Cable Length Calculation – Check if any allowances are omitted

1. Rules for Cable Length Calculation
During cable installation, whether routed through conduits or cable trays, cables are not installed in a fully taut condition. Allowances must be made for slack, waveform curvature and crossings. According to calculation specifications, the laying allowance factor is 2.5%.
Total cable length = (Total straight cable length + Reserve lengths) × 1.025
2. Calculation of Reserve Lengths
Note: Additional and reserve lengths form an integral part of installed cable length and shall be included in the measured quantity.
In other words, the extra length for laying slack, waveform curvature and crossings shall be calculated based on the sum of horizontal & vertical routing lengths shown on drawings plus all applicable reserve lengths.
01. Cable slack, waveform curvature and crossings
An allowance factor of 2.5% shall be applied to the overall length to account for cable slack, waveform curvature and crossings.
02. Cables entering buildings
For external cables along municipal roads (or traffic safety engineering cables) entering a site, a minimum reserve of 2 m shall be considered.
03. Cables entering trenches or cable hangers
Minimum vertical lead-in / lead-out reserve: 1.5 m where cables enter trenches or hangers.
04. Incoming and outgoing cables at substations
Minimum reserve: 1.5 m.
05. Cable terminations
Minimum reserve of 1.5 m for power cable terminations for maintenance purposes.
06. Cable intermediate joints
A reserve of 2 m shall be left at each side of every cable joint box for maintenance.
07. Cables entering control panels, protection panels, mimic panels, distribution boxes, etc.
The reserve length equals the perimeter half of the panel / box face (height + width).
08. High-voltage switchgear and low-voltage distribution panels / boxes
For cables routed in and out below panels, a reserve of 2 m shall be provided.
09. Cables to motors
Starting from the motor terminal box, add a reserve of 0.5 m.
10. Station service transformers
A reserve of 3 m measured from finished floor level.
11. Cables routed around beams, columns and other structures
Additional length shall be calculated according to the cross-section dimensions of the structures bypassed.
12. Elevator cables fixed to cable brackets
A reserve of 0.5 m at each fixing point