Residential Wiring - CH 4

10/28

Branch Circuit - the circuit conductors between the final overcurrent device protecting the circuit and the outlets
Feeder - all circuit conductors between the service equipment, the source of a separately derived system, or other power supply source, and the final branch circuit overcurrent device
In branch circuits, conductors are required to be protected from overcurrent in accordance with the conductor’s ability to continuously carry current (ampacity) under the conditions that exist where the conductor is installed (NEC 240.4)
- Common exception - Motor branch circuit
Branch circuit overcurrent protective device - fuse or circuit breaker
The ampere rating of the branch circuit overcurrent protective device determines the rating of the branch circuit
- Ex: a 20 amp conductor protected by a 15 amp fuse = a 15 amp branch circuit
Standard branch circuits that serve more than one outlet (called a general-purpose or multi-outlet branch circuit) are rated 10, 15, 20, 30, 40, and 50 amps
- 10 amp branch circuits are not p Termitted to supply receptacle outlets
- A branch circuit that supplies an individual load can be of any amp rating (NEC 210.18)

If the ampacity of the conductor does not match up with a standard rating of a fuse or breaker, the next higher standard size overcurrent device may sometimes be used, as long as the overcurrent device doesn’t exceed 800 amps (NEC 240.4 B)
- This is permitted if the circuit supplies fixed loads (lighting, not more than one receptacle for cord-and-plug-connected portable loads)
- This is not permitted for circuits that supply multiple receptacles that can supply more than one cord-and-plug-connected load

The higher the gauge (AWG) number = the smaller the wire
The wire size used for a circuit depends on the maximum current to be carried
The minimum conductor for branch circuit wiring = 14 AWG
Raceway -
Conductors 8 AWG and larger must be stranded when installed in a raceway (310.3C)

Ampacity - The maximum current, in amperes, that a conductor can carry continuously under the conditions of use without exceeding its temperature rating
- Depends on the conductor’s cross-sectional area, whether the conductor is copper, copper-clad aluminum, or aluminum, and the type of insulation around the conductor
Conductors cross-sectional area: A = πr²
- The higher cross-sectional area, the more ampacity
Conductors must not have an ampacity not less than the maximum load to be served
Diameter of conductors = mil.
- Mil. = one thousandth of an inch (0.0001 in)
- Mils² = circular mills
AWG numbers range from 18 AWG (1620 mils²) through 4/0 (211,600 mils²)
- Wire sizes larger than 4/0 are expressed in kmil, like 250kmil (250,000 mils²)

Aluminum conductors have fewer amps than copper of the same size (higher resistance)
Wire connectors (wire nuts, etc) marked AL/CU are suitable for use with aluminum, copper, or copper-clad aluminum
- Connectors not marked AL or AL/CU are suitable for use with copper conductors only
Unless specifically stated, conductors made of aluminum, copper, or copper-clad aluminum may not be used in combination with the same connector

Torque - Twisting force
Terminal Connection Torque - The specific twisting force required for electrical connections
- The torque values shall be as indicated on the equipment or in the installation instructions provided by the manufacturer (110.14D)
- In absence of a marked torque value, use NEC Informative Annex I, Recommended Tightening Torque Tables from UL Standard 486A-486B

Thermoplastic insulation - Most common insulation that softens and can melt and stiffen at certain temperatures; examples: THHN, THHW, THW, THWN, TW; stiffens at temps lower than 14°F

Thermoset insulation - Insulation that can withstand higher and lower temps; cannot be reheated and reshaped, if heated above rated temp, it will char and crack; examples: RHH, RHW, XHH, XHHW

Conductors are listed for wet, dry, damp, and sunlight locations
- Damp locations - Locations protected from weather and not subject to saturation with water or other liquids, but subject to moderate degrees of moisture
- Dry Locations - A location not normally subjected to dampness or wetness (but it could be temporarily)
- Wet Locations - A location that is unprotected and exposed to the weather, subject to saturation with water and other liquids, underground, or in concrete slabs/masonry in direct contact with the earth
  - The interior of raceways installed in wet locations is considered a wet location, so insulated cables and conductors in these locations are required to be listed for wet locations
Insulated cables and conductors used where exposed to direct rays of sun are required to be listed as “sunlight resistant” or be covered in tape of sleeving thats listed as being sunlight resistant
Conductors are also rated by the temperature their insulation system can withstand; electrical industry uses Celsius only
- Type TW: 60°C = 140°F
- Type THWM: 75°C = 167°F
- Type THHN: 90°C = 194°F
  - THHN and THWN are the most popular

Some conductors are also listed for more than one application; ex: THHN/THWN is rated 600 volts, 90°C when used in dry locations but 600 volts, 75°C when used in wet locations

Voltage drop - when the amount of voltage drops; can cause appliances to not work properly
- E = (K x I x L x 2) / CMA
  - E = voltage drop
  - K = ohms (dc only)
  - I = amps
  - L = length in ft from beginning of circuit to the load
  - CMA = cross-sectional area of the conductors in circular mils (Mils²)
    - CMA = 𝜋r² or CMA = 𝜋d²/4
      - r = radius, d = diameter

Romex = common term for Non metallic sheathed cable
Non metallic sheathed cable = A factory assembly of 2 or more insulated conductors enclosed within an overall non metallic jacket