Trade Fundamentals and Safety
This domain tests whether you understand plumbing as a code-governed trade - its vocabulary, units, drawing conventions and the safety rules that decide marks in both theory and viva.
Core rules and concepts
- Plumbing has two halves. Water supply is potable water under pressure; drainage is soil and waste water moving by gravity through traps and vents. The two must never be cross-connected; protection comes from an air gap at the tank, cistern and tap.
- Sizes are nominal bore in mm (15, 20, 25, 32, 40, 50, 75, 100, 150), though fittings are still spoken of as ½", ¾", 1".
- Pressure is quoted in bar or metre head; 10.2 m of water column equals about 1 bar.
- Reference standards to quote: IS 1239 (GI pipes), IS 4985 (UPVC potable water), IS 1742 (drainage), National Building Code 2016 Part 9.
- Safety: helmet, gloves, goggles, safety shoes; shore trenches deeper than about 1.2–1.5 m; isolate electrical supply before touching a pump; ventilate and test a manhole or septic tank before entry, and never enter alone.
Worked example
A 25 mm NB pipe run is 12 m long. How much water does it hold? Area = π/4 × (0.025)² = 0.000491 m². Volume = 0.000491 × 12 = 0.00589 m³, and 1 m³ = 1000 L, so about 5.9 L. The reasoning: convert bore to metres first, find area, multiply by length, then convert.
Traps that cost marks
- Using the outside diameter of the pipe instead of the nominal bore.
- Mixing up bar and metre head.
- Believing a 15 mm pipe carries half of a 25 mm pipe; capacity follows area, so it is roughly one quarter.
- Entering a manhole without forced ventilation or a standby person.