How 120 Volt Wiring Works

120-volt isolated ground circuit

240-volt branch circuit

Breaker Probe

Test for current before touching any parts inside a circuit breaker panel With main breaker turned OFF but all other breakers turned ON. touch one probe of a neon tester to the neutral bus bar and touch other probe to each setscrew on one of the double-pole breakers (not the main breaker) If tester does not light for either setscrew it is safe to work in the panel.

Connecting Circuit Breakers

The last step in a wiring project is connecting circuits at the breaker panel After this is done, the work is ready for the final inspection

Circuits are connected at the main breaker panel, if it has enough open slots, or at a circuit breaker subpanel (pages 194 to 197). When working at a subpanel. make sure the feeder breaker at the main panel has been turned OFF. and test for power (photo, left) before touching any parts in the subpanel.

Make sure the circuit breaker amperage does not exceed the "ampacity" of the circuit wires you are connecting to it (page 177). Also be aware that circuit breaker styles and installation techniques vary according to manufacturer. Use breakers designed for your type of panel.

Everything You Need

Tools: screwdriver, hammer, pencil, combination tool, cable ripper, neon circuit tester, pliers.

Materials: cable clamps, single- and double-pole circuit breakers.

Pole Circuit Breaker Wiring

3 Hold cable across the front of the panel near the knockout, and mark sheathing about inside the edge of the panel. Strip the cable from marked line to end. using a cable ripper (There should be 18" to 24" of excess cable ) Insert the cable through the clamp and into the service panel, then tighten the clamp

How to Connect Circuit Breakers

IShut off the main circuit breaker in the main circuit breaker panel (if you are working in a sub-panel. shut off the feeder breaker in the main panel) Remove the panel coverplate. taking care not to touch the parts inside the panel Test for power (photo, top)

2 Open a knockout in the side of the circuit breaker panel, using a screwdriver and hammer Attach a cable clamp to the knockout

Breaker Bus Bar

4Beno the bare copper grounding ,ure around the inside edge -i 'he panel to an open setscrew ter unal on the grounding bus bar Insert the wire into the opening on •he bus bar and tighten the set-Fold excess wire around mside edge ot the panel

5 For 120-volt circuits bend the white circuit wire around the outside of the panel to an open setscrew terminal on the neutral bus bar Clip away excess wire then strip ot insulation trom the wire using a combination tool Insert the wire into the terminal opening, and tighten the setscrew

6 Strip of insulation trom the end of the black circuit insert the wire into the setscrew terminal on a new smgle-poie circuit breaker and tighten the setscrew

Tape Clamps Busbar

7 Slide one end of the circuit breaker onto the guide hook then press it firmly against the bus bar until it snaps into place (Breaker installation may vary depending on the manufacturer ) Fold excess jiack .ire around the mside edge of the panel

8 120/240-volt circuits (top):

Connect red and black wires lo double-pole breaker Connect white wire to neutral bus bar and grounding wire to grounding bus bar 240-volt circuits (bottom): Attach white and black wires to double-pole breaker tagging white wire with black tape There is no neutral bus bar connection on this circuit

9 Remove the appropriate breaker knockout on the panel cover-plate to make room for the new circuit breaker A smgle-poie breaker recuires one knockout, while a double-pole breaker requires two knockouts Reattach the cover-plate and label the new circuit on the panel index

Main Lug Subpanel

120/240-volt circuit

Strip Whit Poie

Panel index

120 Volt Clamp CircuitHow Connect Double Pole Breaker

4 Strip away out r sheathing from the feeder cable using a cable npper Leave at least of sheathing extending into the subpanel Tighten the cable clamp screws so cable is held securely but not so tightly that the wire Sheathing is crushed

5 Strip of insulation from the white neutral feeder wire, and attach it to the main lug on the subpanel neutral bus bar Connect the grounding wire to a setscrew terminal on the grounding bus bar Fold excess wire around the inside edge of the subpanel

6 Strip away of insulation from the red and black feeder wires Attach one wire to the mam lug on each of the hot bus bars Fol excess wire around the inside edge of the subpanel

7 At the main circuit breaker panel, shut off the mam circuit breaker then remove the coverplate and test for power (page 192) If necessary make room for the double-pole feeder breaker by removing single-pole breakers and reconnecting the wires to slimline circuit breakers Open a knockout for the feeder cable, using a hammer and screwdriver

8 Strip away the outer sheathing from the feeder cable so that at least of sheathing will reach into the mam service panel Attach a cable clamp to the cable, then insert the cable into the knockout, and anchor it by threading a locknut onto the clamp Tighten the locknut by driving a screwdriver against the lugs Tighten the clamp screws so cable is held securely but not so tightly that the cable sheathing is crushed

Copper Wire Stripper

Strip away of insulation from the white feeder wire Attach the wire to one of the setscrew terminals on the neutral bus bar Fold excess wir around the inside edge of the service panel

9 Bend the bare copper wire from the feeder cable around the inside edge of the main circuit breaker ■>anel 3nd connect it to one of the setscrew terminals the grounding bus bar

Strip away of insulation from the white feeder wire Attach the wire to one of the setscrew terminals on the neutral bus bar Fold excess wir around the inside edge of the service panel

Strip Whit Poie
H 4 Strip of insulation from the i I red and black feeder wires Attach one wire to each of the setscrew terminals on the double-poie feeder breaker
Strip Whit PoieRed Black And Green Wires Into Breaker

H Q Hook the end of the feeder I Cm circuit breaker over the guide hooks on the panel, then push the other end forward until the breaker snaps onto the hot bus bars (follow manufacturer's directions) Fold excess wire around the inside edge of the cir cuit breaker panel

4 Q If necessary open two 10 knockouts where the double-pole feeder breaker will fit. then reattach the coverplate Label the feeder breaker on the circuit index Turn main breaker ON. but leave feeder breaker OFF until all sub-panel circuits have been connected and inspected

Sub Panel Feeder Cable

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Responses

  • pervinca
    How 120 volt wiring works?
    7 years ago
  • wolfgang
    How to wire a manin lug panel?
    7 years ago
  • Roxana
    How to wire a 240 volt circuit?
    7 years ago
  • GRIFFO
    WHERE TO TERMINATE A NUETRAL WIRE ON 120 VOLT BREAKER?
    7 years ago
  • matthias
    How a 120 volt circuit works?
    5 years ago
  • Wegahta
    How does 120 volt wiring work?
    5 years ago
  • carson cunningham
    How a 120 volt household circuit works?
    5 years ago
  • fre-swera
    How is wiring connected to 120 volt circuit breaker?
    4 years ago
  • Fiamma
    How to wire a 120 volt double pole breaker in lug type subpanel?
    4 years ago
  • fiona
    What is a 120 volt isolated ground circuit?
    3 years ago

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