A cultivar of a native species; wildlife value varies and some offer less pollen and nectar than the straight speciesIn: Native and pollinator planting
Native plant
A species that occurred in an area before widespread human introduction, judged at the ecoregion scale, not the countryIn: Native and pollinator planting
Nondestructive examination of welds (VT, PT, RT, UT); radiography is the x-ray or gamma volumetric methodIn: Industrial process piping
Ndesign
The design gyration count, set by traffic, where the mix is held to 4 percent air voidsIn: Asphalt mix design (Superpave)
NDIR
Nondispersive infrared, the method good CO2 sensors use to measure carbon dioxide directly by infrared absorptionIn: IAQ monitoring and sensors field guide
The bodies that publish TAB procedural standards, report forms, and the firm and technician certificationsIn: Air balancing report field guide
NEC 110.14(D)
The code section requiring terminations to be tightened to the manufacturer's value, with a calibrated torque tool or approved means where a value is givenIn: Termination torque QA field guide
NEC 242
The NFPA 70 article governing overvoltage protection and SPDs, formerly Article 285In: SPD installation field guide
NEC 645
NFPA 70 Article 645, the optional rules for information technology equipment rooms; 645.10 is the disconnecting-means (EPO) sectionIn: EPO testing field guide
The NEC articles for energy storage systems (706) and for interconnection to the utility supply (705)In: Battery energy storage (BESS)
NEC Article 555
The National Electrical Code article governing marina and dock electrical, written to keep leakage current out of the waterIn: Boat dock and marina construction
NEC Article 625
The NEC article governing EV supply equipment, including the continuous-load and disconnect rulesIn: DC fast charging station design
Sealing the work area with poly and zip walls and holding it below surrounding pressure with HEPA negative-air machines so dust stays in the work zone.In: Interior demolition strip-out
EPA National Emission Standards for Hazardous Air Pollutants, the federal rule that governs asbestos in renovation and demolition, including the survey, abatement, and notification.In: Building demolition planning
NESHAP / AHERA
EPA NESHAP (40 CFR 61 Subpart M) governs emissions, notification, and waste; AHERA governs asbestos in schoolsIn: Asbestos abatement procedures
Noise-equivalent temperature difference, the camera's thermal sensitivity, which sets the smallest rise it can resolveIn: Infrared thermography field guide
The neutral-to-ground connection, made in exactly one place; a second bond puts neutral current on the grounding conductorIn: Generator interlock and backfeed safety
Stopping the acid reaction and lifting residue with a baking soda or ammonia solution, then rinsing clean before sealingIn: Concrete coloring and staining
The public-sewer manhole whose cover elevation sets the code trigger for protecting lower fixturesIn: Backwater valve field guide
NFPA 110 Class
The runtime classification, the minimum hours the plant runs at rated load without refueling, such as Class 72In: Generator fuel system and day tank
NFPA 13
The standard for the installation of sprinkler systems; 13R covers low-rise residential, 13D covers one- and two-family dwellingsIn: Fire sprinkler system design guide
NFPA 20 governs the installation and the acceptance test; NFPA 25 governs the recurring inspection, testing, and maintenanceIn: Fire pump acceptance test
The in-running pinch where a belt meets a pulley, a chain meets a sprocket, or two rollers meet, that draws in and amputatesIn: Conveyor system installation
Nipple
Raceway 24 in or less between enclosures, allowed 60 percent fill and exempt from the more-than-three deratingIn: Conduit fill, NEC Chapter 9
Networked lighting control, and luminaire-level control with a sensor in every fixture, rebate-eligible on the DLC listIn: Lighting controls and dimming
Nominal maximum aggregate size, and the lift-thickness-to-NMAS ratio that sets minimum liftIn: Asphalt compaction window
NMC
Lithium nickel manganese cobalt oxide: higher energy density, less thermally stable than LFPIn: Rack BBU and ride-through
No-load tap
Primary voltage-adjustment tap set with the unit de-energized, commonly 2.5 percent stepsIn: Dry vs liquid transformer guide
No-load taps
Off-load primary connection points, commonly plus or minus 5 percent in 2.5 percent stepsIn: Dry-type transformer guide
NOAEL / LOAEL
No-observed and lowest-observed-adverse-effect levels, the human-exposure limits the design concentration is held againstIn: Clean agent room integrity
NOC
Network operations center, the team and room that watch the IT and network layer, server and link health and service availability, as distinct from the physical plant.In: Data center operations and the NOC
Nominal max aggregate
Largest standard sieve size; coarse aggregate over 1-1/2 in is wet-sieved out before a slump testIn: Concrete slump test
Nominal max aggregate size
The largest standard sieve the coarse aggregate is graded to; drives water demand and member fitIn: Mix design and water-cement ratio
A structure of masonry or galvanized steel stud with cement board, not wood, that carries the counter and resists heat and weatherIn: Outdoor kitchen construction guide
Non-condensable
A gas such as air that will not condense in the system, raising head pressure until the vacuum removes itIn: Refrigerant evacuation field guide
Non-condensable gas
Air or other gas that leaks into a two-phase system and blankets the condenser, degrading heat rejectionIn: Two-phase cooling
The document recording work that failed the spec, tracked through disposition, root cause, and close-outIn: Quality control and the ITP
Non-entry rescue
Retrieving an entrant from outside the space with a harness, retrieval line, and tripod or davit winch, with no one enteringIn: Confined space entry field guide
Non-friable
Bound material that cannot be crumbled by hand when intact, split into Category I and II; releases fibers when cut, ground, or brokenIn: Asbestos abatement procedures
The formal record of work or material that does not meet the requirement, tracked through disposition and corrective action to closureIn: Construction QA/QC program
A written warning that you will record a lien if the bill is not paid by a stated date; required in some states and a common collection tool.In: Mechanics lien and preliminary notice
NOWL
Normal operating water level on a steam boiler; the LWCO trips a set distance below it while water still covers the metalIn: Boiler startup commissioning
The NPDES discharge permit governs wastewater effluent under the Clean Water Act; the Safe Drinking Water Act sets MCLs for drinking waterIn: Treatment plant systems field guide
Net positive suction head available from the system versus required by the pump; NPSHa must exceed NPSHr or the pump cavitatesIn: Hydronic pump install field guide
Certification that foodservice equipment meets the NSF/ANSI sanitation standards for cleanable, food-safe construction, which the health code commonly requiresIn: Kitchen equipment install field guide
NSF/ANSI 53
Certification for point-of-use filters that reduce lead, both soluble and particulateIn: Lead service line guide
NVR is a dedicated recording appliance for small to mid sites; VMS is server or cloud software that scales and integrates with other systemsIn: CCTV system design field guide