Tension and sidewall pressure both pass comfortably for this pull — but the jam ratio lands right inside the danger band, the one check that actually fails.
| Route | 50 ft straight, 50 ft straight, then a 90° bend of 2 ft radius |
| Cable weight | 3.3 lb/ft |
| Coefficient of friction | 0.35 |
| Conduit ID | 4 in |
| Cable OD | 1.45 in |
| Limits | Max tension 5000 lbf, max sidewall pressure 300 lb/ft |
Jam ratios between roughly 2.6 and 3.2 are the recognized danger band for three cables jamming against each other and the conduit wall.
| Check | Requirement | Actual | Status |
|---|---|---|---|
| Final pulling tension | ≤ 5000 lbf | 200.1 lbf | ✓ PASS |
| Sidewall bearing pressure | ≤ 300 lb/ft | 100.1 lb/ft | ✓ PASS |
| Jam ratio | Outside 2.6–3.2 danger band | 2.76 — inside the danger band | ✗ FAIL |
Key insight: A pull can pass every tension-based check and still be a bad pull. Jam ratio is a purely geometric risk (three similarly-sized round objects wedging against a circular boundary) that has nothing to do with how much force is being applied — which is exactly why it's checked as a completely separate, independent criterion rather than folded into the tension limit.
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Open Cable Pulling Tension calculator →This range is where three same-size round cables lying inside a circular conduit can wedge tightly against each other and the conduit wall simultaneously — geometrically, ratios noticeably below 2.6 leave enough clearance to avoid a tight three-way wedge, and ratios above about 3.2 give the cables enough room to shift past each other rather than lock in place.
Either increase the conduit size (pushing the ratio above roughly 3.2) or use a different cable configuration — for example, a single larger multiconductor cable instead of three separate single-conductor cables removes the three-cable jamming geometry entirely, since jam ratio specifically applies to the classic three-cable-in-round-conduit case.