NV Journeyman Plumber common mistakes
NV Journeyman Plumber · Understand the traps and how to avoid them.
Treating the UPC's fixture-unit (FU) values and drain/vent sizing tables as if memorized numbers were enough, and sizing a branch by adding fixture units without applying the correct table row for the pipe material, slope, and occupancy class.
Candidates study the drainage tables by rote and then apply a single 'total FU' figure to every branch, forgetting that building drain, building sewer, branch, and stack sizing each use different tables and that slope changes capacity (a 3-inch drain carries far more at 1/8 inch per foot than the same pipe at 1/4 inch when the table column is slope-dependent).
What to do instead
Practice sizing from a sketch: assign FU per fixture, sum per branch, then look up the branch, stack, and building drain columns separately, noting the slope basis printed in the table header. Build a one-page reference of the FU values for the fixtures you actually see (water closet, lavatory, bathtub, floor drain, washing machine, dishwasher, hose bibb) and re-derive a full example system until the table selection, not the arithmetic, is the hard part.
Sizing and routing vents by 'making it look right'-running a vent horizontally below the fixture flood level rim, using a flat or horizontal dry vent, or skipping a vent entirely on a fixture that is wet-vented or circuit-vented incorrectly.
Venting is the least intuitive part of drainage for candidates who came up in service work, and exam figures often show compact layouts where a shared vent looks plausible. The code's prohibitions (no horizontal dry vent below the flood level rim, vent must rise vertically before offsetting, developed length limits on wet vents) are easy to overlook when the drawing 'works'.
What to do instead
Memorize the venting rules as a checklist: vent takes off above the trap arm's flood level rim, rises vertically at least 6 inches before any offset, dry vents may offset at 45 degrees or steeper, wet vent limits on fixture units and developed length, and the maximum distance from trap to vent per pipe size. Then re-draw three exam-style layouts and mark each vent connection's compliance point by point.
Confusing trap seal protection rules-installing an S-trap, an unvented trap, a trap with more than the allowed fall from fixture to trap, or two traps on one trap arm-because the candidate reasons from 'it drains fine' rather than from the code's list of prohibited trap arrangements.
S-traps and crown-vented traps appear in older buildings and in hand sketches, and the exam deliberately shows plausible-looking arrangements. Candidates also forget the maximum developed length of the fixture outlet pipe to the trap (and the vertical fall limit) and the rule against double trapping.
What to do instead
Learn the prohibited list as named items: S-trap, drum trap (where prohibited), trap with a moving part, two traps on one branch, trap not vented, trap serving more than one fixture, and the fall/developed-length limits from fixture outlet to trap weir. Redraw each prohibited arrangement beside its compliant replacement so the visual pattern is recognized instantly.
Answering backflow and cross-connection questions by device name alone, without matching the degree of hazard and the specific application to the correct assembly (air gap, RPZ, double check, PVB, atmospheric vacuum breaker, spill-resistant vacuum breaker).
The devices are easy to remember as a list, but exam items hinge on whether the hazard is a health hazard (toxic, sewage, chemical) or a non-health hazard, whether the device is under continuous pressure, and whether it is subject to backpressure or only backsiphonage. Candidates pick the most protective device reflexively and get the 'which is required here' item wrong.
What to do instead
Build a decision tree: health hazard vs. non-health hazard, then continuous pressure vs. not, then backpressure vs. backsiphonage, then whether the device may be used indoors or must be protected from freezing. Drill with scenario stems (boiler makeup, irrigation, carbonator, hose bibb, laboratory sink, fire sprinkler with chemical additive) and state the required assembly plus why the next-smaller device fails.
Applying the general building/plumbing code without the Nevada overlay-missing that the state adopts a specific edition of the Uniform Plumbing Code with state amendments, and that local jurisdictions may impose additional requirements or fees.
Candidates study a national code text and assume it is the exam's authority, but Nevada's plumbing statute and regulations adopt a particular UPC edition and add state-specific provisions (licensing, permits, inspection authority, water heater and seismic strapping details, and local amendments). The exam mixes general code with Nevada-specific administration items.
What to do instead
Download the current Nevada statute and the plumbing regulations from the state licensing board's site, and mark every place they adopt, amend, or delete a model-code section. Keep a two-column sheet: model-code rule on the left, Nevada amendment on the right. Re-read the board's licensing chapter until you can state the license classes, qualifying requirements, and disciplinary grounds without notes.
Treating permits and inspections as a formality-assuming a permit is only needed for 'big' jobs, that a homeowner can pull any plumbing permit, or that inspections occur only at final.
Candidates with field experience often work under a contractor's permit and never see the administrative side. Exam items test who may obtain a permit, when a permit is required versus exempt, the sequence of rough-in, top-out, and final inspections, and the consequences of covering work before inspection.
What to do instead
Write out the permit lifecycle from memory: application and fee, plan review where required, rough-in inspection before concealment, and final inspection before use. List the exemptions explicitly and the penalties for work without a permit. Then answer practice items that ask 'what happens next' in a sequence, since these test order of operations, not facts.
Calculating water supply sizing and pressure using only fixture units, ignoring the pressure-loss chain-meter loss, developed length, elevation, and the minimum residual pressure required at the most remote fixture-and failing to convert between static, residual, and flowing pressure.
Candidates memorize the demand tables but skip the pressure budget. Exam items give a street pressure, a meter size, a building height, and a longest run, and expect the candidate to subtract elevation (0.434 psi per foot of rise), meter and device losses, and friction loss to see whether the residual at the top fixture meets the minimum.
What to do instead
Practice a full pressure-budget problem end to end: static street pressure, minus meter loss from the manufacturer table, minus elevation gain, minus friction loss over developed length (including fittings as equivalent length), equals residual at the fixture; compare to the minimum required. Do it once in psi and once in feet of head so the conversion is automatic.
Reading isometric drawings without establishing orientation and scale first-misidentifying which pipe is the building drain versus a branch, or taking off quantities from a plan without accounting for vertical risers and fittings.
Isometrics use a 30-degree convention and no fixed orientation; candidates start counting pipe at the first line they see and miss that vertical runs, offsets, and the difference between plan and isometric views change the takeoff. Material takeoffs then undercount pipe and fittings.
What to do instead
Adopt a fixed procedure: orient the drawing (find the building drain exit and the water service entry), label every run as horizontal or vertical, then take off pipe by run and add fittings at each change of direction and size. Practice on three isometrics where the same system is drawn from different angles, and reconcile your takeoff against a counted fitting list.
Answering water heater items from general knowledge rather than code specifics-missed temperature and pressure relief valve requirements, discharge pipe material and termination, expansion control, and the required strapping or anchoring of the tank.
Water heaters appear in both the fixtures and the gas domains, and candidates know how a heater works but not the code's installation rules: T&P valve rating and setting, discharge pipe size and material, no threads at the discharge termination, no valves or traps in the discharge line, and the pan and drain requirements where leakage would cause damage.
What to do instead
Make a water heater checklist covering: T&P valve and its rating versus tank rating, discharge pipe diameter, material, gravity flow, termination point, pan and drain, expansion tank or thermal expansion control on a closed system, and anchoring. Then apply the checklist to both an electric and a gas installation, adding the gas connector, sediment trap, and venting rules for the gas case.
Skipping the safety, tools, and jobsite-practices domain as 'common sense', and answering confined-space, trenching, and gas-leak items from habit rather than from the required procedures.
This domain feels easy, so candidates spend no time on it, but exam items test specific thresholds and sequences: when a space is a permit-required confined space, the order of atmospheric testing, the depth and slope rules for excavations and when shoring or a competent person is required, and the correct response to a suspected gas leak (no ignition sources, evacuate, notify, do not operate switches).
What to do instead
Study this domain as a procedure list, not trivia: memorize the atmospheric testing order (oxygen, combustibles, toxics), the excavation depth thresholds and access/egress spacing, and the gas-leak response sequence. Practice explaining each procedure aloud in the order it must occur, because exam stems test sequence as often as thresholds.