10.2 Small Commercial Tenant Improvement Integrated Lab

Lab scenario

A 3,600 square foot tenant space in a one-story strip center is being converted from a vacant retail shell into a dental billing office with a reception area, open workstations, two private offices, a break room, an IT closet, a small conference room, and a copy area. The existing panel is 120/208 volt, 3 phase, 4 wire, supplied from a house distribution switchboard. The panel has open breaker spaces, but the as-built panel schedule is unreliable. New work includes LED lighting, receptacles for workstations, a microwave, refrigerator, coffee maker, copier, water cooler, dedicated IT rack receptacles, low-voltage cabling pathways, and two small HVAC units fed from the roof.

The master-level task is to decide whether the proposed design can use the existing panel and feeder, what branch circuits are required, which wiring methods suit the building, and what coordination items must be resolved before rough inspection. Do not confuse an office tenant improvement with a dwelling unit. The load calculation rules, receptacle assumptions, demand factors, and GFCI or AFCI triggers are not the same as a house. Also do not treat a vacant shell as proof that capacity exists.

Capacity is shown by calculation, measured load where permitted and properly documented, equipment ratings, and feeder/service limitations.

Capacity and load sequence

Begin by inventorying the existing electrical system. Record panel voltage, phase, ampere rating, feeder conductor size if accessible, overcurrent protection, interrupting rating, available fault current marking if present, and grounding and bonding arrangement. Verify whether the panel is tenant-only or contains shared building loads. A spare two-pole breaker position does not answer the load question. The feeder might already be near capacity, the neutral might be heavily loaded by line-to-neutral loads, or the distribution equipment might lack series rating documentation for a proposed breaker.

Next build a load schedule. Lighting is generally continuous because it can operate for three hours or more in a commercial occupancy. Many receptacle loads are noncontinuous unless stated otherwise, but exam questions may specify continuous display lighting, sign circuits, IT equipment, or other loads that change conductor and overcurrent sizing. Mechanical equipment must be read from nameplate or problem facts. If roof units list minimum circuit ampacity and maximum overcurrent protection, those are equipment branch-circuit values.

Do not replace them with a generic motor table unless the question asks for motor calculation from horsepower and full-load current.

For general-use receptacles, identify whether the code rule uses a unit load per receptacle or outlet, whether demand is allowed, and whether the occupancy has special rules. Then add dedicated appliances and office equipment as stated. For a copier or IT rack, a field supervisor should ask for actual nameplate data and owner requirements, but on the exam use the facts given. If the question says the IT rack is continuous, treat it that way. If it only says dedicated, do not assume continuous without a stated basis.

Branch circuits and wiring methods

Lay out branch circuits by function and risk. Lighting circuits should not be overloaded by convenience receptacles simply because it is easier to pull cable. Workstation receptacles may need more circuits than a minimum calculation suggests because nuisance trips create business interruption. Break room appliances often deserve dedicated circuits even when a minimum answer could combine some loads. The master exam, however, usually asks for the minimum code result. Separate the exam answer from a better design recommendation.

Commercial wiring method choices depend on construction type, ceiling spaces, physical protection, environmental exposure, and local amendments. In a strip center, common methods include EMT, MC cable where allowed, flexible raceway to equipment, and listed cable assemblies in permitted locations. Above a suspended ceiling used for environmental air, wiring methods and cable ratings require careful checking. Low-voltage cabling cannot be left unsupported on ceiling grid. Fire-resistance-rated walls, draftstopping, and penetrations require coordination so electrical work does not damage the building code strategy.

Code-navigation plan

Start with occupancy and scope, then move to load calculations, branch circuits, wiring methods, boxes and conduit fill, conductor ampacity and adjustment, grounding and bonding, equipment installation, and special systems. Use the NEC index for office, receptacles, lighting load, continuous load, conductor adjustment, metal raceways, cable assemblies, panelboards, and HVAC equipment. If the exam question includes International Building Code or International Fire Code context, use it only for the specific building, fire-resistance, egress, or fire alarm issue being asked. Do not let building code context replace the NEC installation rule.

A reliable scratch-paper method is to draw three columns: code issue, source facts, and decision. For example, lighting load: LED lighting schedule, continuous treatment, branch-circuit ampacity. Workstation receptacles: count or VA rule, demand if allowed, circuit quantity. HVAC units: nameplate MCA and MOCP, disconnecting means, working space. IT closet: dedicated receptacles, grounding path, ventilation coordination, panel schedule accuracy. This prevents the common trap of answering only the first code issue you recognize.

Supervisory corrections

Before rough-in, require an accurate panel schedule, circuit directory, load summary, equipment submittals, and routing plan. Ask the mechanical contractor for exact unit data and disconnect locations. Ask the fire alarm contractor whether notification appliances, smoke control interfaces, or power supplies are in scope. Confirm that receptacles in break rooms, near sinks, outdoors, rooftops, or other GFCI-triggering locations are identified. Confirm working clearances in the IT closet and mechanical areas before equipment racks and shelving are installed.

Inspection failure often comes from coordination, not math. Examples include raceways blocking access panels, unsupported cables above ceilings, missing bonding bushings where required, improper box fill after device changes, panel directories that say spare for energized circuits, and roof disconnects mounted where they cannot be safely serviced. The master electrician is responsible for setting a review process that catches these items. In an exam lab, choose the answer that preserves code compliance and inspection readiness, even when a shortcut appears cheaper.

Structured Decision Aid

• Start with occupancy, tenant load list, panel capacity, available fault current, and existing raceway conditions.
• Identify continuous loads, HVAC/nameplate loads, lighting, receptacle, signage, and special-equipment circuits.
• Check working space, panel labeling, raceway fill, box fill, and fire/life-safety interfaces before approval.
• Escalate utility, service, or fault-current issues before issuing a field change.