meet the requirements of appropriate standards.
Excessive cable entry of electrical equipment must be plugged by plugging components of suitable protection.
Except the intrinsically safe equipment,plugging components can only be removed by special tools.
Cables and conduits connecting of electrical equipment shall meet the requirements of related protection.
There should be a metal washer between the sealing ring and the clamping elements,clamping elements shall meet the requirements of the product specification and shall ensure that the sealing ring press the cables or wires tightly.
Cable outer sheath diameter and sealing ring inner diameter should meet the requirements of the product specification;sealing ring must not be aging.
The products which explosion-proof certifications number has suffix of “U” is Ex components,they can’t be used separately unless get Ex certifications with other equipments.
Electrical equipments which explosion-proof certifications number has suffix of “X” shall be noted its special use condition.
2.2 Lamp installations shall comply with the following requirements:
a) Lamp type,model,and power shall comply with the requirements of the design and technical requirements;
b) Screw bulbs should be tightened,of good contact,not loose;
c) Lamp outer cover should be complete,bolts should be tightened.
2.3 Additional requirements of flameproof "d" enclosure
When installing equipment,ensure the distance between flameproof joint and solid obstacle is less than the value specified in the table below,unless smaller distance is proved acceptable by test.
Table 13 - Minimum distance of obstruction from the flameproof flange joints related to the gas group of the hazardous area
|Gas classification||Minimum distance (mm)|
Quoted from IEC60079-14:2013 Table 13
Flameproof electrical equipment joint should have anti-corrosion measures.During installation please prevent any damage on flameproof surface.
Note:protection measures applicable to the joints:non-condensing grease or preservatives.
But on gas detector it should be used with caution,especially when choosing the material,non-coagulation should be ensured,otherwise it will affect the tightness between joints.
Fastening bolts of flameproof joint shall not be replaced at will,and spring washers should be complete.
The cable and conduit entry system shall meet the requirements of the relevant standards,and ensure the overall explosion -proof performance of flameproof enclosure.Cable entry system shall comply with the requirements of IEC60079-14 conduit engaged with flameproof enclosure at least five buckles.
If electrical equipment cables or cable entries required to be connected by steel pipe,a transition compression element should be used to clamp the sealing ring before connecting pipe;unions can be added if pipe connection is difficult to be achieved.
If the enclosure is designed for conduit connection,but changed to be connected by cables,a flameproof adapter with insulating sleeve and terminal box can be used,which will be connected to enclosure by conduit,conduit length not exceeding 150mm.Then connect the cable to the terminal box (such as flameproof or increased safety type),the terminal box must comply with the requirements of the appropriate type of protection.
2.4 Supplementary requirements for increased safety"e"Protection degree of enclosures with bare live parts shall not be less than IP54;and that of enclosures only containing insulated live parts shall be not less than IP44.
Cable gland shall be suitably applied to the cable,and keep the cable effectively connected with increased safety equipment.
Maintain the type of protection"e"and make the terminal box together with the sealing element reach the protection of IP54.
Internal wiring of terminal box should ensure its clearances and creepage distances,if the multi-conductor connected to a terminal,ensure that each is clamped tightly.
2.5 Additional requirements for intrinsic safety "i"
In the devices meet the requirements of EPL “Gb”,intrinsically safe electrical equipment and intrinsically safe part of associated equipments shall comply with IEC60079-11,at least"ib"type.
In the devices meet the requirements of EPL “Gc”,intrinsically safe electrical equipment and intrinsically safe part of associated equipments shall comply with IEC60079-11,at least"ic"type.
Insulation of intrinsically safe circuit cable should be able to withstand at least 500V AC test voltage of conductor to ground,conductor to shield and shield to ground.
It shall mark electrical parameters (CC and LC) or (CC and LC/RC) of all cables or accept the value of its most unfavorable conditions specified by the manufacturer.
Note:CC means cable distributed capacitance;
Note:LC means cable distributed inductance;
Note:LC means cable distributed resistance;
During installation of intrinsically safe circuits,ensure the intrinsically safe properties without interference from outside electromagnetic fields,such as the impact of top power lines or single-core cable high current.It can be achieved by shield, twisted pair cable or maintaining sufficient distance to electromagnetic fields.Cables no matter in hazardous areas or in non-hazardous areas,should meet the following requirements:
a) Cables of intrinsically safe and non-intrinsically safe circuits should be isolated;
b) Cables in intrinsically safe circuits arranged without mechanical damage;
c) Intrinsically safe or non-intrinsically safe circuits with armored cables,metal sheath or shield.
Cables with intrinsically safe circuit conductors should be clearly marked.
Wires banded to the same intrinsically safe circuit and non-intrinsically safe circuit should be isolated by an insulating layer or grounded metal.
Cables with intrinsically safe circuit conductors should be clearly marked.If the sheathing or surface is identified by color,the color should be light blue,and these cables should not be used for other purposes.If intrinsically safe or non-intrinsically safe circuit cables have armor,metal sheath or shield,the marking is not necessary.
Installation of intrinsically safe electrical equipment shall meet the requirements of IEC60079-14.
2.6 Special requirements for pressurized Ex equipment
1) Ventilation system must be made from non-combustible material,its structure should be strong,the connection should be close,and shall not remain dead angle with gas stranded;
2) Equipment shall be interlocked with ventilation system.It must ventilate first before operation,and when the ventilation rate is greater than 5 times on equipment and pipeline volume ventilation system,can connect to the main power supply of equipment;
3) In operation,the gas enter into equipment and ventilation system shall not contain flammable substances or other harmful substances;
4) In the operation of the equipment and ventilation system,for px or py type equipment,the wind pressure should not be lower than 50pa;for pz type equipment,the wind pressure should not be less than 25pa.When air pressure is lower than the above value,automatically disconnect the main power supply or signal of equipment;
5) The gas exhausted from ventilation process,should not be discharged into explosion hazardous environment;when taken effectively measures to prevent sparks and hot particles blown out from the device and its ventilation system,can be discharged into Zone 2 space;
6) For closed-circuit ventilation pressurized type equipment and its ventilation system,shall be supplied with clean gas;
7) The little gate or cover of equipment enclosure and ventilation system shall take interlocking device or add warning signs and other security measures;
8) Devices must have one or more of the inlet and exhaust port which is connected to the ventilation system.Exhaust port must be closed after ventilation.
In addition to overall inspection,all installation should be checked by professionals,they must meet the requirements of product documents and this specification.
6.1 Places for protective gas entering pipelines should be designed in non-hazardous areas,except canned protective gas.
6.2 Protective gas outlet should be located in non-hazardous areas,or follow the following table to install,which can prevent the existence of a small export in the danger area when flushing.
Table 17-Use of spark and particle barriers
|EPL requirements of pipe
out let area
| A- devices under normal operating conditions generating ignitable sparks;
B - devices under normal operating conditions not generating ignitable sparks.
|a: If a fault occurs in the pressurization,temperature of equipment may result in ignition hazards,protective devices installed in pressurized enclosure can prevent flammable gas quickly into pressurized enclosure.|
Quoted from IEC60079-14:2013 Table 17
6.3 Pressure supply equipment,such as fan and compressor protective gas inlet,should be installed in non-hazardous areas.If the drive motor and/or control devices located in the gas pipeline or unavoidable installed in hazardous areas,these devices should be protected by appropriate explosion-proof measures.
6.4 For installation of equipment without internal source of release,in the event of failure of protective gas,the installation shall meet the requirements of specified method.And for equipment with internal source of release,in accordance with manufacturer's instructions,in case of a failure of protective gas,there should be alarms,take corrective measures to ensure the security of the system.
Table 18-Summary of protection requirements for enclosures without an internal source of release
|EPL requirements||Equipments without pressurization installed
Inside of enclosure are not suitable for EPL
|Equipments without pressurization installed
Inside of enclosure are suitable for EPL Gc.
|Gb||Alarm and power cut off||Alarm|
|Gc||Alarm||Measures are unnecessary|
|Note 1: If alarm starts,immediately take measures to restore the supply of entire system;
Note 2: If automatic power-off may cause a greater risk,take other measures,such as doubling the supply of protective gas.
Quoted from IEC60079-14:2013 Table 186.5 For equipment with internal source of release,in accordance with manufacturer's instructions,in case of a failure of protective gas,there should be alarms;take corrective measures to ensure the security of the system.
6.6 Multiple pressurized enclosures sharing safety equipment should meet the requirements of IEC60079-2.
For the shortest flush time of the pressurized enclosure specified by the manufacturer,the pipeline smallest additional flushing time in unit volume should be added to multiply the time for pipeline receiving.
In Zone 2 areas,if the enclosure and its pipeline internal environment is far below the lower explosive limit (e.g.25% LEL),flush can be omitted. In addition,gas detector can be used to check whether the gas in pressurized enclosure can be ignited.
Gas for flushing,continuous dilution or pressurization should be non-flammable,non-toxic,and does not contain moisture,oil,dust,fibers,chemicals,fuel,or other impurities,because these factors may cause danger or adversely affect the integrity of the equipment and operation.
Usually air is used,sometimes inert gas.Oxygen content of protective gas should not be higher than the oxygen in the air.
If using air as a protective gas,air supply should be in non-hazardous area,and located at where the risk of air mixed can be reduced,the impact of nearby buildings due to the wind direction,wind speed changes may also be considered.
Temperature at the protective gas inlet should not exceed 40 (in special cases,higher or lower temperature gas can be used,but it must be indicated on the pressurized enclosure).
The invasion of flammable gas or vapor through spreading into wiring system or protective gas leakage through the wiring system must be avoided,wiring system should be sealed.
7 Supplementary requirements for equipments used in Zone 2
7.1 If exposed live parts or only insulated live parts within the enclosure,the minimum protection shall be IP54 and IP44 respectively.
7.2 If the application spaces can provide sufficient protection to prevent foreign matters entering,for enclosure with exposed live parts and the enclosure is only with insulated live parts,protection shall be IP4X and IP2X respectively.
7.3 If entering of hard objects or water does not affect the safety of the device,the above requirements may be unnecessary (such as deformeter,heat resistance thermometer,thermocouple,energy-limited equipment).
7.4 For energy-limited equipment and equipment in circuits,the maximum internal capacitance sum with the capacitance of the cable should not exceed the maximum allowable capacitance (two adjacent cable core equivalent as a centralized capacitance),the maximum internal inductance sum with the inductance of the cable should not exceed the maximum allowable inductance (two maximum isolator cable core equivalent as a centralized inductance).These figures shall be marked on the equipments of protection type“n”or files.
7.5 Cable and conduit wiring system should be installed based on standard and meet the following supplementary requirements for cable glands and terminals:
a) Connection of cable should be finished by suitable cable gland.
b) In order to ensure the protection degree of wiring cavity,only cable glands with suitable sealing elements (such as gaskets or thread sealant) between cable and cable gland can be used.
Note: When engagement between threaded cable gland and enclosure is 6mm thick or above,sealing measures may not be applied, but the central axis of the cable gland should perpendicular to the enclosure surface.
c) Seal of breathing-restricted enclosure should ensure the breathing-restricted performance of enclosure.
d) Unused cable entries should be plugged to ensure the protection of enclosure.