Tenant Space Circuit Additions

Purpose

Add branch circuits inside a leased space without leaving the building worse than you found it. The tenant hired you, but the panel, the demising wall and the ceiling plenum belong to the landlord, and each is something you can quietly damage while doing perfectly good electrical work.

The damage is repeatable. A penetration through a rated wall closed with the wrong sealant is a hole in a fire barrier nobody looks at again until there is a fire. Cable pulled through a return-air ceiling without a plenum rating is a smoke source in the path air takes to the rest of the building. And a circuit added without updating the directory leaves the next person a schedule that lies to them.

Scope

Covers adding branch circuits and receptacle, lighting or dedicated equipment outlets inside a leased commercial space fed from an existing panel: small offices, retail suites, salons, professional practices.

Does not cover deciding whether the service or panel has capacity, which the Small Business Panel and Load Assessment SOP owns and this SOP consumes the answer from; installing a new subpanel or feeder, which the Subpanel Installation and Feeder Sizing SOP owns; or commercial kitchen equipment circuits, which the Kitchen Equipment Circuit Service SOP owns.

Roles and handoffs

Procedure

1. Get written landlord permission naming the panel before anything is priced. Acceptance: an email or letter from the owner or manager identifying the panel by location and authorizing work in it, plus written confirmation of which walls in the route are fire-rated. Wrong looks like a tenant saying the landlord is fine with it, which is not a document and does not survive a dispute. Stop rule: no written authorization means no work in that panel, whatever the tenant says. Hazard: none at this step, it is a document check made at a desk.

2. Confirm the panel can take the added load, using measured demand rather than a count of empty spaces. Take the existing calculated load from the Small Business Panel and Load Assessment SOP, which owns the NEC 220.87 measured-demand method, then add the new load computed per NEC Article 220. Acceptance: total calculated load in volt-amperes recorded against the panel and service rating, with the headroom stated. Wrong looks like a capacity decision made by counting empty spaces, which measures the enclosure and not the conductors feeding it. Stop rule: a total at or above the rating stops the addition and routes it back as a service question. Hazard: any reading inside an energized panel is qualified-person work under 29 CFR 1910.332 and 1910.399, in arc-rated clothing per your employer's program.

3. Check the working space in front of the panel before you commit to using it. Confirm the depth, width and headroom required by NEC 110.26 in the edition your jurisdiction has adopted, and confirm the tenant's stock is not in it. Acceptance: clearances measured and recorded, and the space clear at the time of work. Wrong looks like a panel behind shelving the tenant installed after occupancy, which is both a violation and the reason your own work gets done badly. Stop rule: a clearance that cannot be established is raised with the landlord before the circuit is added, since adding circuits to a panel nobody can reach makes the defect worse. Hazard: none at this step, it is a measurement taken with the cover closed.

4. Isolate the panel, lock it, and prove dead where you will be working. Open the feeding overcurrent device, 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. Acceptance: zero volts bus to bus and bus to ground at the point of connection, meter proved both sides. Wrong looks like opening only the branch breaker you plan to use, which leaves the bus live and your hands in it. Stop rule: a bus still live with the feeding device open means a second supply you have not identified; stop and trace. Hazard: an energized bus in a panel whose main is remote is the classic tenant-space surprise, and the before-and-after proof is what stops a meter with a blown fuse reading a clean, believable zero.

5. Route the circuit to the ceiling's actual classification, not its appearance. Determine whether the cavity is used as a return-air plenum and select wiring methods per NEC 300.22(C) in the adopted edition. Acceptance: the method confirmed acceptable for that space with the classification written down, and every support at or under the spacing the method requires. Wrong looks like non-plenum cable pulled through a return plenum because the ceiling looked ordinary, a rip-out when the inspector asks. Stop rule: a cavity whose classification the landlord will not confirm is treated as a plenum. Hazard: unidentified ceiling texture, tile or loose insulation is not cut, drilled or scraped until the owner has it identified, because disturbing it is an inhalation route; conductors already above the ceiling are not on the circuit you locked and are treated as live.

6. Close every penetration of a rated assembly with a listed system that matches the actual conditions. Record the assembly's rating, the penetrant type and size, and the annular space, then install a through-penetration firestop system listed for that exact combination, per its own sheet. Acceptance: the system number recorded per penetration, the measured annular space inside its stated range, and a photograph before the wall closes. Wrong looks like a tube of general-purpose sealant used because it was red. Stop rule: no listed system covering the measured conditions means the penetration stays open until one is obtained; annular space is never adjusted by eye to make a system fit. Hazard: coring or drilling masonry or concrete releases respirable crystalline silica, so use water or on-tool dust collection with the controls at 29 CFR 1926.1153 for construction work or 1910.1053 for general industry, and any respirator is under a written program per 29 CFR 1910.134.

7. Terminate to the torque the equipment states, and give the circuit the protection the adopted code requires. Size conductors and the overcurrent device per NEC Article 210, apply the ground-fault and arc-fault protection the adopted edition requires here, and tighten every termination with a calibrated torque tool to the value marked on the equipment or in its instructions, per NEC 110.14(D). Acceptance: each termination torqued to its marked value, that value and the protection type recorded per circuit. Wrong looks like terminations set by feel, the most common origin of a loose connection that shows up on a thermal scan two years later. Stop rule: no marked value and no manufacturer instruction means the manufacturer is called before the cover goes on. Hazard: the panel stays locked and proved dead through this step; the lock does not come off while landing conductors.

8. Restore power, prove the new protection works, and make the directory true again. Remove the lock and close the feeder from the hinge side rather than square in front of the door, load the new circuits, confirm each holds, and operate the test button on every ground-fault or arc-fault device. Then update the directory per NEC 408.4(A) in the adopted edition, specific enough to identify each load. Acceptance: every new breaker holding under load, every protective device tripping and resetting on its button, and a directory entry naming what each circuit serves. Wrong looks like a directory reading "office," which is every circuit in the panel. Stop rule: a device that will not trip on its button is replaced before handover, not noted. Hazard: energizing is when a conductor pinched behind a device announces itself, so approach the door from the side, keep the tenant out of the working space, and nobody stands in front of an open panel while load is applied.

The record this produces

Per job: the landlord authorization; the step 2 calculation showing existing load, added load and headroom in volt-amperes; the clearance measurements; the ceiling cavity classification and wiring method; a line per rated penetration giving assembly rating, penetrant, annular space, listed system number and photograph; the torque value per termination; the protection type and test result per circuit; and the updated directory photographed in place.

The landlord gets the penetration lines and the directory photograph, the two things that outlive the tenancy. The office keeps the load calculation, because the next request from that suite starts from this number rather than a fresh survey.

Worked pass: three circuits added to a 100 A suite panel, professional office

Step 1: the manager's email names the suite panel and confirms the corridor wall is a rated assembly and the demising wall to the neighbouring suite is not.

Step 2: the measured-demand result carried in from the assessment SOP is a 48 A maximum demand over 30 days, so the existing calculated load is 48 times 1.25, which is 60 A, or 14,400 VA at 240 V. The addition is 9 general-use receptacle outlets at 180 VA each per NEC 220.14(I), which is 1,620 VA, plus a copier at its 1,440 VA nameplate, so 3,060 VA added. Total is 14,400 plus 3,060, or 17,460 VA, against a capacity of 100 A at 240 V, or 24,000 VA. That leaves 6,540 VA of headroom, 27.25 A equivalent, and puts the panel at 72.75 percent of rating. The addition passes.

Step 3: 3 ft of clear depth, 30 in of width and 6 ft 6 in of headroom confirmed, a filing cabinet moved out before work begins.

Step 4: the suite's feeder disconnect is in the landlord's electrical room. Opened, locked and tagged, and the bus proves dead on a known live source before and after, zero volts bus to bus and bus to ground.

Step 5: the manager confirms the ceiling cavity is a return-air plenum, so the wiring method is selected for that condition and supports set at its spacing.

Step 6 fails. The corridor penetration is 2 in EMT through a 1-hour rated gypsum assembly and the measured annular space is 1/4 in, while the system on the truck reads, on its own listing sheet, a maximum annular space of 1/8 in for that penetrant in that assembly. Step 6's stop rule fires: the space is not packed by eye to make the system fit and the wall is not closed. A system listed for a 1/4 in annular space in that assembly with 2 in steel conduit is obtained the next morning, installed to its sheet, photographed and recorded by number. The other two penetrations are in the non-rated demising wall.

Step 7: conductors and devices sized per Article 210, protection as the adopted edition requires here, each termination torqued with a calibrated tool to the value marked inside the panel and recorded.

Step 8: feeder closed from the hinge side, all three breakers hold with the copier and workstations loaded, every protective device trips and resets on its button, and the directory is rewritten to name the copier, the north workstations and the south workstations rather than "office."

References

• NEC Article 210 for branch circuit sizing and protection, 220.14(I) for the general-use outlet load, 110.26 for working space, 300.22(C) for wiring in air-handling ceilings, 110.14(D) for termination torque and 408.4(A) for the directory, in the edition your jurisdiction has adopted
• 29 CFR 1910.333(b)(2) with 1910.332 and 1910.399, and NFPA 70E-2021, 120.5, for the isolation and live-dead-live sequence at step 4
• 29 CFR 1926.1153 for respirable crystalline silica on construction work and 1910.1053 for general industry, with 1910.134 for any respirator, covering the coring at step 6
• The firestop system's own listing sheet, which governs assembly rating, penetrant type and annular space
• See related: Small Business Panel and Load Assessment SOP, Subpanel Installation and Feeder Sizing SOP, Working Clearance Verification Before Equipment Is Set SOP