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Conduit Size Calculator

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Please check.

  • When selecting the wire gauge (SQ], it must match the capacity of the circuit breaker. Using a wire thinner than the load is a direct cause of fire.
  • When filling the inside of conduits (CD pipes, steel pipes, etc.] with electrical wires, they must be filled to 40~50% or less of the pipe's cross-sectional area to ensure smooth heat dissipation and easy wire insertion.
  • When connecting wires, use wire connectors or tighten them securely and finish with electrical tape. Poor contact poses a high risk of arcing and fire.
  • For humid bathrooms or outdoor exposed areas, you must use waterproof plumbing and specialized materials, and make sure to check whether the construction has been properly registered.
  • If there are too many bends in the piping (three or more], wiring work becomes very difficult. Please ensure a straight path whenever possible or install pull boxes for management.

How about this calculator?

Conduit Size Calculator, Selection of CD/GW Pipe Gauges and Determination of Installation Difficulty

In electrical construction, the selection of conduit is directly related to fire safety and ease of maintenance. Forcing wires into a conduit that is too narrow can damage the insulation, causing electrical leakage accidents and making future wire replacement impossible. By entering the wire type, gauge (sq], and number of strands, this calculator calculates the cross-sectional area occupancy rate within the conduit according to the Korean Electrical Code (KEC] and recommends the safest conduit specifications.

Formula for Calculating Conduit Occupancy Rate and Difficulty

It is calculated by applying the pipe cross-sectional area occupancy standards of the Korean Electrical Code (KEC].

Excess cross-sectional area within the pipe
Occupancy Rate (%] = (Total Wire Cross-sectional Area ÷ Conduit Inner Diameter Cross-sectional Area] × 100

According to regulations, it is safe for the wire not to exceed about 32% to 40% of the internal cross-sectional area of ​​the conduit.

Detailed Guide to Calculator Input Items

Please check the material information you intend to use to ensure accurate piping selection.

1. Wire type and specifications (sq]

Select the wire type, such as HFIX (flame retardant], HIV (insulated], or CV (cable], and enter the thickness. The sheath thickness and friction force vary depending on the wire type, affecting the occupancy rate.

2. Number of wire strands (pieces]

Enter the total number of wires for one pipe. For single-phase power, the basic configuration consists of three wires, including the live wire, neutral wire, and ground wire.

3. Pipe Types (CD / GW / PE]

Please select the piping suitable for the construction site, such as CD conduit for concrete embedding, metal flexible conduit (GW] for exposed ceilings, or PE conduit for underground burial.

Recommended capacity by conduit size (based on 2.5 sq]

Piping designation Actual inner diameter (mm] Recommended number of strands characteristic
No. 16 Approximately 16 mm 3 to 4 strands Standards for lighting and switch circuits
No. 22 Approximately 22 mm 5 to 7 strands For general heating and main wiring
No. 28 Approximately 28 mm 8 strands or more For trunk lines or communication line bundles

Expert Know-how and Checklists

These are the key practical points for safe and smooth electrical work.

  • Consider the condition of pipe bends

    Friction increases sharply in sections where the piping bends three or more times. Even if it is theoretically possible, please select a pipe one size larger if there are many bends.

  • Selecting pipe material suitable for the location

    In ceiling interiors or fire inspection zones, metal flexible conduit (GW] or non-combustible conduit must be used instead of ordinary CD conduit to prevent the spread of fire.

  • Utilization of wire oil and urine tape

    HFIX wires have high friction, making wire installation difficult. Even if there is ample space, applying a dedicated wire installation lubricant can prevent wire damage and reduce working time.

Frequently Asked Questions (FAQ]

  • Q. Are No. 16 and 16mm the same thing?
  • A. Although they are used interchangeably in the field, it is actually No. 16. The actual outer diameter is approximately 21mm, and the inner diameter is approximately 16mm.
  • Q. Is it okay to connect wires inside the conduit?
  • A. Absolutely not. Since wiring inside the conduit poses a high fire risk, all connections or branches must be made inside the joint box or outlet box.
  • Q. Why is it not allowed if the market share exceeds 40%?
  • A. This is because the heat generated by the wires is not released, increasing the risk of fire, and the wires are tightly jammed, making future replacement (maintenance] impossible.