Old-Work Box and Fishing Standard
Purpose
Add outlets to a finished wall or ceiling without opening it, and leave a box that holds, a cable that is legal where it runs, and a building whose fire separations are intact. The permission that makes old work possible is narrow: cable fished through a concealed space in a finished building may run unsupported only between access points. This procedure is built around producing those access points before the first hole is cut.
The failure this prevents is the box that comes off the wall the first time somebody unplugs a vacuum, and the quieter one behind it, a hidden splice in a wall cavity that nobody will find until a fault does.
Scope
Covers cutting old-work outlet, switch and luminaire boxes into finished drywall, plaster, panelling and suspended ceilings, and fishing nonmetallic-sheathed cable to them from an attic, a basement, a crawl space or an adjacent accessible cavity, in dwellings and small commercial tenant spaces.
Does not cover the box-fill computation or the pre-inspection self-check, owned by the rough-in inspection readiness SOP; open-framing rough-in, owned by the remodel rough-in standard; or fishing in fire-rated assemblies where an engineered penetration detail applies, which goes to the general contractor's firestop submittal.
Roles and handoffs
| Role | Owns | Hands off |
|---|---|---|
| Estimator | The access plan, meaning which attic, basement or closet the cable comes from | Names the route on the quote, so nobody discovers on the day that the only path is through a finished soffit |
| Technician | Cavity proving, box selection, the fish, the restore | Reports any relocated device to the office the same day, with the reason and the new dimension |
| Office | Customer notice on patching and finish repair | Confirms in writing who patches and paints before the first cut, which is the argument this work reliably produces |
Procedure
Identify the wall or ceiling construction and its finished thickness at each proposed location before anything is cut. Probe an inconspicuous spot or read an existing device opening: drywall, plaster over wood lath, plaster over metal lath, and plaster over masonry each take a different box and a different cutting method. Acceptance: material and total finished thickness written for each location. Wrong looks like a wing-type box specified for plaster over metal lath, where the wings have nothing to close on. Stop rule: a construction you cannot identify from an existing opening is opened at an inconspicuous point and identified before any box is ordered, never guessed from the paint. Hazard clause: in pre-1978 housing, cutting painted surfaces triggers the EPA renovation, repair and painting rule at 40 CFR 745 Subpart E, and plaster, joint compound and masonry release respirable crystalline silica when cut, so use a shrouded tool on HEPA collection per 29 CFR 1926.1153, not a dry keyhole saw.
De-energize and prove dead every circuit that could pass through the cavity you are about to open. Trace from the panel, isolate, lock and tag under 29 CFR 1910.333(b)(2), and prove dead on a known live source before and after the reading per NFPA 70E-2021, 120.5. Acceptance: a zero reading bracketed by two good live-source checks on the same meter, at every device you will open. Wrong looks like a non-contact tester waved at a plaster wall, which reads nothing useful through metal lath. Stop rule: a switch loop or a shared neutral can feed the same cavity from a circuit you did not isolate, so isolate that one too before cutting. Hazard clause: a meter with a blown fuse reads a believable zero, which is what the before-and-after check catches.
Prove the cavity is clear for the full footprint of the box before cutting the opening. Scan for metal and framing, drill one small pilot, and put a borescope in it looking up and down the bay. Acceptance: visual confirmation of a clear cavity across the whole box footprint plus at least 1 in around it, with cavity depth measured against box depth. Wrong looks like a pilot that clears and a saw cut that finds a water line 2 in to the left. Stop rule: any unidentified obstruction relocates the box, and nothing is cut past an obstruction to see what it is. Hazard clause: cutting blind can open a gas line, and if one is nicked everyone leaves immediately without touching a switch, a phone or a light, with the gas utility and 911 called from outside and upwind.
Select a box that is supported by the surface it is mounted in, and confirm it holds the fill. NEC 314.23(C) requires an enclosure mounted in a finished surface to be rigidly secured to it by clamps, anchors or fittings identified for the application, which is why wing boxes suit drywall and metal brackets suit plaster and lath. Acceptance: the box marked with a volume that satisfies the fill computation, support method matched to the material recorded at step 1. Wrong looks like a box that rocks when a plug is pulled. Stop rule: a ceiling box carrying a paddle fan must be listed and marked for fan support per NEC 314.27(C), and no old-work box is used for a fan without that marking. Hazard clause: none at this step, selection made from the step 1 record.
Cut the opening to the box template, with the dust control the material demands. Score plaster through the paper template before sawing so the face does not spall, and cut metal lath with snips or an oscillating tool rather than tearing it. Acceptance: an opening the box seats in with its flange bearing on sound material all round. Wrong looks like an oversized hole with a box floating in it, propped by the cover plate. Stop rule: an oversize opening takes a listed repair bracket or the box relocates, never packed with compound. Hazard clause: torn metal lath is a cutting edge at hand height bonded to nothing predictable, so it is cut and folded back, not grabbed.
Design the fish path between two accessible points and prove it with a tape before pulling cable. NEC 334.30 permits nonmetallic-sheathed cable fished through a concealed space of a finished building to run unsupported where support is impracticable, and that permission is bounded by the words "between access points," so both ends of every concealed run must land at a box or an accessible opening. Acceptance: a fish tape passed end to end in one continuous pull, path length measured off the tape. Wrong looks like a tape that stops 4 ft short at a top plate or a fire block. Stop rule: a blocked path is re-routed or a new accessible opening created, never solved with a splice buried in the cavity, since NEC 314.29 requires every box to stay accessible without removing part of the building. Hazard clause: a steel fish tape pushed into an unproved cavity can bridge a conductor you did not isolate, so the step 2 isolation stands until the pull is complete.
Pull the cable, dress it into the box, and restore anything you opened to make the path. Feed rather than drag, keep the sheath off lath and metal edges, and where you bored a top plate or a fire block, seal the annular space with an approved fireblocking material, since NEC 300.21 requires that penetrations not substantially increase the spread of fire or products of combustion. Acceptance: sheath intact end to end; at least 1/4 in of sheath inside the box per NEC 314.17; at least 6 in of free conductor from where it leaves the sheath with at least 3 in outside the opening, per NEC 300.14; every bored fire block resealed. Wrong looks like a cable pulled hard enough to shine the jacket. Stop rule: a nicked or crushed sheath is pulled back out and replaced, not taped. Hazard clause: reaching into a cavity for a cable end meets staples, glass wool and lath edges, so it goes in with cut-resistant gloves and a light.
Set the box, land the conductors, re-energize, and verify the protection you disturbed still works. Remove the lock and tag, close the panel, and stand to the hinge side rather than square in front when the breaker goes back in. Acceptance: correct voltage and polarity at the new device; every ground-fault and arc-fault device on that circuit tripped and reset on its own button; every device downstream confirmed live. Wrong looks like a new receptacle that works while the ground-fault device ahead of it no longer trips on its button. Stop rule: a protective device that will not trip on test is replaced before the crew leaves, never left in service because the outlet works. Hazard clause: re-energizing is when a fish tape scar or a pinched conductor announces itself, so the area is clear and nobody is on a conductor when the breaker closes.
The record this produces
One old-work sheet per job: the wall construction and finished thickness at each location; the isolation record naming the breakers locked out and the live-dead-live confirmation; the borescope result per opening, including any relocation and its new dimension; the box type and marked volume against the fill computed; the fish path length and its two access points; every fire block or top plate bored and the fireblocking material used to reseal it; and the re-energization results, being voltage, polarity and the trip-and-reset result for each protective device.
The office reads the relocation lines, because a device that moved from where the customer asked for it is a conversation that goes better with a dimension and a reason attached.
Worked pass: two added receptacles, 1952 plaster-over-metal-lath living room
Step 1: plaster over metal lath over wood studs, finished thickness 7/8 in at both locations; pre-1978, so containment and a certified renovator are in place. Step 2: the room's receptacles trace to breaker 8, isolated, locked and tagged, with the meter proving live on a known source, reading zero at both existing openings, and proving live again after. A switch loop in the same bay traces to breaker 14, so breaker 14 is isolated as well.
Step 3: location A scans clear and the borescope shows an open bay. Location B pilots clear but the borescope shows a 1/2 in copper supply riser 1-1/2 in behind the lath, centred in the intended footprint. Stop rule taken. Location B moves 14 in right into the next bay, re-scanned and re-scoped clear, and the new dimension is written on the sheet.
Step 4: metal old-work brackets with 18.0 cubic inch boxes. Each box takes one 14/2 cable and one device: two current-carrying 14 AWG conductors at 2.00 cubic inches each is 4.00, all grounds count as one 14 AWG allowance at 2.00, and the device yoke counts as two at 4.00, for 10.00 required against 18.0 available.
Step 5: both openings scored through the template, lath cut with an oscillating tool, and both boxes seat with the flange bearing all round.
Step 6 fails at location A. The planned path runs from the attic down the bay, measured at 14 ft. The fish tape stops at 9 ft 6 in; 14 minus 9.5 leaves 4.5 ft of path unaccounted for, and the borescope shows a horizontal fire block at the mid-height of the bay. Stop rule taken, so no cavity splice. The run is re-routed through the adjacent bay, which the tape passes end to end at 17 ft. Location B fishes clean at 11 ft.
Step 7: two top plate bores, 3/4 in, both resealed with an approved fireblocking sealant. Sheath intact on both runs, 1/4 in inside each box, and 7 in of free conductor measured at each with 4 in outside the opening, clearing the 6 in and 3 in minimums.
Step 8: locks removed, panel closed from the hinge side. Both new receptacles read correct voltage and correct polarity. The upstream ground-fault device on breaker 8 trips on its button and resets, and the two existing receptacles downstream are confirmed live before the crew leaves.
References
- NFPA 70, National Electrical Code, in the edition your authority having jurisdiction has adopted: 300.14 free conductor, 300.21 spread of fire, 314.17 sheath entry, 314.23(C) support in finished surfaces, 314.27(C) fan boxes, 314.29 accessibility, 334.30 fished cable.
- 40 CFR 745 Subpart E, EPA renovation, repair and painting rule, for pre-1978 target housing.
- 29 CFR 1926.1153 respirable crystalline silica for construction work; 29 CFR 1910.333(b)(2) electrical work practices, with proving per NFPA 70E-2021, 120.5.
- See related: rough-in inspection readiness (box fill and support self-check); remodel rough-in standard (scope boundary and circuit disposition).