Building Electrical Design Notes and Guidelines

This is about design, material selection, and installation of electrical systems in plant buildings and commercial buildings. This article is for electrical installations in non-hazardous areas. For electrical installation. Main keywords for this article are Building Electrical Design Notes, Building Electrical Testing, Building Electrical Installation, Building Electrical Wiring Methods, Insulation Resistance Test.

Building Electrical Design References
National Electrical Manufacturer Association (NEMA)
C80.1 Rigid Steel Conduit – Zinc Coated (GRC)
C80.3 Electrical Metallic Tubing – Zinc Coated (EMT)
WC 7 Cross-Linked-Thermosetting-Polyethylene-Insulated Wire and Cable for theTransmission and Distribution of Electrical Energy (ICEA S-66-524)
WD 6 Wiring Devices- Dimensional Requirements
National Fire Protection Association (NFPA)
70 National Electrical Code, 2008
780 Standard for the Installation of Lightning Protection Systems
International Electrical Testing Association (NETA)
ATS- Acceptance Testing Specifications for Electric Power Distribution Equipment and Systems
Underwriters Laboratories (UL)
4 UL Standard for Safety Armored Cable

What is Busway.

Busways are an assembly of factory-mounted, bare or insulated conductors, which are usually copper or aluminum bars, rods, or tubes installed in a grounded metal enclosure.

What is Wireway.

Wireways are metallic or nonmetallic troughs with covers for housing and protecting wires and cables.

Building Electrical Design Notes and Guidelines

Building Electrical Installation

  • All work shall be performed by skilled personnel.
  • Drilling of holes in flanges of structural members, for mounting small electric and equipment items, shall conform to Field Drilling of Holes in Structural Steel.
  • Where the corrosion protective finish is removed from any equipment or material by, for example, cutting or welding or by accidental damage, the original finish shall be restored.
  • Welding to structures, beams, or equipment which have been stress relieved (heat treated after fabrication) shall not be permitted.
  • The installation of, for example, supports, brackets, and hangers for equipment and materials, shall not weaken the structure to which they are attached.
  • All fastening hardware, for example bolts, nuts, screws, and washers, shall be stainless steel for outdoor use and zinc plated for indoor use. Supports for conduit and equipment shall be hot dipped galvanized steel.
  • Interface wiring to all electrical equipment shall be connected in accordance with equipment specifications and manufacturer’s instructions.
  • All components, equipment, and materials of the same size, rating, and configuration shall be supplied by one manufacturer, and shall be interchangeable.

Building Electrical Power Supply Requirements

  • Process control buildings, commercial buildings and substations shall have a normal and an essential power source. Both power sources shall be 480 V, 3 phase, and high resistance grounded (3 wire).
  • The building power requirements are 480 V, 3 phase, 4 wire. In some cases a small substation may be required.
  • If the load is small or the building is close to a substation, the building can be served with a 480 V feeder from a substation.
  • Where a building is fed from a substation, contractor shall provide the conversion from a three-wire system to a four-wire system.
  • These buildings shall have an essential power supply for essential loads and an uninterruptible power supply (UPS) as an alternative power supply. The UPS shall be on the essential power supply.
  • Work shops, operator shelters, and other small buildings shall be served from a nearby 480 V source. The source can be a substation or another building. The building being served shall have a 480 V main panel as required by NFPA 70 Article 230. Ground fault protection shall be provided where required by NFPA 70. These buildings shall have an essential power supply for essential lights and where UPS systems are installed, there shall be an essential power supply for the UPS alternative power.
  • All building air conditioning (A/C) equipment, for example fans, blowers, compressors, and condensers, shall be served from the building motor control centers (MCC). Wiring shall also be provided for A/C system controls, and an interface with the building fire alarm system.

Distribution Equipment

  1. Lighting loads shall be on separate transformers and panelboards from nonlighting loads.
  2. Receptacle circuits shall be on separate transformers and panelboards from non-receptacle circuits.
  3. For operator shelters and other small buildings, the lighting circuits and receptacle circuits may be combined on a single transformer and panelboard.

Motor Control Centers and Switchboard

The main service entrance equipment for large buildings and buildings with three phase loads shall consist of a MCC, or switchboard with main breakers and motor starters, or both. MCC’s and switchboards shall comply with Electrical System Design Criteria.

Transformers

Building Electrical Panelboards

  • Panelboards shall comply with and Lighting and Receptacle Circuit Wiring Requirements.
  • The circuit breakers shall be sized based on initial loading and ultimate loading according to Lighting and Receptacle Circuit Wiring Requirements.
  • Panelboards shall have 20 percent spare breakers.
  • The selected location of the panelboard shall minimize branch circuit lengths.
  • Branch circuits supplying lighting or other devices that are switched periodically at the panelboard, shall be located in the upper portion of the panelboard. Circuits that are switched from local wall or column-mounted
    switches, and those that supply receptacles and other loads that are normally continuously energized, shall be located in the lower portion of the panelboard.
  • The side gutter of panelboards shall be a minimum of 114 mm wide.
  • The mounting height of the panelboard shall not exceed 1980 mm from the floor to the top of the panelboard cabinet.
  • Aheavy duty external grounding lug and terminal strip shall be provided.
  • Neutral buses in panelboards shall be supplied with space and lugs for the connection of a separate neutral wire for each branch circuit.

Main keywords for this article are Building Electrical Design Notes, Building Electrical Testing, Building Electrical Installation, Building Electrical Wiring Methods, Insulation Resistance Test.

Building Electrical Wiring Methods

  1. Wiring methods shall conform to NEC Wiring System Types & NEC Wireway Systems in Plant Industry and NFPA 70, Article 300.
  2. Separate neutral and ground conductors shall be provided for each branch circuit.
  3. Wiring methods shall be selected as follows:
    a. Electrical conductors enclosed in rigid galvanized steel conduit, conduit bodies, and wireways shall be the principal wiring method
    b. The use of busways and cable trays shall be limited to electrical rooms, buildings, and repair shops
    c. The use of wireways shall be restricted to short runs where many electrical conductors may be collected. Wireways shall not be used as a substitute for conduit.
    d. Conduit shall be electrical metallic tubing (EMT), rigid galvanized steel (RGS), or PVC coated RGS
    e. The use of EMT and intermediate metal conduit shall be restricted to dry, unclassified locations, for example office buildings, and where the installation will not be subject to mechanical damage. EMT shall conform to NEMA C80.3 . Only compression type EMT connectors shall be acceptable.
    f. In buildings where conduit is installed in concrete floors, PVC coated RGS conduit conforming to SES E23-S01shall be used. The minimum
    size for below grade conduit shall be 1 in.
    g. When above-grade conduit may be subjected to mechanical damage, or is installed outdoors in exposed locations, rigid hot dipped galvanized steel conduit shall be used. In corrosive areas, PVC coated rigid galvanized steel conduit shall be used.
  4. The mechanical continuity of all raceways, and the electrical continuity of metal raceways, shall be maintained throughout the electrical system.
  5. Spacing between instrumentation circuits and power, lighting, and control circuits in raceways and cable trays.
  6. See Electrical System Design Criteria for types of circuits that may be run in the same cable tray if separated by a barrier.

Conduit and Fittings

  • Conduit and fittings shall be supplied and installed in accordance with Conduit Types Conduit Fittings and Electrical Boxes and Conduit Installation Guidelines for Engineers.
  • For interior walls of hollow construction, for example sheetrock covered beams, the conduit installation shall be concealed within the building wall space. For building exteriors and interior solid walls, the conduit installation may be surface mounted.
  • The minimum conduit size for power feeders and multiple circuits shall be ¾ in.
  • Junction boxes shall be independently mounted, and shall not rely on the mechanical support of the attached conduit for support.

Wireways

  1. The wireway installation shall be concealed within the building wall space.
  2. Wireway shall be manufactured from galvanized sheet steel with a minimum thickness of 1.7 mm (20 gage).
  3. Wireway accessories shall be of the same make and type as the wireway.
  4. Wireway shall not contain preformed knockout stampings; required holes shall be drilled to suit the installation requirement. In the event of modification, unused holes shall be plugged.

Cable Tray

  • Cable tray shall be supplied and installed in accordance with Cable Tray Installation Guidelines for Engineers.
  • Cable tray shall not be used for routing of conductors to building related electrical equipment, for example lights, receptacles, and HVAC equipment. Cable tray may be used for routing of cables to process equipment, cranes, hoist, conveyors, and other similar equipment.

Busway

  • Busways may be used to feed power to permanently installed equipment, for example lathes, drills, and presses (maintenance tools), conveyor systems, cranes, hoist, and similar equipment. Busways may also be used to provide power to isolated areas in the interior of large rooms, for example warehouse areas, large open office areas and large open areas in manufacturing buildings.
  • Busways shall not be installed in the following locations:
    a. Where subject to physical damage, excessive vibration, or corrosive vapors
    b. Where subject to dust, unless totally enclosed
    c. In any Class I, Division 1 location
    d. In Class I, Division 2 locations, unless enclosed and gasketed
    e. In an unclassified location above a classified location, unless totally enclosed
    f. Above highly flammable materials or areas where personnel may congregate, unless totally enclosed
  • Busway enclosures shall be securely fastened in place, bonded, and grounded in conformance with NFPA 70, Article 364.
  • All bolted busway joints shall be assembled and torqued in conformance with vendor’s instructions.
  • Busway fittings and accessories shall be readily accessible.
  • Busways shall be securely supported at intervals not exceeding 1.52 m (60 in), unless otherwise designed and marked.
  • Busway dead ends shall be closed.
  • Busway overcurrent protection shall be in accordance with NFPA 70, Article 364.

Wire and Cable

  1. All cables shall be supplied and installed in accordance with NEC IEC Based Low Voltage Cables Selection Criteria and Cables Installation, Splicing and Termination Cable Requirements.
  2. For all cable, construction and minimum wire sizes shall be as defined in NFPA 70, NEMA WC 7, Electrical System Design Criteria.
  3. Cables shall be continuous from end to end without splices.
  4. Permanent wire markers shall be installed on all wires at termination points.
  5. Composite power and control cables, where specified, shall be terminated in a way that ensures power and control leads will reach their respective termination points without splicing. Removal of the jacket for the necessary length shall be done without damaging individual conductors.
  6. In buildings with suspended ceilings, armored cable that complies with of UL 4 may be used for general wiring of lighting and receptacle circuits. Type ac cable shall be secured in accordance with NFPA 70 Article 333.
  7. The radii of cable bends shall equal or exceed the minimum values specified by manufacturer. The minimum bending radii specified in NEMA WC7 and in NFPA 70 may be used when manufacturer’s data is not available.
  8. Pulling tensions and sidewall pressures for wire and cable shall not exceed the maximum values specified by manufacturer.

Junction and Pull Boxes

  • Junction boxes and pull boxes shall be supplied and installed in accordance with Procedure for Instrument Junction Box Installation.
  • Junction boxes shall be readily accessible.
  • Junction boxes shall be independently mounted and shall not rely on the mechanical support of the attached conduit for support.

Disconnect Switches

  • Air conditioner compressor units shall have a disconnect switch located within sight of the motor. Switch shall comply with NFPA 70 Article 440.
  • Electric space heating equipment shall have disconnecting means that comply with NFPA 70 Article 424.
  • Electric stoves, electric water heaters, and other appliances shall have dedicated disconnecting means that comply with NFPA 70 Article 422.

Switches and Receptacles

  • Switches and receptacles and their circuits shall comply with Lighting and Receptacle Circuit Wiring Requirements and NFPA 70.
  • The indoor lighting fixtures shall be controlled by one (1) or more multi-way switches located on the wall adjacent to the non-hinged side of the door frame, and spaced at least 100 mm from the door trim or corner of the room when practicable. The switch mounting height shall be 1220 mm above the finished floor.
  • Local switches for lighting shall be rated 20 A, and shall be supplied with an ac rating suitable for the utilization voltage.
  • Outdoor fixtures shall be controlled using photo-controlled, multi-circuit lighting contactors equipped with door mounted hand-off-automatic (HOA) switches.
  • Receptacles and switches shall have external back wiring clamps with an anti rotational strand containment feature.
  • Receptacle mounting height shall be:

a. 915 mm in warehouse and similar areas
b. 460 mm in offices and similar areas

  • The maximum receptacle spacing as measured along each unbroken wall shall be:
    a. 3.2 m between receptacles installed in offices
    b. 15 m between receptacles installed in warehouse
  • Receptacle spacing and mounting height for laboratory and other locations with special purpose equipment shall be as indicated on the drawings.
  • Ground fault interrupter receptacles shall be installed in kitchen, restrooms, outdoor areas, and other areas which tend to be wet during operation.
  • Receptacles shall be as follows:

a. Convenience receptacles shall be supplied in accordance with NFPA 70
b. Receptacle dimensions shall comply with NEMA WD 6
c. Unclassified locations shall use duplex, 2-pole, 3-wire,’U’ shaped grounding, contact type, rated 20 A, 120 V ac. These receptacles shall be installed in a box with wall plate for flush mounting, or in a box with a sheet steel cover for surface mounting.
d. In hazardous areas, receptacles shall be Crouse Hinds type CPS 152211 M6, 120 V ac, 20 A, 2 wire, 3 pole
e. In non-hazardous areas receptacles shall have a pin configuration which ensures that the plugs are not interchangeable with those in the hazardous area
f. Receptacles shall be limited to eight (8) per branch circuit. Circuit loading shall be estimated on the basis of 180 VA for each receptacle.
g. Welding receptacles shall be provided in all shop areas, positioned in a way that a receptacle may be reached by a 30 m cord from any location in the area
h. Welding receptacles shall be arranged in groups of not more than three (3) outlets per each welding circuit. The size of the welding power supply feeder shall be based upon the following total continuous load:
(i) One (1) welding receptacle: 40 kVA
(ii) Two (2) welding receptacles: 70 kVA
(iii) Three (3) welding receptacles: 90 kVA
i. Welding receptacles shall be Crouse-Hinds Type EPC-61042-WT1003-3 circuit breaker with arktite receptacle and APJ No. 10487 rated 100 A, 3wire, 4 pole plug or Appleton type EBR 1034 E100 with CHD 31006 circuit breaker and female 480 V, 3 wire, 4 pole plug.

  • Receptacles should be wall mounted. Floor mounted receptacles should be avoided.
  • Dedicated receptacle circuitry shall be provided for special power requirements, for example computer system circuits, separate outlets for building cleaning equipment, and kitchen appliances. In particular, office areas with computer terminals or other electronic equipment shall be wired to preclude overheating of the branch circuit panels and neutral conductors caused by harmonic currents of non-linear type loads.

Building Electrical Design Lighting

  • The lighting in buildings shall comply with the Electrical System Design Criteria, Lighting Design Requirements in Buildings, Lamp Selection and Applications & Lighting Fixture Selection and Applications, and Lighting and Receptacle Circuit Wiring Requirements.
  • Rapid start fluorescent fixtures shall be used for low ceiling, indoor areas requiring high illumination levels, for example office and control rooms. The fixture ballast voltage may be 120 V or 277 V single phase. Lamps shall be color corrected, cool white.
  • High pressure sodium fixtures with color corrected lamps shall be used in outdoor and indoor applications both in classified and non-classified areas where specified, and with ballast voltages of 120 V or 277 V single phase as required.
  • In offices areas with suspended ceilings, drop-in flush troffers shall be used.
  • Lighting for control room instrument panels and similar installations shall be designed to illuminate vertical panel mounted equipment and details with glarefree uniform intensity.
  • For control room general area, a luminous ceiling metallic grid parabolic system shall be provided.
  • The exterior lighting installation shall be weatherproof and listed for the area installed, if installed in a hazardous location.
  • Luminaries for general illumination shall be mounted minimum 2440 mm above the finished floor.

Special Lighting

  • Lighting for control rooms with video display terminals shall be designed to minimize glare and avoid ceiling reflections on the terminal faces.
  • Light sources shall be positioned out of the mirror-angle of reflection with respect to the task and the operator’s eyes.
  • Recessed fluorescent luminaries with an aluminum parabolic wedge louver shall be provided.
  • A luminary dimming system shall be provided for conference rooms, auditoriums, control rooms, and other rooms where the ability to adjust the lighting level is important for the activities for which the room is intended, for example the use of projectors, control system monitors, and television displays.
  • Fluorescent fixtures installed in rooms with electronic equipment shall be provided with inductance-capacitance filters.

Essential Lighting

  1. Substation and control room lighting shall be fed from the plant essential power system.
  2. Essential lighting shall be provided as follows:
    a. Occupied Areas – selected key luminaries (approximately 20 percent of the fixtures) for general illumination, to permit safe access and egress by personnel and for monitoring critical local controls, shall be assigned to essential power system. These fixtures shall be marked and identified as emergency lighting.
    b. All Areas – exit lights. These fixtures shall be battery pack type fixtures.

Obstruction Lighting

Usually, aviation obstruction lighting is not required on buildings. If a building structure exceeds the height of other nearby structures, see Lighting Design Requirements in Buildings for determination of aviation obstruction lighting requirements.

Building Electrical Design Grounding

  • Grounding and lightning protection of buildings shall be in accordance with NFPA 70.
  • Wall mounted, pre-fabricated, copper grounding bus-bar(s) for non-instrument grounding shall be provided in the building locations shown on the drawings, and shall be connected to the building steel and plant grounding grid as shown on the drawings.
  • Grounding bus-bar units shall be fabricated from 6 mm x 51 mm x 356 mm copper bar (minimum) and as detailed on the drawings.
  • Grounding bus-bar units over 1520 mm in length shall have two (2) connections to the plant grounding grid.
  • All electrical equipment installed in the building shall be connected to a grounding bus-bar.
    Buildings point of view grounding
  • Building frames shall be connected to the main grounding loop.
  • The local building grounding system shall be connected to the plant area grounding system at two locations minimum, with green insulated, 70 mm2 (#2/0 AWG) copper wire.
  • Foundation bolts shall not be used for grounding purposes.
  • Lightning protection shall be furnished for all buildings, in conformance with NFPA 70 and 780, and Grounding and Lightning Protection for Buildings and Substations. The facilities shall include all necessary cable, down conductors, lightning rods/air terminals, connectors, test clamps, and connections to the plant grounding system.

Communication Systems

We will include article related soon.

Fire Alarm Systems

We will include article related soon.

Building Electrical Documentation

Required documentation for the electrical systems for buildings. The documentation required will vary according to the size and function of the building. The electrical documents specified in this section shall be provided.

One Line Diagram

  1. Control buildings, administration buildings, and other larger buildings shall require one line diagrams to show the details of these buildings’ more complex power systems.
  2. The one line diagram shall show the electrical system from the electrical service to distribution panels, motors, HVAC, UPS, and battery chargers.
  3. Equipment numbers and ratings shall be shown.

Equipment Location Plan

  1. Location of transformers, motor control centers, switchboards, panelboards, uninterruptable power supplies, batteries, battery chargers, and automatic transfer switches shall be shown. Ratings and sizes of the equipment shall be shown.
  2. Locations of the interconnecting busways, wireways, cable trays, and conduits shall be shown.

Building Electrical Lighting Plan

  • Locations of lighting transformers and panelboards shall be shown.
  • Locations of receptacle transformers and panelboards shall be shown.
  • Locations of transformers and panelboards of, for example kitchen appliances, and water heaters shall be shown.
  • Locations of welding receptacles shall be shown.
  • Designation of each circuit, conduit, wireway, busway, transformer, and panelboard shall be shown.
  • For each conduit, wireway, busway, show:
    a. Its routing
    b. Its designation
    c. Designations of all circuits inside
    d. Number and size of conductors of each circuit
  • Plan and elevation drawings shall be prepared, to determine if aviation obstruction lighting is required. If aviation obstruction lighting is required, aviation obstruction lighting plan drawings shall be prepared, showing the
    lights and the essential power lighting circuits from the essential power panelboard to the lights, in accordance with Lighting Design Requirements in Buildings and Process Industry.
  • Lighting calculations shall be provided.
  • Installation details shall be provided.

Communications Plan

Article will be soon for Communication systems requirements.

Grounding Plan

  • Building structure grounding shall be shown.
  • Grounding for the building’s electrical system, for example panelboards, transformers, motor control centers, and switchboards shall be shown.
  • Grounding for the communications systems shall be shown.
  • Grounding details shall be shown.

Other Documentation

  1. Panelboard schedules.
  2. Cable schedules.
  3. Installation details.
  4. Lighting calculations.
  5. Test reports.

Building Electrical Testing

The installation shall be tested upon completion of the work, as specified in NETA-ATS, and shall include the tests listed in this section.

  • The installation of all wiring, cabling, terminations, conduit or raceway and device installation shall be visually checked for proper installation, and all wiring continuity shall be checked.
  • All control equipment and circuits shall be checked for proper operation.

Insulation Resistance Test

  1. Tests shall be carried out using a 500 V Megger tester for equipment rated 600 V.
  2. With all apparatus and lamps disconnected and all switches closed, the insulation resistance shall not be less than one (1) MΩ between conductors or conductors to earth.
  3. Where it is not practicable to disconnect the apparatus or remove lamps, with all switches open, the insulation resistance shall not be less than 0.5 MΩ between conductors or conductors to earth.

Polarity Check

Verification of polarity shall be made, to ensure that all single pole control devices are connected to the live conductor only; that the outer contacts of center-contact bayonet and Edison-type screw lampholders are connected to the neutral or grounded conductor; and that cabling has been correctly connected to plugs and receptacles.

Grounding

Ground continuity reading shall be recorded from each piece of equipment to the main grounding terminal. No test reading shall exceed 0.1 Ω.
Main keywords for this article are Building Electrical Design Notes, Building Electrical Testing, Building Electrical Installation, Building Electrical Wiring Methods, Insulation Resistance Test.

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  1. March 26, 2020

    […] for station service and building utilities shall be in accordance with Building Electrical Design Notes and Guidelines. Cabling within the building shall be routed in cable tray. Use of conduit and wire shall be […]

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