Chapter One Electrical System Components

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# Chapter One Electrical System Components - PowerPoint PPT Presentation

Chapter One Electrical System Components. Electrical Components. Electrical components can be divided into 7 categories based on function. Source Transmission Service Entrance Panel (SEP) Conductors Connectors Enclosures Controls. 1 &amp; 2. Generation &amp; Transmission.

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Presentation Transcript
Electrical Components
• Electrical components can be divided into 7 categories based on function.
• Source
• Transmission
• Service Entrance Panel (SEP)
• Conductors
• Connectors
• Enclosures
• Controls
1 & 2. Generation & Transmission

Why is high voltage used for transmission lines?

• Distribution requires multiple voltages.
• High voltage--230 kV and greater
• Medium voltage—Less than 50 kV
• Low voltage—Less than 1 kV
3. Service Entrance Panel (SEP)

What should be written on this label?

• The SEP is the distribution panel for a structure.
• 3 wire 120 volt common for domestic applications and many farm buildings.
• Must be sized for the loads in the building
4. Conductors

Electrical conductors are constructed of either copper or aluminum.

Conductors – cont.

What is AWG an abbreviation for?

Electrical conductors are size by AWG numbers.

The larger the number the smaller the diameter of wire.

The larger the diameter of wire the lower the resistance.

Conductors – cont.
• Common individual wires are:
• XHHW
• THWN
• THHN

What to these letters stand for?

• Conductors can be bundled into cables or used as individual wires.
• Common cables are:
• NM-B (romex)
• SE
• Armored
• UF
5. Connectors

What color of wire nut should be used to attach 2 - #12 wires?

What color of wire nut should be used to attach 3 - #14 wires?

Wireless connectors (wire nuts) are used to complete connections

Wire nuts are color coded for the size(s) of wires they are designed for.

6. Enclosures

The NEMA has established standards for all electrical enclosures based on use and the environment.

NEMA standards have enclosure types for:

Non hazardous locations

Hazardous locations

Code requires that all electrical devices and connections must be installed inside an enclosure.

7. Controls
• A switch is a electrical component that can interrupt the flow of electricity in a circuit or divert it from one conductor to another.

The primary need for agricultural buildings is devices to energize and de energize electrical circuits.

The primary device used are switches.

Building Groups
• Agricultural buildings are defined as any structure used to house farm implements, hay grain, animals or other agricultural produce.
• No habitation or product processing, treatment or packaging.
• Agricultural buildings are categorized into three groups:
• Dry
• Damp
• Dusty
• Different environments have different electrical code requirements.
Building Groups—cont.

Note: these building groups do not include buildings with explosive environments.

Are there any explosive environments in agriculture or public schools?

Dry buildings: machine storage, shops and garages not attached to a residence.

Damp: Livestock, milking centers, ventilated manure pits, well pits, silos, silo rooms, high humidity produce storages and any structures that are washed periodically.

Dusty: fertilizer, dry grain, dry hay storage and grain feed processing centers.

Building Materials for all Buildings

Surface mount

Waterproof

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• For the safest electrical system, only use components approved by the Underwriters Laboratories Inc. (UL)
• Develops specification for minimum safety standards.
• Specifications are based on building environments
Building Groups--Dry

What are some concerns that must be address when surface wiring is used in agricultural buildings?

Dry buildings do not require special electrical materials.

Surface wiring is acceptable.

Building Groups—Dry—cont.
• Solderless connectors (wire nuts) are the preferred means of splicing conductors.
• Insure the correct size is used and that all of the conductors are tight.

Why is NM-B cable restricted to indoor applications?

• NM-B cable is acceptable indoors and were it is not subject to long periods of high humidity.
• Type UF-B cable is used for damp or wet indoor locations, underground use, and out door locations.
Building Group—Damp

Why?

Damp agricultural building require wiring practices, wire, fixtures and devices engineered for that environment.

If surface wired, UF-B cable must be used.

High levels of moisture, dust and gas can quickly corrode metallic equipment.

All boxes and fixtures must be dust and water tight, and corrosion resistant. (Fig. 1-6 & 1-7)

Building Group-Damp-Incandescent lights

Incandescent lights must use appropriate fixtures and heat resistant globes to cover the bulbs. (Fig. 1-4)

Building Group-Damp-Fluorescent lights
• Also note the seal around the wire inlet.

Fluorescent lights must use appropriate fixtures with gasketed cover. (Fig 1-5)

Building Group-Damp—Wire Nuts

What is the difference between wire nuts designed for damp environments compared to ones designed for wet environments??

Solderless connectors used in damp environments must be designed for the environment.

Building Group-Damp—Cable Connectors
• The correct cable connectors must be used for damp environments.
• Metallic can be used in non corrosive environments.
• Non metallic is used in corrosive environments
• Must be thread into box.
• Uses a gasket that compresses and seals when nut is tightened.
Building Group—Damp--Conduct

Table 1-4.

• PVC is the recommended conduct for damp buildings.
• Available in different lengths up to 20 feet.
• Available in diameters from ½ inch to 6 inches.
• Recommended conductors for plastic conduct include:
• THWN
• RHWN
• THHW
• XHHW
Building Group--Dusty

Commercial dusty buildings such as grain elevators require additional precautions. [NEC 502.10(A)]

On farm grain storage and handling facilities are usually wired according to the damp building requirements.

Building Group—Dusty-explosive
• Intrinsically safe circuits are used.
• Current and voltage are limited so that the minimum ignition energy and the ignition temperature of an explosive mixture cannot be reached.
• The production of sparks, arcs or excessive temperatures which might act as a source of ignition are prevented by additional measures and an increased degree of safety.
• Use non sparking tools
• The components which could cause the ignition of a potentially explosive mixture are built into an enclosure which is capable of withstanding the pressure of an explosion.
• It must be ensured that the explosion inside the enclosure cannot be transmitted beyond the enclosure and ignite the external potentially explosive atmosphere
Box Size
• Box must have adequate volume for the devices and conductors.
• Characteristics of inadequate box size.
• Difficult to work in
• Increases work time
• Concentrates heat
• Increases chances of short circuits
Box Size—cont.

Box size is determined by multiplying the equivalent number of conductors by the conductor volume values in Table 1-2.

Box Size—cont.
• The number of equivalent conductors is determined by 8 criteria:
• Each conductor that originates outside the box and terminates in it count as one.
• Each conductor passing through a box without being spliced or connected to a device is counted as one conductor.
• Each conductor that begins and ends in the same box are not counted.
• All grounding conductors are counted as only one conductor unless a second set of equipment grounding conductors are used.
• Up to four (4) fixture wires smaller than 14 AWG entering the box is ignored. Five or more are counted.
• Each of the type of fitting or fixture in a box is counted as one conductor.
• Each internal cable clamp is counted as one conductor.
• A switch or receptacle strap is two conductors.
Box Size—cont.—box fittings

Cable clamp

Fixture stud

Fixture strap

Box Size--Example

Determine the minimum size of box for the illustration when 12 AWG is used.

Box Size—Example 2

Determine the minimum size of box for the illustration when 12 AWG is used.

Wires per Conduct

The NEC limits the number of wires that can be installed in each size of conduct.

For a size of conduct the limit is determined by the type of insulation and the wire size. (Table 1-5)

Electrical Box Wiring Requirements

Boxes must be securely fastened to building.

Cable or conduct must be clamped to the box.

Cables (conductors) must run inside walls, floors and ceilings and be attached close to the box and periodically along the length of the cable.

Metal boxes must be grounded.

Wires must be connected to each other using solderless connectors.

No more than one wire per terminal on switches, receptacle and other electrical devices. [Fig 33-4 not acceptable everywhere]

Hot wires are attached to brass colored screws.

Neutral wires are attached to aluminum colored screws.

Ground wires are attached to green colored screws.

When the white (neutral) conductor is used as a hot conductor (switch loop) it must be marked with black paint or tape.