View
217
Download
0
Embed Size (px)
Citation preview
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