Proposal for contractor review · 120 V, 20 A branch circuits

Garage Circuits Proposal

Three new, independent 20 A circuits from the existing panel, each about 100 ft. Two feed locking ceiling outlets for desks in the garage. One feeds an exterior outlet for occasional outdoor use.

The plan

CircuitBreakerWireRunEnds at
1 · Desk 120 A single-pole, GFCI; AFCI per local code12/2 copper NM-B with ground~100 ftGarage ceiling, NEMA L5-20R locking receptacle
2 · Desk 220 A single-pole, GFCI; AFCI per local code12/2 copper NM-B with ground~100 ftGarage ceiling, NEMA L5-20R locking receptacle
3 · Outdoor outlet20 A single-pole, GFCI12/2 copper NM-B with ground~100 ftExterior 20 A tamper- and weather-resistant duplex, in-use cover

Panel: GE PowerMark Gold, 200 A main, 120/240 V single phase. Its label lists the THQL and THQLGF breaker families. Three full-size spaces appear to be free.

Wiring

New 12/2 NM-B run Removable cord, already purchased
HOUSE ATTIC, ~100 FT RUNS GARAGE CEILING, 8.25 FT AT THE DESKS Main panel GE PowerMark Gold 200 A · 120/240 V 20 A · 1-poleGFCI · circuit 1 20 A · 1-poleGFCI · circuit 2 20 A · 1-poleGFCI · circuit 3 12/2 NM-B · ~100 ft 12/2 NM-B · ~100 ft 12/2 NM-B · ~100 ft · attic, then down a dry interior wall L5-20R lockingceiling outlet 1 L5-20R lockingceiling outlet 2 8 ft cord 8 ft cord Desk 15-15/20R end Desk 25-15/20R end Unplug cords before opening the door brick Exterior 20 A duplex TR + WR, metal box in-use cover Cable enters the back of the box straight through the brick
Each circuit has its own breaker and its own run; nothing is shared between the two desks or the outdoor outlet.

Ceiling drop

Rendered view from below the garage ceiling: a twist-lock plug locked into a ceiling receptacle behind a stainless plate, the cord drooping in a slack loop up to a screw hook driven into a joist, held in the hook by a zip tie, then running straight down to the desk.
The hook carries the cord’s weight through the zip tie. The slack loop means nothing pulls on the plug or the receptacle. To open the garage door: twist the plug to unlock, cut the zip tie, and stow the cord; put on a new tie when it goes back up.

Voltage drop at 100 ft

12 AWG copper, 100 ft each way, 120 V, using NEC Chapter 9 Table 8 resistance at 75 °C. The usual target is about 3% for a branch circuit.

LoadAmpsDrop
Desk, typical computer and monitors51.9 V · 1.6%
Desk, busy83.1 V · 2.6%

At desk loads, 12 AWG stays under 3% on these runs. Actual run lengths decide.

Planned and already decided

ItemStatus
Three independent 120 V, 20 A circuitsPlanned
12/2 copper NM-B with ground, routed through the accessible atticPlanned
Two NEMA L5-20R locking receptacles in the garage ceiling (8.25 ft)Planned Box and support
Two Conntek 8FL520520 cords: 8 ft, 12/3, L5-20P to 5-15/20RPurchased
Desks away from the walls; no cord reels or recessed cabinetsDecided
Exterior 20 A TR/WR duplex in a weatherproof metal box, extra-duty in-use coverPlanned Brick entry detail
No living space above the garage; spray foam at the roof deckExisting
Breaker models and AFCI requirementContractor

Materials

Everything is on the shelf today at Lowe’s S.W. Austin (Brodie Ln.) or The Home Depot South Austin. Prices and stock were read from each store’s website on Oct 10, 2026. Lowe’s prices are shown before your 5% discount. Items in italics are only needed if the contractor calls for them.

QtyItemBuy hereAlso on the shelf at
212/2 solid Romex NM-B with ground, 250 ftAll three runsLowe’sSouthwire Romex SIMpull$155.00 · 117 in stockHome DepotSouthwire 28828269$155.00 · 63 in stock
2NEMA L5-20R locking receptacle, 20 A 125 VCeiling outletsHome DepotLeviton 2310$15.58 · 3 in stockNot on the shelf
2Single locking-receptacle plate, 1.6 in. hole, stainlessCeiling outletsHome DepotLeviton SL721$2.98 · 18 in stockNot on the shelf
21-gang 18 cu. in. PVC new-work boxCeiling outletsLowe’sCantex 18 cu. in.$0.92 · 1,238 in stockHome DepotCarlon B118A$0.92 · 900 in stock
11-gang metal weatherproof box, three ½ in. holesExterior outletHome DepotCommercial Electric WSB350G$5.95 · 181 in stockNot on the shelf
120 A tamper- and weather-resistant duplex receptacleExterior outletLowe’sEaton TR/WR commercial$9.08 · 15 in stockNot on the shelf
1Extra-duty in-use cover, 1-gangExterior outletHome DepotCommercial Electric WCWR1PG$9.98 · 76 in stockLowe’sTayMac Extra Duty$11.28 · 26 in stock
320 A single-pole GFCI breaker, self-test, THQLPanel, one per circuitLowe’sABB (GE) 20 A GFCI$72.98 · 4 in stockHome DepotABB THQL1120GFTA$72.77 · 21 in stock
1½ in. insulated staples for 12/2, 100-packSecuring the runsLowe’sGardner Bender plastic insulated$5.48 · 17 in stockHome DepotGardner Bender MDI-150Y$5.21 · 12 in stock
1⅜ in. NM snap-in connectorsPanel knockouts (3)Home DepotCommercial Electric, 5-pack$3.58 · 100 in stockLowe’sSigma ProConnex, 10-pack$5.78 · 38 in stock
1⅜ in. NM clamp connector with locknutExterior box entryLowe’sSigma die-cast clamp, 10-pack$5.68 · 14 in stockNot on the shelf
2Heavy screw hook into a joistCord support at each ceiling outletLowe’sHillman 4.94 in. hook$1.98 · 13 in stockNot on the shelf
1Black UV-rated zip ties, 8 in., 100-packHolding the cord in each hookLowe’sUtilitech 8 in.$10.98 · 251 in stockNot checked
1Duct seal compoundSealing the brick penetrationLowe’sGardner Bender 16 oz$5.48 · 5 in stockHome DepotIDEAL 31-601$5.97 · 15 in stock
3If AFCI is required, instead of the GFCI breakers: 20 A dual-function AFCI/GFCI breakerPanelLowe’sABB (GE) dual function$74.98 · 9 in stockNot on the shelf
2If the ceiling is drywalled, instead of the new-work boxes: 1-gang PVC old-work boxCeiling outletsLowe’sCantex old-work$1.98 · 386 in stockHome DepotCarlon B120R$3.98 · 373 in stock
1If the exterior end must be wet-rated: 12/2 UF-B with ground, 25 ftExterior entryHome DepotSouthwire 13055921$59.00 · 4 in stockNot on the shelf
1If a sleeve through the brick is wanted: ½ in. × 10 ft Schedule 40 PVC conduitExterior entryLowe’sCantex ½ in. Sch 40$5.97 · 245 in stockHome DepotJM Eagle 67447$5.97 · 205 in stock
1For that sleeve: ⅞ in. SDS-Plus masonry bit (needs a rotary hammer)Exterior entryLowe’sBosch Bulldog Tough$39.98 · 2 in stockNot on the shelf

Where to shop

Everything except the italic items, before tax. The two stores are next door to each other on Brodie Ln.

Lowe’s S.W. Austin · $542.87

$571.44 less 5%. Wire (2), GFCI breakers (3), new-work boxes (2), outdoor duplex, staples, clamp connector, screw hooks (2), zip ties, duct seal.

Home Depot South Austin · $56.63

Leviton L5-20R receptacles (2, only 3 in stock), locking plates (2), weatherproof box, in-use cover, snap-in connectors.

Total: $599.50. The ELEGRP receptacles and plates in the original cart are replaced by the Leviton ones, which are on the shelf and cost $11.64 less.

Before opening the garage door

  1. Shut down the desk equipment.
  2. Unplug each cord at the ceiling outlet.
  3. Cut the zip tie at the hook.
  4. Coil the cords and stow them off the door path.
  5. Check the full door travel is clear, then open.

This is a homeowner’s proposal for review, not an approved design. Code requirements depend on the adopted code edition and the local inspector.