EET 110 - Survey of ElectronicsChapter 23 - Residential Wiring

Requirements and Devices

Residential Wiring Req & Dev.

Objectives NEC Describe ‘electrical service entry’ components Understand the ground system required understand over current protection devices &

requirements

Approval of wiring

NEC - National Electrical Code specifies ‘rules’ that must be followed to

comply intended to promote fire & electrical safety

Approval of wiring

Approval of electrical installations must be performed or approved by a licensed

Master Electrician inspected by state electrical inspector

Electrical Service

May be run overhead or undergroundOVERHEAD WIRES

2 supply lines + neutral from the pole connect to customers equipment at mast neutral wire is used to support the others

Electrical Service

Mast to meter head Meter supplied by power company Service conduit from meter head to entry panel main panel to individual circuits

Main panel/ breaker box (fuse panel)

Underground wiring

Same wires run to meter head from service transformer to meter head

2 ‘hot’ leads, one neutral

Three wire power distribution

Single phase powerrated as 240 volts

1 x 240 volts - 2 x 120 volts + ground

2 hot leads - black or red each is 120 volts to neutral 240 volts between the two ‘hot’ leads

neutral (not ground) whiteonly allowed to fuse or switch the ‘hot’

leads.Never interrupt the neutral leadsneutral is grounded at the main box and at

the meter head may not be at ground (0 volt) potential

elsewhere in the house

General Wiring requirements

Service size requirements 100 amp is common in older homes 200 amp service is standard for installation in

‘new work’ or upgrades

High tension wire provides high voltage to local transformer transformer provides 240 volts center tapped

(gives 2 120 volt lines)

Service entry wiring

Main fuse / breaker with switch to disconnect entire house

Inside the neutral block is grounded.

Circuit breaker protection ‘opens’ if current is excessive mechanical version of fuse may be reset when metal cools DOUBLE Pole for 240 volt circuits SINGLE pole for 120 volt circuits

Branch circuit connections

240 volt from both hot leads through double pole breaker note that both sides of the breaker are

physically tied together

120 volt from either hot lead through a single pole breaker

Wire Sizes depends on AMPACITY of wire No. 2 gauge for 100 A service, 3/0 for 200A

Other circuits

General purpose circuit 14AWG through 15A breaker or 12 AWG/20A one circuit is required for each 500 square feet

Small appliance 12AWG/20A wiring 2 for kitchen, breakfast room, dining room and

pantry no lighting is allowed on these circuits

Individual circuits for special equipment runs from breaker to a single device

• water heater, range

Wiring

conduit rigid pvc or metal (steel/aluminum)

non-metallic sheathed cable wiring ‘ROMEX’ typical AWG with number of conductors

• 12/2 with ground

None - metallic wiring NM - interior NMC - interior but corrosive resistant sheathing UF - rated for direct underground applications

Armor cable semi-flexible metal case

Knob and Tube wiring antique wiring method - very common in older

homes. (pre-1960’s)

Installing romex type wiring

stapled w/in 12 inches of a boxalso stapled or supported at least every 5

feet.Clamped inside box

require 6 inches of free wiring inside the box

Sheathing must be removed carefully do not nick insulation on wires

Boxes

Boxes are required for lights, switches, receptacles, or splices

Steel or plastic are availableOctagon, square, outlet or exterior (all

weather) boxes + ganged

wires run through ‘knockouts’boxes must be physically secured to

structure - mounted to be flush with wall

Receptacles

Connections Screw terminals push in (solderless) Ganged outlets

Lamp holders ceramic …

Switches / Dimmers SPST - simple single circuit switching DPST - 240 V

• both ‘hot’ leads must be broken SPDT - three way switches four way switches

Grounding system safety - electrons take shortest path to ground neutral wire carries electron flow from load

• not a ground

• never break neutral - ie. Switch bare ground wire - to earth ground Ground rod

• sink to earth ground

Water pipe as ground• Meter bonding jumper

Over current protection fuse circuit breaker GFI - Ground Fault Interrupter