How to Safely Install Cables in Infrastructure Projects?

1. Planning and Design

1. Separate the cable types

   • Power cables (LV/MV), low-voltage/weak current (data, telephone, fiber), control cables.

   • If they will be on the same route, the minimum distances between them and the fire compartments must be defined in the project.

2. Create a route plan

   • Clarify existing infrastructures (natural gas, drinking water, sewage, other energy and telecom lines) with maps and excavation permits.

   • As far as possible:

     • A short but accessible route,

     • Avoid risky areas (heavy traffic, heavy loads, chemical environments, high temperatures, flood risk).

   • Detail the crossing points in particular (under road, bridge, manhole, building entrance).

3. Determine the installation method

   • Direct burial (buried in soil),

   • Inside conduit/duct (HDPE, PVC, steel conduit),

   • Cable trays and ladders, tunnels, galleries.

   • Define protection, depth, fill ratio and drainage requirements for each method.

2. Cable and Material Selection

1. Use cables that comply with standards

   • Compliant with the relevant IEC/EN/TSE standard (e.g. IEC 60502 series for power cables, etc.).

   • In indoor areas, prefer halogen-free, low flame spread (LSZH) cables.

   • For outdoor use:

     • UV-resistant, outer sheath resistant to moisture and chemicals,

     • If necessary, armoured cable (against mechanical impacts).

2. Cross-section and conductor type

   • Current carrying capacity, short-circuit withstand and voltage drop must be calculated.

   • Cu/Al selection, single-core/multi-core, screened or armoured must be according to the project calculations.

3. Conduit and duct selection

   • Indoors: PVC or metal conduit; outdoors: HDPE corrugated, steel conduit, etc.

   • Fill ratio should generally not exceed 40% of the conduit cross-section (for future cable additions, heating and pulling ease).

   • Choose conduit/tray size that provides the minimum bending radius specified by the cable manufacturer.

3. Site Occupational Safety

1. Risk analysis and permits

   • Written work permits for works such as excavation, confined spaces, work near live systems.

   • The locations of existing lines must be marked and the plans shown on site.

2. Isolation and securing of energy (LOTO)

   • If possible, the line should be de-energized.

   • Lockout and tagout (LOTO) must be applied at breakers.

   • Absence of voltage must be checked with appropriate equipment.

3. Personal protective equipment

   • Helmet, safety boots, reflective vest,

   • Goggles, work gloves (if necessary insulated gloves),

   • Working at height equipment (fall arresters, etc.) where applicable.

4. Site organization

   • Open trenches must be fenced and equipped with barriers and warning signs.

   • For trenches deeper than 1.2 m, use shoring or adequate slope to prevent sidewall collapse.

   • Use suitable scaffolds or ladders for entering and exiting trenches.

4. Excavation and Route Implementation (Underground Cables)

These are example values; always refer to local regulations and the project.

1. Depth

   • LV power cables: typically ~0.7–0.8 m,

   • MV cables: typically ≥1.0 m,

   • Data/telephone: typically ≥0.6 m.

   • May be increased depending on the load coming from above.

2. Bottom preparation

   • The trench bottom must be cleaned of stones, rubble and sharp objects.

   • Generally, a bedding of about 10 cm of sand or fine material is laid and compacted.

3. Distances between cables

   • If there is more than one cable in the same trench:

     • Horizontal and vertical clearances must be as per the project (e.g. at least 20–30 cm between a power cable and a telecom cable).

   • At crossings with other infrastructures (natural gas, water, etc.) intersect, aim for 90° crossings where possible.

4. Backfilling

   • Place another 10 cm of sand/fine material on top of the cable,

   • Then a warning tape (red – energy, blue – water, etc., according to the utility’s standard),

   • Then backfill with native soil and compact.

5. Laying the Cable (Pulling / Laying Out)

1. Cable drum and preparation

   • The cable drum must be upright and locked, and the risk of tipping must be prevented.

   • Check for cuts, crushing or holes on the outer sheath.

   • Ensure that water has not entered the cable, especially at the ends (use temporary caps/insulation on the ends).

2. Pulling direction and equipment

   • If possible, position the drum so that the cable is paid out from the bottom of the drum (pulling from the top can bend the cable).

   • For long distances, use rollers / slides along the drum route.

   • For pulling through conduits:

     • Use a suitable pulling rope and pulling head (of a type that will not damage the cable),

     • If necessary, use a winch + dynamometer for pulling force,

     • Use cable pulling lubricant to reduce friction.

3. Pulling force and bending radius

   • Do not exceed the maximum pulling force specified in the cable manufacturer’s catalogues.

   • Bending radius:

     • Typically minimum 8× outer diameter for unarmoured cable,

     • Minimum 12× outer diameter for armoured cable (varies by cable type – refer to the catalogue).

   • Protect the cable from sudden bends/kinks and “sharp elbows”.

4. Excess length and slack

   • Leave a certain amount of cable slack at drum transition points (manholes, building entrances, in front of panels).

   • It is invaluable for future joints/modifications.

6. Joints and Terminations

1. Qualified personnel required

   • In particular, MV/HV cable joints and terminations must only be carried out by trained and authorized personnel.

   • Original joint and termination kits must be used; “improvised” solutions with similar materials are dangerous.

2. Cable preparation

   • During cutting, stripping and removal of screens/armour, do not damage the conductors or insulation.

   • Knife marks and scratches may later cause partial discharge or faults.

   • Work in a clean environment and, if necessary, clean the insulation surface with isopropyl alcohol (according to the manufacturer’s instructions).

3. Lug and terminal connections

   • Use cable lugs suitable for the correct cross-section.

   • Crimp with appropriate crimping tools and dies, such as hydraulic presses.

   • For bolted connections, use a torque wrench according to the manufacturer’s torque values.

4. Sealing and insulation

   • Apply heat-shrink or cold-shrink sleeves, resin boxes, etc. on joints and terminations according to instructions.

   • Proper shrinking is important to prevent ingress of moisture, water and dust.

5. Earthing and screen bonding

   • The earthing points of armour, screens and metallic sheaths must be as per the design:

     • Single-point / double-point earthing,

     • Screen separation systems – these must be implemented according to the project engineer’s decision.

   • Connect metal conduits, trays and boxes to the PE bar (equipotential bonding).

7. Fixing Cables and Mechanical Protection

1. Cable trays and ladders

   • Determine tray/ladder spacing by checking load capacity (to avoid sagging).

   • In corrosive environments, use galvanized or painted/stainless materials.

   • Secure with regular cable clamps horizontally and vertically; do not overtighten clamps to crush the cable.

2. Vertical shafts and risers

   • Cable weight increases in vertical runs, so use cable supports/clamps at certain floors.

   • For large cross-section power cables, use a cable clamp system resistant to short-circuit forces.

3. Separation between cables

   • If there are different voltage levels (e.g. 400 V and 24 V) on the same tray, use a divider plate or separate trays.

   • Route power cables and data/fiber cables separately as far as possible; if on the same route, meet spacing and screening requirements.

4. Protection at penetrations and openings

   • At wall/tile penetrations, provide mechanical protection with a cable gland/bushing or sleeve conduit.

   • When passing through fire walls, seal gaps with fire-stopping mortar/kit.

8. Earthing, Equipotential Bonding and Surge Arresters

1. Continuity of protective conductor

   • All sockets, panels, motors and metal enclosures must be connected to the PE conductor.

   • Trays, metal conduits and junction boxes must be connected to the equipotential bar.

2. Lightning protection and surge arresters

   • If the building has a lightning protection system, power cables and metal lines must be designed in harmony with it.

   • Use surge arresters of appropriate class in critical panels (e.g. Type 1 in the main panel, Type 2 in sub-panels, etc., according to the project design).

9. Testing, Inspection and Documentation

1. Visual inspection

   • Are there any breaks, dents, sheath damage, wrong routes, missing clamps or loose connections?

   • Check at sample points that the cable is correctly coded and routed.

2. Electrical tests

   • Continuity test (phase, neutral, PE),

   • Insulation resistance test (megger): at the relevant voltage level, results must be above the minimum required by standards.

   • If required:

     • High-voltage test (for MV cables),

     • Earth resistance measurement,

     • Short-circuit loop impedance, etc.

3. For data and fiber cables

   • Certification testing of data cables (with a tester suitable for the category – Cat6, Cat7, etc.),

   • For fiber cables, OTDR and loss measurements.

4. Labelling and records

   • Each cable must carry a permanent label at both ends and at intermediate manholes/joint points (e.g. line number, panel it supplies, etc.).

   • Update the “as-built” project:

     • Cable route,

     • Cable type, cross-section, length,

     • Joint and manhole locations,

     • Test reports.

10. Common Mistakes and Short Prevention Checklist

Avoid:

• Pulling cables without paying attention to the maximum pulling force and bending radius.

• Filling the same tray with every voltage level without any separation.

• Making joints and terminations in unsuitable environments (mud, dust, under rain).

• Leaving earthing and screen connections “to look at later”.

• Cutting the cable before making sure twice over that it is the correct cable (!).

Mini checklist:

• Are routes and depths compliant with the project and regulations?

• Are cable type, cross-section and protective elements in line with the approved project?

• Have pulling and bending limits been observed?

• Are joints and terminations in accordance with instructions, clean and sealed?

• Are all metal parts and cable armour correctly earthed?

• Have test reports been taken and archived?

• Have cable labels and as-built drawings been updated?