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Understanding the requirements for Switchgear and Control Panel boards

Switchgear and control panels are found in power generating stations, transformer stations, distribution substations, commercial and institutional buildings, industrial plants and factories, refineries, paper mills, metal smelters and any other place where electric energy is utilized or electric power is distributed to any number of zones. There are a few common types of assemblies that cover almost any application. A broad classification according to the location of the switchgear assemblies is whether the gear is installed indoor or outdoor. A further classification for the indoor gear is standard ventilated indoor, indoor with drip hood, indoor for location in sprinklers area, indoor in hazardous location, arc­proof and indoor in corrosive environment.

Typically, switchboard work is part of a larger project such as a service installation. In some projects, switchboard and panelboard installation may be taking on a new twist, with distributed generation applications such as small wind and solar installations. Modification of existing buildings for alternative power sources is increasingly showing up on the project lists for many companies.
If using panelboards for service equipment, provide each one with a main bonding jumper to connect the service neutral conductor to the panelboard’s metal frame. The main bonding jumper is sized in accordance for services with ungrounded conductors up to 1,100kcmil. When the ungrounded conductor is larger than 1,100kcmil, the main bonding jumper must be sized with an area that is at least 12.5% of the largest phase conductor.
        Be sure to locate the terminals for neutral and equipment grounding conductors so a person doesn’t have to reach beyond live parts to make connections. If a 4-wire, delta-connected, 3-phase (high-leg) system supplies a panelboard, the high-leg (or wild-leg) conductor, which operates at 208V to ground, must be terminated to the "B" phase of the panelboard.
        Prior to 1975, the high-leg conductor was terminated on the "C" phase of panelboards and switchboards. However, there's an exception to this rule, which allows the high-leg conductor to terminate on the same phase as the metering equipment when the meter is in the same section of a switchboard or panelboard. In fact, the ANSI standard for meter equipment requires the high-leg conductor (208V to neutral) to terminate on the "C" phase of the meter socket enclosure. This is because the demand meter needs 120V, which is obtained from the "B" phase.
        If one are doing any revision or replacement of a panelboard or other equipment that is supplied by a delta-connected high-leg system, be sure to replace the high-leg conductor in its original location. Otherwise, it may inadvertently connect 120V circuits to the 208V high leg, which would have disastrous results.
        Be sure to properly identify the high-leg conductors. Use orange identification, or some other effective means. Switchboards and panelboards containing a 4-wire, delta-connected system where the midpoint of one phase winding is grounded (high-leg system), must be legibly and permanently field-marked.

The fire department's perspective
        The local fire department responded to an automatic trouble call at the administrative offices of an appliance factory in Tennessee. Unable to determine which breaker controlled which branch circuit, the fire chief issued an order to open all of the breakers. This put two floors of the building in the dark, rather than just the one room in question. Only then did the fire crew enter the affected area.
        The incident resulted in a fine for NEC violations and a report to the insurance company. Proper directory labeling on the panelboard cover would have prevented this, interruption in operations as well as the ensuing fine. If this had been a service panel, rather than just a branch circuit panel, the consequences could have even been more severe.
        Make sure one legibly mark all circuits, and circuit modifications, as to their clear, evident, and specific purpose. That includes spare positions that contain unused overcurrent devices. Identification must include sufficient detail to allow each circuit to be distinguished from all others. The identification must be on a circuit directory on the face or inside of the door of the panelboard and must not be based on transient conditions of occupancy.
        For switchgear assemblies, as heat is generated from the high current flowing, a dust tight enclosure is almost impossible thus a dust proof one is used, instead. The major standards that govern the design, manufacture and testing of these assemblies are: CSA, ANSI, IEC, EEMAC, NEMA. Switchgear assemblies and motor control centers (starters) line­ups can be classified according to their voltage classes. The l.v. equipment is rated in the range of 120/208V single or three phase to 750V AC. The medium voltage ones are 2400/4160V to 44KV . The enclosures for all low voltage construction are metal enclosed. Some constructions include partitions and barriers to give a safer operation over and above the standard construction. For medium voltage switchgear both construction types, metal clad and metal enclosed, are common. In this section the major components of the switchgear assemblies, motor starters and associated ancillaries will be given.
        When a panelboard is supplied from a transformer, the overcurrent protection for the panelboard must be on the secondary side of the transformer. The required overcurrent protection can be in a separate enclosure ahead of the panelboard, or it can be in the panelboard. Don't install more overcurrent devices than the number for which the panelboard is designed, rated, and listed. When applying this rule, a 2-pole circuit breaker is considered to be two overcurrent devices, and a 3-pole circuit breaker is considered to be three overcurrent devices.
        Panel accessories like - Voltmeter, Ampere meter, Frequency meter, Red Indicator, Yelow Indicator, Blue Indicator, Hinge, Lock, Knob, Contactor, Relay, Timer, Insulator, Busbar - Support, Selector Switch, Control Fuse, Push Button, Earth Fault Relay, Over Current Relay, CT, Electric Motor Starter, Power Factor Meter can be dragged from the tool bar and placed upon the panel template as per the need of the design.
        With the help of this software now one can design any type of 3 phase industrial power and electrical control panels - be it a power control centre (PCC), a motor control centre (MCC), an electrical power distribution centre, electrical distribution board or an instrumentation panel. Design cubical power panels, desk type control and instrumentation panels, floor type control and instrumentation panels. A key tool to design 'Contorl & Relay Panels' using PLCs and SCADA system.
        The software lets you draw any type of complecated electrical power and control circuit/diagram. You draw horizontal and vertical lines and put electrical symbols upon the lines to complete your electrical (power or control) circuit. Cross over points are automatically converted into shorting-links or may be changed to jumpers or vise-a-versa. The software contains almost all the symboles in its library required to generate electrical power and control circuits. Label all the electrical symboles through a pop up text box - just enter the name/specification of the item and put it near the the symbol. Put ferrul numbering on each wire as per your convenience and requirement. Rotate electrical symboles by 90 deg or back to best suit the placement upon the power lines. Delete any electrical symbol or power line with right mouse operation. So this software can generate elctrical power and control circuits in semi automatic mode.
        This requirement doesn’t apply to equipment grounding conductors, because removing an equipment grounding conductor doesn’t affect the voltage of a circuit. To satisfy that goal means following detailed requirements for bonding, grounding, and overcurrent protection. But don't forget it has some other goals as well, such as assisting first responders to quickly locate and identify the disconnecting means for a specific room or area of a building in order to respond properly to a life-threatening emergency. Be sure to fill out panel directories accurately, legibly, and with sufficient detail to aid emergency personnel in situations where every second counts.