Technical drawing is an essential skill for professionals in industrial control and installation, enabling precise communication of component layouts, wiring schematics, and installation details. In Kenya, industrial sites ranging from factories to county government water treatment plants rely on accurate plane geometry drawings for safe and efficient system setup. Understanding the conventions and standards of technical drawing ensures that every stakeholder, from installers to inspectors, can interpret and implement designs without confusion. This chapter explores the foundational elements of plane geometry drawings, beginning with the types of lines used to convey information unambiguously.

2.1 Types of Lines in Drawings

In industrial control and installation, lines are more than marks on paper, they are the visual language for representing electrical circuits, piping layouts, enclosure boundaries, and mounting details. Correct use of line types according to international and Kenyan standards is crucial, as misinterpretation may lead to costly installation errors or safety hazards. Professionals must be familiar with line conventions, their meanings, and how to apply them in both manual and CAD-generated geometry drawings.

2.1.1 Meaning and Significance of Lines in Technical Drawings

Meaning of Lines in Technical Drawings

Lines in technical drawings represent different features, boundaries, and instructions. They are not arbitrary; each line type has a standardized meaning.

• Visible lines: Indicate the edges or contours of an object that are directly observable. Used to outline equipment housings, panel edges, and mounting plates.
• Hidden lines: Represent features not visible in the current view, such as internal wiring routes or pipe runs behind panels.
• Centre lines: Denote axes of symmetry or the centre of cylindrical features, often used in marking shaft positions or conduit runs.
• Construction lines: Light, thin lines used as guides during drawing creation, such as layout grids or reference axes.
• Dimension lines: Show measurement information, connecting points or features to dimension values for accurate fabrication.

Significance of Lines in Industrial Control Drawings

Correct line usage ensures clarity, safety, and compliance in installation projects.

• Standardization: Adherence to BS/ISO/Kenya standards allows drawings to be universally understood among engineers, technicians, and regulators.
• Error prevention: Misuse of line types can cause misinterpretation, leading to incorrect wiring, unsafe installations, or delays.
• Efficient communication: Well-structured drawings reduce the need for verbal clarification, speeding up project execution and inspection.
• Legal compliance: Drawings using proper line conventions meet regulatory requirements for documentation, especially in industrial projects overseen by NEMA or county authorities.
• Quality assurance: Accurate representation assists in quality checks during installation, ensuring all components are placed and connected as designed.

2.1.2 Types of Lines Used in Technical Drawing

Technical drawing standards define a variety of line types, each used for specific purposes. For industrial control and installation, the following are most relevant:

• Continuous thick line: Used for visible outlines and edges, such as the perimeter of control panels or mounting brackets.
• Continuous thin line: Applied for dimension lines, extension lines, leader lines, and hatching, marking measurement points and material sections.
• Dashed thin line: Represents hidden features, like internal wiring paths or pipes concealed within walls or enclosures.
• Chain thin line (long dash, short dash): Used for centre lines, referencing the axis of actuators or symmetry of pipe runs.
• Double-dashed thin line: Indicates cutting planes or paths for section views, essential in showing internal arrangement of switchgear.
• Freehand line: Sometimes used in site sketching to indicate flexible routing or temporary features, but not for final technical documentation.

Typical Mistakes in Line Selection

• Using thick lines for dimensions: This may confuse installers, as thick lines are meant for visible outlines.
• Failing to distinguish hidden and visible features: Can result in misinterpretation of wiring routes or mounting positions.
• Incorrect line type for centre lines: May lead to errors in aligning components, especially in symmetrical installations.
• Overlapping multiple line types: Reduces clarity, making drawings difficult to read for technicians.
• Ignoring standard conventions: Leads to non-compliance with Kenya Bureau of Standards and international guidelines.

2.1.3 Standard Conventions for Line Types (BS/ISO/Kenya Standards)

Industrial control drawings in Kenya must comply with recognized standards to ensure uniformity and safety. The relevant standards include:

• BS 8888: British Standard for technical product specification, adopted widely in Kenyan industry.
• ISO 128: International standard for line types in technical drawings.
• KEBS KS 2107: Kenya Bureau of Standards guideline for engineering drawing conventions.

Key conventions:

• Line thickness: Visible outlines (0.5-0.7 mm), hidden lines (0.3-0.5 mm), dimension lines (0.3 mm).
• Line types: Centre lines (long dash, short dash), hidden lines (short dashes), cutting planes (alternating double dashes).
• Colour coding: In CAD drawings, lines may be colour-coded for visibility but must match print conventions for submission.
• Title blocks: Must indicate the drawing standard used, revision status, and approval signatures.
• Scale indication: All geometry drawings must specify the scale used, e.g., 1:1, 1:2, to avoid misinterpretation during installation.

Quality Check: Ensuring Compliance

• Verify line types against standard charts before submission
• Check thicknesses using CAD settings or manual drawing pens
• Ensure all drawing sheets contain a standard-compliant title block
• Double-check scale notation and dimension placement
• Submit sample drawings for review by a qualified supervisor or regulatory officer

2.1.4 Application of Line Types in Plane Geometry Drawings

Plane geometry drawings are foundational for laying out control panels, cable trays, and piping systems in industrial installations. Correct application of line types ensures the drawings are practical and actionable.

• Panel layout: Visible lines outline the panel, hidden lines indicate internal cable routes, centre lines mark the axis for mounting devices.
• Cable routing: Dashed lines show concealed cable runs, continuous thin lines mark measurement points for tray placement.
• Mounting details: Chain lines highlight symmetrical features for bracket installation, dimension lines provide exact distances for drilling.
• Section views: Double-dashed lines define where the drawing is ‘cut’ to show internal arrangements, such as busbar placement.
• Site sketch overlay: Freehand lines may be used in preliminary sketches to plan equipment positioning before producing formal CAD drawings.

Field Practice: Implementing Line Types

• Begin with construction lines to set up the drawing grid
• Draw visible outlines for major components first
• Add hidden lines for internal features after confirming layout
• Apply centre lines to indicate axes and reference points
• Insert dimension lines last, ensuring clarity and non-overlap

Chapter Summary

This chapter provided a comprehensive foundation in producing plane geometry drawings, beginning with a detailed overview of the various types of lines used in technical drawing and their standard applications. It then guided you through the construction procedures for fundamental geometric forms such as squares and circles, emphasizing the importance of accuracy and adherence to drawing protocols. The chapter covered practical methods for constructing a range of angles, supporting your understanding with clear, step-by-step instructions. Techniques for measuring angles were explained, equipping you with the skills necessary to achieve precision in your work. You also learned how to bisect both angles and lines, which is essential for creating symmetrical and balanced drawings. Finally, the chapter concluded with a review of standard drawing conventions, highlighting the importance of following recognized standards to ensure clarity and professionalism in technical documentation. Mastery of these topics ensures you are well-prepared to produce high-quality plane geometry drawings that meet industry requirements.