Estimate the total primary cable for a series circuit from fixture count and average spacing, including feeder, return path, allowances and drums.
A series circuit is one continuous loop, so the cable is the fixture route plus the feeder from the CCR, plus the way back. Enter each stretch of fixtures as a segment, then set the feeder, return path and allowances. The total can be taken straight to the Cable Voltage Drop calculator as the loop length.
| Segment | Fixtures | Average spacing | Gap to next segment | Remove |
|---|
Extra cable for the connection at each isolating transformer. Your own rule.
Allowance for undulation, offsets, slack and repairs, applied to the total. Your own rule.
Always in metres, whatever unit is selected. Used to count drums and in-line joints, with no allowance for offcuts. Transformer connector kits are not counted. Enter your supplier's length.
| Component | Metres | Feet | Basis |
|---|---|---|---|
| Fixture route | — | — | One way, spacings plus gaps |
| Feeder from CCR | — | — | One way |
| Return path | — | — | — |
| Loop length | — | — | Route, feeder and return |
| Fixture connections | — | — | — |
| Contingency | — | — | — |
| Estimated circuit cable | — | — | Order quantity before offcuts |
| Drums | Quantity | Basis |
|---|---|---|
| Drums required | — | — |
| In-line joints | — | One fewer than the drums |
Calculated planning quantity from average spacing — not a final cable order. Take final lengths from the design drawings and verify on site.
Every step is shown so the result can be checked by hand.
Each segment spans one fewer spacing than it has fixtures. The gap joins one segment to the next and is not counted after the last.
With the return along the same route the loop is out and back. With a separate return, the return length is added once instead.
Cable per fixture is added once for every fixture, then contingency is applied to the whole.
Drums are the total divided by the drum length, rounded up. In-line joints are one fewer than the drums. Connector kits at the isolating transformers are not counted.
| Item | Value |
|---|---|
| 100 fixtures at 60 m | 99 × 60 = 5,940 m |
| Feeder 500 m, out and back | 2 × 6,440 = 12,880 m |
| Connections, 2 m × 100 | 200 m |
| Before contingency | 13,080 m |
| Total at 5 % | 13,734 m |
| 500 m drums | 28 drums, 27 joints |
It uses average spacing, so it does not follow curves, offsets or crossings, and it does not size the conductor. Take the total to Calculator #15 as the loop length to check the voltage drop.
Quick answers on how the series circuit cable length, feeder, return path and drums are estimated.
It estimates the total primary cable for an airfield series circuit from the fixture count and average spacing. It includes the feeder from the CCR, the return path, a cable allowance per fixture, a contingency, and the number of drums and in-line joints. It produces a cable schedule and a PDF report.
You enter each stretch of fixtures as a segment, such as one runway edge. Each segment spans one fewer spacing than it has fixtures, so Route = Σ (n − 1) × spacing + Σ gaps. The gap is the cable from a segment's last fixture to the next segment, and it is not counted after the last segment.
A series circuit is one continuous loop. With the return along the same route the loop is out and back, 2 × (feeder + route). With a separate return, the loop is feeder + route + the return length, which is added once. The feeder is the one-way route length from the CCR to the start of the fixture route.
Cable per fixture is the extra cable for the connection at each isolating transformer, added once for every fixture. The contingency is a percentage applied to the whole total for undulation, offsets, slack and repairs. Both are your own rules. The formula is Total = (loop + n × per fixture) × (1 + contingency).
Drums are the total length divided by the drum length, rounded up, and in-line joints are one fewer than the drums. The drum length is always entered in metres, whatever unit is selected, and the count has no allowance for offcuts. Enter your supplier's drum length. Connector kits at the isolating transformers are not included in the joint count.
For 100 fixtures at 60 m spacing the route is 99 × 60 = 5,940 m. With a 500 m feeder, out and back, the loop is 2 × 6,440 = 12,880 m. Adding 2 m of connection cable per fixture (200 m) gives 13,080 m, and 5 % contingency gives 13,734 m. With 500 m drums that is 28 drums and 27 joints.
The total can be taken to the Cable Voltage Drop calculator (Calculator #15) as the loop length. The tool uses average spacing, so it does not follow curves, offsets or crossings, and it does not size the conductor. It is a calculated planning quantity, not a final cable order. Take final lengths from the design drawings and verify on site.
Please read before relying on any content on this page or on any result or record produced by it.