Chapter One Electrical Design and Component Basics

1. Chapter OneElectrical Design and Component Basics

2. Introduction • Rural and domestic electrical systems cause many electrocutions each year. • It is important to know how to work with electricity safely.

3. Electrical Safety • Safety is freedom from accidents. • Accidents are caused by hazards. • To be safe, the risks associated with electricity must be maintained at an acceptable level.

4. Managing Electrical Risk • All electrical installations must meet current standards—National Electric Code. • Insure you include the appropriate people in the design and installation of electrical service and components. (textbook) • Power supplier • Qualified electrician • Electrical equipment supplier • Insurance company • Electrical service high voltage conductors are especially dangerous. • 10 foot rule

5. Codes and Safety • The source of information for the safest installation of electrical service and components is the National Electric Code (NEC). • Published by the National Fire Protection Association (NFPA). • Note: many rural areas do not have local or state agencies to enforce NEC regulations. But: • The NEC should be used for safety reasons and because insurance companies may deny coverage or charge a higher rate for buildings that do not met NEC standards. • Example: Minimum clearance distance for grain storage bins or buildings (Table 1-1.)

6. Building Groups • Safe wiring is influenced by the building environment. • Different environments have different electrical code requirements. • 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

7. Building Groups—cont. • 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. Note: these building groups do not include buildings with explosive environments.

8. Building Materials for all Buildings • 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 Surface mount Waterproof http://assets.twacomm.com/ http://www.nobodybuy.com

9. Building Groups--Dry • Dry buildings do not require special electrical materials. • Surface wiring is recommended • Wiring and devices should be mounted out of the way. Surface mounted wiring must be protected from physical damage.

10. Building Groups—Dry—cont. • 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. • 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.

11. Building Group—Damp • 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) • Dust and moisture accumulation leads to fire and safety hazards by creating short-circuits or heat buildup in fixtures.

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

13. Building Group-Damp-Fluorescent lights • Fluorescent lights must use appropriate fixtures with gasketed cover. (Fig 1-5) • Also note the seal around the wire inlet.

14. Building Group-Damp—Wire Nuts • Solderless connectors used in damp environments must be designed for the environment. • Silicone filled.

15. Building Group-Damp—Cable Connectors • The correct cable connectors must be used. • 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.

16. Building Group—Damp--Conduct • 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 Table 1-4.

17. 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.

18. 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

19. 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

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

21. Box Size—cont. • The number of equivalent conductors is determined by 5 criteria: • Each conductor passing through a box without being spliced or connected to a device is counted as one conductor. • Each conductor connecting to a splice or device is counted as one conductor, unless the conductor is totally contain inside the box. • All grounding conductors are counted as only one conductor unless a second set of equipment grounding conductors are used. • A switch or receptacle is two conductors. • Each of the type of fitting or fixture is a box is counted as one conductor:

22. Box Size—cont.—box fittings • Cable clamp • Fixture stud • Fixture strap

23. Box Size--Example • Determine the minimum size of box for the illustration when 12 AWG is used.

24. Box Size—Example 2 • Determine the minimum size of box for the illustration when 12 AWG is used.

25. 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)