EngiMetric Arena / Engineering Trade-off
Choose a conduit that is neither too full nor oversized
Competency Constraints and trade-offs primary Quantitative reasoning supporting
What you should take away: Evaluate a conduit size against an upper fill limit and a lower utilisation limit, recognising that more than one standard size can comply.
The situation
What is happening
Four 95 mm2 conductors are to be installed in one conduit. The project requires fill between 25 % and 40 %: below 40 % for pulling, and above 25 % to avoid an unnecessarily large raceway. Choose a standard internal area from 344, 557, 965 or 1 313 mm2.
Given
| Quantity | Value | Unit | Note |
|---|---|---|---|
| Conductor count | 4 | conductors | All in one raceway. |
| Area per conductor | 95 | mm2 | Conductor area used by the engine. |
| Total conductor area | 380 | mm2 | Four conductors x 95 mm2. |
| Minimum fill | 25 | % | Avoids an oversized raceway. |
| Maximum fill | 40 | % | NEC limit for three or more conductors. |
Assumptions this challenge makes
- The four conductor areas add directly.
- The 40 % NEC limit applies because there are more than two conductors.
- Only the four listed standard internal areas are available.
Limits this decision must satisfy
| Limit | Requirement | If it is breached |
|---|---|---|
| Maximum fill | not more than 40 % | Above 40 % the conductors are too tight to pull without damaging insulation or exceeding the code limit. |
| Minimum fill | not less than 25 % | Below 25 % the raceway is oversized, adding cost and space without a pulling or thermal benefit. |
Choose 344, 557, 965 or 1 313 mm2. More than one standard area may satisfy the fill band.
Your call
Your answer
Hints
- Total conductor area is four times 95 mm2. Divide by each candidate conduit area.
- The smallest standard areas will exceed 40 %; the largest may fall below 25 %.
- Both limits matter. A conduit can be too small or too large for this project.
Your answer Engine result
Where that comes from
Each limit, checked
Why
- The total conductor area is 4 x 95 = 380 mm2.
- At 344 mm2 the fill is 110.5 %, far above 40 %. At 557 mm2 it is 68.2 %, still above the limit.
- At 965 mm2 the fill is 39.4 %, inside the 25-40 % band. At 1 313 mm2 it is 28.9 %, also inside the band.
- So 965 mm2 and 1 313 mm2 are both defensible. The smaller conduit is cheaper and tighter; the larger one is easier to pull but uses more space and material.
- The project lower limit is a preference, not a code requirement. The NEC upper limit is the mandatory constraint.
What this challenge does not establish
- Conductor areas are inputs; actual cable insulation and construction must match the data.
- The table is a screening set, not a complete conduit catalogue.
- Pull length, bends, jam ratio and ambient derating are not modelled.
- Local code amendments may change the permitted fill percentages.