Acceptable dB loss for fiber depends on the component you're measuring: a single mated connector pair should lose no more than 0. 75 dB, a fusion splice should stay under 0. The total. When testing fiber optic cabling, determining acceptable loss is crucial. This depends on various factors, including who is conducting the test and the phase of the project. While some loss is expected, excessive or unexpected loss can lead to poor performance, network downtime, and signal failure. The estimate, called a "loss budget" is calculated using typical component losses for. Fiber optic loss is one of the most fundamental parameters in optical network engineering, yet it is often misunderstood as a purely theoretical value used only during design calculations.