24-Unit MDU Retrofit With Limited Access and One Splitter Port
A 24-unit, three-story apartment building is being retrofitted with fiber to each unit. Each floor has 8 units and a telecom closet at the elevator lobby; each unit has a 20 mm conduit from the closet that currently carries one Cat5e. The owner will allow a new 25 mm riser conduit from the basement telecom room to each floor closet, but no corridor ceiling access except at the lobby. The ISP provides one 1x32 splitter port in the basement. Six tenants run home-based businesses and require 1 Gb/s symmetrical service. The project window is 10 working days, with unit access only 09:00-16:00. The installer must deliver a design, a testing plan, and a schedule that minimizes tenant disruption. The building has one existing ground at the service entrance.
1. Choose the splitter architecture and fiber count. Justify the choice with a loss estimate and a fill check.
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Use the ISP’s 1x32 splitter in the basement and home-run each unit. At each floor closet, splice a 24-fiber riser cable to individual 2.0 mm drop cables and pull one drop through each unit’s existing 20 mm conduit alongside the Cat5e. The 20 mm conduit has about 343 mm² of area; the Cat5e occupies about 24.6 mm² and the 2.0 mm drop about 3.14 mm², so total fill is roughly 28 mm², or 8% - well within limits. The 25 mm riser conduit has about 490 mm²; a 24-fiber cable at roughly 12–14 mm OD occupies about 113–154 mm², or 23–31%, which is acceptable.
Loss estimate: 1x32 splitter about 17.0 dB, two connectors about 0.6 dB, splices about 0.3 dB, and fiber about 0.2 dB, for roughly 18.1 dB. That is comfortably inside a 28 dB Class B+ budget. A cascaded 1x4 plus 1x8 per floor would be about 17.7 dB, slightly worse and more complex, with no offsetting benefit because the ISP port is already a 1x32. Provide spare fibers in the riser (for example, 36 fibers rather than 24) for future use and breakage.
2. Build a 10-working-day schedule that respects the 09:00–16:00 unit access window and minimizes tenant disruption.
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Day 1: site survey, verify conduit paths and firestopping, confirm tenant contact list, post 48-hour notices, and stage materials in the basement. Days 2–3: install the 25 mm riser conduit and pull the multi-fiber riser cable to each floor closet; install the basement splitter and splice tray. Days 4–6: floor 3, eight units, roughly three units per day with a two-person crew; splice at the closet and pull each drop through the existing unit conduit. Days 7–8: floor 2. Day 9: floor 1. Day 10: testing, labeling, as-builts, punch list, and tenant confirmation.
Use two crews: one on riser and closet splicing, one on unit drops. Keep each unit visit short and predictable; call ahead and work only 09:00–16:00. Do not open ceilings outside the lobby. Where a unit conduit is blocked, stop and document it rather than cutting the Cat5e. Sequence floors from top to bottom so the riser work is complete before drops are pulled, and leave the building clean at the end of each day.
3. Define the acceptance test plan and the documentation package for the owner and ISP.
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Test every drop, not a sample, because the six business tenants require 1 Gb/s symmetrical service and a later failure would be disruptive. For each unit: inspect and clean both endfaces; measure insertion loss at 1310 and 1490 nm with a light source and power meter or a PON-aware tester; verify receive power at the ONT; confirm 1 Gb/s symmetrical throughput at the business units; and check that the ONT registers and remains stable. Use an OTDR on the riser and selected drops to confirm splice and bend quality, recognizing that the splitter limits visibility beyond its port.
Documentation: labeled splitter ports and unit drops, fiber assignments, test records with date and technician, OTDR traces where taken, as-built drawings showing the riser, closets, and unit routes, firestopping records, and a punch list. Provide the owner with a warranty and escalation contact. Acceptance should be signed by the owner’s representative and the ISP, with any blocked conduits or non-compliant unit routes listed as exceptions rather than hidden.