Industrial Electrical Control Panels
Industrial Electrical Control Panels
A control panel is normally a flat, vertical apparatus where the devices to carry-out control and / or monitoring functions are installed. Industrial control panels are factory-wired assemblies of industrial control equipment, such as motor controllers, switches, relays, and auxiliary devices etc. The panels can include disconnect means and motor branch-circuit protective devices. The industrial control panel does not include the controlled loads, including motors, luminaires, heaters, or utilization equipment. Industrial control panels are customized as per their applications and environments, the processes they control, and the systems they integrate. Normally, they are used for systems integration to automate a range of processes, including system start-up, monitoring, and shut-down. Ordinarily, each control panel controls a number of pieces of equipment used for running of the entire process.
Control panels house the electrical components serving the field devices of an automated manufacturing system. Control panel design is to be initiated at the conceptual design phase in order to (i) consider optimal device layout and wiring connections, (ii) meet safety and maintainability guidelines and standards, and (iii) facilitates computer aided design (CAD) in the detailed design phase.
Common devices found in control panels are terminal strips, push buttons, pilot lights, switches, safety disconnect switch, and a PLC (programmable logic controller). Some control panels have a MCR (master control relay) which has the purpose of shutting down the entire panel if the MCR is not engaged. Majority of the control panels have either fuses or circuit-breakers for circuit protection.
There are several types of control panels. Also, there are several different combinations when it comes to these devices. Some of the most basic types include (i) low tension control panels, (ii) high tension control panels, (iii) instrument control panels, (iv) motor control panels, (v) process control panels, (vi) lighting control panels, and (vii) generator control panels etc.
Electrical control panels are designed and used to control mechanical equipment. Each one is designed for a specific equipment arrangement and includes devices which allow an operator to control specified equipment. Electrical panel components control every piece of equipment in several industries. It is difficult to describe all possible combinations since every industry and majority of the organizations have defined component preferences.
The electrical control panels are enclosures fabricated out of steel sheet metal. They provide and control electric power to equipment and appliances. Provision for indicating electrical parameters like voltage, current, frequency, and power factor etc. are required to be available on the face of the panel. Regulation of the power supply is also possible with the help of auto transformer switches and circuit breaker. The sheet metal enclosure for the electrical control panel is designed and fabricated in the unit. The components are bought out from the reputed sources and fitted at appropriate places on the panel as per manufacturers design. The circuit as per the design is laid out and the control panel is tested for the proper functioning as per relevant specifications.
Control panel and cabinet design is fundamental in allowing the user to interact efficiently with the industrial process right on the front-line. Industrial control panels consist of power circuits or control circuits (or both) which provide signals that direct the performance of machinery or equipment. Industrial control panels do not include the main power, nor do they include the controlled equipment, rather, the panel is mounted on a back panel (or sub-panel) or in an enclosure, depending on the application.
The electrical control panel is an essential item in industrial electrification. It regulates the function of the electrical equipment. Electrical panels fitted with necessary relays are also used to protect electrical equipment from being damaged because of the short circuit and overloading. They are open type, semi-enclosed, or totally enclosed type.
Industrial electrical control panels are a special type of assembly which contains at least two power circuits, control circuits, or any combination of power and control circuit components, as defined in America by the NEC (National Electrical Code) section numbered 409.2. Those panels which are covered directly by the UL (Underwriters Laboratories) product category outlined as ‘NITW’ are factory-based wired assemblies of industrial control equipment, such as motor controllers, switches, relays, and auxiliary devices which control equipment in the industrial environment. These types of industrial control panels can include a means of disconnecting that which it is powering, as well as a protective device of the branch-circuit. Industrial control panels covered by UL product category NITW are intended for general-use industrial applications for the control of industrial machineries, lighting, motors, or pump loads or a combination of these loads, and are intended for installation in ordinary locations as per requirements of NEC.
The International Electrotechnical Commission (IEC) standard IEC 60204-1, Electrical Safety Standard related to the machine control panels is required to be considered for electrical control panels. Enclosure degree of ingress protection (IP) is to be IP22 or better. The correct fan is to be selected to suppress temperature rise inside the panel. If a control panel is installed in a location with high humidity, measures against short-circuits are needed. The IP specifies the degree of protection of people against direct contacts and the degree of protection of devices against certain external influences such as ingress of foreign bodies (first digit of the IP code – 0 to 5) and the harmful effects of the ingress of water (second digit of the IP code – 0 to 8), irrespective of where it is installed (indoors or outdoors).
In case of European standards, the control panels are to be built to conform to the requirements of EN 60204 using components manufactured to conform to the requirements EN 60947 and other related component standards and approvals. An approved component is one whose manufacture and performance has been checked and proven to meet the specifications set by the standards authority of an individual country.
It is not at all uncommon to find that the control panels control process equipments, the lighting within a structure, and / or the motors within the facility. There are industrial control panels which are designed for the purpose and intent of controlling specific types of equipment. It is to be noted that the UL listed industrial control panels do not include coverage of any externally connected loads. Industrial control panels can also be designated for the control of specific equipment, such as industrial machinery, and cranes, which may not be suitable for use with other equipment as well as industrial control panels which have been inspected for special applications covered by other product categories.
Understanding the applications and limitations of different industrial control panel listings and their corresponding markings are necessary for ensuring that the appropriate industrial control panel is used for its intended purpose so that a safe installation can be achieved. It is to be understood that a UL listed industrial control panel certification mark only covers the industrial control panel. The certification does not include any of the equipment controlled by the industrial control panel or the equipment to which the industrial control panel has been mounted on. Also, it is to be remembered that industrial control panels have not been inspected for any externally connected loads.
Industrial control panels are as customized as their applications and environments, the processes they control, and the systems they integrate. Normally, they are used for systems integration to automate a range of processes, including system start-up, monitoring, and shut-down. Ordinarily, each control panel controls a number of pieces of equipment to run the entire process. Nearly any industrial process can be a candidate for process automation.
Machines and their control panels are deployed in several different industrial sectors under extremely diverse ambient conditions. Whether it is the mining or automotive industry, semi-conductor manufacture, ship-building or the railway sector, each application places specific demands on machines and control panels. Machine and control panel manufacturers face several challenges in designing products which can meet these demands. One major consideration is selection of the right components to install in the machine or control panel. In addition to suitability for the application in question, there are of course several other factors which play a decisive role in the selection of products. While a machine needs to meet the relevant requirements, it is also to be reasonably priced.
The total costs of a machine do not just comprise the material costs of the individual components. A considerable proportion of the costs is also allocated to engineering, design and documentation, as well as assembly and wiring. This means that the manufacturer not only needs a product portfolio of technically coordinated products, but also needs fast and easy access to all of the necessary technical data, documents, and information.
Process control panels are used for the control and monitoring of a process. The process control panel is normally a flat, vertical apparatus where control or monitoring instruments are mounted. These panels are one part of a process automation system. Modern control panels are driven by LCD (liquid-crystal display) touch screens and customized software, with embedded controllers such as (PLCs), fan-less PC (personal computer), and programmable automation controllers (PACs).
The NITW industrial control panel category has three main types of identities. These are identified as (i) industrial control panel enclosure, (ii) enclosed industrial control panel, and (iii) open industrial control panel. The following outlines a brief description of each of these identities.
Industrial control panel enclosures – These types of enclosures are typically inspected for ensuring that the unit complies with the construction-based requirements as outlined in the UL 508A. These are not inspected with the electrical components in place, hence, once the components have been added, they are needed to be re-evaluated by the AHJ (Authority Having Jurisdiction) who is the head over that field.
Industrial control panel enclosures have only been investigated for verifying that the enclosure complies with the construction requirements contained within UL 508A, the UL Standard for Safety for Industrial Control Panels. Since they have not been inspected with electrical components, the suitability of any field installed electrical components is required to be determined by the AHJ in the field. In several cases, AHJ is confronted with a UL listed industrial control panel enclosure containing a variety of components, such as contactors, relays, terminal bars, push-buttons and pilot lights. Since the overall assembly has not been inspected and certified by UL, the AHJ is required to treat the assembly as unlisted equipment and apply all applicable NEC requirements to that installation. If an AHJ is unsure if the installation complies with all the applicable NEC requirements, they can always need a third-party field evaluation of the unlisted equipment to UL 508A.
Enclosed industrial control panels – An enclosed industrial control panel is comprised of the enclosure, all components located within the enclosure, and all components mounted to the walls of the enclosure. The construction of the entire unit has been inspected, including its ability to safely function within the specified marked voltage, current, and short circuit current ratings (SCCRs). With that said, it is to be noted that the industrial control panels are only inspected for electrical fire and shock hazards and not for their ability to control equipment.
One can also refer to section 90.7 of the NEC, which in part states that except to detect for alterations or damage, the factory-installed internal wiring or the construction of equipment need not be inspected by the AHJ at the time of installation, provided the equipment has been listed by a qualified electrical testing laboratory, such as UL. Hence, when inspecting a UL listed enclosed industrial control panel, the AHJ is only needed to verify that the equipment has not been damaged, its marked ratings are sufficient for the load and intended application, the field connections are properly terminated, and there have not been any field modifications to the wiring schematic drawing.
These types of electrical control panels include the enclosure, the electrical components within, as well as the items which are used to mount to the walls or to simply close in the panel. These are inspected for ensuring that they pose no electrical fire hazard or any type of shock hazard. They are not reviewed for their unique ability to effectively control electrical equipment.
Open industrial control panels – An open industrial control panel is comprised of a mounting sub-panel and all components mounted to the sub-panel. It is intended for installation into an enclosure in the field. This category also covers industrial control panel enclosures. The enclosures can contain ventilation openings, observation windows, conduit fittings, environmental control devices, or maintenance luminaires. These control panels include wiring, terminals, and several other types of components, as well as mounting devices attached to a sub-panel which do not include a complete enclosure. The enclosure which is included with this type of industrial control panel is only intended to be a part of the overall installation.
An open industrial control panel includes internal wiring, field wiring terminals, and components mounted on a sub-panel without a complete enclosure. The enclosure is intended to be supplied as a part of the installation. Unlike an enclosed industrial control panel, additional factors need to be considered when approving the installation of an open industrial control panel. Some of these include (i) to verify suitability for installation and use in conformity with the provisions of the NEC, (ii) to verify the mechanical strength and durability of the required enclosure necessary to protect the open industrial control panel, (iii) to ensure the enclosure does not encroach in the required wire-bending and conductor termination space necessary for a safe installation, and (iv) any other factors which contribute to the practical safe-guarding of persons using or likely to come in contact with the open industrial control panel, such as exposure to live parts, proper grounding or bonding and arch flash hazards, just to name a few. If a control panel is installed in a location with high humidity, measures against short-circuits are needed.
Open industrial control panel enclosures are intended to house open-type industrial control panels or individual items of industrial control equipment installed in the field. Unless otherwise marked, industrial control panels covered under this category are intended for general-use industrial applications for control of machineries, lighting, motors or pump loads, or a combination of these loads. Industrial control panels designated for control of industrial machinery are not suitable for use with other equipment. Industrial control panels marked ‘flame control panel’ on the unit’s name-plate contain controls for fossil fuel-burning equipment, such as incinerators, kilns, and drying ovens, intended for industrial applications. These control panels can additionally contain controls for other loads. Industrial control panels marked ‘crane control panel’ or ‘hoist control panel’ on the unit’s name-plate contain controls for over-head cranes and hoists for industrial applications. These panels are not suitable for use with equipment other than cranes and hoists.
Industrial control panels marked ‘industrial control panel for refrigeration equipment’ or ‘industrial control panel for air conditioning equipment’ on the unit’s name-plate contain controls for hermetic refrigerant compressor motors for industrial applications. These control panels are not e suitable for use with equipment other than refrigeration equipment. Industrial control panels marked for service equipment use are provided with ground-fault protection for services or major feeders. The circuit(s) so protected are identified by a marking, such as on a wiring diagram or on the equipment. Instructions are provided for on-site testing of the ground-fault protection at the time of installation.
Markings – Industrial control panels are marked with the electrical ratings for each source of supply to the panel. The panel or wiring diagram provided with the panel is marked with the electrical ratings of the intended load equipment, such as motors, heaters, lighting, or appliance loads. Industrial control panels are provided with a complete schematic diagram of the panel as built by the manufacturer. When the schematic wiring diagram includes components which are not supplied with the industrial control panel, such as remote-control devices, motors or similar devices, a notation, or similar means is used to identify such components. When additional installation instructions are provided on a separate drawing, a reference to the drawing containing the information is marked on the name-plate of the industrial control panel. The name-plate of industrial control panels is marked with the SCCR for each supply such as ‘short circuit current – ‘x’ kA rms (root mean square) symmetrical, ‘y’ V maximum’, or the equivalent.
UL 508A includes all of the marking requirements referenced in NEC section 409.110 as well as several more. The majority of UL 508A needed markings are to be located so that they are visible after installation of the field wiring. However, some markings are permitted to be on the field wiring diagram or installation instructions which are referenced on the industrial control panel name-plate. The field wiring diagram or installation instructions are needed to be shipped with the industrial control panel.
In addition to the needed markings, UL 508A also needs that an industrial control panel is to be provided with a complete electrical schematic wiring diagram including all the components provided by the manufacturer. For compliance with the NEC, an AHJ is required to review section 409.110, which needs that industrial control panels are to be marked with such information as (i) manufacturer’s name, trade-mark, or other descriptive marking by which the organization responsible for the product can be identified, (ii) supply voltage, number of phases, frequency, and full-load current for each incoming supply circuit, (iii) industrial control panels supplied by more than one power source such that more than one disconnecting means is needed to disconnect all power within the control panel is to be marked to indicate that more than one disconnecting means is needed to de-energize the equipment, (iv) SCCR of the industrial control panel based on one of the following (a) SCCR of a listed and labeled assembly, and (b) SCCR established utilizing an approved method, (v) if the industrial control panel is intended as service equipment, it is to be marked to identify it as being suitable for use as service equipment, (vi) electrical wiring diagram or the identification number of a separate electrical wiring diagram or a designation referenced in a separate wiring diagram, and (vii) an enclosure type number is to be marked on the industrial control panel enclosure.
Ratings – Industrial control panels are rated 600 V or less. Each power circuit output from the control panel is rated in current or power, voltage, and the intended load type, such as a motor. Each supply input to the industrial control panel is rated in full load amperes (FLA), rating of largest motor load, voltage, number of phases, and frequency. Each supply input is additionally provided with a SCCR indicating the maximum rms (root mean square) symmetrical amperes and voltage available at the input terminals of the industrial control panel or, for an industrial control panel not supplied with branch-circuit protection, the maximum rms symmetrical amperes and voltage available on the line side of the over-current protection installed in the field.
Environment ratings – Industrial control panel enclosures are marked with the enclosure type ratings for which they are inspected. Enclosed industrial control panels are marked with an enclosure type rating. The type rating of the industrial control panel can differ from the rating of the basic enclosure because of the presence of components or assemblies installed through the enclosure walls by the manufacturer.
Wiring of control panels – Wiring work is necessary for the manufacture of the control panels, and it accounts for the majority of the lead time for control panel manufacturing. Hence, if one can make wiring work easier and faster, one can dramatically shorten the manufacturing lead time for the control panels.
The guidelines for the wiring in the feeder and branch circuits for all internal wiring are (i) all internal wiring conductors are to be of copper, (ii) all conductors in the power circuit are to be labeled at the termination point with letters or numbers corresponding with the wiring diagram provided in the industrial control panel, (iii) power circuit conductors are not to be smaller than 2.5 square millimeters (sq-mm), (iv) for single loads, power circuit conductors for motors or heater loads are to be sized for an ampacity not less than 125 % of the full-load current, (v) for multiple loads, such as multiple motors or a motor with other loads, power circuit conductors are to be sized for an ampacity not less than 125 % of all heater loads plus 125 % of the largest motor load plus the FLA ere ratings of all remaining motors and other loads which are simultaneously operable, and (vi) the wire size is selected based on the calculated wire ampacity.
The guidelines for the field wiring are (i) conductors not smaller than 2.5 sq-mm, (ii) for single loads, the field wiring conductors are to be sized for an ampacity of 125 % of the full-load current, (iii) for multiple loads, such as multiple motors or a motor with other loads, the field wiring is sized based on the sum of 125 % of the largest motor FLA, plus the sum of the other full-load currents of the remaining loads, and (iv) the wire size is selected based on the calculated wire ampacity.
Control panel and industrial connection technology continues to advance. In addition, there has been a movement among standards organizations to harmonize world-wide standards which apply to the deployment of industrial equipment, including control panels. No doubt, there are developments in this area which affect the increasingly distributed processing architectures which are used to reduce plant wiring and speed the process of commissioning and retrofitting controls. Innovative approaches are reducing the effort involved in commissioning the next generation of machines and control panels.
Normally when people hear about wire connection methods, they tend to think about securing wires by tightening screws. And in reality, several of the control devices used in control panels use screw terminals, and such devices have become common. Also, screw terminals have a long track record, are the method most recognized by customers, and are hence considered reliable. However, screw terminals need that the person loosens the screw, attaches the wire (crimp terminal), and then tightens the screw, which is a lot of work.
Screw-less connections, which have recently become common in several countries, eliminate the need to tighten screws dramatically reduce the work needed for wiring and they are gradually becoming popular in control panels around the world. The work of loosening and tightening screws has been replaced by merely inserting wires to complete wiring work, greatly reducing work time. First a person is required to learn about screw-less connections and then experience how efficient this method is.
Ever since the first control panels have been installed on the floor of industrial plants, there have been attempts to reduce the quantity of wiring and effort which goes into connecting industrial processes and machines to their controls. Decades ago, PLCs began replacing several control relays, and their associated wiring, used to sequence machine operations. Then industrial networks distributing the input / output (I/O) modules closer to the process inputs and actuators emerged to eliminate the need for lengthy runs of discrete wires between the PLC controller and distributed I/O modules. These undertakings continue today.
Advances in technology now permit use of rapid connection techniques such as insulation displacement connectors. Communication bus technology has evolved over the years to include specialized protocols and formats which are optimized for roles in industrial sensing and control. More recently, industrial bus technology has evolved to a point where it can take over some kinds of discrete cabinet wiring in an economical way. Specifically, it is now quicker to run bus-lines to individual control panel components such as indicators, displays, and switches than to make their connections with discrete point-to-point wiring.
Electrical control panel descriptions – If control panels are new to some persons and they want to learn about them the first step is learning the terms used to describe them, i.e., what the major descriptive categories are and how each one is described. An example of how to describe important control panel attributes is (i) safety ratings such as third-party safety certification, and SCCR, (ii) enclosure ratings such as NEMA (National Electrical Manufacturers Association) rating, (iii) material of construction such as 304 grade stainless steel, (iv) mounting such as wall mount or floor mount, (v) door mechanism such as lockable handle with three point door latch, (vi) main power both incoming power e.g., 440 V three-phase through a main circuit breaker, and outgoing power, (vii) control Power such as 110 V AC or 120 V AC and 24 V DC, (viii) door mounted operator devices, (viii) sequence of operation, and (ix) remote control interface.
Electrical control panel design – Designing of the industrial control panels can be a complex process, because of the need to meet all applicable regulatory standards and safety requirements. Developing the design matrix (DM) needs identification of user requirements. For the control panel of the automated modular construction machine, the user requirements include (i) to provide a 110 V AC or 120 V AC / 24 V DC control panel, (ii) to conform to standards, and (iii) to conform to best practices. All other requirements, such as maintainability, safety, and prevailing guidelines, which are included in these user requirements, comprise the high-level functional requirements (FRs). These requirements can be combined into one main requirement, which is to build a 110 V AC or 120 V AC / 24 V DC control panel. Hence, building a control panel is also to be understood to be fulfilling its safety, functionality, and maintainability requirements. Through the application of engineering knowledge, low-level FRs are generated to support the main requirement. Fig 1 shows the DM formed from the mechanical, electrical and safety FRs and DPs (design parameters) which conform to control panel design standards.
Fig 1 Control panel design matrix
A general design process follows several steps as described here. The design process starts with the gathering of technical requirements and the sequence of operation or functional specification. This step takes into account process goals, existing equipment and environment specifications, and system operator needs. The next step is to weigh design requirements and specifications. After this, the components which are suitable for the application (as needed) are sourced. It is to be ensured that the components have the ratings necessary for the application. After this, the schematics of the control panel are to be prepared to make sure the components are wired correctly, as well as a physical layout.
The feeder ampere rating is sized based on the sum of the ampere rating of the largest branch protective device plus the full load currents of the other loads (motors, heater, and the primary of the transformer). The over-current feeder ampere rating is not to exceed the conductor ampacity rating on the load-side.
The rules which apply to manual motor controllers for motor loads only are described here. A single set of fuses or breaker can be used if certain conditions are met. These conditions are given below.
All power circuit devices are rated for group motor use as indicated on the component, heater tables or instruction publication. The tap rules which are to be met consist of the conductors to the individual loads are not less than 1/10 the ampacity of the branch circuit protection for each circuit provided with a manual motor controller (MMC) marked suitable as tap conductor protection in group installations. Also, the conductors on the load side of the MMC is not to have an ampacity less than 125 % of the motor FLA.
The branch circuit protection is sized by the sum of (i) if the branch protection is a circuit breaker, 250 % of the largest motor FLA, plus the sum of the remaining motor loads, (ii) if the branch protection is a time delay fuse, 175 % of the largest motor FLA, plus the sum of the remaining motor loads, or (iii) if the branch protection is a CC (current-carrying capacity) fuse, 300 % of the largest motor FLA, plus the sum of the remaining motor loads, and (iv) the branch circuit protection is not to exceed the ampere rating as specified in the group installation marking of the power circuit components and the type specified.
There are several ways to build a branch circuit for a motor load. Each method provides short-circuit protection, motor overload protection, and the ability to start and stop the motor. Some additionally provide a means to disconnect the branch circuit for maintenance and safety purposes. Combination motor controllers (CMCs) (manual motor protector + contactor + line-side adapter) provide the most efficient means to build a branch circuit for a motor. CMCs are designed for motor loads such that they do not need to be oversized (as breakers and fuses are) to prevent tripping during motor start-up. CMCs not only take up less space, but also get installed more quickly.
Basically, for all motor circuits four functions are needed. These are (i) disconnect (main switch), (ii) short-circuit protection, (iii) operational switching (contactor), and (iv) overload protection. These functions can separately incorporate equipment or can be combined in one device. Fig 2 shows schematics of simple control panel circuits.
Fig 2 Schematics of simple control panel circuits
After the preparation of the schematics, the enclosures for meeting the requirements are selected and procured. The next step is the implementation of the solution including installation, commissioning, and training. This can involve integration of existing components, PLC / HMI (human machine interface) software development, custom computer screens for operator interfaces, custom report generation software, annotated documentation, installation and operator documentation, training, and engineering drawings.
The process for industrial control panel and systems integration specification and selection frequently needs iterative design and collaboration between plant process specialists and suppliers. The information is to be gathered for facilitating the process of specifying process automation component systems include (i) needed codes, ratings, and customer / industry certifications which frequently include, UL label, and electrical codes, environmental rating, NEC short circuit current rating, and local electrical codes, and (ii) location of the panel i.e., indoors or outdoors, shade or direct sunlight, in a corrosive or hazardous area, (iii) minimum and maximum ambient temperature, (iv) humidity, dust, vibration, and other environmental challenges, and (v) labeling and tagging requirements.
Some environments need thermal management to preserve the performance and service life of critical electronics. These control systems need a specialized thermal management system. After reviewing thermal management challenges, a thermal management control panel can be designed for regulating the temperature within the environment. For thermal control panel sizing and selection, the system is to take into account the size of the enclosure, target temperature range, temperature outside the cabinet, and ambient conditions outside the enclosure.
Control panel designs are simple. Cost is always important, but so is an attractive appearance, simple operator controls and reliable operation. Simple panel designs are less expensive to produce and easier to operate and maintain. It helps when one understands that design is a process. Frequently persons think that they know exactly what they want when they get started, but they find that they wanted something different when they are done.
When persons first put the design requirements on paper they seem not organized, which is normal. No one gets everything right in one attempt. Design is a process and it takes time to get it right. The requirements are rewritten until they are properly organized and clear. Persons are to understand what is wanted. It is to be written down using clear language, then proceeded with the actual hardware design.
Good control panel design includes physical and electrical requirements. No short-cut is to be used in the design process. The schematic drawings are made without making the physical lay-out drawings. The design is alternated between the physical and electrical until all potential issues have been solved. Good control panel design includes accurate physical layout drawings and schematic drawings. This minimizes issues and delivery delays because of the unresolved physical layout issues discovered during production or testing.
NEC required clearance for power wiring and UL required clearance around heat producing devices are to be provided. NEC requires bending radius clearance for incoming and outgoing power connections for ensuring that the installing electrician has adequate room to make their power connections. UL needs manufacturer recommended clearance for heat producing devices such as PLCs, and VFDs (variable frequency drives) to ensure for adequate room for ventilation.
The power circuits are to be analyzed. Each power circuit is to be identified and the needed wire size and circuit protection are to be determined. The right wire size ensures that the circuit can deliver the needed load current. The right circuit protection ensures the wiring does not overheat and start a fire.
The power wire size is to be selected based on load current. The power circuit protection is to be selected based on wire size. Then the best power component type for use based on the function is determined and the right size based on voltage and load current is selected. The right type ensures that the component is going to function as desired and the right size ensures that it is going to reliably handle the load.
The best control type is to be used. It is necessary to always start with simple control components (relays, and timers etc.). When the simple components do not get the job done, the something with more functionality like a programmable smart relay or a PLC is to be used. These provide considerably more functionality, but they also need a computer and programming software and someone who knows how to program the desired functionality. Some control panel designers start with a PLC. Sometimes a PLC is the way to go, but one is always to use the simplest control type appropriate to the application.
For control panel, the best operator device type is to be used. The process is to be always started with simple operator devices (push-buttons, pilot lights, and digital panel meters etc.). For a stylish appearance a colour graphic door laminate is added. When simple solutions do not get the job done, a colour touch screen display is used as the HMI (human machine interface). This provides considerably more functionality, but it also needs a computer and programming software and someone who knows how to program the desired functionality. Some control panel designers start with an HMI. Sometimes an HMI is the way to go, but one is always to use the simplest operator device type appropriate to the application.
Experienced control panel designers use the best-in-class products by product category. This is subjective based on product awareness. Experienced control panel designers are aware of the collection of products available in a product category. This allows them to compare and use products which provide the best balance of price, form, and function. Several of the control panel designers try to use one manufacturer for all components in a panel. Sometimes there is a reason why this makes sense, but normally it limits the ability of the designers to use best in class products by product category.
Some of the critical components of electrical control panel are air circuit breakers (ACB), arc guard system, circuit monitoring system, contactors and overloads, DIN rail components, disconnects, drives, interface relays, limit switches, manual motor starters, miniature circuit breakers, moulded case circuit breakers, pilot devices, PLCs, power distribution, bus systems, power supplies, panel boards, residual current devices, safety locks, safety relays and PLCs, safety switches, sensors, soft-starters, starters, surge protective devices, timers and monitors, transformers, and universal motor controllers.
Electrical control panel components which are logical control devices are electrical control components. They are used to control the sequence of events which define how a control panel functions. Some are manually actuated like a light switch and easy to understand but majority are electrically actuated control components. In their simplest form, electrical control panel components are single components (relays, and timers etc.) which perform a single logic function. In their advanced form, electrical control panel components are component packages (PLC) which perform several logic functions.
A control relay is the simplest electrically actuated control component. The simplest type is a normally open 1-pole single throw (1PST) control relay. It is like a light switch a person uses to turn a light on and off. The difference is that one actuates the switch manually and a control relay actuates the switch electrically. At a minimum, a control relay has an electrical operating coil, a spring, a stationary electrical contact, and a movable electrical contact which operate as (i) off – when the coil is de-energized the spring keeps the movable contact away from the stationary contact to open the switch, (ii) on- when the coil is energized, the magnetic field of the coil draws the movable contact to the stationary contact to close the switch.
Control relays typically have 1 set to 4 sets of contacts (1 pole to 4 pole). The number of poles defines how many independent electrical circuits, the relay can control. Each pole typically has three switch contact connections (common, normally open, and normally closed). Normal describes the switch contact’s connection to ‘common’ when the coil is in its normal state or de-energized. Control relays can be procured with some useful options. The value of these options is most evident during the quality control testing, field start-up, and trouble-shooting. The different options are (i) coil (energized) indicator which is to visually confirm when the coil is energized, (ii) contact (state) Indicator which is to visually confirm when contacts are in energized state, (iii) manual (button) actuator which is to move contacts to energized state (momentarily), and (iv) manual (lever) actuator which is to move contacts to energized state (maintained).
A ‘timing relay’ is the next simplest electrically actuated control component. Timing relays are control relays with built-in timers to control when their contacts change state. Timing relays turn other devices on and off at specific times. The most common timing functions are (i) ‘on timer’ which controls when its contacts change state after its coil is energized, (ii) ‘off timer’ which controls when its contacts change state after its coil is de-energized, (iii) ‘interval on (one shot) timer’ which controls how long its contacts remain in the energized state after its coil is energized, (iv) ‘repeat cycle (synchronous / flasher) timer’ which controls how long its contacts remain in the energized and de-energized state after its coil is energized (energized ‘x’ seconds, de-energized ‘x’ seconds, and repeat), and (v) ‘repeat cycle (asynchronous) timer’ which controls how long its contacts remain in the energized and de-energized states when its coil is energized (energized ‘x’ seconds, de-energized ‘y’ seconds, and repeat).
A PLC is a collection of electrical control panel components (relays, and timers etc.) in one package which can be programmed. PLCs are packaged in different forms and can have a wide price range. There are potential advantages and disadvantages of using a PLC compared as compared to using a collection of individual electrical control panel components. The potential advantages are (i) user appeal, i.e., a PLC can make the users like more the equipment package, (ii) material cost, i.e., a PLC can be less expensive than multiple control components, (iii) physical size, i.e., a PLC can be smaller than several control components, and (iv) flexibility, i.e., a PLC can be easier to re-program than re-wiring several control components. The potential disadvantages are (i) user appeal, i.e., a PLC can make the users like less the equipment package, (ii) material cost, i.e., a PLC can be more expensive than individua control components, (iii) tool cost, i.e., a PLC needs programming tools (computer, software, and cables etc.), and (iv) skills cost, i.e., a PLC needs training to program the PLC to function as desired.
A control panel is the central nervous system of modern industrial processes and production lines. As such, it is useful to review how the contents of the panel typically get defined. The control panel is one of the entities specified after engineers have determined the sensors, actuators, and controls which the given process or production line at hand needs. The process of defining controls normally includes determining the physical location and capacity of remote I/O, the necessary specifications for the sensors involved, and operating characteristics of motor starters, contactors, and drives powering the actuators. With this information in hand, panel designers can begin estimating the foot-print needed by the controls running the process. In laying out a panel, designers are to plan not only for the existing controls and other panel components but also are to allow for changes in the production line or process which can result in the addition of more control points later on, or the removal of some I/O if parts of the line become inactive because of the changes in the product line-up.
Panel design also involves connection styles which frequently depend on industry preferences. Some industries, for example, demand ring lugs on specific kinds of controls. However, screw-type connections are the most widely used connection style today. Estimates are that 15 % to 18 % of control cabinets use spring-cage-type terminations which eliminate the need for screw connections. Insulation displacement connections also account for around 5 % of the terminations within control cabinets. Both spring-cage and insulation displacement connections are more resistant to loosening caused by vibration and are more widely adopted by industry since majority of the OEM (original equipment manufacturers) panels are subject to vibration during transportation to the end user.
Panel designers size the cabinet based on the components’ foot-print, space for wiring ducts, heat dissipation needs, and space for future expansion. Cabinet materials can vary depending on factors which include the UL enclosure type rating, whether the cabinet are to be stainless steel of a specific gauge, special panel finishing, and so forth. Similarly, the cost of the cabinet itself depends on these factors as well as use of a particular style of door, latching method, and other factors related to cabinet hardware and mounting.
Panel designers also lay out components with regard to such practices as defined in IEC standards such as IEC 60204 safety standard for industrial equipment. These documents dictate factors such as colour coding of ground and bond wires, factors for E-stop (emergency stop) selection, minimum clearance between conductors operating at specified voltages, and connections for main disconnect switches with door-mounted rotary handles, and several other practicalities associated with components mounted in panels.
It is important to note that UL 508A applies only to what are called industrial machinery panels. UL 508A does not apply to the panels for applications not classified as industrial machines. There are also standard practices for control panels which are not spelled out in standards. For example, panels which contain operator controls and displays are normally mounted at the eye level of the operator. Where several panels mount in a row, the panel doors are typically all configured to open in the same direction. Where a panel mounts near a room entrance / exit, its door is typically configured so it does not block the exit in an emergency (such as an arc flash).
These standards effectively ensure that, among other things, panels have internal dimensions big enough to guarantee safe operation given the number of conductors they handle and power levels they control. However, the practicalities of industrial plants are frequently such that floor space available for control panels comes at a premium. So, the designers are normally pressured to minimize the panel foot-print while simultaneously meeting safety requirements and ensuring that any rewiring associated with future control changes can take place with minimum effort. Space becomes a premium for floor-mounted control cabinets as well as control panels which have to be mounted on OEM machines.
Control panels typically undergo a detailed panel check-out procedure once they are fabricated. This normally includes basic tests such as a power-up and verification of the short-circuit current rating of the panel, a hot verification of all PLC output points as well as continuity checks and ground-fault checks of all high-voltage circuits. Technicians normally check torque on terminal blocks and verify name-plates and wire tags. It is also common practice to check circuit functions by running I/O simulations and exercising the operator interface.
The need to rapidly commission a control panel and simplify any ensuing panel changes poses a challenge for today’s panel designers. Despite advances over the years which have reduced the quantity of discrete wiring associated with each I/O point, space constraints result in panels having wiring ducts Which are full to overflowing. The panel testing which takes place as part of commissioning can be as simple as ringing out each wire with a continuity test, in the case of one-of-a-kind type cabinets.
Control panel builders making multiple identical units frequently devise test fixtures and simulation programmes which can put panels through their paces. But it goes without saying that this sort of wiring verification and check-out can be time-consuming. This is particularly true of industrial control panels which serve automated processes incorporating a large number of sensors and actuators. Standard practice dictates that each wire be tagged, checked for continuity, and verified against schematics. This is a laborious task for technicians during the commissioning of lines and retro-fits.
Several techniques have emerged which both simplify panel wiring tasks and reduce the time needed to make alterations in the field. These schemes can also incorporate jumper bars for power connections between modules which eliminate the need to provide discrete power connections to panel components. A point to keep in mind is that connections to conventional rail blocks use discrete wires and still are to be made one at a time. Technicians are to strip each wire for connection, and connections are made through a screw-down or a spring-loaded clamp.
In recent decades, field-bus networks have increasingly reduced wiring loads run between controls and far-flung resources such as sensors and actuators. In particular, industrial versions of Ethernet are now widely used in plants. This is partly because of the development of hardened versions of both the Ethernet hardware layer, including connectors, cables, and switches, and the software layer. Though Ethernet started out as a relatively slow protocol running over an unshielded twisted pair of wires, it now can handle speeds of up to 1,000 Mb/sec (mega-bytes per second) over long distances.
Ethernet, though, has come to refer to a collection of standards. There is no single Ethernet standard covering industrial automation. The situation is frequently explained using the ‘Open Systems Inter-connection’ (OSI) stack, wherein Ethernet forms the bottom two layers, physical and data link. Majority of the industrial versions of Ethernet use software handling the upper layers as well as media access control hardware modifications which enable real-time performance.
Ethernet protocols for industrial uses are frequently categorized by their real-time performance, i.e., non-real-time, real-time, and hard real-time. Real-time types minimize cycle times and prioritize data packets through different software techniques. Hard real-time protocols use custom hardware and special switches to implement real-time response. There is no special hardware or software needed to build an Ethernet / IP (internet protocol) device. This lets other protocols which use standard unmodified Ethernet co-exist in the same device. Ethernet / IP is basically an adaptation of the common industrial protocol (CIP) to the Transmission Control Protocol/Internet Protocol (TCP/IP) suite of standards for networking.
CIPs are frequently called device-level protocols since they handle networking among factory-floor devices such as sensors and actuators for the purpose of data collection, peer-to-peer inter-locking, real-time I/O, drive and motion control, and safety. Other device-level protocols include the Process Field Bus Decentralized Peripherals (PROFIBUS DP) and Controller Area Network Open (CANopen). Both are protocols used to operate sensors and actuators through a centralized controller in plant automation applications.
Instead of using traditional point-to-point wiring connections in control panels, a new panel wiring solution can replace the myriad of wires with a single cable which connects motor control components to manufacturers’ PLCs. This solution reduces time needed for wiring, testing, and commissioning by up to 85 %.
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