Master Plumber Exam Philippines Master Plumber Code and Regulations 2 — Questions and Answers
Question 1: Under the NPCP, what is the minimum slope (grade) required for a 100 mm (4-inch) horizontal drainage pipe?
- 1:200 (0.5%)
- 1:100 (1%) (Correct answer)
- 1:50 (2%)
- 1:40 (2.5%)
Correct answer: 1:100 (1%)
The NPCP requires a minimum slope of 1:100 (1% or approximately ¼ inch per foot) for 100 mm horizontal drainage pipes.
The National Plumbing Code of the Philippines specifies minimum slopes for horizontal drainage pipes to ensure self-cleansing velocity — the water flow must be fast enough (approximately 0.6 m/s) to carry solids without settling. For pipes 75 mm (3 inches) and smaller, the minimum slope is 1:50 (2%), equivalent to ¼ inch per foot. For 100 mm (4 inches) and larger, the minimum is 1:100 (1%). In practice, a slope of ¼ inch per foot (approximately 2%) is commonly used for 4-inch pipes for added assurance. Insufficient slope leads to solids settling, blockages, and odor problems; excessive slope can cause liquids to outrun solids, also causing blockages.
Question 2: In water supply design for buildings, what is the typical minimum residual pressure at the highest fixture outlet required by the NPCP?
- 35 kPa (5 psi)
- 70 kPa (10 psi) (Correct answer)
- 100 kPa (14.5 psi)
- 140 kPa (20 psi)
Correct answer: 70 kPa (10 psi)
The NPCP requires a minimum residual pressure of 70 kPa (approximately 10 psi) at the highest fixture outlet during peak demand.
The National Plumbing Code of the Philippines sets minimum pressure requirements to ensure adequate flow at all fixtures throughout the building. A minimum of 70 kPa (10 psi) residual pressure must be maintained at the highest and most remote outlet during simultaneous use conditions. Most fixtures require a minimum of 35 kPa (5 psi) to operate properly, but the 70 kPa figure provides a safety margin for pressure losses due to pipe friction, fittings, valves, and elevation head. Water closet flush valves and shower heads typically require 105–140 kPa (15–20 psi) for proper operation, so building design should target higher pressures where these fixtures are installed.
Question 3: According to Philippine plumbing standards, what is the correct color coding for a PVC pipe designated for potable water supply?
- Blue (Correct answer)
- Gray
- White
- Green
Correct answer: Blue
PVC pipes for potable water supply are color-coded blue under Philippine National Standards to differentiate them from drainage and other piping systems.
Philippine National Standards (PNS) for PVC pipes follow color coding conventions to prevent cross-connection and misidentification during installation. Blue-colored or blue-striped PVC pipes are designated for potable (drinking) water distribution under pressure. White or gray PVC pipes are used for drainage and sewer applications (non-pressure). Green pipes typically indicate sewage or irrigation use. Yellow indicates natural gas lines. This color-coding system is critical for preventing accidental cross-connections between potable water and waste lines, which could result in serious contamination. During PRC board examinations, candidates must know these color codes as they appear in system identification questions.
Question 4: What is the required minimum air gap between a water supply outlet and the flood level rim of a fixture, as specified in the NPCP?
- Equal to the supply pipe diameter
- Twice the supply pipe diameter (Correct answer)
- Three times the supply pipe diameter
- Equal to 25 mm regardless of pipe size
Correct answer: Twice the supply pipe diameter
The NPCP requires an air gap of at least twice the internal diameter of the supply pipe, but not less than 25 mm (1 inch).
An air gap is the most reliable method of backflow prevention, providing a physical break in the water supply to prevent contaminated water from siphoning back into the supply system. The National Plumbing Code of the Philippines requires the air gap to be at least twice the effective opening of the supply pipe or outlet, and not less than 25 mm (1 inch). For example, a 12 mm supply pipe requires a minimum 25 mm air gap (since twice 12 mm = 24 mm, rounded up to minimum 25 mm). Air gaps are required at fixtures such as lavatories, sinks, and storage tanks. Unlike mechanical backflow preventers, air gaps require no maintenance but must be maintained — faucets must never be submerged in fixture contents.
Question 5: Under the National Building Code of the Philippines (PD 1096) and NPCP, what is the minimum size of the building sewer for a residential structure?
- 75 mm (3 inches)
- 100 mm (4 inches) (Correct answer)
- 150 mm (6 inches)
- 200 mm (8 inches)
Correct answer: 100 mm (4 inches)
The minimum building sewer size for residential structures is 100 mm (4 inches) per the NPCP and related Philippine building standards.
The National Plumbing Code of the Philippines specifies that no building sewer shall be less than 100 mm (4 inches) in diameter. This minimum size applies even for small residential structures with minimal fixture counts, because the building sewer must accommodate occasional large volumes such as flushing of toilets and bathtub drainage, and must maintain self-cleansing velocity. The building sewer must also slope at a minimum of 1:100 (1%) toward the public sewer or private disposal system. For larger buildings with more fixtures and higher drainage loads, the sewer size must be increased based on drainage fixture unit calculations per the code's sizing tables.
Question 6: In the NPCP, what is the maximum developed length of a vent pipe from its connection to the drainage system to its termination outdoors for a 50 mm (2-inch) vent?
- 15 m (50 ft)
- 30 m (100 ft) (Correct answer)
- 45 m (150 ft)
- 60 m (200 ft)
Correct answer: 30 m (100 ft)
For a 50 mm (2-inch) vent pipe, the maximum developed length is 30 m (approximately 100 feet) per the NPCP vent sizing tables.
The National Plumbing Code of the Philippines provides maximum developed length tables for vent pipes based on pipe diameter and the number of fixture units connected. For a 50 mm (2-inch) vent serving up to 12 fixture units, the maximum developed length is 30 m (100 feet). Exceeding this length increases air resistance in the vent, reducing its effectiveness in equalizing pressure in the drainage system. When the required length exceeds the maximum for a given diameter, the vent pipe size must be increased. Developed length includes all horizontal runs, vertical rises, and the equivalent length of fittings such as elbows and tees, calculated using the NPCP fitting equivalent length table.
Question 7: According to the NSCP (National Structural Code of the Philippines) and related plumbing standards, what is the minimum water supply fixture unit (WSFU) demand value for a bathtub with a shower combination?
- 2 WSFU
- 3 WSFU
- 4 WSFU (Correct answer)
- 5 WSFU
Correct answer: 4 WSFU
A bathtub with shower combination is rated at 4 water supply fixture units (WSFU) for supply pipe sizing under Philippine plumbing standards.
Water Supply Fixture Units (WSFU) represent the probable simultaneous demand for water at each fixture and are used to size water supply piping. Under the NPCP Table 6-3, a bathtub with shower combination is assigned 4 WSFU (2 WSFU for hot, 2 WSFU for cold). In comparison, a lavatory is 1 WSFU, a shower stall is 2 WSFU, a water closet with flush tank is 3 WSFU, and a kitchen sink is 1.5 WSFU. The WSFU values are converted to design flow rates using the Hunter's Curve or probability curves. Accurate WSFU calculation ensures pipes are neither oversized (wasteful and costly) nor undersized (inadequate pressure and flow at peak demand).
Master Plumber Exam Philippines Master Plumber Code and Regulations 2
Under the NPCP, what is the minimum slope (grade) required for a 100 mm (4-inch) horizontal drainage pipe?