Download - Basic Electrical Class NEC Code 101
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Basic Electrical DesignNEC Code Applications
Class 101
Jim Fuller
4/9/08
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Two basic principles
Heat is your Enemy Harmonic overheat transformers
Overheating motors
Overheating wire and circuit breaker
Energy is conserve: Law of Conservation Transformer: Input = Output + losses
Motor: input = output + losses
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Objective
Electrical Codes Enclosures
Basic Electrical Formulas
Conduit Sizing
Cable Ampacity Table NEC 310-16 Conductor Sizing
Sizing Transformer CB, Cable and Conduit
Transformer Formula
Ground Wire Sizing Sizing Conductor and OCPD for 480V Motors
Rule of Thumb
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Electrical Codes
NFPA 70 = NEC (national Electrical code)(sizing wire, conduit, transformer, safety and etc.)
NFPA (National Fire Protection Assoc.)(example NFPA 101 life safety fire alarm, egress and etc..)
UL = national laboratory(testing lab for quality of equipment)
NEMA National Electrical Manuf Assoc.(Quality of equipment, size i.e. MG-1 for motors
IEEE(Manuf criteria, example BIL level, short circuit rating)
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Nema type EnclosuresNON-CLASSIFIED LOCATION ENCLOSURESNEMA enclosures 2, 5, 12, 12K and 13 are not intended to provide protection against conditions such asinternal condensation. NEMA enclosures 3, 3R, 38, 4, 4X, 6 and 6P are not intended to provide protection against conditions such as internal condensation orinternal icing.
Type 1 Enclosures Type 1 enclosures are intended for indoor use primarily to provide a degree
of protection against limited amounts of falling dirt in locations where unusual
service conditions do not exist. Type 2 Enclosures Type 2 enclosures are intended for indoor use primarily to provide a degree
of protection against limited amounts of falling water and dirt. Type 3 Enclosures Type 3 enclosures are intended for outdoor use primarily to provide a degree
of protection against rain, sleet, and wind-blown dust; and to be undamagedby the formation of ice on the enclosure.
Type 3R Enclosures Type 3R enclosures are intended for outdoor use primarily to provide a
degree of protection against rain and sleet; and to be undamaged by theformation of ice on the enclosure. They must have a provision for a drainhole.
Type 3S Enclosures
Type 38 enclosures are intended for outdoor use primarily to provide adegree of protection against rain, sleet, and wind- blown dust, and to providefor operation of external mechanisms when ice laden.
Type 4 Enclosures Type 4 enclosures are intended for indoor or outdoor use primarily to provide
a degree of protection against windblown dust and rain, splashing water, andhose-directed water; and to be undamaged by the formation of ice on theenclosure.
Type 4X Enclosures Type 4X enclosures are intended for indoor or outdoor use primarily to
provide a degree of protection against corrosion, windblown dust and rain,splashing water, and hose-directed water; and to be undamaged by theformation of ice on the enclosure.
Type 5 Enclosures Type 5 enclosures are intended for indoor use primarily to provide a degree
of protection against settling airborne dust, falling dirt, and drippingnoncorrosive Type 4 Enclosures Type 4 enclosures are intended for indoor or outdoor use primarily to provide
a degree of protection against windblown dust and rain, splashing water, andhose-directed water; and to be undamaged by the formation of ice on theenclosure.
Type 4X Enclosures Type 4X enclosures are intended for indoor or outdoor use primarily to
provide a degree of protection against corrosion, windblown dust and rain,splashing water, and hose-directed water; and to be undamaged by theformation of ice on the enclosure.
Type 5 Enclosures Type 5 enclosures are intended for indoor use primarily to provide a degree
of protection against settling airborne dust, falling dirt, and drippingnoncorrosive
Type 6 Enclosures Type 6 enclosures are intended for indoor or outdoor use primarily to provide
a degree of protection against hose-directed water and the entry or waterduring temporary submersion at a limited depth; and to be undamaged by theformation of ice on the enclosure.
Type 6P Enclosures Type 6P enclosures are intended for indoor or outdoor use primarily to
provide a degree of protection against hose-directed water and the entry ofwater during prolonged submersion at a limited depth; and to be undamagedby the formation of ice on the enclosure.
Type 12 Enclosures Type 12 enclosures are intended for indoor use primarily to provide a degree
of protection against circulating dust, falling dirt, and dripping noncorrosiveliquids.
Type 12K Enclosures Type 12K enclosures are intended for indoor use primarily to provide a
degree of protection against circulating dust, falling dirt, and drippingnoncorrosive liquids. The knockouts shall be provided only in the top orbottom walls, or both.
Type 13 Enclosures Type 13 enclosures are intended for indoor use primarily to provide a degree
of protection against lint, dust, spraying of water, oil, and noncorrosivecoolant.
CLASSIFIED LOCATION ENCLOSURES
Type 7 Enclosures Type 7 enclosures are for indoor use in locations classified as Class I,
Groups A, B, C, or D, as defined in the National Electrical Code. Type 8 Enclosures Type 8 enclosures are for indoor or outdoor use in locations classified as
Class I, Groups A, B, C, or D, as defined in the National Electrical Code. Type 9 Enclosures Type 9 enclosures are intended for indoor use in locations classified as Class
II, Groups E, F, and G, as defined in the National Electrical Code. Type 10 Enclosures (MSHA)Type 10 enclosures shall be capable of meeting
the requirements of the Mine Safety and Health Administration, 30 C.F:R.,Part 18.
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Basic Electrical Formula:
Three Phase Systems
Volts = I x R = amps x resistance
= Input Kilowatts
KVA
= Input Watts x PF
1000
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Basic Electrical Formula:Single Phase Systems
Volts = I x R = amps x resistance
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Conduit fill (sizing)
Sample Problem: Is 5 inch conduit sufficient for (3)1/c00MCM 15KV + 1/0 Grd 15KV?
% fill = total area of cables x 100Area of Conduit
Area of Cable =
= 3 (p x (1.49 Dia)2 + (px (1.07 Dia) 2= 6.13 inch2
4 4
Area of Conduit = = 3 (px (5.047 Dia)2 = 20 inch24
% fill = Area of conduitx100 =6.13 inch2
x100 = 30%Total area of cables 20 inch2
5 PVC, (3) 1/c 500MCM,#1/0 G 15KV
5 5.047 20.0 6.2 8.0 10.6
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CableAmpacityper NEC
The lug rating of CB,starter, disc sw are basedon 75deg C. If specified inspec then the wires can bebased on 75deg C
600 C
< 100A
750 C> 100A
900 C ambient
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Conductor Sizing Sections 220-3(a), 220-10(b),
and 384-16(c). The NEC requiresthe branch circuit computed loadfor conductor sizing to be sized at125% of the continuous load, plusthe noncontinuous load (100%).
Continuous Load: above 3 hoursi.e.. Lighting, HVAC motors
Non continuous Load: less than 3hours, i.e.. Bridge crane, elevators
Example: 175 amp continuous load
175A x 125% = 218.7A
Choose next size larger from NEC table 310.16a
= #4/0 AWG
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Sizing Transformer CB and cable and conduitsbased on 30 deg C ambient and 75 deg C cable
Example: 75KVA transformer = 125A CB, HV cable; 3#2 in 1 C, LV cable 3#4/0 & 1#6 in 2 C
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Transformer Formula
Suppose we have a 500kVA, 480V delta/208 wye/120V transformer.
What are the transformer's primary and secondary currents?
ILine = (rated kVA x 1000) / (1.73 x VLine)
=(500 x 1000) / 1.73 x 480)
=500,000 / 830=603A
ILine =(rated kVA x 1000) / (1.73 x VLine)
=(500 x 1000) / 1.73 x 208)
=500,000 / 360=1388A
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Ground Conductor Sizinghttp://www.electrician2.com/calculators/t122_122.html
Equipment ground(GroundConductor for OCPD for motors)
System Ground (Ground
conductor for Service entrance)
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Sizing Conductor and OCPD for Motors
Motor Full Load current NEC table 430.250
Motor Lock rotor Current NEC table 430-251 (b)
Cable Ampacity NEC 310.16
Ground wire NEC 250.122
Example: 60HP, 150A MCP, 100A Disc
Switch, 3#2 + 1#6 in 1 inch conduit
example
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Rule of ThumbElectrical principles
Receptacle are usually rated 180VA but we usually onlyput 5 or 6 per circuit because of computer loads.
At 480V : 1HP = 1KW
Min. size power circuit is #12AWG Instrument cable is #18 or #16 for single pair and #24 for
multi-pair
Heat is your enemy in electrical design
Energy is conserved in transformer: amps go up thenvoltage goes down, volts go up then current goes down
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Conclusion Electrical Codes
Enclosures Basic Electrical Formulas
Conduit Sizing
Cable Ampacity Table NEC 310-16
Conductor Sizing
Sizing Transformer CB, Cable and Conduit
Transformer Formula
Ground Wire Sizing
Sizing Conductor and OCPD for 480V Motors
Rule of Thumb