Classroom explanation - not to scale.
Inspecting pre-woven “spliced overlap” of shielding braid can be achieved using this measuring technique which applies for all 3 classes of product.
The illustration may be used for clarity. The reference “Db” is used to identify the “Diameter of the bundle”. The diameter of the bundle is used to gauge or measure the length of the overlap in the spliced area. The reference is used as 1x, 2x, or 3x times the diameter of the bundle.
The shield braid splice area is shown at the split of the cable. The diameter of the bundle (Db) is illustrated in 3 increments down the length of the split. As stated in the IPC 620B, Section 15.4.1, page 15-21 and 15-22- the following conditions are required:
- Target – 2x Db’s Acceptable – 1, 2 or 3x Db’s
- Defect – < 1x Db Process Indicator > 3x Db’s
When inspecting a cable splice, another cable of the same gauge (or specialized tooling) may be used by intersecting (off 90 degrees) at one end of the spliced area to visually determine the number of times the diameter can be measured in relation to the length of the splice.
Note that the illustration is not to scale and shows an exaggerated example.