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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