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Field glossary

Terms — U

63 field terms starting with U, 11 with a full reference page. Each links to the Anvilfield guides where the term is used on the job.

U
Conductance of the assembly in Btu per hour per square foot per degree F, the inverse of R-valueIn: Manual J load calculation field guide
U / RU
Rack unit, 1.75 in (44.45 mm) of vertical mounting height on a 19 in EIA-310 rackIn: Data center cabinet and rack types
U-factor
The rate of conductive heat transfer through the glazing; film affects it less than it affects SHGCIn: Commercial window filmRoof insulation and cover board
U-factor / R-value
Assembly conductance and its inverse, how the envelope conducts heatIn: Manual J load calculation field guide
U-factor / SHGC
Heat-loss rate and solar-heat-gain coefficient of the glazing, the two energy numbers that govern selectionIn: Skylight curb installation and flashing
U-space / elevation
The U-by-U map of what mounts where in the cabinet, 1U being 1.75 in (44.45 mm) of mounting heightIn: Rack-and-stack deployment field guide
UCS
Unconfined compressive strength, the lab value used to accept a treated layerIn: Subgrade stabilization
UEF
Uniform Energy Factor, the DOE efficiency rating that replaced the older Energy FactorIn: Water heater typesWater heater sizing and selection
Ufer
Concrete-encased electrode, 20 ft of 1/2 in rebar or #4 copper in the footing per 250.52(A)(3)In: Grounding and bonding field guide
ug/L (ppb)
Micrograms per liter, equal to parts per billion, the unit for lead concentration at the tapIn: Lead service line guide
UGR
Unified glare rating, lower is less discomfort glareIn: Commercial lighting design
UL 181
The listing standard for rigid and flexible air ducts and ductboardIn: Ductwork types field guide
UL 181A / 181B
The listings for tapes and closures used on rigid duct (181A) and flexible connectors (181B)In: Duct leakage testing field guide
UL 300
The listing standard a kitchen suppression system must meet for modern cooking equipment; pre-UL-300 systems are obsoleteIn: Hood suppression semi-annual guide
UL 325
The product safety standard for the operator, its entrapment protection, and its usage classesIn: Automatic gate operator field guideCommercial fence and gate install
UL 325 entrapment protection
The requirement that a powered door sense an obstruction and reverse, using two independent monitored meansIn: Overhead door and dock leveler field guide
UL 48
The safety standard for electric signs; a listed sign carries markings and installation instructions that are part of the listingIn: Electric sign installation
UL 50 / 50E
The standards an enclosure is tested to in order to carry a NEMA type ratingIn: NEMA enclosure ratings
UL 924
The product standard for emergency lighting and exit-sign equipmentIn: Emergency and egress lighting
UL 9540 / 9540A
The listing for the energy storage system as a product (9540) and the test method for thermal-runaway fire propagation (9540A)In: Battery energy storage (BESS)
ULSD / B5
Ultra-low-sulfur diesel, often with up to 5 percent biodiesel; both are hygroscopic and shorten storage lifeIn: Generator fuel system and day tank
Ultimate load
The overload the system survives without collapse, commonly about twice the rated concentrated load on data sheets; the factor of three is the ICC-ES AC48 safety factor on tested ultimate strength, not an ultimate-to-rated ratio; verify the specified classIn: Raised floor acceptance packet
Ultrasonic cleaning
Immersion cleaning using cavitation to lift soot and grime from detailed hard goodsIn: Contents pack-out and inventory
Unbilled parts
Parts installed on a job that never reach the customer invoice, a pure margin lossIn: Service truck inventory and van stock
Unconditional waiver
A lien waiver that takes effect the moment it is signed, whether or not payment is received; do not sign one before funds clear.In: Mechanics lien and preliminary notice
Unconfined edge
The free edge of a pass with nothing beside it, which spreads and runs lean under the rollerIn: Asphalt paving joints and handwork
Underbilled (costs in excess of billings)
Work ahead of the billing; your cash funding the job, real profit and cash earned but not yet invoicedIn: Construction cash flow and WIP
Underbilling
Earned revenue in excess of billings; an asset, since it is work done and not yet billedIn: WIP report and over/under billing
Undercut
Excavating soft or unsuitable material and replacing it with compacted structural fillIn: Pavement base and subgrade compaction
Underdrain
A perforated pipe in the reservoir that carries off water the soil cannot infiltrate fast enoughIn: Porous and permeable pavementBioretention and rain gardens
Underlay / overlay
The physical routed spine-leaf network and the virtual tenant network built on top of itIn: Spine-leaf network architecture
Underlayment
The secondary water barrier under the shingles, felt or synthetic; it backs up the shingles, it is not the roofIn: Steep-slope shingle roofingRoofing underlayment types
Underpinning
Carrying an existing settled foundation down to firm soil on new piers, connected by brackets under the footing, to stop or reverse settlement.In: Helical piers and screw pilesFoundation underpinning and repair
Ungrounded conductor / phase / hot
A line conductor, phase colors by convention, not NEC-mandatedIn: Conductor color code and phase ID
Unidirectional / non-unidirectional
Laminar piston flow versus turbulent mixed flow, set by the classIn: Cleanroom HVAC field guide
Uniform (distributed) load
Weight spread evenly across the panel, expressed as load per unit area (psf or kPa)In: Raised floor load rating testRaised floor acceptance packet
Uniformity ratio
Evenness of the light across the grid, as max-to-min or average-to-minIn: Whitespace footcandle verification
Unit cooler / evaporator TD
The unit cooler is the in-box finned evaporator with fans; TD is the temperature difference between the coil's refrigerant saturation and the entering air, which sets capacity and humidityIn: Commercial refrigeration field guide
Unit cost
The cost to install one unit of an item, labor and material togetherIn: Landscape estimating and bidding
Unit equipment
Self-contained emergency light with its own battery, charger, and transfer (the bug eye)In: Emergency and egress lighting
Unit heater
A self-contained heater and fan in one hung cabinet that blows warm air directly into the space, with no ductworkIn: Unit heater field guide
Unit price vs lump sum
Unit price pays measured quantities at set rates; lump sum is one price for the whole scopeIn: Asphalt paving estimating
Universal precautions
Treating all human blood and certain body fluids as if known to be infectious for bloodborne pathogens, the principle under OSHA 1910.1030In: Biohazard and trauma cleanup guide
Universal waste
EPA category (40 CFR 273) for simplified handling of spent mercury lamps and similar wastesIn: LED lighting retrofit
Unvented conditioned attic
An attic foamed at the roofline and brought inside the building envelope, with no ventilationIn: Roof attic ventilation
Upblast fan
A roof exhaust fan that discharges vertically up and away from the roof, used for dirty or greasy airIn: Kitchen grease duct field guideCommercial exhaust ventilation guide
Upfeed
Distribution that pushes water up from the bottom on street or pump pressureIn: Water distribution system types guide
Uplift zone
The field, perimeter, or corner band under ASCE 7; the corner sees the highest suctionIn: Roof edge metal and coping
UPS
Uninterruptible power supply, which conditions power and carries the load through a source disturbance from stored energyIn: Data center power distribution chainUPS and STS commissioning hold points
UPS bypass
The mode that routes load around the UPS inverter; the EPO must stop the UPS from feeding the room, not just shift it to bypassIn: EPO testing field guide
Uptime Tier
The Uptime Institute rating of facility redundancy, Tier I through Tier IVIn: Data center types field guide
Usable / inside area
Inside width times depth of the tray, with depth capped at 6 in for the NEC multiconductor fill rulesIn: Cable tray fill and copper takeoff
Usable capacity
Installed capacity minus the redundancy reserve and the continuous-load derateIn: Stranded capacity and power utilizationPower density and capacity planning
Usable storage
The fraction of tank volume delivered before the outlet sags, commonly 70 to 80 percentIn: Water heater sizing and selection
Usage class I to IV
I residential, II commercial or general access, III industrial or limited, IV restricted or guarded high-securityIn: Automatic gate operator field guide
USC FCCCHR
The USC Foundation for Cross-Connection Control and Hydraulic Research, source of the common field test procedureIn: Backflow test procedure guide
USDOT number
The FMCSA identifier for a motor carrier, kept current with the biennial MCS-150 updateIn: DOT compliance for contractors
Use case
The specific operational decision the twin is built to supportIn: Digital twin for operations
Use zone / fall zone
The surfaced, obstacle-free area around equipment where a falling child lands; 6 ft minimum, larger for swings and slidesIn: Playground safety surfacing
UST
Underground storage tank, a tank with 10 percent or more of its volume buried, governed by EPA 40 CFR 280In: Fuel storage tank field guide
Utilization
Used capacity as a share of usable capacity, after the continuous derate and the redundancy reserveIn: Stranded capacity and power utilizationField time tracking and labor hoursEquipment cost recovery and own vs rentData center TCO cost model
Utilization / billable hours
The share of a technician's paid time that lands on a customer invoiceIn: Service dispatch and scheduling
UTS
Universal total station, a robotic instrument giving millimeter-class machine positionIn: Grade control and machine control
TV

All glossary terms

On the job

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