A cabling contractor offers to certify 10% of links instead of 100%. The saving is real and the reasoning sounds plausible: if the workmanship is consistent, a sample proves the batch.
The problem is that cabling failures are rarely systemic. They are individual: one termination with a nicked conductor, one bend radius crushed under a tray, one connector with contamination on the end-face. A 10% sample does not detect these. It detects only the failure mode you did not have.
What a sample actually tells you
Sampled testing answers a narrower question than people assume. It tells you the installer's average workmanship was acceptable on the links they happened to pick. It does not tell you which links pass, which is the question your operations team asks when something fails at 02:00.
With full certification you get a per-link result. When a link misbehaves you can look up whether it was tested, when, and at what margin. With a sample you get a statistical statement and a guess.
The native export matters
Ask for the certifier's native file export, not only a PDF summary. Native exports carry the tester, serial, calibration date and per-parameter results, which is what makes them defensible in a warranty or dispute conversation. A PDF can be regenerated from anything.
Two related habits are worth insisting on:
- Calibration evidence. A certifier out of calibration produces confident nonsense. Ask for the calibration certificate covering the test period.
- Failures stay visible. The contractor who hands you 100% pass results with no re-terminations recorded has either done flawless work or has quietly replaced the failures. Both re-test evidence and the original failure belong in the pack.
What full certification costs
Roughly, certification adds between five and ten percent to a cabling labour cost depending on link count, fibre type and how much rework the first pass uncovers. On a 14,000-link refresh, that is a rounding error against the cost of one unplanned outage traced to an uncertified link.
The decision is not really about test coverage. It is about whether, at handover, you receive a document that describes your cabling — or a document that describes a sample of it.
Need this applied to your site?
Our engineers run these checks as standard on every delivery. Send us the scope and we will tell you what we would look at first.