The two terminations of a cross-connect, each needing a full location and port identifier so the circuit can be traced end to endIn: Cross-connect patch records
A-side / B-side
The isocyanate (A) and polyol resin (B) mixed 1:1 by volume at the gun to make the foamIn: SPF roof field guide
A/D director
The qualified person who directs crane assembly and disassembly under OSHA Subpart CCIn: Crane and rigging safety
Lower-GWP refrigerants replacing HFCs: A2L blends (mildly flammable), CO2 (R-744, high pressure), and naturals like propane (R-290, flammable) and ammonia (R-717, toxic)In: Commercial refrigeration field guide
Base ampacity from NEC Table 310.16, read in the 90 degree C column for 90 degree C insulationIn: Conductor ampacity derating, NEC
A_c
Cross-sectional area of one insulated conductor, from NEC Chapter 9, Table 5, for the size and insulation actually installedIn: Conduit fill, NEC Chapter 9
Disconnect at both ends, de-energize, verify dead, and leave the dead wire where it isIn: Knob and tube wiring
Abandoned cable
Cable not terminated and not tagged for future use; the accessible portion must be removed under the NECIn: Cabling pathways and firestop
ABC
Automatic baseline correction, an algorithm that recalibrates a CO2 sensor by assuming its periodic low reading equals fresh outdoor airIn: IAQ monitoring and sensors field guide
Damage from non-living causes such as compaction, deep planting, drought, excess water, salt, or mechanical injury, the source of most declineIn: Plant health care (PHC)
Abrasive media (non-silica)
Garnet, slag, or steel grit/shot used to blast, in place of silica sand, which causes silicosisIn: Protective coatings and blasting
A continuous path from the access aisle to the entrance, no steps, max 5 percent running slopeIn: ADA accessible parking layout
Acclimation
Letting the wood reach equilibrium moisture content with the conditioned space before install, with the HVAC runningIn: Millwork and casework install
Acclimatization
The body's adaptation to heat over roughly 1 to 2 weeks of gradual exposure; lost after time away from the heatIn: Heat illness prevention
Accountable plan
An IRS-recognized reimbursement structure under which per diem and expenses stay non-taxable when properly substantiatedIn: Hours, overtime, and per diem proof
Recognizing an expected cost in the period the related revenue is earned rather than when the cash goes out, which is the matching idea behind a warranty reserve. How it is booked is the CPA's call.In: Warranty reserve and cost management guide
The structural concrete code, for strength acceptance and the anchoring-to-concrete provisions in its Chapter 17In: Data center structural QA
ACI 318 / ACI 117
The structural concrete code for placement requirements, and the tolerance specification for cover and dIn: Rebar pre-pour inspection
Acid stain (reactive stain)
Metallic salts in a mild acid that react with the lime in the concrete to deposit permanent, variegated, earth-tone colorIn: Concrete coloring and staining
Acidic condensate
The weak acid a condensing appliance makes when flue-gas water vapor condenses, commonly pH 3 to 4 on gasIn: Condensate neutralizer field guide
ACR / ASCS
ACR is the NADCA standard; ASCS is the Air Systems Cleaning Specialist, the NADCA individual certificationIn: Air duct cleaning field guide
ACR copper
Air-conditioning-and-refrigeration tube, cleaned, dehydrated, and capped, sized by actual outside diameterIn: Refrigerant line sizing field guide
The pest count or damage level that justifies treating; below it, you monitor and do not treatIn: Landscape IPM field guide
Activated sludge / biological treatment
The suspended-growth secondary process where microorganisms in aerated mixed liquor eat the organic waste, then settle outIn: Treatment plant systems field guide
Activation energy
The Arrhenius parameter for temperature sensitivity, often 40,000 to 45,000 J/molIn: Concrete maturity method
Active chilled beam
A beam fed with ducted primary air whose nozzles induce room air across the coil, delivering ventilation and added sensible coolingIn: Chilled beam commissioning
Active RDHx
A rear door with its own fans that draw exhaust through the coil, taking the back pressure off the server fansIn: Rear-door heat exchanger commissioning
Active converts RF to fiber and re-amplifies at remote units for large buildings; passive is a BDA feeding coax and antennas for smaller onesIn: DAS and public-safety radio
Electric or pneumatic motor, usually spring-return, that closes a smoke or combination damper on signalIn: Fire and smoke damper field guide
ACV vs RCV
Actual cash value is replacement cost minus depreciation; replacement cost value is the full cost to replace the roof todayIn: Storm and hail damage restoration
Refrigerant added beyond the factory charge, calculated from liquid-line length and diameter and weighed inIn: VRF commissioning field guide
Additional insured
An endorsement naming another party on your policy so your coverage defends them for your workIn: Contractor insurance and bonding
Adhesion test
A small coated patch or fabric pull tab cured and pulled to confirm the coating bonds to the substrate before the field coatIn: Roof coating restoration system
Adhesive / chemical anchor
A rod or rebar bonded into a drilled hole with structural adhesive; strength is the bond, not expansionIn: Adhesive anchor installation
The TIA-606 discipline of identifying, labeling, and recording the cabling infrastructure so any component can be named and any link tracedIn: TIA-606 labeling and administration
Admixture
Anything besides cement, water, and aggregate added to the mix to change a propertyIn: Concrete admixtures
Assured equipment grounding conductor program, the written OSHA program that tests and records the ground path on temporary power equipmentIn: Temporary power field guideAEGCP field guide
Aeration / dissolved oxygen (DO)
Blowers and diffusers supply oxygen to the bugs; DO in mg/L is the measured oxygen in the tank, commonly held above about 2 mg/LIn: Treatment plant systems field guide
Aerator
The screen at the tip of a faucet that mixes air into the stream and catches scale and debris; the number-one single-fixture restrictionIn: Low water pressure guide
AFCI
Arc-fault circuit interrupter, protects the building by detecting the signature of an arcing faultIn: GFCI and AFCI protection
Affected employee
A worker who operates or works near the equipment but does not perform the servicing, and who must be notifiedIn: Lockout/tagout field guide
Air carried into or trapped in the pump; noisy and performance-robbing, but it does not implode and erode like cavitationIn: Pump cavitation and NPSH field guide
Air break
A waste pipe ending below the flood rim but above the trap seal, allowed for lower-hazard clear-water dischargesIn: Indirect waste and air gap guide
Air chamber
The old capped pipe stub fix that waterlogs as its air dissolves into the water and then failsIn: Water hammer arrestor guide
Air change rate
The room volume exchanged per hour, the measure of how fast the air is diluted and sweptIn: Cleanroom HVAC field guide
Post-work air sampling against a clearance level, PCM around 0.01 f/cc or TEM specific to asbestos, signed by an independent partyIn: Asbestos abatement procedures
Air content
Total air as a percent of concrete volume, the field-tested number judged against the specified targetIn: Air entrainment
Air curtain / air door
A unit over an opening that blows a high-velocity stream across it to separate inside from outsideIn: Air curtain field guide
Regulator and restriction that tops off supervisory air or nitrogen slowly, so a real operation drops pressure faster than it refillsIn: Dry-pipe and pre-action trip test
Air mixer
A venturi that adds combustion air to propane for a clean burn; not needed for natural gasIn: Outdoor fire feature guide
Air mover
High-velocity fan that evaporates moisture from wet surfaces into the air for the dehumidifier to removeIn: Water mitigation and drying guide
Air leakage per unit area at a test pressure, in cfm per square foot at 0.3 in. w.c., measured by ASTM E2178 and E2357In: Roof vapor retarder and air barrier
Air separator
A loop fitting that strips entrained air from the water, placed at the hot, low-pressure point off the boiler supplyIn: Expansion tank and air field guide
Air terminal
The rod or point that intercepts the strike, also called a lightning rod or strike termination deviceIn: Lightning protection (NFPA 780)
Air vent
A manual or automatic valve at each system high point that lets collected air out so the pump does not have to move itIn: Hydronic water and glycol field guide
Air-cooled rejects heat to room air and needs clearance; water-cooled rejects heat to condenser water and uses more waterIn: Commercial ice machine field guide
Air-cooled vs water-cooled chiller
Heat rejected to outdoor air with a condenser coil, versus to a cooling tower through a condenser-water loopIn: Chilled water vs DX cooling
Air-entraining admixture (AEA)
The surfactant added at the plant that creates and stabilizes the entrained air, specified to ASTM C260In: Air entrainment
Air-free CO
Carbon monoxide corrected for excess air so readings compare against a target; calculated from measured CO and O2In: Combustion analysis field guide
Airflow management
Getting cold supply to every inlet and hot exhaust back to the units without the two streams mixingIn: Data center airflow management
The Specification for Structural Steel Buildings, the design and construction standard for structural steelIn: Data center structural QA
AL / AL-CU
Connector markings for conductors the lug is listed to terminate: aluminum only, or aluminum and copperIn: Termination torque QA field guide
AL9CU / AL/CU
A connector marking meaning it is listed and tested for both aluminum and copper conductorsIn: Splices and terminations
Alarm fatigue
The state where too many false or nuisance alarms train the operator to ignore, mute, or disable the detection system, which makes the technology worthless. Fixed by tuning the detection zones.In: Proximity warning and struck-by safety tech
Alarm rationalization
Reviewing every potential alarm against an alarm philosophy so only meaningful, actionable, prioritized alarms remain, each with a documented consequence and response.In: Data center operations and the NOC
Albedo / solar reflectance
The fraction of sunlight a surface reflects; concrete is higher than dark asphaltIn: Asphalt vs concrete pavement
Alert / Action / Fire 1 / Fire 2
The rising alarm levels of a multi-stage aspirating detector, from earliest warning to the threshold that drives suppressionIn: Aspirating smoke detection
All-air / all-water / DX
The three distribution carriers: conditioned air in duct, hot or chilled water in pipe, or refrigerant in line setsIn: HVAC system types field guide
A fixed point that holds the pipe still and the supports that let it slide lengthwise while staying in line, used to direct thermal movementIn: Pipe hangers and seismic bracing guide
Anchor bolt setting plan
The manufacturer's drawing giving the location, pattern, projection, and diameter of every anchor bolt the frames land onIn: Metal building erection
Anchor point
An engineered fixed tie-off rated to hold a fall, commonly 5,000 lb per worker or designed to a safety factor of twoIn: Rooftop permanent fall protection
Anchor profile
The peak-to-valley roughness the blast cuts into the steel, measured in mils, that the coating gripsIn: Protective coatings and blasting
Anchorage
What the system ties off to, rated at 5,000 lb per worker or engineered to a safety factor of twoIn: Roof fall protection
Conductors change direction in the box, sized at 6x the largest raceway plus the others in the rowIn: Pull box sizing, 314.28
Angle stop
The shutoff valve on a fixture supply stub-out, trimmed with an escutcheon, that isolates the fixture for serviceIn: Fixture rough-in and setting guide
Ordinary float glass that breaks in shards, heat-treated glass that breaks in pebbles, and bonded glass that holds together on an interlayerIn: Glass replacement and glazing repair
Annex B / 310.60
The NEC duct-bank ampacity figures, Annex B for low voltage and 310.60 tables for 2001 V to 35000 V; verify against the adopted editionIn: Concrete-encased duct bank field guide
Annex C
Lookup tables giving the maximum conductor count when all conductors are the same size and insulationIn: Conduit fill, NEC Chapter 9
Annual
A plant that completes its life in one growing season and is replaced rather than overwintered, the basis of color rotationIn: Seasonal color and annual rotation
The panel, usually at the fire command center, that reports system trouble such as AC loss, low battery, and donor or antenna failureIn: DAS and public-safety radio
Anode / rectifier
The anode is where corrosion is directed; the rectifier is the AC-to-DC power source that drives an ICCP systemIn: Cathodic protection field guide
The IEEE C37.2 identifiers for relay functions: 50 instantaneous overcurrent, 51 inverse-time overcurrent, 87 differential, 27 undervoltage, 59 overvoltage, with G or N for groundIn: Coordination study field guide
ANSI/SPRI ES-1
The national test standard for low-slope roof edge systems, with the RE-1, RE-2, and RE-3 wind testsIn: Roof edge metal and coping
ANSI/SPRI RP-4
The wind design standard for ballasted single-ply roofs, turning height, exposure, slope, and parapet into a ballast designIn: Ballasted roof systems
Anteroom
A small airlock between an isolation room and the corridor that holds an intermediate pressure for a staged cascadeIn: Healthcare HVAC ventilation field guide
Anti-graffiti film
A clear sacrificial layer that takes tags and scratches so the film is replaced, not the glassIn: Commercial window film
Anti-icing
Treating dry pavement before a storm to stop snow and ice from bonding to the surfaceIn: Snow and ice management
Anti-islanding
Protection that disconnects on-site generation from a de-energized utility line, per IEEE 1547 and UL 1741In: Data center on-site generation
Anti-oxidant compound
Joint compound applied to aluminum connections to break and exclude the oxide filmIn: Splices and terminations
An automatic compensating shower valve listed to ASSE 1016, pressure-balance, thermostatic, or combination, that holds outlet temperature when pressure shiftsIn: Fixtures and water efficiency
Anti-strip
Hydrated lime or a liquid additive that restores the binder-aggregate bond against moistureIn: Warm mix asphalt (WMA)
Antioxidant compound
Oxide-inhibiting joint compound applied to aluminum connections where required, to break and seal out the aluminum oxide filmIn: Termination torque QA field guide
Antiquing
The secondary accent color left in the grout lines and low texture, from the release or a separate tinted productIn: Stamped concrete install guide
AOS (apparent opening size)
The opening size that controls which soil particles pass, written O95; a smaller AOS retains finer soil.In: Geotextile separation fabric
The allowed number of apprentices to journeyworkers on prevailing-wage work, set by the registered programIn: Apprenticeship and training program
Apprenticeship
A paid, earn-while-you-learn pathway combining on-the-job hours with classroom instruction, often running 18 to 48 monthsIn: Data center staffing and workforce
A review stamp allowing the work to proceed with the reviewer's markups incorporated, without a resubmittalIn: RFI and submittal process
Appurtenance
Anything mounted on the tower beyond the structure: antennas, RRUs, mounts, platforms, lines, lights, each adding load and wind areaIn: Cell tower and antenna install
Custom non-box woodwork built for a project: trim, paneling, desks, casing, and one-off pieces, as opposed to the cabinet boxesIn: Millwork and casework install
Arcing current
The current that actually flows in the arc, lower than the bolted fault current; a method must operate at less than this to workIn: Arc energy reduction methods
Arcing ground fault
A line-to-ground arc drawing far less than the phase device trip level, which burns the gearIn: GFPE field guide
The qualified engineer's documented analysis that sets the class, division or zone, group, and extent for a spaceIn: Hazardous classified locations
Area divider
A raised double member on a continuous deck that relieves thermal stress by breaking a large membrane field into sections; it does not allow movementIn: Roof expansion joint installation
A code-defined line a short distance outside the array, commonly 1 ft, that splits the inside and outside voltage limitsIn: PV rapid shutdown (NEC 690.12)
The drawings marked to show what was actually installed, including every field change, redlined as the work happensIn: Punch list and closeout
As-built drawing
The construction set marked by the contractor to show what was actually installed, including every field change from the designIn: As-built record drawings
As-built model
The accurate digital record of what was actually built, the foundation the twin stands onIn: Digital twin for operations
As-built verification
Overlaying the scan of installed work on the design model to find deviation, often as a heat-mapIn: Reality capture and scan-to-BIM
The measured value recorded at the close of a test, the baseline the building is re-tested against for the rest of its lifeIn: Proof packet assembly
Asbestos / ACM
A group of fibrous minerals used in building products; asbestos-containing material is anything above the regulatory asbestos contentIn: Asbestos abatement procedures
Asbestos / NESHAP
EPA National Emission Standards for Hazardous Air Pollutants, the federal rule governing asbestos in renovation and demolition, including the survey, abatement, and notification.In: Interior demolition strip-out
Asbestos survey
A pre-work building inspection by an accredited inspector that locates, samples, and reports asbestos-containing materialIn: Asbestos abatement procedures
The tracer-gas test that proves hood containment by measuring how much tracer reaches a mannequin's breathing zone, run as-manufactured, as-installed, and as-usedIn: Lab fume hood exhaust guide
ANSI/ASHRAE/ASHE Standard 170 and the FGI Guidelines, the governing requirement for healthcare ventilation, with a space-by-space tableIn: Healthcare HVAC ventilation field guide
ASHRAE Standard 241-2023, Control of Infectious Aerosols, which sets equivalent clean airflow requirements to reduce disease transmission riskIn: IAQ monitoring and sensors field guide
ASHRAE audit levels
Standard 211's three depths: Level 1 walk-through, Level 2 detailed survey, Level 3 investment-grade engineering.In: Energy audit and management field guide
ASHRAE recommended and allowable
The TC 9.9 intake envelopes; recommended is the efficiency aim, allowable is the outer limit, both at the intakeIn: Delta-T and return temperature
The Process Piping code that governs design, materials, fabrication, examination, and testing of process pipingIn: Industrial process piping
ASME B31.9
Building Services Piping, the usual code for data center chilled-water and HVAC piping; sets the hydrostatic test at 1.5 times design pressureIn: Chilled water hydro test package
ASME Section IV
The boiler code section for heating boilers: steam to 15 psig, hot water to 160 psi or 250 degrees FIn: Boiler startup commissioning
Available static pressure for the duct, in inches of water column, after the components are subtracted from the rated external staticIn: Manual D duct design field guide
Engraving or stamping an ID on tools and recording serial numbers so an item is harder to fence and can be matched on recoveryIn: Jobsite security and theft prevention
Asset utilization
How much an owned or rented asset is actually used versus sitting idle, used to right-size the fleetIn: Connected jobsite and RTLS
AST
Aboveground storage tank, set on a pad, governed by NFPA 30 and 30A, UL 142, and SPCCIn: Fuel storage tank field guide
ASTM D7877
The standard guide for electronic methods of detecting and locating leaks in waterproof membranes, covering both voltage methodsIn: Electronic leak detection
ASTM D8231
The standard practice for a low-voltage electronic scanning system for detecting and locating membrane breachesIn: Electronic leak detection
The consolidated bolt specification carrying A325, A490, F1852, and F2280 as gradesIn: High-strength bolting (RCSC)
Aterm
Ampacity in the column matching the lowest-rated termination, usually 75 degrees C, per NEC 110.14(C)In: Conductor ampacity derating, NEC
Atmospheric / Category I
A gas unit that takes combustion air from the room and vents by natural draft up a vertical flueIn: Unit heater field guide
ATP verification
Swab-and-luminometer test measuring adenosine triphosphate as organic residue in relative light units, to confirm cleaning was effectiveIn: Biohazard and trauma cleanup guide
The bolted and flashed board that fastens an attached structure to the house, the same connection as a deck ledgerIn: Pergola and shade structure guide
Attachment / anchoring system
A wet-glaze structural-silicone bead or a mechanical batten that ties the film edge to the frame so it resists, not just holds shardsIn: Commercial window film
Attic stock
The specified spare materials handed to the owner at closeout: tiles, lamps, filters, paint, keys, and the likeIn: Punch list and closeout
ATU / mound / pressure dosing
Alternative methods for poor sites: an aerobic treatment unit adds oxygen for higher treatment, a mound builds the field up in sand, pressure dosing pumps even timed doses to the fieldIn: Septic system field guide
Audio / wiretap consent
The legal requirement to obtain consent before recording audio, one-party or all-party depending on jurisdictionIn: Jobsite camera and video monitoring
Authorized employee
The worker who applies the lockout and performs the servicing on the equipmentIn: Lockout/tagout field guide
An actuated valve that closes on detection to stop the flow and isolate the affected loop or rack in secondsIn: Liquid-cooling leak detection
Autonomous / machine-control equipment
Earth-moving equipment guided to a design surface by GPS, either semi-autonomous with an operator in the cab or fully autonomous with noneIn: Construction robotics
A covered trough supplementing equipment locally, NEC Article 366, commonly limited to about 30 ft beyond the gearIn: Wireway and gutter field guide
Availability
The fraction of time or producible energy the plant was able to operate rather than sitting on a faultIn: Solar PV O&M field guide
Availability / MTTR
Availability is the percent of time the load was up, quoted in nines; MTTR is mean time to repair or recover, how fast operations restores after a failure.In: Data center operations and the NOC
The Architectural Woodwork Institute quality grade, Economy, Custom, or Premium, setting materials, joinery, tolerances, and finish; now paired with a separate duty level, 1 to 4In: Millwork and casework install
AWWA D102
The AWWA standard for coating the inside and outside of steel water-storage tanksIn: Tank coating and lining