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www.infoPLC.net DISCLAIMER This document is intended to provide general technical information on particular subject or subjects and is not an exhaustive treatment of such subjects. Accordingly, the information in this document is not intended to constitute application, design, software or other professional engineering advice or services. Before making any decision or taking any action, which might affect your equipment, you should consult qualified professional advisor.
www.infoPLC.net TABLE OF CONTENTS Contents Introduction to North American Standards 1. Comparison between two cultures and markets: The United States and the European Union. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 1.1 Different juridical approaches: how are "safety" and "security" implemented . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 1.2 Market control systems and Control bodies . . . . . . . . . . . . . . . . 8 1.3 The role of the AHJ . . . . . . . . . . . . .
www.infoPLC.net TABLE OF CONTENTS Branch Circuit 1. Starting, load protection and motors (Branch Circuit) . . . . . . . . . . . . 37 1.1 Different types of branch circuit . . . . . . . . . . . . . . . . . . . . . 37 1.2 Motor branch circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 1.2.1 Motor starter “Type A” . . . . . . . . . . . . . . . . . . . . . . . 39 1.2.2 Motor starter “Type B, C and D” . . . . . . . . . . . . . . . . . . 39 1.2.3 Motor starter “Type E” and “Type F” . . . . . . . .
TABLE OF CONTENTS www.infoPLC.net 1.7 Low-Voltage Limited Energy Circuit . . . . . . . . . . . . . . . . . . . 81 1.7.1 Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 1.7.2 Overcurrent Protection . . . . . . . . . . . . . . . . . . . . . . 82 1.7.3 External Wiring and Terminal . . . . . . . . . . . . . . . . . . . 83 1.7.4 Internal Wiring . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 1.7.
www.infoPLC.net INTRODUCTION TO NORTH AMERICAN STANDARDS 1. Comparison between two cultures and markets: The United States and the European Union 1.1 Different juridical approaches: how are "Safety" and "Security" implemented? In the European Union The national technical regulations are subject to provisions of articles 28 and 30 of the treaty establishing the European Community (the EU treaty) that prohibit quantitative restrictions and all other measures having equivalent effect.
www.infoPLC.net INTRODUCTION TO NORTH AMERICAN STANDARDS 1.2 Market control systems and Control bodies The control structure in the European Union is carried through the Production Ministry (or Industrial and Commerce Ministries) and from the local organisations (in Italy, for example, the ASL or SPISAL Services of Prevention and Protection).
www.infoPLC.net INTRODUCTION TO NORTH AMERICAN STANDARDS Canadian Centre for Occupational Health and Safety (CCHOS): it is the Canadian equivalent of the American OSHA. From 1978 the role of this Centre is to provide occupational safety guidelines for factories and working places, which are valid throughout the Canadian federation. Like for OSHA, the rules defined by CCOHS can be modified by the Labour ministry of each state provided it enhances safety. 1.
www.infoPLC.net INTRODUCTION TO NORTH AMERICAN STANDARDS ■ to import into North America: compliance with federal laws, obligation to attest component conformity and in some cases, to submit the product to authorised inspectors. 2. Historical evolution of the North American regulations The historical reasons that justify the differences described are found not only in the cultural diversity but also in the communication difficulty between two worlds, at least up to the end of the XIX century.
www.infoPLC.net INTRODUCTION TO NORTH AMERICAN STANDARDS Canada had a different development from the USA, as it was British empire colony and therefore theoretically subject to the same rules in force in the United Kingdom. In fact, in 1917 Canada creates an independent normative body, the Canadian Engineering Standards Association (CESA).
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www.infoPLC.net INTRODUCTION TO NORTH AMERICAN STANDARDS Finally it is important to mention the Council for Harmonization of Electrotechnical Standardization of North America (CANENA), a body that deals with harmonising standards within the NAFTA countries 2.1 Certifying authorities The principal laboratories that certify products are: Underwriters Laboratory Inc.
www.infoPLC.net INTRODUCTION TO NORTH AMERICAN STANDARDS Organisations currently recognised by OSHA as NRTL: (the list may change; please refer to OSHA web site: http://www.osha.gov/dfs/otpcal/nrtl/index.html Applied Research Laboratories, Inc. (ARL) Canadian Standards Association (CSA) (also known as CSA International) Communication Certification Laboratory, Inc. CCCL) Curtis-Straus LLC (CSL) Electrical Reliability Services, Inc. (ERS) (also know as Conformity Services and formally as Electro-Test, Inc.
www.infoPLC.net INTRODUCTION TO NORTH AMERICAN STANDARDS Particularly OSHA is more restrictive in the prescriptions for components admitted for use in the electrical plants/equipment. OSHA regulations only permit the use of components that have been tested and certified by an NRTL test laboratory. Meanwhile NEC foresees the use of components that are considered still suitable for use.
www.infoPLC.net INTRODUCTION TO NORTH AMERICAN STANDARDS The CEC, also known as CSA 22.1, a specific standard for “Industrial Control Panel” (CSA 22.2 #14) is added to the CEC, also known as CSA 22.1.The standard contains applicable additional prescriptions for the sector of the automation panels. 3.1 Component certification A component certification is evident by applying a mark by the certifying laboratory.
www.infoPLC.net INTRODUCTION TO NORTH AMERICAN STANDARDS This recognition has resulted in the introduction of unified marks. Where the suffix refers to Canada and the United States respectively. Before this unification products will have to be tested and recognised individually by Canada and the United States. 4.
FEEDER AND BRANCH CIRCUITS 1. www.infoPLC.net Switching and protection of the electrical equipment 1.1 The different types of circuit The North American standards divide the power circuits into two parts, better defined as: • Feeder Circuit • Branch Circuits This distinction, neglected in the European environment is, on the other hand basic in North America for the choice, sizing and wiring of components inside electrical equipment.
www.infoPLC.net FEEDER AND BRANCH CIRCUITS An example of feeders and branch circuits Figure: Feeder circuit Feeder: all the conductors and the circuits up line from the supply side of the branch circuit overcurrent protective device. BCPD: Overload protection device (e.g. circuit breaker, fuses).
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www.infoPLC.net FEEDER AND BRANCH CIRCUITS 2. Disconnecting means 194R 1494V The main disconnecting means is a necessary part of all electrical equipment but can be provided by the final user (unlike the provisions of European standards). In this case it is necessary to clearly specify the characteristics of the device in the attached documentation. In this section, the devices suitable for switching and their sizing independently of their nature will be analyzed (switch or circuit breaker ).
FEEDER AND BRANCH CIRCUITS www.infoPLC.net Sect. 1.25 x (22 + 8 + 4) >= 42.5 A Cond. 1.25 x 22 + 1.25 x 8 + 4 > = 41.5 A AWG 10 (40 A) Disconnect switch (or switch with fuses) (UL 489 or UL 98, “Enclosed and DeadFront Switches” Sizing follows different rules according to the type of load. a) one or more loads, no motor: the size in current of the switch should not be less than 115% of the total current (sum of the rated currents of all the branch circuits).
www.infoPLC.net FEEDER AND BRANCH CIRCUITS Sect. (1.15x22) + 8 + 4 >=37.3 A Cond. 1.25 x 22 + 1.25 x 8 + 4 > = 41.5 A AWG 8 (50 A) The suitable IEC/UL/CSA component is a 194R-NN060P3 (CCN,WJAZ, conforming to UL 489) while in a NEMA start a 1494F-N60 (CCN,WHTY, conforming to UL 98) is used, both with power rating equal to 15 hp (230V). 2.
FEEDER AND BRANCH CIRCUITS www.infoPLC.net added to both values.The two values obtained are considered FLA and LRA of a single virtual motor representing the full machine, the power of which (in HP) can be obtained from the tables for example tab 50.1 of UL 508A). The switching device should have an hp size above that of the virtual motor (remember that the LRA of the switch is set at 6 times the FLA exactly like the conductors).
www.infoPLC.net FEEDER AND BRANCH CIRCUITS 2.6 Components accepted with restrictions The UL 508A standard allows “Industrial Control Equipment” called “Manual Motor Controllers” certified and marked as “Suitable as Motor Disconnect” as UL 508 switch device. These switches should generally be protected by fuses against over currents.This protection however may be provided in the field.
FEEDER AND BRANCH CIRCUITS www.infoPLC.net 3 Feeder overcurrent protection 140U 1489 1494V 1491 140F The devices protecting the panel from over currents are explicitly required only in the case of Industrial Machinery1) by NFPA 79 (and relative section of the UL 508A), but its presence is also provided for in NEC and CEC in which sizing rules are given. Obviously the protection of the lines powering the equipment is not the responsibility of the machine manufacturer.
www.infoPLC.net FEEDER AND BRANCH CIRCUITS EXAMPLE As in the previous example a feeder protection and switch with circuit breaker (series 140U) is taken up again. The switching function requires a size of no less than 40 A but the calculation of the value a) as overcurrent protection requires the size not to be more than: 22 + 8 + 4 = 34 A The incompatibility of the design data is clear Prot 22 + 8+ 4 <= 34 A Sect. 1.25 x (22 + 8 + 4) >=42.5 A Cond. 1.25 x 22 + 1.25 x 8 + 4 > = 41.
FEEDER AND BRANCH CIRCUITS www.infoPLC.net For example the motor (FLA = 22 A) can be protected with time delay fuses rather than an “Type E” combination motor controller. In this case the calculation of the BCP would lead to a value of 35 A (for the calculation of the size please refer to publication 3 “Branch Circuit” with J type 35 A fuses in the relative fuse holder 1492 – FBJ60. The calculation of value a) now could be 35 + 8 + 4 = 47 A.
www.infoPLC.net FEEDER AND BRANCH CIRCUITS The designer is limited in the choice and use of some components because the standard provides that the starts of the motor be realized exclusively with UL 248 fuses or UL 489 circuit breaker contactor and thermal relay. On the other hand, if disconnecting devices are planned with the feeder protection function, there are no restrictions in the use of the components in the electrical equipment.
FEEDER AND BRANCH CIRCUITS www.infoPLC.net 4.1 Distribution mounts, Power Block For panels of large capacities it is sometimes necessary to make distribution systems to make it possible to power several users with different and/or smaller cross-sections. All the distribution “mounts” or “commercial” bars used should be NRTL approved because they are particularly critical components in the case of short circuit.
www.infoPLC.net FEEDER AND BRANCH CIRCUITS 4.2 Sizing of the Feeding Conductor In UL 508 A and CEC the current is determined according to the single loads, such as: 125% rated current of the largest motor added to 100% of rated currents of all the remaining loads where the rated current of the motors is the FLA in the USA, the rating plate value in Canada. In the case of resistive loads, the CEC introduces a modification in the calculation that is also present in NFPA 79 for Industrial Machinery.
FEEDER AND BRANCH CIRCUITS www.infoPLC.net The same calculation must be applied if the data is required for power conductors of the machine and relative connection power blocks. Cond. 1.25 x 22 + 1.25 x 8 + 4 > = 41.5 A 4.3 Reduction of the sections down line from the feeder conductors Once the feeder conductor has been cleared, it is also possible to define the branches with a smaller cross-section called like “tap conductors”.
www.infoPLC.net FEEDER AND BRANCH CIRCUITS • the tap should not extend further than the BCP of the powered loads • to guarantee the mechanical protection, the derivation should always be enclosed in conduits or raceways (not walk over covers) the connection points obviously excluded.The CEC furthermore requires the conductors to be metallic. Furthermore the NEC provides: • if the tap leaves the panel it shall have a capacity of not less than 1/10 of the size of the feeder protection Maximum 10 ft (3.
FEEDER AND BRANCH CIRCUITS www.infoPLC.net Under no circumstances may a tap conductor be derived from another tap conductor. Derivations with reduced cross-sections can only be made directly from the feeder. Maximum 10 ft (3.05 mt) Between 10 ft and 25 ft (7.63 mt.) 5.
www.infoPLC.net FEEDER AND BRANCH CIRCUITS suitable as Branch Circuit Protection and as general panel protection) and several other types of control fuses (adapted to the use of just control circuits: Supplemental Fuses). Note that the NEMA standards are construction standards: the fuses are, in terms of sizes and dimensions, identical regardless of the manufacture (as it happens in Europe).
FEEDER AND BRANCH CIRCUITS www.infoPLC.net 6.1 - Class CC fuses These are the most common and used in the protection of transformers, loads and motors (they have both a “Fast” intervention curve and a “Time Delay” curve), they are ideal for Feeder and Branch circuits and are similar to European 10x38 fuses. Their limit is the size; ranging only from 0 to 30 A. Attention: these fuses require their own dedicated fuse holder the 1492-FB for CC class fuses, as specified in the NEC.
www.infoPLC.net BRANCH CIRCUIT 1. Starting, load protection and motors (Branch Circuit) 1.1 The different types of branch circuit The main types of power circuits can be distinguished inside the electrical equipment of a machine: • • • • • motor lighting heater appliance receptacle motor start lighting heater general device (power) connector The different types of branch circuit will be described in the following paragraphs.
BRANCH CIRCUIT www.infoPLC.net 1.2 Motor branch circuit The motor branch circuit is identified with what is generally called motor starter. In fact there are various types of motor starters (called direct, star-delta, with inversion etc) and for each of them there are special regulations. This document will initially refer to the simplest case of a direct start then it’ll go onto considering other mostly common cases.
www.infoPLC.net BRANCH CIRCUIT 1.2.1 Motor Starter “Type A” This is the classic North American motor starter that consists of: • • • • Sectioning device (UL 98) Fuses UL 248 Contactor Overload relay 194R-J30-1753 Fusible Disconnect or Disconnector 3 Fuses (only when using a Disconnector) 1.2.2 Motor Starter “Type B, C and D” Motor starter Type B is rarely used.
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www.infoPLC.net BRANCH CIRCUIT 1.2.3.1 Differences between a motor protector “Manual Motor Controller” and a “Manual self-protected combination motor controller Type “E” in the United States1) The size of the product, for instance, is one of the most important elements of differentiation between UL 489 and UL 508.
www.infoPLC.net BRANCH CIRCUIT For instance the motor protectors of the 140 M series with one “specific stretcher accessory” feeder adapter 140M-C-TE to be installed on the connection side to the line, comply with the new distances included in the UL 508. With this special accessory, the motor protector can be certified as a Manual selfprotected combination motor controller Type “E”.
www.infoPLC.net BRANCH CIRCUIT The certification as TYPE “E” remains the same even if the distribution combs of the 140M- .. – W series are used only when combined with the new connection systems such as the 140M-C-WTE or the 140M-F-WTE.
www.infoPLC.net BRANCH CIRCUIT 1.3 Sizing of the protections and of the branch circuit components. 1.3.1 Three-phase direct starter The reference schematic is: Branch Circuit Protection: the last protection against over currents and in particular, short circuits.
www.infoPLC.net BRANCH CIRCUIT For the drawing and the dimension of the motor start, we will proceed from the motor up to the branch protection by sizing the field insulator, the thermal protection, the meter for the protection against short-circuits (fuses, automatic switch or motor protector). 1.3.1.1 Motor First of all it is necessary to clearly identify the rated current of the motor that must be used for the scaling.
www.infoPLC.net BRANCH CIRCUIT The same value is also reported on the same NEC and CEC tables. 1.3.1.2 Disconnecting Means 194-E UL 1494 NEMA The term “disconnecting means” indicates a selector switch for the break off of one or more motor starters for the purpose of carrying out safe servicing. In NEC and CEC it is specified that a sectioning is necessary: • for each motor starter; • for each motor. Is it enough to have a single device in order to perform all these functions, (e.g.
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www.infoPLC.net BRANCH CIRCUIT The thermal protection is required for all the motors regardless of the size, unless the motor is marked and authorised as self protected (impedance of the windings is sufficient to prevent overloads). Thermal relays, fuses, all the overload relays are admitted as protection from the overload. The power converters e.g.
www.infoPLC.net BRANCH CIRCUIT 1.3.1.4 Controller 100-C UL 500 NEMA The definition of controller is somewhat generic because this term refers to any components that enable a load to be commanded: for example even a motor protector when manually operated is considered to be a controller. In this analysis the magnetic controllers, or contactors are taken as a reference.
www.infoPLC.net BRANCH CIRCUIT 1.3.1.5 Branch Circuit Protection (BCPD) 140-U 140F fuse holder 140M The protection of the motor starter from the short circuit can be done in different ways The most used components are: fuses, manual self-protected motor controller “type E”, automatic circuit breakers. THE FOLLOWING ARE NOT ALLOWED: modular miniature circuit breakers (with the exception of those with UL 489 approval), motor controllers that are NOT “type E”, fuses approved for control circuits.
www.infoPLC.net BRANCH CIRCUIT It is known that the value calculated in the "current x coefficient" is the maximum magnetic protection calibration value. For example, an “inverse time” automatic circuit breaker installed upline from a motor with a current equal to 10 A, should have a magnetic threshold of 10 A x 250% = 25 A.
www.infoPLC.net BRANCH CIRCUIT The protection device must have size/regulation that does not exceed the product “current x coefficient”, but if the value calculated does not coincide with a standard size/regulation, the use of the one immediately above is acceptable. Take for example a 10 A motor: using rapid fuses (nontime-delay) the coefficient is 300% and the product is equal to 10 A x 300% = 30 A, standard size.
www.infoPLC.net BRANCH CIRCUIT c) Motor protector type E: the 140M-C2E-C10 previously chosen on the basis of the thermal protection is kept.The additional use of fuses or magnetic only circuit breakers is not required, provided the spacing adapter 140M-C-TE is used (as is clearly indicated on the label). 1.4 Wye-delta starting 170 540 The wye-delta starters are dealt with special rules and tables and the UL508A in particular dedicates an entire paragraph to it.
www.infoPLC.net BRANCH CIRCUIT The following terms can be used as an analogy with the motors: ➞ “Locked Rotor Ampacity” (LRA) is the current established at the moment the contactors close, i.e. the make current; ➞ “Full Load Ampacity” (FLA) is the current that the contactor must open to interrupt operation, i.e. the break current. This is the value normally indicated in the catalogues For the motors it is specified that LRA = 6 x FLA unless they are specifically marked with a different ratio.
www.infoPLC.net BRANCH CIRCUIT The choice of the contactors occurs as in a normal direct starting supposing that each of them commands a dummy motor with current, at fully capacity and with blocked rotor, equal to those calculated. In the catalogue, the contactors are specified by power so it is necessary to convert the calculated current values into power output (hp).
www.infoPLC.net BRANCH CIRCUIT The choice of the contactors occurs as in a normal direct starting supposing that each of them commands a dummy motor with current, at full capacity and with blocked rotor, equal to those calculated. In the catalogue, the contactors are specified by power so it is necessary to convert the calculated current values into power values (hp).
www.infoPLC.net BRANCH CIRCUIT The same motor as in the previous example is assumed: 20 hp (15 kW) a 480 V. The line to be used is the second, already highlighted, for the motor values between 15 hp and 40 hp: il “NEMA size” required is 2 for all three contactors. To make the example clearer the contactors manufactured according to NEMA standards, the 500 series is looked for in the catalogue.
www.infoPLC.net BRANCH CIRCUIT Contactor code LRA FLA 1M 0.33 x 243 A z 80 A 0.577 x 27 A z 16 A 2M 0.577 x 243 A z 140 A 0.577 x 27 A z 16 A S 0 0.33 x 27 A z 9 A The choice of the contactors occurs as in a normal direct starting supposing that each of them commands a dummy motor with current, at fully capacity and with locked rotor, equal to those calculated.
www.infoPLC.net BRANCH CIRCUIT Sizing of protections Protection from the short circuit (BCPD) remains the same and is calculated over the entire FLA of the motor. The thermal protection must be installed downline from the line contactor(M1) and with calibration of no more than 1.15 times the 57.7% of the motor's FLA.
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www.infoPLC.net BRANCH CIRCUIT The NFPA 79 standard for Industrial Machinery (and the relative UL508A section) allows a group installation in accordance with points a) and b), but point c) changes in the definition of the lowest value for the choice of the BCP: the one linked to the markings remains the same while the other is no longer obtained by a calculation but by a table (tab. 66.
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www.infoPLC.net BRANCH CIRCUIT As a rule, it is not allowed to use the motor protectors even if they are certified as TYPE “E”, as protector of inverters, if they are not specified in the manual supplied by the drive manufacturer.
www.infoPLC.net BRANCH CIRCUIT 1.9 Heater branch circuit 156 The heater branch circuits are the circuits that feed the heater resistors. The present analysis contains a description of the required standards for the process heating, i.e. linked to the functioning of the machine, and not that linked to the heating of the environments (“fixed electric space-heating”).
www.infoPLC.net BRANCH CIRCUIT The same calculation for the minimum capacity is also applied for the conductor inside the panel: the uprated cross-section is AWG 12 (25 A). The resistive load command requires the use of a contactor sized in current. Solid state contactors are particularly suitable for this application: for example, use can be made of the 156-C20xA3, three-phase with rated current of 20A and maximum voltage of 600V. 1.
BRANCH CIRCUIT www.infoPLC.net Supply can be provided through: • transformers with separate winding down line from the main disconnect of the machine; the secondary must be protected; • transformers with separate winding up line from the main disconnect of the machine; the secondary must be sectioned; • one 120 V control circuit with its own protection against over currents.
www.infoPLC.net BRANCH CIRCUIT • the type and size of BCP indicated on the markings of the device; in the absence of indications on the device, the following applies: • if the appliance consists of at least one motor it must be protected as a motor (or group of motors) with the same power output; • if the ’appliance does not contain a motor it is necessary to verify the rated current: if the current is less than 13.
www.infoPLC.net CONTROL CIRCUITS 1 Control Circuits 1.1 Definition of Remote control Circuit In the National Electrical Code (art. 100 Part I) and in the Canadian Electrical Code (section 0) the following definition is given: • Remote control circuit: any electric circuit that controls any other circuit through a relay or an equivalent device.
www.infoPLC.net CONTROL CIRCUITS The UL508A links up with both NEC and CEC codes, but it gives additional instructions on how to ease the application. • Control circuit: this is not clearly identified but it can be traced back to a Class 1 non limited circuit: there are no power or voltage limits (within the 600 V that specify the low voltage).
www.infoPLC.net CONTROL CIRCUITS 5. An electrically operated counter shall comply with the Standard for TimeIndicating and -Recording Appliances, UL 863; 6. An audible signal appliance, including a horn, bell, or buzzer, shall comply with the Standard for Audible Signal Appliances, UL 464; and 7. A coil or input circuit to another control circuit switching device or to a load controller shall comply with other component requirements in this standard.
www.infoPLC.net CONTROL CIRCUITS In the definition of the individual components in a control circuit, reference is made to a general direct current circuit with one side connected to the equipotent protection circuit.A distinction is made between: Supply: power source, in this case a power supply unit (but also a transformer). Overcurrent Protection: overcurrent protection, in this example an supplementary protection 1492 –SP (but also a fuse).
www.infoPLC.net CONTROL CIRCUITS 1.3.2 External Wire The conductors outside the panel follow the same rules given for power conductors, except that for the calculation of the section. For the control circuits it is sufficient for the cable capacity not to be less than the rating of the Overcurrent Protection either up line or in the case of control transformers with protection on just the primary, less than the rated current of the transformer's secondary.
www.infoPLC.net CONTROL CIRCUITS The Class 1 circuit terminal block should be clearly indicated with a marking. EXAMPLE A control circuit made of AWG 18 cross section conductors is assumed. If the interface terminal block accepts a AWG 18 – AWG 14 cross-section interval, one can go ahead regularly; if on the other hand the terminal block only accepts sections AWG 18 – AWG 16 then the maximum cross-section to be used should be indicated, for example on the schematics. 1.3.
www.infoPLC.net CONTROL CIRCUITS 1.3.5 Overcurrent Protection 1492-SP 140F The choice of overcurrent protection depends first and foremost on how the control circuit is powered: 1) Downline from a pre-existing BCP (Branch Circuit Protection).
www.infoPLC.net CONTROL CIRCUITS circuit and can be either devices suitable for the branch circuit (UL508), or protections called “supplementary”: in particular “supplementary fuses” and “supplementary protector” (miniature circuit breaker, for example in accordance with UL1077, such as the 1492-SP). 2) Control Circuit derived directly from the feeder The control circuit is derived directly from the general powering (feeder) of the panel.
www.infoPLC.net CONTROL CIRCUITS The North American standards require the protection of all the conductors that are not connected to the equipotent circuit. EXAMPLE A general control circuit is assumed to be derived of a special branch circuit Q2 protection down line, for example a circuit breaker (UL489) 140UH2C3-C15 of 15 A or 1489-A2C150, that protects a solenoid valve assembly (Y1,Y2,Y3) and an electronic component (U1). From table 29.1 the protected BCP cross-section, or AWG 14 (20 A) is obtained.
www.infoPLC.net 1.4 CONTROL CIRCUITS Special prescriptions for Control Circuit class 1 If the control circuit is derived downline from a branch circuit protection that already exists, an overcurrent protection should be installed at the point of derivation of the control circuit conductors. For the equipping of general machines UL508A it is required to install a protection, sized in accordance to the general rules previously listed.
www.infoPLC.net CONTROL CIRCUITS EXAMPLE A derivation of a control circuit down line from a BCP is assumed for a woodworking machine, Industrial Machinery.The circuit is confined within the panel and the BCP has a size of 25 A. The circuit is made with a AWG 16 cable that, in accordance with tab. 28.1 of UL508A, carries 10 A. The control circuit protection should not be greater than 10 A, but in the hypotheses advance it is possible for it not to be more than 20 A (and not 10 A).
www.infoPLC.net CONTROL CIRCUITS In the absence of the over-temperature test the component can be used, but the output current must be downgraded to 50% (that is to say a 10 A power unit should be limited with a special 5 A protection). The protection of the power units should be done in accordance to the indications given in the instructions, making sure however that the components envisaged are suitable at the point of installation in accordance with CEC or NEC (see the overcurrent protection).
CONTROL CIRCUITS www.infoPLC.net 1.6.1 Power supplies The control circuits Class 2 are fed by sources intrinsically limited. In particular UL508A imposes 1. transformers: CCN XOKV, XOKV2 (UL 1585 ”Class 2 transformer”); 2. transformers: CCN NWGQ, QQGQ2 (UL 1950 “Information Technology Equipment”) only if use in Class 2 circuits is expressly indicated in the marking. All the derived circuits down line of a Class 2 supply are to be considered Class 2 circuits if properly wired. 1.6.
www.infoPLC.net CONTROL CIRCUITS It should be noted that if internal non approved conductors are used (for example N07V-K or H05V-K), what has been said above is no longer applicable and it is necessary to separate or segregate these conductors. 1.
www.infoPLC.net CONTROL CIRCUITS 4. batteries; 5. Current transformers: CCN XODW2 (UL506 ”Specialty Transformers”); 6. Current transformers with 5 A secondary: approved or otherwise. 1.7.2 Overcurrent Protection To assure that the circuit power is limited it is necessary to install an overcurrent protection down line from the supply dimensioned as in 43.
www.infoPLC.net CONTROL CIRCUITS have three different power supplies but a single 10 A feed can be used (for example 1606-XL240E-3, three-phase power unit) with three overcurrent protections down line (e.g. supplementary protector UL1077) graded to values of not more than 4 A: two at 4 A (for example 1492-SP1C040) and the last one at 2 A *e.g. 1492-SP1C020). The three circuits derived down line from the protections respect all the conditions to be defined Low-Voltage Limited Energy.
www.infoPLC.net CONTROL CIRCUITS 1.7.4 Internal Wiring Approved conductors of Low-Voltage Limited Energy circuits should be separated or isolated from conductors of the other circuits unless they are insulated for the maximum voltage present. It should be noted that (as for Class 2 circuits) if internal non approved conductors are used for example N07V-K or H05V-K, what has been said above is no longer applicable and it is necessary to separate or isolate these conductors. 1.7.
www.infoPLC.net CONTROL CIRCUITS 1) NEC (and UL508A): it is possible to protect “only on the primary” or “on the primary and secondary”. The protection on the secondary can be omitted only in the case of transformers with primary and secondary with two conductors (i.e. single and dual phase) or in the case of three-phase transformers with delta-delta connection. In both cases secondary should be single (i.e. multiple windings on the secondary each require its own protections).
www.infoPLC.net CONTROL CIRCUITS The conductor to the secondary should carry at least 5 x 10 = 50 A.Table 29.1 of UL508A is used to select a AWG 8 (60 A), considerably greater than the AWG 14 (20 A) that would have been sufficient considering the single current to the secondary.
www.infoPLC.net CONTROL CIRCUITS The protection to the primary should not be more than 1.88 x 2.5 = 4.7; 4 A fuses are used. The protection on the secondary theoretically should not be more than 18.8 x 1.25 = 23,5 A. However, note [a] allows the use of the standard size immediately above and 25 A and fuses can be used. If, say, the secondary powers three different circuits, each with their own protection (e.g.
CONTROL CIRCUITS www.infoPLC.net The conductors to the primary and the secondary should have a capacity of no less than the rating of the relative protection. 1.8.1 Protections Allowed The protection should be made with suitable components at the point of installation of the transformer/auto transformer.
www.infoPLC.net 1.9 CONTROL CIRCUITS Control of the temperature in the panel American and Canadian standards do not make any reference to specific over temperature tests of the panel but they require the control of the temperature in the panel to guarantee its full functionality. The over-temperature can be avoided with fans, anti condense resistors and conditioners.
INDUSTRIAL MACHINERY www.infoPLC.net Industrial Machinery 1. NEC 2005 and article 670 on Industrial Machinery In September 1941 the metal working machinery industry elaborated its first electrical standard to make machinery safer for operators, more productive and cheaper to maintain, as well as to improve quality and performance of electrical components.
www.infoPLC.net INDUSTRIAL MACHINERY 1.
INDUSTRIAL MACHINERY www.infoPLC.net 2. Special requirements Besides all information presented and pointed out in the previous chapters for industrial machinery, both NFPA 79 and UL508A (clause 65) set out more restrictive specifications that must to be respected.
www.infoPLC.net INDUSTRIAL MACHINERY 2.5 Conductor colours NEC and CEC (and UL508A in the general section) only define the colours for neutral and equipotential conductors: 7 white or grey: neutral 7 green (green-yellow also allowed): ground connection All other conductors can be identified with any colour provided that the above colours are not used. The NFPA 79 standard for Industrial Machinery (and section 66.
INDUSTRIAL MACHINERY www.infoPLC.net 3. Short Circuit Current Rating 3.1 Short Circuit Current Rating 3.1.1 National Electric Code Changes Overview National Electrical Code Introduces Article 409 for Industrial Control Panels In 2005, the National Electrical Code (NEC) introduced Article 409 for Industrial Control Panels requiring that panel builders and original equipment manufacturers (OEM) analyze and mark their panels with short circuit current ratings (SCCR).
www.infoPLC.net INDUSTRIAL MACHINERY NEC Article 409.110 An industrial control panel shall be marked with the following information that is plainly visible after installation: 1. Manufacturer’s name, trademark, or other descriptive marking by which the organization responsible for the product can be identified. 2. Supply voltage, phase, frequency, and full-load current. 3. Short-circuit current rating of the industrial control panel based on one of the following: a.
INDUSTRIAL MACHINERY www.infoPLC.net Installation Sheets Nameplate User Manual Examples of short circuit current rating product markings on nameplates and in reference documents b) The short circuit current rating determined by the voltage rating of the component and the assumed short circuit current rating from Table SB 4.1; If the power circuit component does not have a short circuit current rating or has not been required to have a rating in the past,Table SB4.
www.infoPLC.net INDUSTRIAL MACHINERY STEP 2 Modify the available short circuit current within a portion of a circuit in a panel due to the presence of current limiting components as specified in SB4.3, when applicable; This second step takes into account the effect of any current limiting devices in the feeder circuit. Current limiting refers to the ability of a protective device to clear a short circuit fault in less than one half cycle and typically within one quarter cycle.
INDUSTRIAL MACHINERY www.infoPLC.net STEP 3 Determine the overall short circuit current rating of the panel as specified in SB4.4. The short circuit current ratings of the individual components are compared to their branch circuit protective device.The smaller of the two ratings are applied to the line side of the branch circuit protective device. If a control circuit is located in a branch, then the overcurrent protective device for the control circuit must also be considered.
www.infoPLC.net INDUSTRIAL MACHINERY 3.1.3 High Fault Short Circuit Current Ratings Although table SB 4.1 is used to determine the assumed short circuit current rating of unmarked components, it also provides a reference for the standard fault ratings of various products. Components with only these ratings may significantly limit the maximum attainable panel short circuit current rating. High fault rated components have short circuit current ratings that exceed these values.
INDUSTRIAL MACHINERY www.infoPLC.net PowerFlex Drives NEMA and IEC Fused Disconnect Switches Power Distribution Blocks 3.1.4 High Fault Component Short Circuit Current Rating Information Is Available Online High fault short circuit current rating information can be easily accessed online at: http://www.rockwellautomation.com/products/certification/ul508a/ Rockwell Automation.
www.infoPLC.net INDUSTRIAL MACHINERY NEMA Power Components • Contactors • Overload Relays • Starters • Disconnect Switches IEC Power Components • Motor Protection Circuit Breakers • Motor Circuit Protectors • Contactors • Overload Relays • Starters • Disconnect Switches Circuit Protection • Molded Case Circuit Breakers • Miniature Circuit Breakers • Fuse Blocks Connection Systems • Bus Bar Mounting Systems • Commoning Links • Distribution Blocks Soft-Starters Drives Servo Drives 3.1.
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www.infoPLC.net Publication UL-WP001A-EN-P – March 2007 Copyright ©2007 Rockwell Automation, Inc.All Rights Reserved.
