Jamming is the wedging of three or more cables when pulled into a conduit. This usually occurs because of crossovers when the cables twist or are pulled around bends. The jam ratio is the ratio of the conduit inner diameter $Dd_i$ and the cable outside diameter $D_e$.
In calculating jamming probabilities, a 5% factor was used to account for the oval cross-section of conduit bends.
The cable diameters should be measured, since actual diameters may vary from the published nominal values.
|Probability for jamming||lower range||upper range|
|very small||$JR_p$ < 2.4||$JR_p$ ≥ 3.2|
|small||2.4 ≤ $JR_p$ < 2.5||3.0 ≤ $JR_p$ < 3.2|
|moderate||2.5 ≤ $JR_p$ < 2.6||2.9 ≤ $JR_p$ < 3.0|
|significant||2.6 ≤ $JR_p$||$JR_p$ < 2.9|