Inspection and maintenance of explosion-proof electrical equipment in hazardous area

1.Requirements of inspection for explosion-proof equipment

1.1 General
Initial inspection shall be made to minimize the ignition risk of the electrical equipment used in hazardous areas before devices and equipment are put into service and/or during the acceptance checking of the project handover after final installation.And the electrical equipment shall be continuously monitored and regularly checked in order to ensure that it is in good condition and may be continuously used in hazardous areas.
NOTEThe complete initial inspection is not required if some items were checked by manufacturer equally and the components checked are not possible to be affected by the installation,e.g.initial detailed inspection for the clearance of flameproof in explosion-proof motors is not required, however, initial inspection of terminal boxes dismantled to facilitate field wiring connections shall be carried out after installation.

1.2 Qualifications of personnel
Persons involved in the electrical inspection and maintenance in hazardous areas shall possess the following:
a) Understanding of the general principles of explosion protection;
b) Understanding of the general principles of types of protection and marking;
c) Understanding of those aspects of equipment design which affect the protection concept;
d) Understanding of content of certificates and relevant provision;
e) General understanding of inspection and maintenance requirements of IEC 60079-17;
f ) Familiarity with the particular techniques to be employed in the selection and erection of relevant equipment;
g) Understanding of the additional importance of permitting to work systems and safe isolation in relation to explosion protection.
The inspection and maintenance of explosion-protected equipment shall be carried out only by persons whose training has included instruction on the various types of protection and installation practices,relevant rules and regulations and on the general principles of area classification.
Appropriate continuing education or training shall be undertaken by personnel on a regular basis and certificates of relevant experience and training shall be obtained.

1.3 Continuous monitoring and regular inspection
1.3.1 Continuous monitoring
Continuous monitoring shall be carried out by professional personnel as required and be record.
Care shall be taken off if there is any unusual phenomenon found.Continuous monitoring shall include the following items.
1) Explosion-proof electrical equipment shall be operated under prescribed conditions specified by the equipment manufacturer.
For the product with certificate numbers which have the suffix “X” shall comply with specific conditions required by the relevant documentation for safely using.
2) The enclosure and surrounding environment of the explosion-proof electrical equipment should be kept clean,sundries and flammable items that obstruct the safe operation of the equipment shall be cleared away,and personnel shall to be specified to test and analyze the concentration of surrounding explosive compound around equipment frequently.
3) There should be good condition for ventilation and heat dissipation when the equipment is working,and inspection shall be taken to ensure that the surface temperature and temperature rise of enclosure is not exceeded to the product requirements.
4) Check the running equipment that shall not be suffer the external damage,and there shall be no incline,friction between components or abnormal sound.The vibration value shall not exceed the specified.
5) The completion and tightness of fixed bolts and spring washers on enclosure shall be checked and shall be secured against loosening.
6) Enclosure shall be checked that there are no cracks or mechanical deformation which may undermine explosion-proof performance.Cable entry devices shall be sealed reliably.Unused cable entries shall be sealed with a flameproof blanking element appropriate to the protection type.
7) Various device of protection,blocking,detection,alarm and grounding shall not be arbitrarily removed and the integrity, sensitivity and reliability shall be maintained.
8) Whether the explosion-proof lighting fittings maintain its structure and integrity of protective cover,and whether the surface temperature of lighting fittings does not exceed the predetermined value of products shall be checked. Whether power source and the lamp model are consistent with the lighting markings,and whether lighting installation position is in line with the provisions described shall also be checked.
9) The operator could shut down the electrical equipment and take emergency measures and then notify the professional to take inspection and treatment if the following occurs:
a) The load current exceeds the predetermined value suddenly or phase running state is confirmed;
b) The temperature of motors or switches rises up highly or emit smoke;
c) Motors or other equipment produce noise or sparks due to the friction caused by loosening of components;
d) The mechanical load has severe fault or may endanger the electrical safety.
10) To minimize the risk of ignition caused by electrical equipment used in dust hazardous areas,whether the original design conditions have changed shall be checked (dust type,maximum thickness of the dust layer,etc.).
11) Mobile electrical equipments (hand-held,portable or moveable equipment),are particularly prone to be damaged or misused,the time between two inspections could be shortened according to actual needs.Mobile electrical equipment shall be taken general inspection every 12 months at least.For the enclosure needs to be often opened (such as a battery cover) detailed inspection shall be taken.Moreover,visual inspection shall be taken before using this kind of equipment to ensure the device is not obviously damaged.

1.3.2 Periodic inspection
Further detailed inspection could be necessary after Periodic inspection of visual check or general check may need.
For the determination about degree of inspection and the gap time between two inspections,situations about equipment type,manufacturer's instructions,factors affect the damage degree,the operation location and the results of the previous inspection.
These experiences shall be utilized to ensure the degree of inspection and the gap time between two inspections about this kind of equipment.
NOTE:The main factors causing deterioration of equipment, includingbeing susceptible to corrosion and exposed to chemicals or solvents，possibility of accumulation of dust or dirt,possibility of water ingress,being exposed to high ambient temperature,the risk of mechanical damage,subjecting to intense vibration,training and experience of personnel, unauthorized modifications or adjustments,inadequate maintenance, such as maintenance which is not followed the manufacturer's recommendations.
Periodic inspection should be entrusted to the safety testing and inspection organization with professional qualifications of explosion-proof equipment，and generally,the time interval shall not be more than three years.Enterprises shall take timely corrective action based on test result，and the inspection reports and rectification shall be recorded in production safety supervision and management departments.
All the results of initial,regular and continuous monitoring shall be recorded.

2.The maintenance requirements of explosion-proof electrical equipment
2.1 Remedial measures and equipment replacement
All equipment shall be required to indicate that the general conditions,appropriate remedial measures shall be taken if necessary.It should pay attention to maintaining the integrity of the type of protection,which could require consulting with the manufacturer.Replacement parts should be carried out in accordance with the requirements of the relevant security documents.
The parts which will,if replaced,adversely affect the safety performance of the equipment specified in security documents shall not be done so unless permitted by the relevant departments.
NOTE1:It should be taken to avoid conflict with the measures that manufacturers taken to reduce static electricity affection.
NOTE2:When replacing the bulb of lighting fittings,the of power and models of lamp source shall comply with the provisions of fitting markings, or it may cause overheating.
NOTE3:Overheating may be caused by the corrosion,being painted or covered of transparent cover or incorrect installation of light fittings.
2.2 Maintenance of flexible cable
Flexible cables,flexible connecting pipe and terminal segment connected could be easily damaged,so it shall be checked by a predetermined time interval and be replaced if damaged or missing.
2.3 Shutdown
If electrical equipment and other equipment must be shut down during maintenance,the bare wire shall meet one of the following conditions:
a) Correctly connected to the appropriate enclosure;
b) Disconnected with all the power supply and insulated;
c) Disconnected with all the power supply and being ground.
If electrical equipment is shut down and will not be operated permanently,all power supply conductors associated shall be disconnected,dismantled or correctly connected to the appropriate enclosure.
2.4 Fasteners and tools
Special screws,fasteners or special tools shall be prepared and be utilized where necessary.
2.5 Environmental conditions
Electrical equipment used in hazardous areas may be affected by the adverse effects of environmental conditions,major factors such as corrosion,ambient temperature,ultraviolet radiation,water entering,accumulation of dust or sand, mechanical and chemical action shall be considered with.
The type of equipment protection and protection degree could be affected by the effect of metal corrosion or chemical substances (especially solvent) to plastic or elastic components.It shall be replaced if the enclosure or components is corroded seriously.Plastic enclosure may appear the overall surface cracks.The metal enclosure of device,when necessary, shall be protected appropriately by use of appropriate protective coating as anti-corrosion treatment.The frequency and methods of such treatment shall be according to the environmental conditions.
It shall be verified whether the electrical equipment designed can withstand the maximum and minimum ambient temperatures likely to be encountered.
NOTE: If the marking of the electrical equipment does not include an ambient temperature range,the equipment is designed to be used within the temperature range -20°C to 40°C.If the marking of the electrical equipment includes an ambient temperature range,the equipment is designed to be used within this range.
All components of the device should be kept clean,and there shall not be accumulation of dust and similar hazardous substances which could cause the temperature rise.
Measures shall be taken to ensure to maintain the performance of weather-proof of electrical equipment. Damaged gasket shall be replaced.
Anti-condensation device,such as breathing and draining devices or heating unit shalbe checked to ensure the correct operation.
Tightness of bolts and cable entries of equipment shall be paid specially attention to if subjected to vibration.
Measures shall be taken to avoid producing static electricity when cleaning non-metallic enclosures for electrical equipment.
2.6 Isolation of equipment maintenance
Electrical equipment shall be isolated to all power supply including neutral line before being opened in hazardous area,and effective measure shall be taken to avoid the inadvertently re-energized when opened.
2.6.1 Devices other than intrinsically safe circuits
a) For the electrical equipment with intrinsically safe circuits built-in installed in hazardous locations,before it is isolated with all input connection or isolated with the output connection including neutral conductors when there is existence for zero line to ground,the cover shall not be opened,except for item b or c on specification.Here being isolated means to pull out fuse link,or disconnect isolator and switch. The enclosure could only be opened until enough time passes by and the surface temperature or stored electrical energy cannot cause ignition.
b) Within the time required for planning work,if the responsible department or personnel could ensure that there will not be explosive environment and make the written approval,the main operation of exposed live parts could be taken after taking general security measures.
c) If permitted by the relevant laws and regulations,the requirements on item a and b could be loosened but only in Zone 2.
Operation could be taken after taking general security measures if it meets the following conditions and is certificated by security assessment:
1) The planning operation on the live part could not produce combustible spark;
2) The circuit has the structure to prevent sparking;
3) There is no hot surface on electrical equipment and associated circuits used in the hazardous area which may cause ignition. The planning operation could be taken after taking general security measures if it is complied with these conditions.
Results of the safety assessment shall be recorded in the file,which contains the following information：
※ The form of the planning operation on live equipment;
※ Assessment results,including the test results made in the assessment;
※ Any related conditions for maintenance of live equipment required about the assessment.
Evaluator personnel of equipment shall：
※ Being familiar with all relevant standards,the requirements of regulations being implemented and the existing explanatory material;
※ Could obtain a variety of materials required for the evaluation;
※ When necessary,could use the test equipment and make test procedures similar to national inspection department.
2.6.2 Intrinsically safe devices
Maintenance on live equipment could be taken if it meets the following conditions：
a) Maintenance work in hazardous areas
Any maintenance work shall be limited to the following condition：
1) When disconnect,remove or replace some electrical equipment components and cables;
2) When adjust the control device required for electrical equipment or systems calibration;
3) When remove and replace the plug-in unit or components;
4) Using inspection equipment required in the documents,when inspection equipment is not specified in the document,only using instruments that will not affect the safe performance of the circuit;
5) Other maintenance activities specifically allowed by relevant documents.
After the completion of these tasks,personnel to perform these functions should ensure that the intrinsic safety system or supporting intrinsically safe electrical equipment complies with the requirements of relevant documents.
b) Maintenance in non- hazardous areas
For maintenance of non-hazardous area associated electrical equipment and partial intrinsically safe circuit,when these electrical equipment or circuits are still partly connected to intrinsically safe circuit in hazardous areas,they should be limited to the content in term a).
Before disconnecting circuit in hazardous areas,grounding connection of barriers should not be dismantled to facilitate test of grounding resistance,except when double grounding device installed,single ground can be removed.
Only after the electrical equipment or circuit is disconnected from circuit in hazardous places,maintenance work can be done for associated equipment or parts in intrinsically safe circuit in non- hazardous areas.
2.7 Maintenance requirements of combustible dust explosion-proof electrical equipment
For electrical equipments which must be opened for maintenance should be located in dust free places.
Otherwise,appropriate measures need to be taken to prevent dust from entering the enclosure.
When removing the seals,joints,etc,if not replacing them,they must not be damaged.
When reassembling,you should provide and comply with the manufacturer's recommendations of seal.
Electrical apparatus in combustible dust environments shall be inspected and maintained according to schedule.Inspection and maintenance intervals depend on the environmental conditions,device quantities and the manufacturer's recommendations.
2.8 Grounding and equipotential bonding connection
Grounding and equipotential connection in hazardous area need to be made sure in good condition.

3 Ex electric apparatus check list(the following tables and contents only for reference)
3.1 Inspection schedule for Ex “d”

Check for Ex “d”		Grade of inspection
		Detailed	Normal	Visual
A	EQUIPMENT
1	Equipment is appropriate to the EPL/zone requirements of the location	X	X	X
2	Equipment group is correct	X	X
3	Equipment temperature class is correct	X	X
4	Equipment circuit identification is correct	X
5	Equipment circuit identification is available	X	X	X
6	Enclosure,glass parts and glass-to-metal sealing gaskets and/or compounds are satisfactory	X	X	X
7	There is no unauthorized modifications	X
8	There is no evidence of unauthorized modification		X	X
9	Bolts,cable entry devices (direct and indirect) and blanking elements are of the correct type and are complete and tight
	- physical check	X	X
	- visual check			X
10	Flange surfaces are clean and undamaged and gaskets are satisfactory
11	Dimensions of flanged joint gaps are within maximum values permitted	X	X
12	Lamp rating,type,and position are correct	X
13	Motor fans have sufficient clearance to the enclosure and/or covers	X
14	Breathing and draining devices are satisfactory	X	X
B	INSTALLATION
1	Type of cable is appropriate	X
2	There is no obvious damage to cables	X	X	X
3	Sealing of trunking, ducts, pipes and/or conduits is satisfactory	X	X	X
4	Stopping boxes and cable boxes are correctly filled	X
5	Integrity of conduit system and interface with mixed system maintained	X
6	Earthing connections, including any supplementary earthing bonding connections are satisfactory (for example connections are tight and conductors are of sufficient cross-section)
	- physical check	X
	- visual check		X	X
7	Fault loop impedance (TN systems) or earthing resistance (IT systems) is satisfactory	X
8	Insulation resistance is satisfactory	X
9	Automatic electrical protective devices operate within permitted limits	X
10	Automatic electrical protective devices are set correctly (auto-reset not possible)	X
11	Specific conditions of use (if applicable) are complied with	X
12	Cables not in use are correctly terminated	X
13	Obstructions adjacent to flameproof flanged joints are in accordance with the appropriate requirements	X	X	X
14	Variable voltage/frequency installation complies with documentation	X	X
C	ENVIRONMENT
1	Equipment is adequately protected against corrosion, weather, vibration and other adverse factors	X	X	X
2	No undue accumulation of dust and dirt	X	X	X
3	Electrical insulation is clean and dry

 

3.2 Inspection schedule for Ex “e”

Check for Ex “e”		Grade of inspection
		Detailed	Normal	Visual
A	EQUIPMENT
1	Equipment is appropriate to the EPL/zone requirements of the location	X	X	X
2	Equipment group is correct	X	X
3	Equipment temperature class is correct	X	X
4	Equipment circuit identification is correct	X
5	Equipment circuit identification is available	X	X	X
6	Enclosure,glass parts and glass-to-metal sealing gaskets and/or compounds are satisfactory	X	X	X
7	There is no unauthorized modifications	X
8	There is no evidence of unauthorized modification		X	X
9	Bolts,cable entry devices (direct and indirect) and blanking elements are of the correct type and are complete and tight
	- physical check	X	X
	- visual check			X
10	Lamp rating,type,and position are correct	X
11	Electrical connections are tight	X
12	Condition of enclosure gaskets is satisfactory	X
13	Motor fans have sufficient clearance to the enclosure and/or covers	X
14	Breathing and draining devices are satisfactory	X	X
B	INSTALLATION
1	Type of cable is appropriate	X
2	There is no obvious damage to cables	X	X	X
3	Sealing of trunking, ducts, pipes and/or conduits is satisfactory	X	X	X
4	Stopping boxes and cable boxes are correctly filled
5	Integrity of conduit system and interface with mixed system maintained	X
6	Earthing connections, including any supplementary earthing bonding connections are satisfactory (for example connections are tight and conductors are of sufficient cross-section)
	- physical check	X
	- visual check		X	X
7	Fault loop impedance (TN systems) or earthing resistance (IT systems) is satisfactory	X
8	Insulation resistance is satisfactory	X
9	Automatic electrical protective devices operate within permitted limits	X
10	Automatic electrical protective devices are set correctly (auto-reset not possible)	X
11	Specific conditions of use (if applicable) are complied with	X
12	Cables not in use are correctly terminated	X
13	Obstructions adjacent to flameproof flanged joints are in accordance with the appropriate requirements
14	Variable voltage/frequency installation complies with documentation	X	X
C	ENVIRONMENT
1	Equipment is adequately protected against corrosion, weather, vibration and other adverse factors	X	X	X
2	No undue accumulation of dust and dirt	X	X	X
3	Electrical insulation is clean and dry	X

 

3.3 Inspection schedule for Ex “n”

Check for Ex “n”		Grade of inspection
		Detailed	Normal	Visual
A	EQUIPMENT
1	Equipment is appropriate to the EPL/zone requirements of the location	X	X	X
2	Equipment group is correct	X	X
3	Equipment temperature class is correct	X	X
4	Equipment circuit identification is correct	X
5	Equipment circuit identification is available	X	X	X
6	Enclosure,glass parts and glass-to-metal sealing gaskets and/or compounds are satisfactory	X	X	X
7	There is no unauthorized modifications	X
8	There is no evidence of unauthorized modification		X	X
9	Bolts,cable entry devices (direct and indirect) and blanking elements are of the correct type and are complete and tight
	- physical check	X	X
	- visual check			X
10	Lamp rating,type,and position are correct	X
11	Electrical connections are tight	X
12	Condition of enclosure gaskets is satisfactory	X
13	Enclosed-break and hermetically sealed devices are undamaged	X	X	X
14	Restricted breathing enclosure is satisfactory	X
15	Motor fans have sufficient clearance to the enclosure and/or covers	X
16	Breathing and draining devices are satisfactory	X	X
B	INSTALLATION
1	Type of cable is appropriate	X
2	There is no obvious damage to cables	X	X	X
3	Sealing of trunking,ducts,pipes and/or conduits is satisfactory	X	X	X
4	Stopping boxes and cable boxes are correctly filled
5	Integrity of conduit system and interface with mixed system maintained	X
6	Earthing connections, including any supplementary earthing bonding connections are satisfactory (for example connections are tight and conductors are of sufficient cross-section)
	- physical check	X
	- visual check		X	X
7	Fault loop impedance (TN systems) or earthing resistance (IT systems) is satisfactory	X
8	Insulation resistance is satisfactory	X
9	Automatic electrical protective devices operate within permitted limits	X
10	Automatic electrical protective devices are set correctly (auto-reset not possible)	X
11	Specific conditions of use (if applicable) are complied with	X
12	Cables not in use are correctly terminated	X
13	Obstructions adjacent to flameproof flanged joints are in accordance with the appropriate requirements
14	Variable voltage/frequency installation complies with documentation	X	X
C	ENVIRONMENT
1	Equipment is adequately protected against corrosion,weather,vibration and other adverse factors	X	X	X
2	No undue accumulation of dust and dirt	X	X	X
3	Electrical insulation is clean and dry	X

 

3.4 Inspection schedule for Ex“i”

Check for Ex “I”		Grade of inspection
		Detailed	Normal	Visual
A	EQUIPMENT
1	Circuit and/or equipment documentation is appropriate to the EPL/zone	X	X	X
2	Equipment installed is that specified in the documentation－(only for permanent installation)	X	X
3	Circuit and/or equipment category and group correct	X	X
4	Equipment temperature class is correct	X	X
5	Installation is clearly labeled	X	X
6	Enclosure,glass parts and glass-to-metal sealing gaskets and/or compounds are satisfactory	X
7	There is no unauthorized modifications	X
8	There is no evidence of unauthorized modification		X	X
9	Diode safety barriers,relays and other energy limiting devices are of the approved type,installed in accordance with the certification requirements and securely earthed where required	X	X	X
10	Electrical connections are tight	x
11	Printed circuit boards are clean and undamaged	x
B	INSTALLATION
1	Cables are installed in accordance with the documentation	X
2	Cable screens are earthed in accordance with the documentation	X
3	There is no obvious damage to cables	X	X	X
4	Sealing of trunking,ducts,pipes and/or conduits is satisfactory	X	X	X
5	Point-to-point connections are all correct	X
6	Earth continuity is satisfactory (e.g.connections are tight,conductors are of sufficient cross-section)	X
7	Earth connections maintain the integrity of the type of protection	X	X	X
8	Intrinsically safe circuit is insulated against ground or grounded at one point (refer to document)	X
9	Separation is maintained between intrinsically safe and non-intrinsically safe circuits in common distribution boxes or relay cubicles	X
10	Short-circuit protection of the power supply (if applicable) is in accordance with the documentation	X
11	Specific conditions of use (if applicable) are complied with	X
12	Cables not in use are correctly terminated	X
C	ENVIRONMENT
1	Equipment is adequately protected against corrosion,weather,vibration and other adverse factors	X	X	X
2	No undue accumulation of dust and dirt	X	X	X

 

3.5 Inspection schedule for Ex“p”

Check for Ex “p”		Grade of inspection
		Detailed	Normal	Visual
A	EQUIPMENT
1	Equipment is appropriate to the EPL/zone requirements of the location	X	X	X
2	Equipment group is correct	X	X	X
3	Equipment temperature class or surface temperature is correct	X	X
4	Equipment circuit identification is correct	X
5	Equipment circuit identification is available	X
6	Enclosure,glasses and glass-to-metal sealing gaskets and/or compounds are satisfactory	X	X	X
7	There is no unauthorized modifications	X
8	There is no evidence of unauthorized modification		X	X
9	Lamp rating,type,and position are correct	X
B	INSTALLATION
1	Type of cable is appropriate	X
2	Type of cable is appropriate	X
3	Earthing connections,including any supplementary earthing bonding connections,are satisfactory,for example connections are tight and conductors are of sufficient cross-section
	- physical check	X
	- visual check		X	X
4	Fault loop impedance (TN systems) or earthing resistance (IT systems) is satisfactory	X
5	Automatic electrical protective devices operate within permitted limits	X	X	X
6	Automatic electrical protective devices are set correctly	X
7	Protective inert gas inlet temperature is below maximum specified	X
8	Ducts,pipes and enclosures are in good condition	X	X	X
9	Protective gas is substantially free from contaminants	X	X	X
10	Protective gas pressure and/or flow is adequate	X	X	X
11	Pressure and/or flow indicators,alarms and interlocks function correctly	X
12	Conditions of spark and particle barriers of ducts for exhausting thegas in hazardous area are satisfactory	X
13	Specific conditions of use (if applicable) are complied with	X
C	ENVIRONMENT
1	Equipment is adequately protected against corrosion,weather,vibration and other adverse factors	X	X	X
2	No undue accumulation of dust and dirt	X	X	X

 

3.6 Inspection schedule for Ex“tD” (dust-ignition-proof)

Check for Ex “tD”		Grade of inspection
		Detailed	Normal	Visual
A	EQUIPMENT
1	Equipment is appropriate to the EPL/zone requirements of the location	X	X	X
2	Degree of protection (IP grade) of equipment is appropriate for the dust conditions	X	X	X
3	Equipment maximum surface temperature is correct	X	X
4	Equipment circuit identification is available	X	X	X
5	Equipment circuit identification is correct	X
6	Enclosure,glass parts and glass-to-metal sealing gaskets and/or compounds are satisfactory	X	X	X
7	There is no unauthorized modifications	X
8	There is no evidence of unauthorized modification		X	X
9	Bolts,cable entry devices (direct and indirect) and blanking elements are of the correct type and are complete and tight
	- physical check	X	X
	- visual check			X
10	Lamp rating,type,and position are correct	X
11	Electrical connections are tight	X
12	Condition of enclosure gaskets is satisfactory	X
13	Motor fans have sufficient clearance to the enclosure and/or covers	X
B	INSTALLATION
1	Installation to minimize the risk of accumulation of dust	X	X	X
2	Type of cable is appropriate	X
3	There is no obvious damage to cables	X	X	X
4	Sealing of trunking,ducts,pipes and/or conduits is satisfactory	X	X	X
5	Earthing connections,including any supplementary earthing bonding connections are satisfactory (for example connections are tight and conductors are of sufficient cross-section)
	- physical check	X
	- visual check		X	X
6	Fault loop impedance (TN systems) or earthing resistance (IT systems) is satisfactory	X
7	Insulation resistance is satisfactory	X
8	Automatic electrical protective devices operate within permitted limits	X
9	Specific conditions of use (if applicable) are complied with	X
10	Cables not in use are correctly terminated	X	X
C	ENVIRONMENT
1	Equipment is adequately protected against corrosion,weather,vibration and other adverse factors	X	X	X
2	No undue accumulation of dust and dirt	X	X	X