Bathroom Remodel Electrical Scope

Purpose

Set the bathroom's electrical scope from two things the fixture layout decides and nothing else does: where the wet zones fall, and how much air has to leave the room. Every other item on the sheet, the circuit, the receptacles, the luminaires, the heated floor, follows from those two.

The failure this prevents is the luminaire or fan installed inside the tub and shower zone without a location marking that permits it, which an inspector finds in ten seconds and which cannot be corrected without opening a finished, tiled ceiling. The quieter one is a fan that meets its rating on the box and moves half that at the grille, leaving a customer with a mirror that fogs and a ceiling that grows mould two winters later.

Scope

Covers producing and installing the electrical scope for a residential or small commercial bathroom remodel: wet-zone mapping, ventilation sizing and fan circuit, the bathroom branch circuit, receptacle and luminaire placement, and the added loads a modern bath carries such as heated floor, towel warmer and hydromassage tub.

Does not cover a like-for-like exhaust fan swap, owned by the bathroom exhaust fan replacement SOP; the decision to upgrade existing bath circuits on a partial remodel, owned by the kitchen and bath circuit upgrade SOP; or duct routing and roof or wall termination detailing, which belongs to the mechanical scope even when your crew installs the fan.

Roles and handoffs

Procedure

1. Draw the tub and shower zone on the fixture layout before any device or luminaire is placed. NEC 410.10(D) governs luminaires in the zone measured 3 ft horizontally and 8 ft vertically from the top of the bathtub rim or shower stall threshold, requiring equipment there to carry a location marking suitable for the exposure, and NEC 404.4 governs switches in damp and wet locations. Acceptance: the zone drawn to scale with those two dimensions on it, and every proposed luminaire, fan and switch shown inside or outside it. Wrong looks like a zone assumed rather than measured, particularly where a freestanding tub sits away from the wall and drags the zone into the middle of the ceiling. Stop rule: equipment landing inside the zone carries the marking the article requires or it is relocated on the drawing, not argued at inspection. Hazard clause: none here, measurement off a layout.

2. Size the ventilation from the room, pick the fan against the duct route, and treat the published rating as a starting point rather than an answer. Residential local exhaust rates are set by the mechanical code and ventilation standard your jurisdiction has adopted, commonly 50 cubic feet per minute intermittent or 20 continuous for a bathroom. A fan is rated at a stated static pressure, and long flexible duct with elbows will not deliver that rating. Acceptance: required rate written with the code or standard and edition it came from, fan model and rated flow, and the duct length, material and elbow count the selection assumed. Wrong looks like a fan chosen on the carton number with no duct route decided. Stop rule: if the duct route changes after selection, the fan is re-checked before installation. Hazard clause: none here, selection at a desk.

3. Schedule the bathroom branch circuit and write down what may share it. NEC 210.11(C)(3) requires at least one 20 A branch circuit to supply the bathroom receptacle outlets, and the article limits what else that circuit may serve depending on whether it feeds one bathroom or several. Acceptance: the circuit scheduled at 20 A with every outlet assigned to it, and the sharing rule from the adopted edition written on the sheet next to it. Wrong looks like a bath receptacle circuit picking up a hallway light because the wall was convenient. Stop rule: a load the article does not permit on that circuit comes off and gets its own. Hazard clause: none at this step, schedule work.

4. Place receptacles off the basin, and keep them out of the countertop face. NEC 210.52(D) requires a receptacle outlet installed within 3 ft of the outside edge of each basin, located as the article permits relative to the basin and the countertop, and NEC 210.8(A) requires ground-fault protection for the bathroom receptacles. Acceptance: the 3 ft dimension measured and written for each basin, every bath receptacle assigned ground-fault protection, none shown face-up in a countertop. Wrong looks like one receptacle serving a double vanity from a point more than 3 ft from the second basin. Stop rule: a basin not reached within 3 ft takes an added receptacle on the drawing before rough-in. Hazard clause: none here, measurement off a layout.

5. Select luminaires, the fan and the switches for the location each actually occupies. Anything inside the zone drawn at step 1, and anything over a tub or in a shower, carries the damp or wet location marking the adopted edition requires, and is installed only where its instructions permit. Acceptance: a schedule line per fitting naming its location marking and whether it sits inside or outside the zone. Wrong looks like a general-purpose recessed can over a shower because the trim was rated and the housing was not. Stop rule: a fitting whose marking does not cover its location is exchanged and the substitute re-checked against the same drawing. Hazard clause: none here, selection from the step 1 drawing.

6. Give the added loads their own circuits and their required disconnecting and protection arrangements. Heated floor mats, towel warmers and hydromassage tubs each carry a nameplate and installation instructions that govern. A hydromassage bathtub's electrical equipment is supplied through ground-fault protection under NEC 680.71 and must stay accessible without damaging the building structure under NEC 680.73, which makes the access panel a framing decision rather than a finish decision. Acceptance: a circuit line per added load with its nameplate figure, plus the access panel dimensioned on the plan for any tub motor. Wrong looks like a tub motor tiled in. Stop rule: an access panel the tile layout cannot accommodate is resolved with the general contractor before the tub is set. Hazard clause: none here, layout and schedule work.

7. Rough the room, cutting and demolishing with the controls the existing materials demand. Acceptance: every box, fan housing and mat lead placed to the drawing, the housing set to the finished ceiling thickness, and the duct connection made before the ceiling closes. Wrong looks like a housing set for 1/2 in board in a ceiling getting 5/8 in and a skim coat. Stop rule: a duct joint unreachable once the ceiling closes gets made and taped now. Hazard clause: demolishing tile, mortar bed, plaster or backer board liberates respirable crystalline silica, so cut and grind with a shrouded tool on HEPA collection per 29 CFR 1926.1153 for construction work; sheet flooring and adhesive in a pre-1981 building is presumed asbestos-containing under 29 CFR 1926.1101 until sampled, and is not sanded, ground or dry-swept.

8. Energize at trim, verify every protective function, and measure the airflow the fan actually delivers. Isolate, lock and tag under 29 CFR 1910.333(b)(2) and prove dead on a known live source before and after per NFPA 70E-2021, 120.5 before landing conductors. Acceptance: correct voltage and polarity at every receptacle; each ground-fault device tripped and reset on its own test button, including any protecting a hydromassage tub; heated floor mat resistance read against the manufacturer's stated value both before and after tile; and airflow measured at the grille with a flow hood or vane anemometer, meeting or exceeding the rate written at step 2. Wrong looks like a fan that runs, sounds right, and moves well under its rating. Stop rule: a measured airflow below the required rate is a duct or fan correction while the ceiling is still accessible, not a note on the invoice. Hazard clause: the first energization puts live circuits in a room whose floor, tub and basin will shortly hold water, so the room is dry, nobody is in the tub, and the crew stands to the hinge side of the panel when the breaker closes.

The record this produces

One bathroom scope sheet per job: the zone drawing with both dimensions; the required ventilation rate with the code or standard and edition it came from; the fan model, rated flow, and the duct length, material and elbow count assumed; the branch circuit and its sharing rule; the 3 ft basin dimensions; a location-marking schedule per fitting; the added-load circuits with any tub access panel dimensioned; and the trim results, being voltage, polarity, each protective device tested, heated-floor resistance before and after tile, and the measured airflow.

The technician reads the zone drawing before hanging anything, and the office reads the fan line whenever the mechanical trade changes a duct route. The measured airflow is what answers a fogging complaint two years later without anybody guessing.

Worked pass: 1978 hall bath, tub converted to a walk-in shower

Step 1: the shower threshold sits 26 in from the near ceiling can, so that can falls inside the 3 ft horizontal by 8 ft vertical zone. It is drawn on the layout with both dimensions written. Step 2: local exhaust requirement confirmed at 50 cubic feet per minute intermittent from the adopted mechanical code, and a fan rated above that is selected against a planned 12 ft rigid duct with one elbow.

Step 3: one 20 A bathroom branch circuit scheduled, with the sharing rule from the adopted edition written beside it. Step 4: single basin, receptacle placed 22 in from the basin edge, inside the 3 ft limit, and assigned ground-fault protection.

Step 5: the can inside the zone is exchanged for a housing and trim assembly whose combined listing covers a shower location, and the exchange is noted against the same zone drawing. Step 6: a heated floor mat on its own circuit at its nameplate rating; no hydromassage tub in this scope.

Step 7: tile and mortar bed removed with a shrouded grinder on HEPA collection, and the vinyl sheet floor beneath, being pre-1981, is left intact and covered rather than sanded, with a note to the general contractor.

Step 8 fails on airflow. The general contractor's framer re-routed the duct to 22 ft of flexible duct with two elbows without telling anyone. Measured at the grille with a flow hood, the fan delivers 41 cubic feet per minute against the 50 required, short by 9. Stop rule taken while the ceiling is still open: the run is rebuilt in 6 in smooth-wall rigid duct with one elbow at 14 ft, and re-measured at 58 cubic feet per minute, clearing the requirement by 8. The rest of step 8 passes: correct voltage and polarity at the receptacle, the ground-fault device trips and resets on its button, and the heated floor mat reads within the manufacturer's stated range both before and after tile.

References

• NFPA 70, National Electrical Code, in the edition your authority having jurisdiction has adopted: 210.8 ground-fault protection, 210.11(C)(3) bathroom branch circuit, 210.52(D) basin receptacle, 404.4 switches in damp and wet locations, 410.10(D) luminaires in the tub and shower zone, 680.71 and 680.73 hydromassage bathtubs.
• The mechanical code and residential ventilation standard your jurisdiction has adopted, in the adopted edition, for the local exhaust rate and the duct sizing that has to deliver it.
• 29 CFR 1926.1153 (silica) and 29 CFR 1926.1101 (asbestos) for construction work; 29 CFR 1910.333(b)(2) electrical work practices, with proving per NFPA 70E-2021, 120.5.
• See related: bathroom exhaust fan replacement; kitchen and bath circuit upgrade on a remodel; expanded ground-fault requirement check before a quote.