Mechanical, Electrical and Plumbing Systems Vocabulary

811

The national 'call before you dig' phone number that notifies utility owners to locate and mark underground lines before excavation; in Ohio the service is run by OHIO811 (OUPS).

Similar definitions: call before you dig, one-call system, OUPS

Example: "Before trenching for the new sewer lateral, the crew called          so the gas and electric lines would be marked."

Accessible route

A continuous, unobstructed path at least 36 inches wide with a running slope no steeper than 1:20 that connects all accessible spaces and elements of a building or site.

Example: "The new restroom must be reached by an          with no steps."

Accumulator

A suction-line component in a refrigeration system that traps liquid refrigerant to prevent it from entering and damaging the compressor.

Similar definitions: suction accumulator

Example: "Heat pumps with fixed metering devices often have an          located just before the compressor."

Acrylonitrile butadiene styrene (ABS)

A black plastic pipe used mainly for drain, waste, and vent piping and joined with a one-step solvent cement.

Similar definitions: ABS pipe

Example: "The plumber glued the black          drain fittings without using primer."

Affected employee

Under lockout/tagout, an employee who operates or works in the area of equipment being serviced but is not the one applying the locks.

Example: "The machine operator was an         , so he was notified before the maintenance crew locked out the pump."

Air admittance valve (AAV)

A one-way valve that lets air into the drainage system when negative pressure develops and closes by gravity to keep sewer gas from escaping.

Similar definitions: AAV, cheater vent

Example: "Under the island sink, an          was installed because a vent could not be run through the roof."

Air conditioning

The treatment of air to control its temperature, humidity, cleanliness, and distribution at the same time to meet the needs of a conditioned space.

Similar definitions: AC

Example: "Central          cools the air and also removes moisture through the evaporator coil."

Air gap

The unobstructed vertical distance through open air between the outlet of a water supply pipe or faucet and the flood level rim of the receptacle it serves.

Example: "The space between the faucet spout and the top of the sink is an          that prevents back-siphonage."

Alternating current (AC)

Electric current whose direction reverses back and forth at regular intervals; standard U.S. building power alternates at 60 hertz.

Similar definitions: AC

Example: "The receptacles in a house supply 120-volt         ."

American Wire Gauge (AWG)

The standard U.S. system for wire sizes in which a smaller gauge number means a larger conductor diameter and higher ampacity.

Similar definitions: wire gauge

Example: "A 12          conductor is thicker than a 14 conductor and is used on 20-ampere circuits."

Americans with Disabilities Act (ADA)

A federal civil rights law that prohibits discrimination against people with disabilities in everyday activities, including employment and access to buildings.

Example: "Under the         , a new public restroom must include an accessible route and fixtures a wheelchair user can reach."

Ampacity

The maximum current, in amperes, that a conductor can carry continuously under the conditions of use without exceeding its temperature rating.

Similar definitions: current-carrying capacity

Example: "The breaker size must match the          of the wire it protects."

Ampere

The unit of electric current; one ampere equals one coulomb of charge passing a point per second.

Similar definitions: amp

Example: "A hair dryer drawing 12.5         s on a 120-volt circuit uses 1,500 watts."

Anchorage

A secure point of attachment for lifelines, lanyards, or deceleration devices in a personal fall arrest system.

Similar definitions: anchor point, tie-off point

Example: "The worker clipped his lanyard to a rated roof          before stepping near the edge."

Annual fuel utilization efficiency (AFUE)

A rating that compares the heat actually delivered by a furnace or boiler to the fuel energy supplied over a year, expressed as a percentage.

Similar definitions: AFUE

Example: "A furnace with 95 percent          turns 95 of every 100 Btu of gas into useful heat."

Appliance connector

Rigid metal pipe, semirigid tubing, or a listed and labeled flexible device that connects a gas appliance to the gas piping system.

Similar definitions: gas connector

Example: "A listed flexible          links the range to the gas shutoff valve."

Appliance shutoff valve

A manual valve installed in the gas supply to an appliance, within 6 feet of it and upstream of the connector or union, so the appliance can be shut off for service.

Similar definitions: gas cock

Example: "Before disconnecting the dryer, the technician closed the          behind it."

Apprenticeship

A registered training program that combines paid on-the-job training with related technical (classroom) instruction and ends with a nationally recognized, portable credential.

Similar definitions: registered apprenticeship, earn-while-you-learn

Example: "After high school, Maya entered a five-year plumbing          that paired job-site work with night classes."

Approved

Accepted as meeting code by the authority having jurisdiction, such as the building official.

Example: "Only          materials may be installed without special permission from the inspector."

APWA uniform color code

The standard colors used to temporarily mark underground utilities: red for electric, yellow for gas/oil/steam, orange for communications, blue for potable water, green for sewer and drain lines, purple for reclaimed water, pink for survey marks, and white for proposed excavation.

Similar definitions: utility marking colors

Example: "Under the         , the green paint across the yard showed where the sewer line ran."

Arc-fault circuit interrupter (AFCI)

A device that recognizes the characteristics of dangerous arcing and de-energizes the circuit to help prevent electrical fires.

Similar definitions: AFCI

Example: "Bedroom circuits in new homes require          protection to reduce fire risk from damaged cords."

Architect's scale

A measuring tool used to read and lay out building drawings drawn at reduced sizes, such as 1/4 inch = 1 foot-0 inches.

Similar definitions: architectural scale

Example: "Using the 1/4 edge of the         , the apprentice measured the bathroom as 8 feet wide."

Attachment plug

A device on the end of a flexible cord that, when inserted into a receptacle, connects the cord's conductors to the receptacle's conductors.

Similar definitions: plug, cap

Example: "The drill's          had a missing grounding prong, so it was tagged out of service."

Attendant

In confined-space work, the person stationed outside a permit space who monitors the authorized entrants and summons rescue if needed.

Similar definitions: hole watch

Example: "The          stayed at the manhole opening and kept radio contact with the worker inside the vault."

Authorized employee

Under lockout/tagout, a person who locks out or tags out machines or equipment in order to perform servicing or maintenance on them.

Example: "Only the          who placed the lock may remove it after the boiler repair is finished."

Backflow

The flow of water or other substances into the potable water supply from any source other than the intended source.

Similar definitions: reverse flow

Example: "A garden hose left in a bucket of fertilizer can allow          into the drinking water."

Backflow preventer

An assembly, device, or method used to prevent backflow into the potable water supply.

Similar definitions: backflow prevention device

Example: "A          is required on the lawn irrigation system connection."

Backpressure

Pressure in the downstream piping that is higher than the supply pressure, which can push contaminated water back into the potable supply.

Similar definitions: back pressure

Example: "A boiler system at higher pressure than the city main can cause          backflow."

Backsiphonage

Backflow of contaminated water into the potable system caused by supply pressure dropping below atmospheric pressure.

Similar definitions: back-siphonage

Example: "A water-main break that creates a vacuum in the piping can cause          from a submerged hose."

Backwater valve

A valve installed in a building drain or sewer that prevents sewage from backing up into lower levels and fixtures.

Similar definitions: backflow valve (drainage)

Example: "The basement bathroom has a          to stop the city sewer from backing up into the house."

Bait and switch

An alluring but insincere offer to sell a product or service the seller does not intend to sell, used to switch the customer to something else, usually at a higher price.

Similar definitions: bait advertising, deceptive advertising

Example: "The contractor advertised a $99 furnace tune-up and then pushed every caller toward a $4,000 replacement, a classic         ."

Benching

A method of protecting workers from cave-ins by excavating the sides of an excavation into one or a series of horizontal steps.

Similar definitions: benching system

Example: "Because the trench was in Type A clay, the crew used          to step the walls back."

Body harness

A set of straps that distributes fall-arrest forces over the thighs, pelvis, waist, chest, and shoulders and attaches to a personal fall arrest system.

Similar definitions: full-body harness

Example: "Body belts are banned for fall arrest, so each roofer wore a          connected to a lanyard."

Bonding

Permanently joining metal parts to form an electrically conductive path that ensures continuity and can safely carry any fault current likely to be imposed.

Similar definitions: bonded, equipotential bonding

Example: "         the metal gas piping to the grounding electrode system reduces shock hazards."

Bonding jumper

A conductor that ensures the needed electrical conductivity between metal parts that must be electrically connected.

Similar definitions: jumper

Example: "A          was installed around the water meter so the metal piping stayed electrically continuous."

Branch circuit

The circuit conductors between the final overcurrent device protecting the circuit and the outlets.

Example: "The kitchen countertop receptacles are supplied by a 20-ampere         ."

Branch vent

A vent connecting one or more individual vents to a vent stack or stack vent.

Example: "The individual vents from three lavatories tie into a single         ."

Brazing

A metal-joining process using a nonferrous filler metal that melts above 1,000 degrees F but below the melting point of the base metals, drawn into the joint by capillary action.

Similar definitions: silver soldering, hard soldering

Example: "Refrigerant lines are joined by          with a phosphorus-copper filler rod."

British thermal unit (Btu)

The amount of heat needed to raise the temperature of one pound of water by 1 degree Fahrenheit.

Similar definitions: Btu

Example: "A furnace input rating of 80,000          per hour describes how much heat energy it burns each hour."

Building drain

The lowest piping of the drainage system that receives discharge from soil, waste, and other drainage pipes inside the building and conveys it to the building sewer, extending 30 inches beyond the exterior wall.

Similar definitions: house drain

Example: "All the stacks connect to the          running under the basement floor."

Building information modeling (BIM)

A process in which a 3D digital model of a building is shared among designers and contractors to coordinate work and prevent conflicts before construction.

Similar definitions: BIM

Example: "The          model showed that a duct and a sewer pipe would collide above the ceiling."

Building official

The officer or authority charged with administering and enforcing the building, plumbing, mechanical, and electrical codes.

Similar definitions: code official, authority having jurisdiction (AHJ)

Example: "The          must approve the rough-in inspection before walls are closed."

Building sewer

The part of the drainage system that extends from the end of the building drain to the public sewer, private sewer, or septic system.

Similar definitions: sewer lateral

Example: "The          runs from the house foundation out to the street main."

Carbon monoxide (CO)

A colorless, odorless, poisonous gas produced by incomplete burning of fuel in appliances, generators, and engines.

Similar definitions: CO, the invisible killer

Example: "A cracked heat exchanger can leak          into the home, so CO alarms are required near sleeping areas."

Cave-in

The sudden separation and movement of soil or rock from the side of an excavation into the excavation in enough quantity to trap, bury, or injure a person.

Similar definitions: trench collapse

Example: "A cubic yard of soil can weigh as much as a car, so a          in an unprotected trench is often fatal."

Check valve

A valve that allows flow in only one direction and closes automatically to prevent reverse flow.

Similar definitions: non-return valve, one-way valve

Example: "A          on the sump pump discharge keeps pumped water from draining back into the pit."

Chlorinated polyvinyl chloride (CPVC)

A rigid cream or tan plastic pipe modified from PVC to handle hot water, used for hot and cold water distribution.

Similar definitions: CPVC pipe

Example: "Because it can carry hot water,          is used for water supply lines instead of standard PVC."

Chlorofluorocarbon (CFC)

A refrigerant compound of chlorine, fluorine, and carbon, such as R-12, that destroys stratospheric ozone and has been phased out.

Similar definitions: CFC

Example: "Older refrigerators used R-12, a          with a very high ozone depletion potential."

Circuit breaker

A device that opens and closes a circuit manually and opens automatically on a predetermined overcurrent without damage to itself.

Similar definitions: breaker

Example: "When the motor overloaded, the          tripped and could be reset after the problem was fixed."

Circuit vent

A vent that connects to a horizontal drainage branch and vents two to eight traps or trapped fixtures connected in a battery.

Example: "A row of floor drains in the locker room was vented with a         ."

Class 2 circuit

A low-voltage, power-limited circuit, such as thermostat, doorbell, or communication wiring, whose limited power provides protection from fire and electric shock.

Similar definitions: low-voltage circuit

Example: "The 24-volt thermostat wiring is a          supplied by a small transformer."

Class A fire

A fire involving ordinary combustible materials such as wood, cloth, paper, and many plastics.

Similar definitions: ordinary combustibles fire

Example: "A burning pile of cardboard boxes and lumber scraps is a         ."

Class B fire

A fire involving flammable or combustible liquids, greases, and gases, such as gasoline, solvents, propane, or natural gas.

Similar definitions: flammable liquid fire

Example: "Spilled PVC cement that ignites creates a         ."

Class C fire

A fire involving energized electrical equipment; a nonconductive extinguishing agent must be used.

Similar definitions: electrical fire

Example: "Smoke pouring from a live panelboard indicates a         , so water must never be used."

Class D fire

A fire involving combustible metals such as magnesium, titanium, or sodium.

Similar definitions: combustible metal fire

Example: "Burning magnesium shavings require a special dry-powder extinguisher rated for a         ."

Class K fire

A fire involving cooking oils and fats in commercial kitchen appliances.

Similar definitions: kitchen fire, cooking oil fire

Example: "A deep fryer blaze in a restaurant kitchen is a         ."

Cleanout

An access opening in the drainage system, such as a removable plug or cap, used to remove obstructions.

Example: "The plumber removed the          plug at the base of the stack to snake the clogged drain."

Cohesive soil

Clay or soil with high clay content that has cohesive strength, does not crumble, and can be excavated with vertical sides.

Similar definitions: clay soil

Example: "Because          sticks together and can be molded when moist, it may qualify as Type A soil."

Combustion air

The air needed for complete burning of fuel in an appliance, including theoretical air and excess air.

Example: "A furnace in a closet needs openings to the outdoors to supply enough         ."

Common vent

A vent connecting at the junction of two fixture drains or to a fixture branch that serves as the vent for both fixtures.

Similar definitions: shared vent, unit vent

Example: "Back-to-back lavatories in a duplex share a         ."

Competent person

One who can identify existing and predictable hazards on a job site and has the authority to take prompt corrective measures to eliminate them.

Example: "OSHA requires a          to inspect the trench daily before workers enter."

Compressor

The 'heart' of the refrigeration cycle that compresses low-pressure, low-temperature refrigerant vapor into high-pressure, high-temperature vapor.

Example: "The          in the outdoor unit pumps refrigerant vapor to the condenser."

Condensate

The liquid that forms when a gas or vapor, including moist air or flue gas, cools below its dew point.

Example: "The          from the evaporator coil drains through a trapped line to the floor drain."

Condensation

The phase change of a substance from gas to liquid as heat is removed.

Similar definitions: condensing

Example: "In the condenser coil,          turns hot refrigerant vapor back into a liquid."

Condenser

A heat exchanger that removes heat from refrigerant vapor so it changes into a liquid.

Similar definitions: condenser coil

Example: "The outdoor fan blows air across the          to reject heat from the house."

Condensing unit

A factory-matched assembly of one or more compressors, a condenser, and accessories that is usually installed outdoors in a split system.

Similar definitions: outdoor unit

Example: "The          sits on a pad outside and connects to the indoor coil by refrigerant lines."

Conditioned space

An area inside the building's thermal envelope that is directly or indirectly heated or cooled.

Example: "Ducts run through the attic are outside the         , so they must be sealed and insulated."

Conduction

Heat transfer through stationary matter by direct physical contact.

Example: "Heat moves through the copper pipe wall by         ."

Conductor

A material, such as copper or aluminum, through which electric charge can easily move.

Example: "Copper is the most common          used in building wiring because of its low resistance."

Conduit body

A separate portion of a conduit system with removable covers that provides access to the interior at a junction or terminal point.

Similar definitions: LB, condulet

Example: "The electrician used an LB          where the conduit turned 90 degrees through the exterior wall."

Confined space

A space large enough for a worker to bodily enter, with limited or restricted means for entry and exit, and not designed for continuous occupancy.

Example: "A crawl space, manhole, or large ductwork plenum can be a         ."

Conflict of interest

A situation in which a person's personal gain or outside relationships could improperly influence their professional decisions, such as during project bidding.

Example: "Awarding the HVAC subcontract to your brother-in-law's company without disclosing it creates a         ."

Construction documents

The written, graphic, and pictorial documents, including drawings and specifications, that describe the design, location, and physical characteristics of a project.

Similar definitions: contract documents, plans and specs

Example: "The          list the pipe material, fixture models, and duct sizes for the job."

Contamination

An impairment of potable water quality that creates an actual health hazard through poisoning or the spread of disease by sewage, industrial fluids, or waste.

Example: "A cross connection with a boiler containing chemicals could cause          of the water supply."

Continuous load

A load where the maximum current is expected to continue for 3 hours or more.

Example: "Store lighting that stays on all day is a         , so its circuit is sized at 125 percent of the load."

Convection

Heat transfer by the movement of a fluid, such as air or water.

Example: "Warm air rising from a baseboard heater and circulating through a room is an example of         ."

Copper tube Type K

The thickest-walled copper water tube (green markings), used mainly for underground water service lines.

Similar definitions: Type K copper

Example: "The water service from the curb stop to the house was run in         ."

Copper tube Type L

Medium-wall copper water tube (blue markings) commonly used for interior hot and cold water distribution.

Similar definitions: Type L copper

Example: "Most inspectors expect          for interior water supply piping."

Copper tube Type M

Thin-walled copper water tube (red markings) that is lighter and cheaper, used for some interior water lines where allowed.

Similar definitions: Type M copper

Example: "         is not suitable for underground service because of its thin wall."

Cross connection

Any physical connection or arrangement between a potable water system and a pipe or vessel containing nonpotable water, chemicals, or other substances.

Example: "A hose connected from a faucet to a chemical sprayer creates a         ."

Cross slope

The slope of a walking surface measured perpendicular to the direction of travel; for an accessible route it may not exceed 1:48.

Example: "The sidewalk's          was too steep and caused wheelchairs to drift sideways."

Cross-linked polyethylene (PEX)

Flexible plastic tubing used for hot and cold water distribution that can bend around obstacles and reduces the number of joints.

Similar definitions: PEX tubing

Example: "Red and blue          lines were run from a manifold to each fixture."

Cyber hygiene

The routine practices that protect devices, accounts, and data, such as strong passwords, software updates, and recognizing suspicious messages.

Similar definitions: cybersecurity habits

Example: "Locking your tablet and never sharing your login are basic parts of good          on a job site."

Damp location

A partially protected location, such as under a canopy or roofed porch, or an interior area subject to moderate moisture, such as some basements.

Example: "The light fixture on the covered porch must be listed for a         ."

Detail

An enlarged drawing of a small portion of a building that shows exactly how materials and connections fit together.

Similar definitions: detail drawing

Example: "A          drawn at 1-1/2 inches = 1 foot showed how the pipe passes through the fire-rated wall."

Developed length

The length of a pipeline measured along the centerline of the pipe and fittings.

Similar definitions: centerline length

Example: "The          of the trap arm includes the extra length through each fitting."

Device

A unit of an electrical system, such as a switch, receptacle, or circuit breaker, that carries or controls electric energy but does not consume it as its main function.

Similar definitions: wiring device

Example: "A duplex receptacle is a         , while a lamp is utilization equipment."

Direct current (DC)

Electric current that flows in only one direction, such as from a battery.

Similar definitions: DC

Example: "Cordless tools run on          supplied by their battery packs."

Direct-vent appliance

An appliance built and installed so that all combustion air comes directly from outdoors and all flue gases are discharged directly outdoors.

Similar definitions: sealed-combustion appliance

Example: "A          water heater draws air and exhausts gases through a concentric pipe in the outside wall."

Disconnecting means

A device or group of devices by which the conductors of a circuit can be disconnected from their source of supply.

Similar definitions: disconnect

Example: "A          must be installed within sight of the outdoor air-conditioning unit."

Draft hood

A device built into or attached to an appliance that lets flue gases escape if there is no draft or a backdraft and keeps chimney draft from affecting the burner.

Example: "The water heater's          mixes room air with flue gases before they enter the vent."

Drain-waste-vent system (DWV)

The piping system that carries wastewater and sewage away from fixtures by gravity and provides vents to admit air and protect trap seals.

Similar definitions: DWV

Example: "PVC Schedule 40 is commonly used for the          in houses."

Drainage fixture unit (DFU)

A measure of the probable discharge of a plumbing fixture into the drainage system, used to size drain pipes.

Similar definitions: DFU

Example: "A residential water closet is rated at 3         s when sizing the building drain."

Drainfield

A shallow, covered excavation in unsaturated soil where pretreated septic tank effluent is discharged through perforated pipes to be treated by the soil.

Similar definitions: leach field, soil absorption field

Example: "Driving heavy equipment over the          can crush pipes and compact the soil."

Duct

A tube or conduit used to carry air.

Similar definitions: ductwork

Example: "The supply          carries conditioned air from the furnace to each room."

Duct system

A continuous passageway for moving air that includes ducts, fittings, dampers, plenums, fans, and air-handling equipment.

Similar definitions: air distribution system

Example: "Leaks in the          can waste 20 to 30 percent of the conditioned air."

Ductless mini-split system

A heating and cooling system with one or more indoor evaporator/air-handling units connected to an outdoor condensing unit by refrigerant piping and wiring, without ductwork.

Similar definitions: mini-split

Example: "A          was installed to heat and cool the garage addition without running new ducts."

Effluent

The liquid that flows out of a septic tank (or treatment unit) after solids have settled out.

Example: "Septic tank          is distributed through perforated pipes into the drainfield."

Eighth bend

A 45-degree drainage fitting used to change the direction of flow.

Similar definitions: 45-degree elbow, 1/8 bend

Example: "Two         s were used to offset the drain around a floor joist."

Electric current

The flow of electric charge through a conductor, measured in amperes.

Similar definitions: current, amperage

Example: "Ohm's law shows that          increases when voltage increases and resistance stays the same."