North Carolina (NC) (PU) Public Utilities Contractor Practice Exam Questions & Correct Answers (Verified Answers) Plus Rationales 2026 Q&A | Instant Download Pdf

1. A contractor is installing a new 4-inch water service line from the city main to a commercial building. The tap must be made on a ductile iron water main that is under pressure. According to NC regulations, what is the primary requirement for making this connection? a) A corporation stop must be installed using a tapping machine while the main is under pressure. b) The main must be shut down and drained completely before any connection is attempted. c) A saddle clamp can be used without a tapping machine if the main is less than 6 inches in diameter. d) The connection must be made with a PVC saddle and a hand drill. Correct Answer: a) A corporation stop must be installed using a tapping machine while the main is under pressure. Rationale: NC public utilities standards, consistent with industry best practices, allow for "wet taps" on pressurized mains using a tapping machine. This method installs a corporation stop (corp stop) that seals the connection, allowing the main to remain in service, which is critical for public water supply continuity. Shutting down a main (b) requires extensive notification, dewatering, and can disrupt service to a large area.Saddle clamps (c) may be used but still require a tapping machine for a pressurized connection. Using a PVC saddle and hand drill (d) is unsafe and not permitted on a live main due to the risk of blowout and inability to control the tap. 2. You are backfilling a trench for a new sanitary sewer line in North Carolina. The pipe is 8-inch PVC. What is the most critical factor regarding the backfill material immediately surrounding the pipe (the "haunch" and "initial backfill")? a) The material must be the native soil excavated from the trench to ensure compatibility. b) The material must be free of rocks, large clumps, and debris to prevent point loading and pipe deflection. c) The material must be 100% compacted sand to provide a rigid support system. d) The material type is irrelevant as long as the final grade is achieved with a vibratory roller. Correct Answer: b) The material must be free of rocks, large clumps, and debris to prevent point loading and pipe deflection. Rationale: The zone from the pipe bedding up to the springline (the haunch and initial backfill) is critical for pipe support. Material containing rocks or debris can create point loads that damage the pipe, especially PVC, leading to cracks or excessive deflection. While native soil can often be used if properly screened (a), the defining requirement is that it is free of deleterious materials. While sand (c) is an excellent bedding material, it is not a strict requirement for all applications if the native soil is suitable and compacted correctly. The final grade and compaction (d) are important, but the material immediately surrounding the pipe is paramount for the pipe's structural integrity. 3. A North Carolina Public Utilities contractor is performing a hydrostatic pressure test on a new water main. What is the minimum test pressure and duration typically required for a new ductile iron pipe system? a) 100 psi for 1 hour b) 150 psi for 2 hoursc) 200 psi for 4 hours d) The system must be tested to 1.5 times the maximum working pressure for a minimum of 2 hours. Correct Answer: d) The system must be tested to 1.5 times the maximum working pressure for a minimum of 2 hours. Rationale: NC Department of Environmental Quality (DEQ) and standard engineering specifications require that new water mains be pressure tested to at least 1.5 times the maximum operating pressure. The duration is typically a minimum of 2 hours, though longer durations may be specified to ensure stability and to allow for the dissipation of trapped air and temperature equalization. Options a, b, and c provide specific numbers that are not universally applicable, as the test pressure is a factor of the designed working pressure of the specific system. 4. When installing a fire hydrant in North Carolina, what is the standard orientation for the hydrant's main valve opening relative to the water main? a) The valve opening should face the main to minimize friction loss. b) The valve opening should face the street to allow for easy access by fire departments. c) The valve opening should be oriented perpendicular to the main. d) The valve opening should face the nearest building to provide the shortest response time. Correct Answer: c) The valve opening should be oriented perpendicular to the main. Rationale: Standard practice and many NC municipal specifications require that the hydrant's main valve (the "shoe") be installed so that the opening is perpendicular to the water main. This orientation provides a straight, unobstructed flow path from the main into the hydrant barrel and minimizes stress on the connection. It also ensures the hydrant's breakaway flange is correctly positioned. Orientation towards the street (b) is a common requirement for the hydrant's outlet orientation, not the main valve connection.5. A contractor is installing a gravity sanitary sewer line. What is the primary purpose of performing a mandrel test on the installed pipe? a) To verify the watertightness of the pipe joints. b) To check the pipe for ovality or deflection that could restrict flow. c) To confirm the pipe's resistance to external hydrostatic pressure. d) To ensure the pipe material meets the specified crush strength. Correct Answer: b) To check the pipe for ovality or deflection that could restrict flow. Rationale: A mandrel is a device that is pulled through a sewer line to verify that the internal diameter has not been compromised due to improper bedding, haunching, or backfilling. For flexible pipe like PVC, excessive deflection is a common problem. If the mandrel does not pass, it indicates the pipe is deformed. This test is separate from a leakage test (a) (air or water). Resistance to hydrostatic pressure (c) is related to the pipe's structural design and joint integrity, but the mandrel test is specifically for shape. Crush strength (d) is a material property, not something tested in the field with a mandrel. 6. In North Carolina, who has the primary authority for permitting and inspecting the installation of a new individual septic system (onsite wastewater system)? a) The North Carolina Department of Transportation (NCDOT) b) The local city or town building inspections department c) The North Carolina Department of Environmental Quality (NC DEQ), typically through the local County Health Department d) The North Carolina State Board of Examiners of Plumbing, Heating and Fire Sprinkler Contractors Correct Answer: c) The North Carolina Department of Environmental Quality (NC DEQ), typically through the local County Health Department. Rationale: Authority for onsite wastewater systems (septic systems) is delegated by NC DEQ to local health departments (LHDs). They are responsible for site evaluations,permit issuance, and final inspection. While municipal building departments (b) may be involved with the building structure, the utility itself falls under environmental health jurisdiction. NCDOT (a) has no authority over private septic systems. The State Board (d) licenses plumbing contractors, but the environmental permitting is separate. 7. What is the purpose of a "tracer wire" installed with a new plastic (HDPE or PVC) natural gas or water service line? a) To provide a path for cathodic protection to prevent corrosion. b) To allow for future location of the non-metallic pipe using electronic locating equipment. c) To serve as a grounding electrode for the building's electrical system. d) To carry a low-voltage current to heat the pipe in freezing conditions. Correct Answer: b) To allow for future location of the non-metallic pipe using electronic locating equipment. Rationale: Non-metallic pipes (plastic) are not detectable by conventional metal detectors or pipe locators. A tracer wire is a copper or coated steel wire buried directly above or with the pipe. It allows a locate technician to connect a transmitter to the wire, energizing it so the pipe's path can be traced above ground. This is a critical safety requirement for utilities like gas and is a best practice for water to prevent accidental strikes during future excavation. It is not used for cathodic protection (a) as plastic doesn't corrode; it's used for locating. 8. A contractor is excavating near an existing 8-inch cast iron water main. The shoring system being used is a trench box. What is the most critical requirement regarding the trench box and the existing utility? a) The trench box must be suspended by an excavator at all times to prevent it from settling onto the pipe. b) The trench box must be installed so it does not bear weight on or against the existing water main. c) The trench box must be set on top of the water main to provide a stable base for theexcavation. d) The trench box must be made of non-conductive material to prevent electrolysis on the cast iron pipe. Correct Answer: b) The trench box must be installed so it does not bear weight on or against the existing water main. Rationale: A trench box (or shield) is designed to protect workers from cave-ins, but it must not transmit loads to existing utilities. Placing the weight of the shield, the excavator, or the backfill against the existing main can cause it to crack or break, leading to a catastrophic failure and potential flooding or loss of service. Shielding is typically set to straddle the utility or is installed in a way that the utility passes through the open area of the shield. Suspending it (a) is not a standard or safe practice. Setting it on top (c) would crush the pipe. 9. When joining ductile iron pipe with push-on joints, what is the function of the rubber gasket? a) To provide electrical continuity across the joint for cathodic protection. b) To act as a lubricant to facilitate the assembly of the pipe. c) To create a watertight seal by being compressed between the spigot and the bell. d) To provide structural strength to the joint against shear forces. Correct Answer: c) To create a watertight seal by being compressed between the spigot and the bell. Rationale: The rubber gasket in a push-on joint is the primary sealing element. When the plain end (spigot) is inserted into the bell, the gasket is compressed against the spigot and the internal surface of the bell, forming a flexible, watertight seal that can accommodate slight deflection and expansion/contraction. Lubricants (b) are used to aid insertion but are not the function of the gasket itself. Electrical continuity (a) is not provided by rubber, which is an insulator. The joint's structural strength is limited; thrust blocking or restrained joints are needed for changes in direction.10. In North Carolina, what is the minimum required depth of cover for a residential water service line to prevent freezing? a) 12 inches b) 18 inches c) 24 inches d) There is no specific statewide depth; it is based on the local frost line, typically 12-18 inches in most of NC. Correct Answer: d) There is no specific statewide depth; it is based on the local frost line, typically 12-18 inches in most of NC. Rationale: North Carolina does not have a single, state-mandated depth for water lines. The depth is determined by the local jurisdiction's plumbing code or utility standards, based on the 50-year frost penetration depth for that area. In most of NC, this ranges from 12 to 18 inches, though some mountainous regions may require 24 inches or more. A contractor must verify the requirement with the local authority having jurisdiction (AHJ) before installation. 11. What is the primary purpose of a "blow-off" assembly on a water distribution system? a) To release trapped air at high points in the system. b) To allow for the controlled flushing of sediment and debris from the main. c) To provide a connection for fire department pumper trucks. d) To serve as a pressure relief valve in case of a water hammer event. Correct Answer: b) To allow for the controlled flushing of sediment and debris from the main. Rationale: A blow-off assembly is typically located at the end of a water main or at low points. It consists of a valve and a short pipe that allows the operator to open the valve and flush out accumulated sediment, silt, or stagnant water, especially after construction or repairs. Air release valves (a) are used at high points. A fire hydrant or standpipe (c)serves fire protection. A pressure relief valve (d) is a safety device typically found on pumps or within buildings, not as a standard appurtenance on distribution mains. 12. When installing a trench for a sewer line that will be subject to traffic loads, what type of backfill compaction is typically required in the upper layers (e.g., below pavement)? a) No compaction is required as the pavement will distribute the load. b) Compaction to 85% of maximum dry density (Standard Proctor). c) Compaction to 95% of maximum dry density (Standard Proctor) or per local specifications. d) Compaction must be achieved by flooding the trench with water (jetting). Correct Answer: c) Compaction to 95% of maximum dry density (Standard Proctor) or per local specifications. Rationale: For areas under pavement or traffic loads, high compaction is critical to prevent future settlement, which would lead to pavement cracking, depressions, or failure. NCDOT and municipal standards generally require compaction in the upper layers to 95% or more of the maximum dry density determined by the Standard Proctor test (ASTM D698). Option a is incorrect as pavement will settle without proper support. Option b (85%) is typically acceptable for non-traffic areas. Jetting (d) is an unacceptable method for achieving specified compaction in structural zones