Data Center Cabling: Earned Value, Change Order, and Dirty Endfaces
A contractor is cabling a 6,000-strand data-center campus on a 26-week, $3.4 million contract. At the end of week 14, the control account shows PV $1.90 million, EV $1.62 million, and AC $1.85 million. A fire-rated penetration change adds 480 firestop sleeves and requires third-party re-inspection; the contractor estimates $140,000 and three weeks. The customer refuses a time extension because the commissioning date is fixed and asks for acceleration. The contractor has 40 technicians and six splicers; overtime carries a 15% premium. OTDR testing is the bottleneck: one tester and two test crews. Separately, 8% of tested links fail, and rework shows contaminated endfaces.
1. Calculate CPI, SPI, EAC using CPI, and TCPI. What does the result say about the project?
Read the worked answer
- CPI = EV / AC = 1.62 / 1.85 = 0.876
- SPI = EV / PV = 1.62 / 1.90 = 0.853
- EAC = BAC / CPI = 3.4 / 0.876 = $3.88 million
- TCPI = (BAC − EV) / (BAC − AC) = (3.4 − 1.62) / (3.4 − 1.85) = 1.78 / 1.55 = 1.148
The project is about 12.4% over cost and 14.7% behind schedule. To finish at the original budget, the remaining work must be performed at roughly 115% of the planned cost efficiency, which is unlikely without a change in method or scope. The EAC points to a $480,000 overrun before the firestop change order is added. That change would raise BAC to $3.54 million and worsen the forecast. The numbers should trigger a recovery plan and a formal change-order discussion, not silent overtime.
2. Evaluate the change order and acceleration options; recommend a course of action that respects the fixed date.
Read the worked answer
The firestop change is legitimate added scope: 480 sleeves and third-party re-inspection. Submit a written change order for $140,000 and three weeks, and state the schedule impact separately. The customer's fixed commissioning date does not transfer the risk of added scope to the contractor for free.
Acceleration options:
- Add a second OTDR tester and a third test crew. Testing is the stated bottleneck, so this buys more schedule than adding general technicians.
- Use overtime only on splicing and testing, where the 15% premium buys direct critical-path progress.
- Pre-terminate harnesses and pre-test cables off the critical path.
- Re-sequence so firestop inspection happens zone by zone, not as one final inspection.
Recommendation: propose a shared acceleration package with a written direction. The contractor absorbs none of the change-order cost; the customer pays the change and a defined acceleration premium, or accepts a later commissioning date. Do not promise the fixed date until the second tester is on site and the inspection sequence is agreed.
3. Analyze the 8% link failures and recommend corrective action, including the cost and schedule implication.
Read the worked answer
An 8% failure rate with contamination on the endfaces points to a process problem, not random defects. Likely causes are missing inspection, dirty adapters or test leads, caps left off, or cleaning with the wrong consumable.
Corrective action:
- Inspect every connector with a scope before mating and after cleaning; use the IEC 61300-3-35 acceptance criteria.
- Clean with lint-free wipes and the correct cleaner, and clean test leads and adapters as well as the link under test.
- Quarantine suspect test equipment and re-reference the OTDR.
- Add a second tester so rework does not consume the only test capacity.
Cost and schedule: 8% of tested links must be reworked, and each rework consumes test time on the bottleneck resource. Even if the material cost is small, the schedule cost is large because it displaces first-pass testing. Track first-pass yield daily; if it does not improve within one week, stop production and retrain the termination crews.