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

Garage Circuits Proposal

Two new 20 A circuits from the existing panel, sharing one cable run of about 100 ft. One feeds the Desk 1 ceiling outlet; the other feeds the Desk 2 ceiling outlet and an exterior outlet for occasional outdoor use.

The plan

CircuitBreakerWireRunEnds at
A · Desk 1One 20 A 2-pole GFCI, shared by both circuits12 AWG THHN in conduit to the attic, then one 12/3 NM-B run through all three outlets~100 ft totalGarage ceiling, NEMA L5-20R locking receptacle
B · Desk 2 and outdoorGarage ceiling L5-20R, then exterior 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; the 2-pole breaker uses two.

The two circuits share one neutral (a multi-wire branch circuit): black is circuit A, red is circuit B, white is shared. The 2-pole breaker shuts both off together and gives both GFCI protection. At every outlet box the neutral is spliced with a short pigtail to the receptacle, so removing a receptacle never opens the shared neutral. From the panel, a new ¾ in. PVC conduit runs up the outside wall into an attic junction box carrying four 12 AWG THHN conductors (two black, one marked with red tape; one white; one green), which join the 12/3 NM-B there. No AFCI: the house has none today.

Both ceiling receptacles sit at one spot, in two 1-gang boxes mounted side by side with a short 12/3 jumper between them. A 2-gang plate with two 20 A twist-lock openings is not a stock part at either store or from the usual makers; the side-by-side boxes take the in-stock Leviton SL721 plates.

Wiring

New 12/3 NM-B run New ¾ in. PVC conduit with THHN Removable cord, already purchased
HOUSE CONDUITATTIC GARAGE CEILING, 8.25 FT AT THE DESKS Main panel GE PowerMark Gold 200 A · 120/240 V 20 A · 2-pole GFCIpole 1 · circuit Apole 2 · circuit Btrip together ¾ in. PVC up the wall 4 × #12 THHN Attic junction box One 12/3 NM-B run · ~100 ft in all 12/3 on 12/3 on, down a wall L5-20R lockingDesk 1 · circuit A L5-20R lockingDesk 2 · circuit B 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 · circuit B 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.

Exterior route

Photo of the exterior brick wall with the main panel and meter, with the new conduit drawn in: a 3/4 in. PVC run from a top knockout on the panel straight up the brick and siding to an LB fitting that turns into the attic, held by two-hole straps.
Drawn in yellow: the new run, to the right of the existing conduits so it crosses nothing. Four 12 AWG THHN conductors ride in it. Exact knockout, LB height and wall penetration are the contractor’s call on site.

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
Two 120 V, 20 A circuits on one 12/3 run, one 2-pole GFCI breakerPlanned
12/3 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
No AFCI, matching the rest of the houseDecided

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
112/3 solid Romex NM-B with ground, 100 ftThe one run: attic box → Desk 1 → Desk 2 → outdoorHome DepotSouthwire purple coil$165.00 · 1 in stockOut of 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 24.5 cu. in. PVC box, new or old workCeiling outlets, side by side: two 12/3 cables plus the receptacle need 20.25 cu. in.Home DepotCarlon B125AB$2.14 · 53 in stockLowe’sCantex 23 cu. in., new work$1.08 · 392 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
120 A 2-pole GFCI breaker, self-test, THQLPanel: both circuitsHome DepotABB THQL2120GFTA$134.00 · 10 in stockLowe’s lists it at $124.00; store stock not shown
1¾ in. insulated staples for 12/3, 100-packSecuring the 12/3 runLowe’sGardner Bender ¾ in. plastic insulated$6.98 · 9 in stockNot checked
1⅜ in. NM snap-in connectorsNM-B into the attic junction boxHome 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
1¾ in. × 10 ft Schedule 40 PVC conduitPanel up the wall into the atticLowe’sCantex ¾ in. Sch 40$7.97 · 330 in stockHome DepotCantex A52AG12H$7.97 · 86 in stock
1¾ in. PVC LB conduit bodyTurning the run through the wall into the atticLowe’sCantex Type LB$5.48 · 14 in stockHome DepotCantex R5133664$6.43 · 23 in stock
2¾ in. PVC male terminal adapterConduit into the panel and the attic boxLowe’sCantex terminal adapter$0.67 · 91 in stockHome DepotCantex R5140104$0.77 · 147 in stock
2¾ in. conduit locknutOn each terminal adapterElectrical aisle at either store; online stock not confirmedNot on the shelf
1¾ in. PVC two-hole straps, 20-packStrapping the conduit to the brickLowe’sCantex two-hole clamp$5.38 · 28 in stockNot on the shelf
1Tapcon ¼ × 1¼ in. masonry screws, 8-packFastening the straps into brickLowe’sTapcon$7.98 · 14 in stockNot on the shelf
1Gray PVC conduit cement, 8 ozGluing the conduit jointsLowe’sCantex PVC cement$6.78 · 32 in stockNot on the shelf
14 × 4 × 4 in. PVC junction boxAttic: THHN joins the NM-B runsLowe’sCantex 4 × 4 × 4$17.68 · 5 in stockNot on the shelf
1Twist-on wire connectors, red/yellowAttic-box splices and neutral pigtails at each outletLowe’sIDEAL red/yellow, 150-pack$14.98 · 40 in stockNot on the shelf
112 AWG black stranded THHN, 50 ftBoth hots in the conduit (~15 ft each); tape one redLowe’sSouthwire 50 ft$47.00 · 2 in stockNot on the shelf
112 AWG white stranded THHN, 25 ftThe shared neutral in the conduitLowe’sSouthwire 25 ft$24.00 · 4 in stockNot on the shelf
15 ft12 AWG green THHN, by the footShared ground in the conduitHome DepotSouthwire, cut to length$1.02/ft · 397 ft in stockNot on the shelf
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 · $171.71

$180.75 less 5%. Conduit kit (conduit, LB, terminal adapters, straps, Tapcons, cement, attic box, wire connectors), black and white THHN, outdoor duplex, staples, clamp connector, screw hooks (2), zip ties, duct seal.

Home Depot South Austin · $375.21

12/3 Romex, 100 ft (only 1 in stock), 2-pole GFCI breaker, ceiling boxes (2), Leviton L5-20R receptacles (2, only 3 in stock), locking plates (2), weatherproof box, in-use cover, snap-in connectors, 15 ft green THHN cut at the store.

Add the Lowe’s list to a cart Open the Home Depot cart

Each link fills a cart with this list for whoever opens it; set pickup to the Brodie Ln. stores at checkout. The two ¾ in. locknuts are not in either cart.

Total: $546.92, plus two ¾ in. locknuts. That is $260.34 less than the three-circuit plan.

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.