Exam Cheat Sheet · Quick Reference

Tennessee CMC-A Mechanical Plumbing

Tennessee  ·  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
110
Passing score
73%
Exam time
295 min
Administered by
PSI Services Contractor
Format
Reference materials allowed

Tennessee State Portion 110 questions

General Knowledge and Math 14 Q · 13%
Arithmetic operations and formula solving for plumbing applicationsUnit conversions and measurement systems (English and metric)Geometric shapes, area, and volume calculationsPythagorean theorem and right triangle solutionsPipe offset, diagonal, rise, and run calculations using angle constantsWater pressure, head, and force calculationsIPC definitions and plumbing code terminologyIPC scope, permit requirements, and inspection procedures
General Requirements (not including Gas) - Administrative, Structural, Backflow, Materials and Supports, Joints and Connections, Storm Drains, Testing 10 Q · 9%
AdministrativeStructuralBackflowMaterials and SupportsJoints and ConnectionsStorm DrainsTesting
Water Supply and Distribution 10 Q · 9%
Potable water protection and cross-connection controlBackflow prevention devices and assembliesPipe materials, fittings, and joining methods for water service and distributionWater pressure requirements, pressure-reducing valves, and booster systemsHot water supply system requirements and thermal expansion controlWater piping system sizing using fixture units and segmented loss methodWater heater installation, safety devices, and relief valve discharge pipingWater volume, pressure, and capacity calculations
Fixtures, including Water Heaters 6 Q · 5%
Water HeatersMinimum number of required plumbing fixtures by occupancy classificationFixture installation requirements and clearancesFaucets and fixture fittings including shower valves and temperature limiting devicesSafety devices for water heaters including relief valves and discharge pipingWater heater installation requirements including access, location, and connectionsHot water supply system requirements including temperature limits and recirculationBackflow protection for plumbing fixtures and appliancesFixture-specific standards and waste outlet requirements
Drain, Waste, and Vent Systems, including Indirect and Special Waste 28 Q · 25%
Indirect WasteSpecial WasteDrainage fixture unit (DFU) values and system sizingHorizontal drainage pipe slope and installation requirementsCleanout placement, sizing, and access requirementsTrap requirements, prohibited trap types, and trap seal protectionVent types, sizing, and terminal requirementsGrease interceptors and other interceptors and separatorsSumps, ejectors, and below-grade drainage systemsPipe materials, fittings, and joint methods for drainage and vent systems
Traps, Cleanouts, and Interceptors 6 Q · 5%
TrapsCleanoutsInterceptorsProhibited trap typesTrap seal depth requirements and protection methodsGrease interceptor sizing and installation requirementsOil separator requirements and designCleanout spacing, sizing, and access requirementsSand and specialty interceptors (clothes washer, bottling, slaughterhouse)Venting and maintenance of interceptors and separators
Isometric Analysis 20 Q · 18%
Center-to-center and end-to-end pipe length calculationsFitting allowances for threaded, copper, PVC, and welded fittings45-degree offset calculations using diagonal and rise/run constantsOffset calculations for other fitting angles (60°, 22½°, 11¼°, 72°) using trigonometric constantsThree-pipe diagonal assembly layout and pipe length determinationRolling offsets and true offset calculationsParallel offset spacing and equal spacing calculationsReading and applying pipe fitting data tables from appendix references
Gas Appliances and Piping 12 Q · 11%
Gas AppliancesGas PipingGas piping materials and fittings (metallic pipe, copper tubing, CSST, polyethylene plastic)Pipe sizing methods (longest length, branch length, hybrid pressure)Pressure testing and leak checks of gas piping systemsCombustion air requirements for gas appliances (indoor, outdoor, and combination methods)Venting systems for gas appliances (vent types, connectors, termination, sizing)Appliance location, clearances, and installation requirementsSpecific gas appliance requirements (furnaces, unit heaters, unvented room heaters, clothes dryers, water heaters)
OSHA Safety 4 Q · 4%
Employer accident prevention responsibilities and safety programsPersonal protective equipment (PPE) selection, provision, and paymentFall protection systems — guardrails, safety nets, and personal fall arrestExcavation safety — cave-in protection, sloping, shoring, and competent person inspectionsConfined space entry procedures and permit-required confined spacesFire protection and prevention — extinguishers, flammable liquid storage, and fire prevention plansHazardous substances exposure limits and asbestos handling requirementsWelding and cutting — compressed gas cylinder handling and storage

Key Distinctions

Copper (soldered) fitting allowancevsThreaded fitting allowance

Copper allowance equals center-to-face minus the depth of the solder cup with no thread-in deduction, while threaded fittings require a thread-in (engagement) deduction step.

Mathematics for Plumbers, Unit 10, Pages 56-57 (Allowances for Copper Fittings)
PVC (plastic) fitting allowancevsThreaded fitting allowance

PVC allowance is measured from center to the outside shoulder of the hub cup using the same steps as copper, with no thread-in deduction required, unlike threaded fittings.

Mathematics for Plumbers, Unit 12, Pages 60-61 (Allowance for Plastic Fittings)
Equal center-to-center lengthsvsEqual end-to-end lengths

Equal spacing fixes equal center-to-center lengths, but because a 90° ell and a 45° ell have different fitting allowances, the end-to-end (cut) lengths will differ.

Mathematics for Plumbers and Pipefitters (8th ed.), Chapter 1 — Equal Spacing
Gas appliance in a private garagevsGas appliance in a public garage

IFGC 305.5 requires a minimum 6 feet of clearance above the floor in private garages versus 8 feet in public garages, with an exception where the appliance is protected from motor vehicle impact and installed per Section 305.3.

IFGC 2021 Section 305.5
RisevsRun

In an offset, the distance between two parallel vertical pipes is called the rise, while the same dimension between two parallel horizontal pipes is called the run ('set' is short for offset).

Mathematics for Plumbers and Pipefitters (8th ed.), Chapter 2 — Offset, Diagonal, Rise, and Run
Stack vent sizing (IPC Table 906.1)vsIndividual vent sizing (IPC Section 906.2)

Stack vents are sized by reading Table 906.1 for the stack size and DFU load against developed length, while individual vents are sized at half the fixture drain diameter (never less than 1¼ in.) with one nominal size increase when developed length exceeds 40 feet.

IPC 2021 Table 906.1
Disinfection at 50 ppm chlorinevsDisinfection at 200 ppm chlorine

IPC 610.1 permits filling the system with not less than 50 ppm chlorine held for 24 hours, or not less than 200 ppm chlorine held for 3 hours; either way the system is then flushed until chlorine is purged.

IPC 2021 Section 610.1
Horizontal stack offset sizingvsVertical stack sizing

Per IPC 710.1.1, a horizontal offset in a stack must be sized as required for building drains using Table 710.1(1), not by the stack table.

IPC 2021 Section 710.1.1
Wet 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.

Segmented loss method fitting allowance (add 50%)vsResidential maximum developed length factor (×1.2)

The segmented loss method adds 50 percent of the developed length for fittings and valves when sizes are unknown, while IPC E104.1 Item 3 multiplies the actual length to the most remote fixture by 1.2 to compensate for fitting pressure loss.

IPC 2021 Page E-4 (Section E103.3, Step 6)
Water supply system test (IPC 312.5)vsDWV air test (Section 312.3)

The water supply system is tested tight at not less than the working pressure held not less than 15 minutes, while the DWV air test uses a uniform gauge pressure of 5 psi (or a 10-inch mercury column) held not less than 15 minutes, and plastic piping shall not be air tested.

IPC 2021 Section 312.5
Invert elevationvsCenterline elevation

Most pipes are measured to the centerline, but house sewers and house drains show elevations measured to the invert — the inside bottom of the pipe — which is a solid surface for installation.

Mathematics for Plumbers and Pipefitters (8th ed.), Page 129 (Unit 34)

Key Terms

Effective opening IPC 2021 Page 2-3
Per IPC Section 202, the minimum cross-sectional area at the point of water supply discharge expressed as the diameter of a circle (or an equivalent-area circle if not round); for faucets and similar fittings it is measured at the smallest orifice in the fitting body or supply piping.
Developed length IPC 2021 Page 2-3
Per IPC Section 202, the length of a pipeline measured along the centerline of the pipe and fittings, following the actual pipe path rather than a straight-line distance.
Branch interval IPC 2021 Section 202 (Branch interval)
Per IPC 2021 Section 202, 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 branch interval.
Wet vent
A pipe that vents one or more fixtures while also carrying the discharge of another fixture, typically within a single bathroom group.
Backsiphonage IPC 2021 Section 202 Definitions
Per IPC 2021 Section 202, the backflow of potentially contaminated water into the potable water system caused by the pressure in the potable system falling below atmospheric pressure of the fixtures, pools, tanks or vats connected to the distribution piping.
Cross connection IPC 2021 Section 202 Definitions
Per IPC 2021 Section 202, any physical connection or arrangement between two otherwise separate piping systems, one containing potable water and the other water of unknown or questionable safety or steam, gas or chemical, where flow from one to the other is possible.
Low head backpressure Mathematics for Plumbers and Pipefitters (8th ed.), Chapter 4 / IPC 2021, Section 202
Per 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.
Asbestos-containing material (ACM) 29 CFR 1926, §1926.1101(b)
Per 29 CFR 1926.1101(b), any material containing more than one percent asbestos.
Asbestos PEL (8-hour TWA) 29 CFR 1926, Subpart Z, §1926.1101(c)(1) and (i)(1)
Per 29 CFR 1926.1101(c)(1) and (i)(1), 0.1 fiber per cubic centimeter of air as an 8-hour TWA; protective clothing (coveralls, head coverings, gloves, foot coverings) is required for employees exposed above this limit.
Lead-free solder IPC 2021 Section 605.12.3
Per IPC Section 605.12.3, solder and flux used for joining water supply piping having a chemical composition equal to or less than 0.2-percent lead.
Invert Mathematics for Plumbers and Pipefitters (8th ed.), Page 129 (Unit 34)
The inside bottom of the pipe, the reference point to which house sewer and house drain elevations are measured.
Diagonal (travel) Mathematics for Plumbers and Pipefitters (8th ed.), Chapter 2 — Offset, Diagonal, Rise, and Run
The center-to-center length of the connecting pipe where two parallel pipes are joined by fittings other than 90°; the diagonal is preferred because it restricts flow less.
Low-heat (residential) appliance IFGC 2021 Section 202, Appliance Type definitions
Per IFGC 2021 Section 202, any appliance in which the products of combustion at the point of entrance to the flue under normal operating conditions have a temperature of 1,000°F (538°C) or less.
Crown vent (prohibited) IPC 2021 Section 909.3
Per IPC 2021 Section 909.3, a vent connected within two pipe diameters of the trap weir (3 in. for a 1½-inch trap, 4 in. for a 2-inch trap) is a prohibited crown vent.
Trap arm maximum distance (Table 909.1) IPC 2021 Table 909.1
Per IPC 2021 Table 909.1, the maximum distance from trap weir to vent — 6 feet for a 1½-inch trap and 8 feet for a 2-inch trap — with water closets treated as self-siphoning fixtures whose distance is not limited.
Nonpotable water piping identification IPC 2021 Section 608.9.2
Per IPC 608.9.1, 608.9.2 and 608.9.2.3, nonpotable distribution piping shall be purple and marked 'CAUTION: NONPOTABLE WATER – DO NOT DRINK,' using identification tape not less than 3 inches wide fastened not less than every 10 feet and run the entire pipe length, with outlet signage lettering not less than 0.5 inch high.

Formulas to Know

Static (gauge) pressure from vertical head, and head required for a given pressureStatic pressure (psi) = vertical height of water above the point (ft) × 0.433 psi/ft; Height (ft) = pressure (psi) ÷ 0.433. Only the vertical elevation difference counts (e.g., 46 ft × 0.433 = 19.9 ≈ 20 psi; 30 ÷ 0.433 = 69.3 ft; between two fixtures, (38 ft − 6 ft) × 0.433 = 13.9 psi).
45° offset travel and runTravel = set × 1.414 and Run = set × 1.000 (run equals set). Example: 16 × 1.414 = 22.62 ≈ 22-5/8 in.; 20 × 1.414 = 28.28 ≈ 28-1/4 in.
22½° offset travelTravel = set × 2.613. Example: 10 × 2.613 = 26.13 ≈ 26-1/8 in.; 20 × 2.613 = 52.26 ≈ 52-1/4 in.
Rolling offset true offset and travelTrue offset = √(set² + roll²); then Travel = true offset × 1.414 for 45° fittings. Example: √(12² + 9²) = 15.0 in.; 15.0 × 1.414 = 21.2 in.
Cut length of threaded pipe between two fittingsCut length = center-to-center − (fitting takeoff × 2) + (thread engagement × 2). Examples: 42 − (2 × 2¼) + (2 × ½) = 38½ in.; 36 − (2 × 2) + (2 × ½) = 33.00 in.
Drain fall, downstream invert, and percent slopeTotal fall = run (ft) × grade (in./ft), converted to feet by ÷12; Downstream invert = upstream invert − total fall; Percent slope = (rise in inches per foot ÷ 12) × 100. Examples: 32 ft × 1/8 in./ft = 4 in.; 48 ft × 1/4 in./ft = 12 in. = 1.00 ft, so 100.00' − 1.00' = 99.00'; (0.25 ÷ 12) × 100 = 2.08%.
Cylinder/pipe volume and gallon capacityVolume = π × r² × h (r = ½ diameter); Gallons = cubic feet × 7.48. Examples: π × 1.5² × 5 = 35.34 cu ft × 7.48 = 264 gal; π × 2² × 6 = 75.4 cu ft × 7.48 ≈ 565 gal (half height: π × 2² × 3 = 37.7 cu ft = 282 gal); 100 ft of 2-in. ID pipe = π × (1/12)² × 100 = 2.18 cu ft × 7.48 = 16.3 gal.
Water heater recovery rate (gallons per hour)Usable heat = input BTU/hr × efficiency; BTU per gallon = 8.33 lb/gal × temperature rise (°F); GPH = usable heat ÷ BTU per gallon. Example: 40,000 × 0.75 = 30,000; 8.33 × 70 = 583.1; 30,000 ÷ 583.1 = 51.4 GPH.
Maximum allowable friction loss rate for pipe sizingAllowable friction rate (psi per 100 ft) = (available pressure ÷ total equivalent length including fittings) × 100. Example: (22 psi ÷ 250 ft) × 100 = 8.8 psi per 100 ft.
Equivalent/maximum developed length allowances for fittings and valvesSegmented loss method: equivalent length = developed length × 1.5 (add 50%), e.g., 225 ft × 1.5 = 338 ft. Residential method (IPC E104.1 Item 3): maximum developed length = actual length from source of supply to most remote fixture × 1.2.
Start free practice Full study guide