The Importance Of Carrying Capacity

Summary : In the main building electrical distribution line equipment and materials ; Currently there are cables and busbar , if strengthen scientific management, rational use of cables and busbar , all aspects of strict control and identification distribution lines carrying capacity , help to reduce electrical fires , saving valuable copper resources , reduce project cost , to achieve energy saving .

Keywords: mineral insulated cable wire and cable fire busbar busbar cable current carrying capacity of the standard distribution line carrier capacity limit temperature rise test installation commissioning works come to expect lower electrical fire detection saves valuable copper resources.

Thirty years of reform and opening up , China's economy developed rapidly , in just three years time, completed the construction of a modern building developed a hundred years time . Rapid development and construction also makes the project quality management seriously out of line , buried security risk . This article describes the construction of electrical distribution lines carrying capacity , the current general location and distribution lines are wires, cables, busbar , fire fighting equipment and distribution lines are mineral insulated cables, fire resistant cables , fire busbar , minerals fire busbar etc. ; present the following problems :

① Wires, cables, mineral insulated cable product standards and product certification type pilot test , there is no current-carrying capacity test, carrying capacity is calculated by reference to the actual data -carrying capacity have gaps.

② Design reference data sources due to the current carrying capacity of inaccurate data , resulting in most of the designers enlarged wire, cable cross-section , resulting in a waste of copper resources engineering , some while amplifying circuit breaker rated current overload caused by higher circuit breaker fails to protect lower electricity transmission lines ;

③ Construction specifications for the laying of cabling requirements are not clear , due to cooling problems , skin effect and reactor problems, resulting in the current carrying capacity decreased, while causing fever .

④ Incoming inspection : Field no incoming inspection measures , sampling inspection stations to send test, test products qualified majority of substandard products in the field of quality management out of touch .

⑤ Busway , fire busbar current carrying capacity are inadequate , both ends of the head welding of copper , aluminum, copper, copper clad aluminum instead of copper , some carrying capacity of less than 60% of the rated current , busbar or cable at the project site no checked out , pose a safety hazard .

⑥ Site supervision , investors electrician construction unit , time management quality, but without responsibility and authority without thin tube ; go to the scene of the design and quality control station regulators, the right to manage , but there is no time and unmanageable. Caused by a mismatch between the quality management .

⑦ Electrical engineering Construction Quality Acceptance , focusing only on the quality of construction , while ignoring the quality of materials and equipment monitoring , it should be the quality of the whole project , the current quality of the feed material is basically no site inspection , causing serious gap in quality management .

Because of the above problems, to bury electrical engineering safety hazard , waste copper resources , preventing the Chinese norms integrity of wires , cables , busbar development of enterprises, in order to survive in difficult to fake and shoddy products business has been rapid development opportunity.

If you want to change the above problem, need wires, cables, mineral insulated cable regulations and product standards to improve the carrier type testing. Building electrical design , electrical engineering quality acceptance , on-site inspection , quality control personnel authorized on-site quality management powers should be played with the greatest responsibility to field engineering staff , good control of distribution lines carrying capacity , to prevent electrical engineering security risks. Reduce electrical fire accidents, to achieve energy saving .

Here 's wire and cable distribution lines and busbars and current carrying capacity related standards, product certification , test methods and design selection, engineering, installation, project quality management, project acceptance and analysis for your reference .

First, wire, cable standards and type testing

1) GB / T 3048-2007 Test methods for electrical properties of
2) GB / T 5013-2008 rated voltage 450/750V rubber insulated cables
3) GB / T 5023-2008 rated voltage 450/750V and below PVC insulated cables
4) GB / T 12527-2008 rated voltage 1KV and below overhead insulated cables
5) GB / T 12706-2008 Rated voltage 1kV (Um = 1.2kV) to 35kV (Um = 40.5kV) extruded insulation power cables and accessories
6) GB/T13033-2003 rated voltage 250V and below the mineral insulated cables and their terminations and other parts
7) GB/T19666-2005 flame retardant and fire-resistant wires, cables General

Above wire and cable : includes fire-resistant cables , mineral insulated cables , etc., all products there is no standard type test current carrying capacity of the pilot project , the current carrying capacity of the verification mainly on the basis JB / T 10181 cable ampacity calculations and GB / T 16895.15-2002 " electrical installations of buildings - Part 5: selection and erection of electrical equipment " on page 523 : " wiring system ampacity " standard, according to parties understand these ampacity is calculated , there is no current carrying capacity is the actual detection out accurate data ; calculations and the actual test is a difference , because the current carrying capacity is directly related to the skin effect , heat capacity , reactance , impedance, eddy current , conductor resistivity, laying method , the installation process , etc., and . Multiple cables in parallel with phase derating data is incalculable accurate ; Busway experience in previous calculations and the actual detection of the gap is large, some serious gaps 50% , I issue the following market research and a big gap between current-carrying capacity . For example :

① GB / T 16895.15-2002 standard copper cable inside the aluminum cable is 75% to 80 % of the current-carrying capacity , are not allowed : because the conductivity of copper 97%, resistivity ≤ 0.01777Ω·mm2/m, the conductivity of aluminum 59% , resistivity ≤ 0.029Ω·mm2/m; while at the actual load current busbar test , the same row regulation , aluminum row are only about 60% copper .

② Phase multi-core parallel derating data related to reactance and skin effect , the current carrying capacity derating larger standard there is no detailed mention credible and reliable derating factor issue.

③ Most of our projects, the cables are usually laid in a closed compartment ( bridge ) , the heat dissipation is poor, have seriously affected their carrying capacity , some projects severe cases, the current carrying capacity of only ladder bridge the 50%, but within the standard shown in Table 52-B2 to give a carrier to the user data to the reference , in fact, the laying of the bridge structure is not the same, the difference between the actual current carrying capacity greater .

④ Different external jacket and the insulating material , the thermal capacity of different , the internal conductor temperature very different, of course , there are differences between the current carrying capacity .

</ table>

In Table 52-A , the polyvinyl chloride (PVC) conductor temperature is 70 ℃ , cross-linked polyethylene (XLPE) and ethylene propylene rubber (EPR) conductor temperature is 90 ℃ , the reason for this is because these settings different temperatures of heat insulating material , however , a different mineral insulated cable , standard temperature were 70 ℃ and 105 ℃ jacket temperature of the product structure is different, the temperature of the inner conductor and the jacket temperature of the surface of a gap, cause and heat insulating materials related to the ability . A single temperature can not be identified from the surface temperature of the inner conductor , if the surface temperature of 105 ℃, some products internal and surface temperature 30 ~ 40 ℃, copper conductor generates reach 105 ℃ annealing temperature increased resistance during operation voltage drop increased carrying capacity will decline, according to the internal temperature of the conductor should prevail .

⑥ Ambient temperature
GB / T 16895.15-2002 523.2.2 air temperature is 30 ℃, buried cables ambient temperature of 20 ℃. Maximum temperature in most parts of 40 ℃, so our standard ambient temperature is 40 ℃, low voltage switchgear , including Busway ambient temperature 40 ℃. If the insulating material is 90 ℃ materials , according to the limit count conductor temperature rise should not exceed 50 ℃, which is ≤ 50K , you can ensure that no super-insulating materials, heat resistance ; while GB/T16895.15-2002 standards in regulations ambient temperature of 20 ℃, 30 ℃ when the calculated current-carrying capacity than 40 ℃ ambient temperature current carrying capacity by 8 to 15 percent.

Above aspects summary : Cable standards and certification type tests when the current carrying capacity should be increased with the limits of temperature rise is directly related to the pilot project , with the products used in heat-resistant insulating material temperature of minus 40 ℃ temperature difference between the value of the standard ambient temperature to allow temperature rise , limit is 70K, and low voltage switchgear , busbar current carrying capacity of the same . Phase multiple parallel grooves cassette laying has to be done and what various tests available to the designer to ensure accurate data carrying capacity design selection .

Second, busbar standards and type testing

Busway , refractory bus standard has improved our current industry standards and national standards.
1) GB 7251.2-2006 Low-voltage switchgear and control equipment - Part 2: for busbar trunking systems ( busways ) special requirements
2) JB / T 8511-2011 air insulated busbar trunking systems ( air insulated busbar )
3) JB / T 9662-2011 densely insulated busbar trunking systems ( intensive insulated busbar )
4) JB / T 10327-2011 Refractory busbar trunking systems ( fire busbar )

⑤ GB / T 16895.15-2002 Table 52-A maximum operating temperature of various insulation
Insulation Type Temperature limits ( see Note 1)
Polyvinyl chloride (PVC)
Cross-linked polyethylene (XLPE) and ethylene propylene rubber (EPR)
Mineral insulated (PVC sheath or jacket can be touched bare ) cable
Mineral insulated ( not accessible and not in contact with combustible nude sheath ) cable
70 ( conductor )
90 ( conductor )
70 ( sheath )
105 ( Sheath ( see Note 2 )
Note :
1 listed in Table 52-A maximum allowable temperature taken from IEC Publication 60502:1983 and 60702:1981 , Table 52-C1 to Table 52-C4 and Table 52-C9 to 52-C12 flow values ​​are contained in this is the maximum permissible temperature value tables .
2 Conductor temperature exceeds 70 ℃ , should be identified with the conductor terminals connected device temperature is appropriate.
3 Pairs of certain types of cables can have a higher operating temperature , depending on the temperature and the rating of the cable ends , environmental conditions and other external influences.
Busway type of pilot projects
Pilot project Provisions of No. Testing purposes
Temperature rise limit verification 8.2.1 </ td> Current carrying capacity verification
Dielectric performance verification 8.2.2 Insulation
Short circuit withstand strength verification 8.2.3 Short circuit mechanical strength
Protection circuit validation 8.2.4 Fault current evacuation capability
Clearances and creepage distances validate 8.2.5 Verify clearances and creepage distances
Mechanical operation verification 8.2.6 Plug the operational performance of the switch box
Protection Level Authentication 8.2.7 Room temperature, dust, water capacity
Busbar trunking systems electrical performance validation 8.2.9 A conductor conductor resistance reactance B C D total impedance conductor size
Structural strength verification 8.2.10 Withstand mechanical stress
Sliding touch trunking systems durability verification 8.2.11 Durability verification
Pressure resistance performance verification 8.2.12 Pressure
Abnormal heat resistant insulating material verification 8.2.13 Heat resistance of insulating materials
Prevent the spread of flame verification 8.2.14 Verified against flame spread
Building structure fire damper validation 8.2.15 Fire performance verification
Fire water test GA/T537 4.3.1 On fire 30 minutes after the fire sprinkler test water resistance test
Fire performance verification GA/T537 4.3.2 Fire resistance ; fire 60 minutes than GB/T19216 ,21-2003 or BS 6387 for fire 950 ℃, more than three hours

Above criteria within the busbar current carrying capacity test is to detect the main busbar temperature rise limits , test methods for low voltage high current , busbar rated current in the long run , temperature probe, detection busbar ; connector and conductor temperature at the interface plug , ABCN phases , each phase to be detected ; highest temperature point minus busbar outside air temperature difference between the ambient temperature value , that is, temperature rise , in units of K, 70K is 70 ℃ temperature . The ambient air temperature changes, internal busbar temperatures are followed by changes , but temperature constant ; therefore type-tested products , product structure unchanged , unchanging materials , production processes remain unchanged , the temperature difference is constant , current-carrying ability does not change, so the temperature rise determined busbar current carrying capacity .

Third . Product Certification

Country in 2003 before wires, cables , busbar has industry production license, in 2001 , after China's accession to the WTO , in order to open the door , fair trade , the implementation of a national compulsory CCC, both cable and busbar in the first , nineteen categories of 132 kinds of products mandatory CCC certification directory . Cable because in the first directory specify one of five cables , some cables have not been named so far not implemented certification. Busway : In the first group : the third largest category within the division , and low voltage switchgear , low voltage switchgear is GB7251 series of products: low voltage switchgear, busbar, power distribution cabinets, distribution boxes, meter boxes, control boxes, cabinets and other capacitors , low voltage switchgear busbar is from GB7251.1-GB7251.8 GB7251.2 includes all the Busway , so all Busway need CCC.

Resistant cables , mineral insulated cables and special cables because the cable has not been named so far no mandatory certification. Quality management appear disjointed . At present, these products have not certified nor carrying capacity test , and some have not even national standards adopted in the part of foreign standards pilot project commissioned tests can also be used in our engineering popularity , in order to project the safety certification is not required cables should require departments to accelerate the improvement unified CCC. Meanwhile Busway and current carrying capacity of wire and cable and related shape structure, conductor size , temperature rise and other data should be placed online publicity , is conducive to the project site when the query and the quality of supervision.

Fourth , design specifications and design selection

① Wire, cable design and current carrying capacity

Present, China's industries and countries related to design specifications JGJ16-2008 civil electrical design specifications , JGJ 242-2011 residential building electrical design specifications , GB500054-2011 low-voltage power distribution design specifications that the cable is the cable design selection model specifications, data on the current carrying capacity , the majority accordance with the " standard atlas ", " design Manual " and "JB/T10181 cable ampacity calculations " , and "GB/T16895.15-2002 building electrical equipment , wiring systems ampacity standard " and the manufacturer's selection guide to selection . These standards specification manual wire, cable current carrying capacity is not an item is actually detected the real data. Even though some companies inspected, tested and tested but it is also related to the above criteria are calculated according to the data . This article mentioned above vary doubt on the current carrying capacity calculations and the actual data discrepancies , the following points worth questioning originally designed and related professionals to explore , scrutiny. For example :

a) The same phase multiple cables and used, due to the skin effect , reactance , carrying capacity decline was unable to calculate accurate ;

b) Cable laying in a closed tank fit within the tray , because heat problem , the carrier dropped some serious reach 50% , the calculated how much discount ?

c) Present the manuals and the actual data has not been detected , it provides reference data and real operational data in the end how much difference ?

d) Design construction laying schemes, current carrying capacity change is also different, even far , therefore, should be clearly laying method ; cable conductor current carrying capacity shall be detected inside the inner conductor temperature rise to verification, conductor maximum temperature does not exceed 105 ℃, due exceeds 105 ℃ , annealed copper conductor will ; aluminum conductor is lower. China generally agreed within the standard ambient temperature 40 ℃, namely: the standard temperature rise of the cable , the cable should be heat-resistant insulating material temperature minus ambient temperature of 40 ℃, the allowable temperature rise limit , the maximum allowable value

e) Aluminum conductor conductivity was 59 % and the copper conductor rate was 97 % of the conductivity of aluminum is only 60% of copper , aluminum conductor equivalent in the standard cross-section , the same insulating material is 75% -80% of copper ; Busway same structure , the same conductor rate of only about 60% of copper , calculated carrier is accurate.

② Why the need to enlarge the cable design , the higher rated current of the circuit breaker should not be too large.

Cable current carrying capacity are too many uncertain factors , therefore, either alone or some reference books, can not determine the actual cable current carrying capacity . Resulting industry or professional field , in the design selection, often as possible in order to enlarge the design safety margin . But some designers put cable specifications enlarged, while the superior circuit breaker rated current is also amplified , then there is a big security risk. Imagine : If the cable due to higher current carrying capacity of less than the rated current of the circuit breaker , and when the superior technical performance of the circuit breaker capacity 10% over conventional take about two hours before disconnecting , super-capacity 20%, takes about 20 -30 minutes before action switches off . Cable carrying capacity is insufficient , the higher the circuit breaker does not operate , then the heat will cause the risk of electrical fires . I believe that the circuit breaker ( frame switch ) of the rated current, according to the design to calculate the current 10% or so , some of the cable only safety margin should be enlarged .

③ Busbar design selection should explicitly limit the temperature rise ≤ 70k.

Present many engineering design Busway because there is no clear temperature rise , design of current should only need to mark the temperature rise , because of the different temperature , different temperature insulating materials , if only by national standards , the design temperature rise when there is no clear , there is a dispute in the project , because China is now implementing the standard IEC60439 converted to GB GB7251; IEC international standards adapted to the global environment temperature: some countries the ambient temperature reaches over 60 degrees ; some countries have lower ambient temperature . The limit temperature is the highest point of the conductor temperature minus ambient temperature , but in Europe and the United States , Japan, Korea , China , Hong Kong and Macau all the limit specified in the temperature rise ≤ 50K-65K , with most of the national standard ambient temperature is 40 ℃ , the ambient temperature heating appreciation ≤ 105 ℃, because copper annealing temperature of 105 ℃, those countries and regions conductor temperature rise limits specified ≤ 50K-65K.

Of compulsory CCC certification began in 2002 , type test standard conventions : Conductor limit temperature rise ≤ 70K; followed in 2011 , the industry standard JB8511-2011, JB9662-2011, JB10327-2011 All agreed conductor temperature limit is ≤ 70K. However, China Busway IEC International Standard is converted to GB7551.2-2006 when , in accordance with the International Electrotechnical Standards literally pirated . Maximum temperature in accordance with the ambient temperature and the heat resistance of insulating materials based on , standard limits the heat insulating material to determine the limits of temperature rise of the conductor , therefore , raise the temperature of the heat insulating material , so that the temperature rise in accordance with the standard interpretation products allowed values ​​increase , giving the small current high current busbar paste the text from the standard interpretation of signs to be in compliance. However, when the design margin is not large, intense heating equipment such products may ignite the connection wire and cable, electrical fire brewing : Because the switch is not likely to cause higher action, high temperature burn connecting wire and cable insulation material . In some projects, technical staff that the inner conductor temperature rise of 90K or higher , as long as the beginning of the section is less than 70K, but also will not burn the cable , which is indeed Myth : Because busbar temperature rise type test done , its starting end section exposed to the air , the heat directly from the air circulated ; but the actual installation in the trunk , beginning end once installed , has a box covered , heat is not good if the case , the carrying capacity decreased , then the temperature is usually in the head leading end will be higher than the interface connector and plug conductor temperature . If the heat resistance of cable insulation material is much lower than the busway , even though some items close to the rated current of the load is only 60% of it will burn out the cable , causing a fire. Therefore the design of busbar temperature rise is clearly very important. Busway limit temperature rise should also design specifications stipulated ≤ 70K.

④ Why the bus before the actual load plus 10% best

Busway designed ≤ 70K rise , its design circuit rated current value is calculated according to the design current of 10% is ideal. Because Busway product standard type tests done verify current carrying capacity limits of temperature rise test , the current is very accurate , if the design has made it clear temperature rise , according to the design plus 10 % of the calculated current is the ideal choice. Moreover , most of the busbar class B insulation material selection , while class B insulation temperature 130 ℃, China ambient temperature of 40 ℃. Designed to limit the temperature rise ≤ 70K, 40 ℃ +70 ℃ = 110 ℃, ambient temperature at 40 ° full load operation , ≤ 70K busway long full load operation , the internal maximum temperature ≤ 110 ℃, 20 ℃ insulation material and margin of long-term overload about 10%, 10% higher current breaker overload will automatically trip about two hours , security is guaranteed ; if the ambient temperature 20-25 ℃, long-term overload capacity more than 20 %, if the actual load current of only 90 % , at an ambient temperature of 20-25 ℃ design selection at maximum conductor temperature ≤ 70K, the actual load current is more than 30 % of the margin , forming a secure distribution system. Therefore Busway plus 10% margin fully meet the actual needs of operational safety .

Fifth , installation and quality acceptance

① Incoming require site inspection

In construction of the building electrical engineering, installation and acceptance , the main current standard version number is : "GB50303-2002". However, this standard, no busbar current carrying capacity related technical parameters of the test items ; while wires, cables have detected resistivity.

In our engineering and construction period of vigorous development , the status quo is the most prominent of many engineering and inspection station staff is so small that regulatory authorities related personnel for on-site supervision of the quality of materials and equipment has always been powerless . Therefore, we should put the rights and responsibilities under the supervision of the site and installation personnel , the implementation of "Who verify who bears the responsibility ."

Past wire and cable testing, basically submission to the local inspection station or test detected . In recent years, wires, cables, sample test results to the inspection station are all qualified products, and the truth is the current project on the use of cable is most unsatisfactory , the reason lies in the management out of touch, the inspection of products and live the actual construction of different products ; coupled with the sampling of the test sample is only responsible for the sampling , not in charge of works , on-site supervision of installation personnel and inspection stations that have been sampling inspection , with inspection reports have been completed on-site staff responsibilities , there is a work of quality and safety vulnerabilities. If you change the processes and methods , for example: 5% to goods -site sampling of products resistivity, site inspection can give full play to on-site installation and technical personnel, users , supervision of responsibility, and to improve the detection level of technology , can effectively control the current construction projects existence of serious cable quality issues in order to maintain the integrity of the wire and cable industry norms healthy and orderly development .

② Installation cable laying and construction of the current carrying capacity for

Cable laying and laying interlayer spacing will affect the wire, cable current carrying capacity , most of our projects in a closed groove box cabling , and closed groove box carrying capacity derating data , to be worth further practical tests. Existing "GB/T16895.15-2002" standard reference data and the actual many different industry deserves a lot of attention and get to the bottom . Also multiple cables in parallel on the same circuit when used with phase cut should pay attention to the following points :

1) Multiple cables with phase due to the skin effect and reactor problems carrying capacity derating is no clear and detailed data can reference or theoretical calculations ;

2) Multiple cables and use the same phase, if there was a cable installation, the connector is not connected, may be most of the current from the other phase cable through , it will cause other phase cable heating caused by a short circuit or a more serious fires.

③ Project commissioning and acceptance

Project commissioning acceptance in the "GB50303-2002" Section 10.2.4 chapters , " on 630A conductor or busbar connections, load operation in the case of design calculations should be done sampling tests and record temperature , stable and not greater than the design temperature rise value . " this provision in general terms , of which this provision is the only current-carrying capacity on the trunk of the test items . In the past 10 years , most of the quality control and supervision no Busway stations and cable connectors do temperature tests , ie : the past 10 years , since the quality inspection departments do not pay attention , " General Conditions ", so , Busway , cable installation is complete, and current carrying capacity of the test items not on the test . Therefore, quality control is out of line , buried security risk .

Cable, wire and busbar incoming inspection work should be the need to strengthen management and supervision. Incoming inspection can only be done on-site to manage the quality of materials and clear accountability . Construction projects like the construction of manufactured products , the factory matched inspectors , meanwhile, set up incoming inspection, process inspection , factory inspection and other processes, but , if there is no inspection of the enterprise , there is no clear need to detect the items , then , quality inspection staff positions is no obligation , because the staff do not know what to check . And if the enterprise is no clear test procedures can not ensure the quality of products, then , should be the corporate responsibility . Therefore, the same token, the same electrical engineering , construction quality acceptance inspection procedures with the same factory , the factory inspection procedures guiding the factory quality control personnel to good quality ; acceptance of construction quality norms to guide all of the country engaged in the construction of electrical technical personnel ( including those engaged in electrical engineering construction units, technical staff , supervision and inspection station personnel, etc. ) of the guide specification. If you do not clearly require inspection items , field personnel will not go testing, quality management project appear disjointed , which appears to be attributed to the quality of the writing group responsibility . In a modern building electrical construction should control the incoming inspection, construction inspection, engineering completed commissioning testing. With high-quality materials to build quality projects , so incoming inspection, it should be an important building electrical construction quality checks link ; engineering installation , commissioning and acceptance, before the handover of the finished product testing, in order to have security project quality.

④ Quality control should be decentralized

Present, China's construction of electrical engineering is the right major acceptance in the design personnel and inspection stations , although it works on both the supervision , but there job right , going through the motions , because: Building Electrical Construction Quality Acceptance There is no need to explicitly specify the quality of the project site supervision methods , on-site construction units and supervision under no obligation to live a good quality of products . Some of the items specified sampling inspection to inspection stations to test , not only increasing the cost of the project , but did not reach a substantive role . Thus causing a mismatch between management , the quality of the blind spot .

I believe that only quality control checks on-site technical personnel directly involved can be achieved , but only explicitly require regulators need to examine project site personnel , as well as test methods and practical guidance emphasizes the implementation of remote monitoring can play a role . Site quality not manage well , go on-site personnel assume responsibility , regulators can implement penalty system on-site personnel , serious criminal liability. Design staff, quality inspection station does not participate in the specific inspection work , the designer is responsible only for the design drawings ; should not participate in project acceptance , quality inspection station staff responsible for monitoring the quality of strict audit information , check with the actual products certified product data related site acceptance testing parameters compliance and consistency ; right supervision , Party electrical charge and electrical construction unit responsible implementing regulation. Site inspection of the construction site as much as possible by the person in charge of the electrical units , electrical charge and supervision of the user who is responsible for the electrical charge of inspection and supervision, accountable , who is who is responsible for inspection , in order to improve the country engaged in the construction of electrical staff responsibilities and enhance lifelong technical level , truly clear responsibilities clearly-defined responsibilities . Decentralized management will reduce the inspection station staff workload , and can effectively control the quality of the project .

Sixth , GB50303-2013 electrical engineering construction quality acceptance , the manuscript with the current carrying capacity related disputes .

2002 years, China's construction of electrical engineering Busway installation , in accordance with GB50303-2002 is currently building electrical construction quality acceptance criteria. The standard is not relevant for the current carrying capacity of busbar test items : No incoming inspection , and no installation process inspection , and only when the installed equipment commissioning temperature rise test , the test methods written in the GB50303-2002 10.2.4 strip within the general terms of the general terms of all of the country for quality inspection stations do not pay attention , the majority did not examine the past 10 years to the project planted a serious security risk , so that the norms of corporate survival difficult to make large-scale low-quality products used in the project , do violation of inferior products enterprises have developed rapidly . After 10 years of hard survive regulate business , the original modification GB50303-2002 saw the hope, but standardized perfect but very long and difficult road . In respect of standards and current carrying capacity are directly related to the following issues for our consideration :

① Incoming goods should be checked and the temperature rise type test report CCC report

GB50303-2013 " Building Electrical Construction Quality Acceptance" revision of the manuscript 3.2.17 Section 1 , "3C type test report and the temperature rise due to report : the report should conform with the product specifications , and the complete contents of the report , " manuscript discussion : either cancel this provision , or provisions to" have objections to provide . " Compulsory 3C certification in our online publicity Busway certification data , only current specifications , IP protection class , Icw short-circuit withstand strength parameters , but the relationship is related to the ability to stream out Busway technical parameters , but no certificate and online publicity . Such as product mix , extreme temperature, conductor size , conductor material, shell material, those with current carrying capacity is directly related to the same material, same size conductor busbar , the result in different structures , and some products carrying capacity gap of 20% ~ 50% , so the CCC type test reports with the 3C certificate used simultaneously, providing products 3C type test reports should be provided , and should be provided for each current specifications Busway product test reports in order to identify the temperature rise because of CCC certification is a certificate covering multiple current specifications, type tests only cover a small current -current , covered by a small current is not doing the type test temperature , the other type of pilot projects of the technical parameters , due to the large current through the test, if the same structure , the resulting small current covered almost . However, the temperature rise is directly related to the current carrying capacity issues , some products covering every square millimeter of small current capacity greater than the test current specifications energized , so the temperature rise should be required to provide test reports to prove the cover current carrying capacity .

② Check report Conductor Size

3.2.17 Article 1 ( 3 ) point that "the conductor size should 3C type test report conductor specifications consistent , when the current carrying capacity of the conductor have objections should be sent to a qualified laboratory or testing unit to do limit temperature rise test , the temperature rise of the rated current shall meet the design requirements , the design not specified , the temperature rise should not exceed 70K ", submitted for review to engage in discussions to cancel ≤ 70K limit , according to the standard , the standard of busbar ≤ 3C type test standards 70K industry standard JB/T9962-2011, JB/T8511-2011, JB/T10327-2011 is ≤ 70K, national standards with international standards, the current implementation of national standards GB7251.2-2006 limit temperature rise limited by the following factors : < /p>

1 Conductor material limit temperature

2 To adjoining equipment may affect

3 Insulating material in contact with the conductor allowable temperature limits

4 Connected thereto conductor temperature of electrical document

5 Contacts for connection , the contact materials and surface treatment

If GB7251.2-2006 in accordance with the provisions of the standard interpretation , its temperature rise according to the above factors to be determined , do not specify the permissible limit temperature rise . In practical engineering and design process , investors, construction, inspection process and product standards do not look at the basic field use conditions connected with the busbar material is able to withstand , for example: according to GB , if not explicitly Party when ordering temperature rise , to limit temperature rise of a conductor goods products is 90K, or even higher than 100K, is often seen in engineering .

Is assumed : If the insulation material used class H , busbar conductor temperature rise limit of 140K product, carrying capacity is only 60% of current ≤ 70K , according to the standard interpretation of the provisions , compared with qualified products. Therefore, the temperature rise to be clear , current, and power distribution systems in order to ensure the safety . According to actual needs into ordinary fire distribution lines and distribution lines , fire using fire busbar ≤ 100K, other bus should be ≤ 70K. Due to fire busbar insulating material high temperature, fire needs to run when put into full operation , the running time is often less than 24 hours, you can increase the temperature rise .

GB/T16895.15 mineral cable also different from ordinary cable , general cable detection conductor temperature 70 ℃, 90 ℃, while minerals cable detection sheath temperature 70 ℃ -105 ℃, minerals actual cable conductor temperature than ordinary cable also increased 30 ~ 50 ℃, current carrying capability gap.

③ Test conductor resistivity ensure Conductor Material

GB50303 manuscript 3.2.17.3 " according to current national standards ( wire and cable electrical performance test methods - Part 2 , the metal material resistivity test ) GB/T3049.2 relevant test methods , field sampling Busway body resistance rate should follow the " electrical copper, aluminum and its alloy bus " GB/T5585 the relevant provisions of the scene when the environment does not have the test conditions , should be sent to a qualified laboratory for testing , " some companies discussed in this manuscript made to cancel .

Author comments : In the GB50303-2002 specification, wires and cables are sampling, testing resistivity, wires, cables, due to the design only clear model specifications, in the engineering sense resistor ratio can control the quality, should also be detected Busway resistivity. Busway design is current to whether the goods meet current , GB50303-2002 is no identification of conductor size , there is no test conductor material incoming inspection, incoming inspection works do not guarantee quality of the project ; manuscript provided in GB50303-2013 3C temperature rise type test reports and reports can only control incoming goods check conductor size , just clear the certification test conductor size, shape structure, conductor materials and temperature rise ; but the material goods to the site must be on-site detection conductor the resistivity of the conductor to ensure the quality . Some Busway site product conductivity of only 70 % to 85% , and some close to the conductor aluminum conductor conductivity. There are copper clad aluminum and copper welding head ends , and some copper to aluminum instead of copper used in engineering , carrier capacity is insufficient , serious security risks planted , only field testing to control the good conductor resistivity conductor material . Therefore Busway site inspection resistivity is indispensable items.

I believe that the number of each sampling site specifications should be less than 5% at least one ; wire and cable should also be on-site testing, is conducive to on-site construction and technical personnel , supervision and users, technical personnel and improve technology to improve accountability level to ensure project quality .

④ Field sampling temperature rise

GB50303-2013 manuscript 10.1.3 clauses "400A current devices and above large -capacity wire or bus connections, should be designed to measure the rated load operation temperature rise ," discussion group that the removal of this provision , I believe that retention , but also to be implemented into the strong pieces in the GB50303-2002 standard , the current of the times the original is changed 630A 400A, because the old specification does not define the number of sampling to draw 10% joint, temperature rise due to poor field conditions can relaxation 5K ensure project quality. Reasons are as follows :

a) The original specification is 630A, the general provisions in 10.2.4 inspection station most do not pay attention , there is no clear number of workload, there is no clear test method , there is no inspection , resulting in working out of touch ;

b) 400A ~ 500A current , if the use of cables, two cables and use a relative large , 630A using cable over two or more cables are mostly used in the same phase and use two or more cables in parallel use the same phase , if the installation which has a cable connector installation fails , and current good cable connection from the other plus load flow, easily lead to other cable heating phase short circuit caused a fire accident occurred .

c) 400A ~ 1000A uses a single cable , fully connected, on-site construction is very difficult, if not good connector easily cause fever . Therefore required to initiate testing of joints from 400A temperature rise , eliminate hidden dangers.

d) Busbar and busbar connection connector bad installation or start connecting ends with distribution cabinets , cable headend busbar connector , if installed easily lead to bad joints , fever, and finally lead to short circuit and fire disasters, particularly is large currents. Therefore 400A must be installed above each phase sampling connector temperature rise .

e) The number of each size sampling sampling 10% to 20 %, can control the quality of the project , to reduce the workload .

f) Installation commissioning sampling, you can control and shoddy products into the works.

⑤ Project acceptance test required wire , cable laying methods and interlayer distance

In this project acceptance wire , cable laying method GB50303-2002 features a clear and acceptance process , supervision, inspection stations basically no tubes, but laying and spacing between layers and different carriers bridge larger capacity gaps in this revision GB50303-2013 for cable laying and spacing between layers should be required to clearly or explicitly by GB / T 16895.15-2002 electrical installations of buildings - Part 5: selection and erection of electrical equipment - section 523 : wiring system load flow or GB 50168-2006 electrical equipment installation engineering construction and acceptance of cable lines .

Conclusion

Distribution lines carrying capacity , not only the cross-sectional area of ​​the conductor and the copper content , the current carrying capacity related to the product structure, heat capacity , skin effect , eddy current , reactance , impedance, ambient temperature, insulation materials heat resistance , extreme temperature rise , laying method , surface treatment , processing technology , the installation process with the current-carrying capacity , and therefore the need to limit temperature rise test to ensure that the power- carrying capacity .

This article chapters GB50303-2013 5:00 manuscript problems associated with current carrying capacity is directly related to distribution lines per one pair of current carrying capacity are very important , the lack of control work easy touch. The specification is the quality of our electrical engineering unique specifications. Since the GB50303-2002 specification has been implemented for 11 years , want to write the relevant group leaders and experts , to our long-term goal of building works and the quality of people's lives and property safety , the content should not be more than 5:00 lack of GB50303-2013 electrical engineering construction quality Acceptance should be tightly controlled distribution lines carrying capacity , reduce our electrical house on fire accidents.

Most important is the construction of electrical distribution lines carrying capacity , as the main structure building civil engineering structures as important to do well, may cause bridges or buildings collapsed , distribution lines carrying capacity without control good cause electrical fires , will involve people's lives and property safety , in order to control the current carrying capacity of distribution lines , it is necessary wires, cables , busbar product standards certification type test , accurate data on the ability of carriers available to the designer selection . Before installation should be strict incoming inspection and engineering installation commissioning and acceptance in all aspects of the work of comprehensive checks to ensure that the building 's electrical power transmission lines carrying capacity, electrical engineering energy saving , reducing electrical fire accidents, reduce project cost , saving valuable copper resources , and guide enterprises technological innovation, and improve standards and norms in order to ensure that the current carrying capacity of distribution lines , in order to lead the technological development , the revitalization of the sound development of national economy entities , diligence and wisdom of Chinese people eventually make low quality products to the world, to achieve industrial rejuvenation of the Chinese nation . Rely on the state to change policies, laws and various ministries specification improvement, will be able to lead the future development of Chinese enterprises .


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