Exam Cheat Sheet · Quick Reference
Mississippi Plumbing
Mississippi · PSI Services Contractor
Verified, not estimated. Every figure below is drawn from the official exam structure we maintain — question counts, passing standard and topic weighting. Practice questions are grounded in the source law with statute citations. We omit any figure we can't verify rather than guess at it.
Total questions
70
Passing score
70%
Exam time
180 min
Administered by
PSI Services Contractor
Format
Reference materials allowed
Mississippi State Portion 70 questions
General Plumbing Regulations
4 Q · 6%
Plumbing system installation requirements and prohibited locationsMaterial identification, third-party certification, and standards compliancePipe and system protection (freezing, physical damage, corrosion, structural safety)Trenching, excavation, bedding, and backfill requirementsRequired tests and inspections (water, air, drainage, backflow, and shower liner tests)Piping support intervals and hanger spacing by material typeRodentproofing requirements for plumbing systemsCondensate disposal systems and auxiliary drain requirements
Safety
4 Q · 6%
Confined space identification, classification, and permit requirementsHazardous atmosphere recognition and atmospheric testing proceduresRoles and responsibilities of entry supervisors, attendants, and authorized entrantsConfined space rescue procedures and emergency servicesGeneral contractor safety and health provisions and employer responsibilitiesPersonal protective equipment requirements and selectionMedical services, first aid requirements, and emergency action plansPermissible exposure limits for airborne contaminants including lead
Cleanouts
4 Q · 6%
Cleanout placement intervals for horizontal drains, building drains, and building sewersCleanout requirements at changes of direction greater than 45 degreesCleanout size requirements relative to pipe size servedRequired clearance distances from cleanout openings to obstructionsCleanout access requirements and prohibited concealed locationsCleanout plugs: approved materials and head typesCleanout equivalents (fixture traps as substitutes)Prohibited use of cleanout openings for fixture or piping extensionsCleanout requirements at building drain and building sewer junctionCleanout installation at changes of horizontal direction greater than 45 degreesCleanout sizing requirements relative to pipe size servedRequired clearance distances for cleanout access openings
+3 more
Fixtures and Equipment
5 Q · 7%
Minimum number of plumbing fixtures by occupancy classificationFixture material standards and quality requirementsInstallation clearances and spacing for fixturesWater closet and urinal requirements and prohibitionsShower compartment construction and lining requirementsFaucet and fixture fitting standards including temperature controlAccessible plumbing fixture requirementsWater heater installation safety devices and discharge pipingProhibited fixtures and fixture connectionsFixture material quality and standardsInstallation requirements for fixtures including spacing and clearancesFlushing devices for water closets and urinals
+2 more
Water Heaters
2 Q · 3%
Temperature and pressure relief valve requirements and installationRelief valve discharge piping specificationsWater heater installation requirements and access clearancesSafety devices: antisiphon, vacuum relief, and shutdown provisionsWater heater pan requirements and drain terminationDrain valve requirements for tank-type water heatersWater temperature controls and maximum temperature limitsWater heater labeling, pressure markings, and insulation requirements
Piping, valves, controls
3 Q · 4%
Approved materials and standards for water service and distribution pipeApproved materials and standards for drainage and vent pipePipe joint and connection methods by material type (copper, PVC, CPVC, PEX, steel, cast iron)Valve types, placement requirements, and shutoff valve locationsBackflow prevention devices, types, and applicationsWater pressure requirements, pressure-reducing valves, and booster systemsPipe sizing for water distribution systemsProhibited joints, connections, and fitting types
Water Supply
6 Q · 9%
Backflow prevention devices, assemblies, and applicationsWater service pipe materials, standards, and sizing requirementsWater distribution system design criteria and pipe sizing methodsProtection of potable water supply from cross-connections and contaminationHot water supply system requirements and temperature controlsValve placement requirements for water supply and distribution systemsIndividual water supply systems, well construction, and disinfectionWater pressure regulation, booster systems, and water hammer arrestors
Hangers and Supports
3 Q · 4%
Pipe support intervals by material type (Table 308.5 horizontal and vertical spacing)Hanger and anchor material requirements and prohibition of galvanic actionStructural attachment of hangers and anchors to building constructionSway bracing for horizontal drainage pipes at direction changesAnchorage and restraint of drainage piping at changes in direction and diameterSeismic support requirements for plumbing pipingExpansion joint fittings for pipe expansion and contractionSupport requirements for thermal expansion tanks and parallel water distribution manifolds
Drain, Waste, and Vent
15 Q · 21%
Drainage fixture unit (DFU) values and fixture load calculationsSizing of horizontal drainage pipes, building drains, and building sewersSlope requirements for horizontal drainage pipingApproved materials for above-ground and underground drain, waste, and vent pipeVent system types and installation requirements (individual, common, wet, circuit, air admittance valves)Trap requirements, prohibited trap types, and trap seal protectionCleanout location, spacing, size, and access requirementsInterceptors and separators (grease, oil, sand) requirements and applications
Backflow
3 Q · 4%
Definitions of backflow, backsiphonage, backpressure, and cross connectionApplication and selection of backflow prevention devices by hazard level (Table 608.1)Types of backflow preventers and applicable standards (air gap, reduced pressure principle, double check, vacuum breakers, dual check)Protection requirements for specific connections (boilers, sprinkler systems, irrigation, beverage dispensers, hose connections, health care equipment)Installation requirements for backflow preventers (critical level, location, access, freeze protection)Inspection and testing of backflow prevention assemblies (annual inspections, testing standards per Section 312.10)Identification and labeling of nonpotable water systemsThermal expansion control where backflow preventers are installed on water heater supply
Traps and Interceptors
4 Q · 6%
Trap seal depth requirements and prohibited trap typesFixture trap installation requirements including distance limitations and double-trapping prohibitionTrap seal protection methods for floor drains subject to evaporationGrease interceptor requirements, sizing, and applicable facilitiesOil separator design and installation requirements for garages and service stationsSpecific interceptor requirements for clothes washers, bottling plants, and slaughterhousesVenting, access, and maintenance requirements for interceptors and separatorsSand interceptors and automatic grease removal devices
Developed length
2 Q · 3%
Center-to-center vs. end-to-end pipe length measurementsFitting allowance calculations for threaded, copper, and plastic fittingsDeveloped length measurement for cleanout spacing requirementsDiagonal and offset calculations using angle constantsDeveloped length of vent piping for sizing and distance limitationsConverting center-to-center measurements to cut lengthsDeveloped length measurement along drainage piping for trap-to-vent distance
Isometric Analysis
12 Q · 17%
Calculating center-to-center (c-c) pipe lengths from isometric drawingsCalculating end-to-end (e-e) pipe lengths using fitting allowances45-degree offset calculations using diagonal and offset constantsRise, run, and diagonal relationships in pipe offsetsThree-pipe offset diagrams with 45-degree fittingsRolling offsets and true offset calculationsParallel offset pipe length differences using spread constantsEqual spacing and pipe cut list calculations from isometric diagrams
Joints and Connections
3 Q · 4%
Joint types and methods for PVC plastic pipe (solvent cementing, mechanical, threaded, push-fit)Joint types and methods for copper and copper-alloy pipe and tubing (solder, brazed, mechanical, press-connect, push-fit)Joint types and methods for cast-iron pipe (caulked, compression gasket, mechanical coupling for hubless)Joint types and methods for ABS plastic pipe (solvent cementing, mechanical, threaded, push-fit)Joints between different piping materials (transition fittings, mechanical compression joints, dielectric fittings)Prohibited joints and connections in sanitary drainage and water supply systemsHeat-fusion joints for polyethylene, polyolefin, polyvinylidene fluoride, and polypropylene plastic pipeJoint types and methods for galvanized steel pipe (threaded and mechanical)
Key Distinctions
Flow pressurevsStatic pressure (head)
Flow pressure is the pressure in the supply pipe near the faucet/outlet while that outlet is wide open and flowing, whereas static pressure change is the no-flow pressure gain or loss from elevation computed at 0.433 psi per foot.
IPC 2021 Page 2-4Copper/plastic fitting allowancevsThreaded fitting allowance
The copper allowance is the center-to-face dimension MINUS the depth of the solder cup (PVC: center to the outside shoulder of the hub cup), with no thread-in deduction because the joints are soldered/solvent welded, while threaded fittings require deducting the thread-in (engagement) amount (allowance = 2A − 2B).
Mathematics for Plumbers, Unit 10, Pages 56-57 (Allowances for Copper Fittings)Copper fitting allowance measurementvsPVC (plastic) fitting allowance measurement
Copper allowance equals center-to-face minus the depth of the solder cup, while PVC allowance is measured from center to the outside shoulder of the hub cup; the calculation steps are otherwise the same.
Mathematics for Plumbers, Unit 10, Pages 56-57 (Allowances for Copper Fittings)Developed lengthvsStraight-line (direct) distance
Developed length is measured along the centerline of the pipe and fittings, following the actual path of the piping, not the straight-line distance between two points.
IPC 2021 Page 2-3Segmented loss method fitting allowance (add 50%)vsSection E104.1 sizing factor (×1.2)
In the segmented loss method you add 50 percent of the developed length (× 1.5) for fittings and valves, while the E104.1/AP104 method multiplies the actual length to the most remote fixture by 1.2 to compensate for pressure loss through fittings.
IPC 2021 Page E-4 (Section E103.3, Step 6)Short sweep (or long sweep)vsSanitary tee
A short sweep is permitted for horizontal-to-horizontal changes of direction in drainage, while a sanitary tee is permitted only for horizontal-to-vertical connections (a standard quarter bend in horizontal-to-horizontal use is limited to specific small fixture drains).
IPC 2021 Table 706.3Copper tubing Types K and LvsCopper tubing Types M and DWV
For building sewer pipe, copper or copper-alloy tubing is limited to Type K or L; Types M and DWV are not permitted.
IPC 2021 Table 702.3Approved building sewer materialsvsGalvanized steel pipe
Vitrified clay, cast-iron, and concrete pipe (ASTM C14, C76, CSA A257.1/A257.2) are listed as approved building sewer materials, but galvanized steel pipe is not listed/permitted for building sewer.
IPC 2021 Table 702.3Water supply system testvsDrainage/vent air test
The water supply system is tested tight at a water pressure not less than the system working pressure held not less than 15 minutes, while the DWV air test uses a uniform gauge pressure of 5 psi (or balancing a 10-inch mercury column) held not less than 15 minutes, and plastic piping shall not be air tested.
IPC 2021 Section 312.5Urinal substitution in assembly and educational occupanciesvsUrinal substitution in all other occupancies
Urinals may be substituted for not more than 67 percent of required water closets in assembly and educational occupancies, versus a 50-percent limit in all other occupancies.
IPC 2021 Page 4-12Wet ventvsCircuit vent / combination waste-and-vent
A wet vent vents one or more fixtures while also carrying the discharge of another fixture (classic single bathroom group), whereas circuit vents serve batteries of fixtures and combination waste-and-vent is a different, more restricted system.
Trap arm limit (Table 909.1)vsCrown vent prohibition (Section 909.3)
Table 909.1 sets the maximum distance from trap weir to vent (e.g., 6 ft for a 1½" trap, 8 ft for a 2" trap, with self-siphoning water closets not limited), while Section 909.3 sets the minimum: no vent within two pipe diameters of the trap weir.
IPC 2021 Table 909.1Metallic piping contact with framing/masonryvsMetallic piping contact with corrosive soil
Cast iron, ductile iron, and galvanized steel are excepted from the prohibition on direct contact with steel framing, concrete, cinder walls/floors and masonry, but the prohibition on contact with corrosive soil applies to all metallic piping without exception.
IPC 2021 Section 305.1Written emergency action planvsOrally communicated plan
An employer with 10 or fewer employees may communicate the emergency action plan orally and need not maintain a written plan; otherwise a written plan is required.
29 CFR §1926.35(e)(3)Key Terms
Flow pressure IPC 2021 Page 2-4
The pressure in the water supply pipe near the faucet or water outlet while the faucet or water outlet is wide open and flowing.
Faucet IPC 2021 Page 2-4
A valve end of a water pipe through which water is drawn from or held within the pipe.
Effective opening IPC 2021 Page 2-3
The minimum cross-sectional area at the point of water supply discharge, expressed as the diameter of a circle (or of an equivalent-area circle if not circular); for faucets and similar fittings it is measured at the smallest orifice in the fitting body or in the supply piping to the fitting.
Developed length IPC 2021 Page 2-3
The length of a pipeline measured along the centerline of the pipe and fittings.
Backsiphonage IPC 2021 Section 202 Definitions
The backflow of potentially contaminated water into the potable water system as a result of the pressure in the potable water system falling below atmospheric pressure of the fixtures, pools, tanks or vats connected to the potable water distribution piping.
Cross connection IPC 2021 Section 202 Definitions
Any physical connection or arrangement between two otherwise separate piping systems, one containing potable water and the other containing water of unknown or questionable safety or steam, gas or chemical, whereby flow from one system to the other is possible.
Low head backpressure Mathematics for Plumbers and Pipefitters (8th ed.), Chapter 4 / IPC 2021, Section 202
A pressure less than or equal to 4.33 psi (29.88 kPa), the pressure exerted by a 10-foot column of water.
Branch interval IPC 2021 Section 202 (Branch interval)
A vertical length of stack of 8 feet or more between the connections of horizontal branches; branches connecting less than 8 feet apart fall within the same interval.
Vent stack IPC 2021 Section 202
A separate vertical vent pipe installed to circulate air through the drainage system, connecting near the base of the soil stack and rejoining the stack vent above the highest fixture.
Wet vent
A pipe that vents one or more fixtures while also carrying the discharge of another fixture, typically within a single bathroom group.
Invert Mathematics for Plumbers and Pipefitters (8th ed.), Page 129 (Unit 34)
The inside bottom of the pipe; sewers and house drains show elevations measured to the invert rather than the centerline.
Cleanout equivalent IPC 2021 Chapter 7 — Sanitary Drainage, Section 708.1.6
A fixture trap or a fixture with an integral trap that is removable without altering concealed piping is acceptable as a cleanout equivalent; a removable P-trap with slip or ground joint connections may serve as the cleanout for drain piping one size larger than the P-trap.
Concealed cleanout location (crawl space) IPC 2021 Chapter 7 — Sanitary Drainage, Section 708.1.11
A prohibited concealed location includes a crawl space where the height from the crawl space floor to the nearest obstruction along the path from the crawl space opening to the cleanout is less than 24 inches.
Exempt work (permit not required) IPC 2021 Page 1-4
Clearing stoppages, repairing leaks in pipes, valves or fixtures, and removal/reinstallation of water closets are exempt from a permit, provided the work does not involve replacement or rearrangement of valves, pipes or fixtures.
Abandoned permit application IPC 2021 Page 1-4
An application for a permit is deemed abandoned 180 days after the date of filing unless pursued in good faith or a permit has been issued, with extensions of up to 180 days each allowed by the code official.
Prohibited water closets IPC 2021 Page 4-1
Water closets having a concealed trap seal or an unventilated space, or walls that are not thoroughly washed at each discharge, are prohibited (trough urinals are also prohibited).
Shower liner test IPC 2021 Page 3-5
The floor and receptor area is filled with potable water to a depth of not less than 2 inches measured at the threshold (a temporary threshold is built where the threshold is less than 2 inches) and retained not less than 15 minutes with no leakage.
Crown vent (prohibited) IPC 2021 Section 909.3
A vent connected within two pipe diameters of the trap weir; such a connection is prohibited.
Formulas to Know
Static pressure loss/gain due to elevation (head)
psi = 0.433 psi per foot × elevation change; e.g., 14 ft × 0.433 = 6.06 psi, subtracted from available pressure when the fixture is above the source.Length allowance for fittings and valves in water pipe sizing
Segmented loss method: equivalent length = developed length × 1.5 (add 50% of developed length); e.g., 225 ft × 1.5 = 338 ft. Section E104.1/AP method: maximum developed length = actual length from source to most remote fixture × 1.2.Minimum individual vent size
Base size = ½ × fixture drain size, but never smaller than 1¼ in; if the vent's developed length exceeds 40 ft, increase one nominal size for its entire length (e.g., 1½" drain → 0.75 → 1¼" min; at 44 ft → 1½"; 3" drain → 1½").Stack vent sizing from Table 906.1
Enter the table on the row for the stack size and its DFU load, then select the smallest vent size whose permitted developed length equals or exceeds the actual developed length (e.g., 3" stack / 53 DFU, 77 ft → 2"; 3" stack / 10 DFU, 282 ft → 2½"; 4" stack / 140 DFU, 68 ft → 3").Offset travel and run using printed constants
45°: travel = set × 1.414 and run = set × 1.000 (run equals set); 22½°: travel = set × 2.613; 60°: travel = offset × 1.155. (0.707 is the inverse, used to find offset from a known diagonal.)Rolling offset true offset and travel
True offset = √(set² + roll²); e.g., √(12² + 9²) = 15.0 in; then travel = true offset × fitting constant (15.0 × 1.414 = 21.2 in at 45°; 15.0 × 1.155 = 17.3 in at 60°).Cut length of threaded pipe
Cut (end-to-end) = center-to-center − (2 × fitting takeoff/center-to-face) + (2 × thread engagement); e.g., 42 − (2 × 2¼) + (2 × ½) = 38½ in; 36 − 4 + 1 = 33.00 in; or e-e = c-c − [2A − 2B] = 48 − [3 − 1] = 46 in.Cut length of soldered (sweat) copper pipe
Cut = center-to-center − (fitting allowance × 2 ends); with a ½ in allowance per fitting end: 24 − 1 = 23.00 in and 18 − 1 = 17.00 in (total 40.00 in for both segments).Fall (drop) of horizontal drainage and resulting invert elevation
Fall = grade × run (¼ in/ft × 18 ft = 4½ in; 1/32 in/ft × 35 ft = 35/32 ≈ 1⅛ in; 32 ft × ¼ = 8 in plus 24 ft × ⅛ = 3 in → 11 in total = 11/12 = 0.92 ft); downstream invert = upstream invert − total fall (101.00 − 0.92 = 100.08 ft); moving upstream, elevation rises (⅛ in/ft ≈ 0.01 ft/ft: 0.01 × 25 = 0.25 ft, 91.55 + 0.25 = 91.80 ft).Total DFU load and stack sizing
Branch/stack load = sum of connected fixture DFU values (5 + 5 + 2 + 2 = 14 DFU; 2 + 3 + 4 = 9 DFU); then choose the smallest pipe whose table rating covers the load (14 ≤ 48 DFU → 3 in stack).Oil separator capacity (garages/service stations)
Capacity = 6 cubic feet for the first 100 sq ft of floor area + 1 cubic foot for each additional 100 sq ft; 500 sq ft → 6 + (4 × 1) = 10 cubic feet.