Reference

Power-equipment glossary for North American projects

58 terms a buyer, estimator or engineer meets when specifying transformers, switchgear, battery storage and EV charging in the United States and Canada — each defined in one paragraph with the governing ANSI/IEEE, UL, CSA or code reference. Written by Entogo’s engineering team; every term has a stable link you can cite.

Transformers & substations

Ratings, construction types and the ANSI/IEEE C57 vocabulary used to specify distribution and power transformers in the United States and Canada.

kVA rating (apparent power)

Also: MVA

A transformer is rated in kilovolt-amperes (kVA) or megavolt-amperes (MVA): rated voltage multiplied by rated current, independent of the load power factor. To size a unit, divide the connected or calculated load by the intended loading (often 80 %) and round up to the next standard rating on the ANSI/IEEE C57.12.00 ladder — 75, 112.5, 150, 225, 300, 500, 750, 1000, 1500, 2000 and 2500 kVA for three-phase distribution units.

Pad-mounted transformer

Also: pad-mount, padmount

A liquid-filled distribution transformer in a tamper-resistant, dead-front steel cabinet that sits on a concrete pad at ground level and is fed by underground primary cable. Three-phase units follow IEEE C57.12.34 (single-phase: C57.12.38) with enclosure integrity per ANSI C57.12.28. Typical North-American ratings: 15 / 25 / 35 kV class primary, 208Y/120 V or 480Y/277 V secondary, 75–2500 kVA — the range Entogo builds to DOE 10 CFR 431 efficiency.

Pole-mounted (overhead) transformer

Also: overhead distribution transformer, CSP transformer

A distribution transformer hung on a utility pole and fed from overhead lines through high-voltage bushings, protected by fuse cutouts and surge arresters — or, in a CSP (completely self-protected) unit, by an internal secondary breaker, primary fuse and arrester. Built to IEEE C57.12.20; single-phase units run from about 10 to 167 kVA and are the standard way North-American utilities serve rural and suburban secondary networks.

Dry-type transformer

Also: ventilated dry-type, cast-resin transformer

A transformer whose windings are cooled and insulated by air (ventilated, encapsulated or cast-resin) instead of a liquid, so it can be installed indoors close to the load without oil containment or fire separation. Low-voltage units are built to UL 1561 / CSA C22.2 No. 47 and medium-voltage units to UL 1562, with DOE 10 CFR 431 efficiency levels; insulation systems are typically 220 °C class with 80, 115 or 150 °C temperature rise.

Liquid-filled (oil-immersed) transformer

Also: oil-filled transformer, ester-filled transformer

A transformer whose core and windings are immersed in mineral oil or a less-flammable natural-ester fluid that both insulates and carries heat to the tank and radiators. Liquid units tolerate overload better and are more efficient per kVA than dry-type, which is why pad-mounted, substation and power transformers are almost always liquid-filled (IEEE C57.12.00 / C57.12.90). Indoor installations need the vault or containment rules of NEC Article 450 or CEC Section 26.

Amorphous-core transformer

Also: amorphous metal transformer, AMDT

A distribution transformer whose core is wound from amorphous (non-crystalline) iron-based ribbon instead of grain-oriented silicon steel. The random atomic structure cuts no-load (core) loss by roughly 60–70 %, which matters because core loss is paid 24 hours a day regardless of load. The trade-off is a somewhat larger, heavier core. Entogo offers amorphous-core dry-type units for owners who buy on lifetime energy cost rather than first cost.

Wound-core (3-D triangular core) transformer

Also: three-dimensional wound core

A transformer whose core is wound from continuous steel strip rather than stacked from cut laminations. In a three-dimensional triangular wound core the three limbs sit at 120°, so every phase sees an identical, joint-free magnetic path: lower no-load loss, lower magnetising current and inrush, and less audible noise than a conventional stacked core. Entogo supplies this construction in oil-filled or dry-type distribution ratings.

Basic impulse insulation level (BIL)

Also: basic lightning impulse insulation level

The peak of the standard 1.2/50 µs lightning-impulse voltage wave that a transformer or switchgear insulation system is designed to withstand. BIL is tied to voltage class in ANSI/IEEE C57.12.00 and C37.20.2: typically 95 kV for 15 kV class, 125 kV for 25–27 kV class and 150 kV for 34.5–38 kV class. Specify the BIL the utility or the interconnection study requires — it drives clearances, bushings and the arrester rating.

Voltage class (15 kV / 25 kV / 35 kV)

The North-American way of grouping medium-voltage systems by insulation level rather than exact operating voltage. 15 kV class covers 12.47 kV and 13.8 kV systems, 25 kV class covers 24.94 kV, and 35 kV class covers 34.5 kV; switchgear expresses the same tiers as rated maximum voltages of 15, 27 and 38 kV (ANSI/IEEE C37.20.2). A transformer or switchgear is specified by class first, then by the actual system voltage and BIL.

Percent impedance (%Z)

Also: transformer impedance

The transformer’s internal impedance expressed as the percentage of rated primary voltage needed to circulate rated current with the secondary short-circuited. It sets the secondary fault current (approximately rated current ÷ %Z, so a 5.75 % unit can deliver about 17 times rated current into a bolted fault) and the voltage regulation under load. Utilities and engineers specify it to keep downstream switchgear ratings and voltage drop within limits.

Temperature rise (55 / 65 / 80 / 115 / 150 °C)

The average winding temperature rise above a 30 °C average ambient at rated load. Liquid-filled units are rated 55 °C or 65 °C rise; dry-type units 80, 115 or 150 °C rise on a 220 °C insulation system. A lower rise means more copper or aluminium and a lower-loss, longer-life design with built-in overload margin — a 65 °C liquid unit, for example, can carry a 55 °C rated load with about 12 % extra capacity.

DOE 10 CFR 431 efficiency (DOE 2016 / 2029)

Also: DOE efficiency, NRCan efficiency

The U.S. Department of Energy minimum efficiency levels for distribution transformers (liquid-filled, low-voltage dry-type and medium-voltage dry-type), measured at a reference load — 50 % of rating for liquid and MV dry-type, 35 % for LV dry-type. The 2016 levels apply to units made since 1 January 2016; the April 2024 final rule raises them for units manufactured from 2029. Canada enforces equivalent levels through NRCan’s Energy Efficiency Regulations (CSA C802 series). Entogo designs its North-American transformers to the DOE levels.

Loop-feed vs. radial-feed

The two primary-cable arrangements of a pad-mounted transformer. A radial-feed unit has one set of primary bushings and is the dead end of a feeder. A loop-feed unit has two sets of bushings and loop (sectionalizing) switches, so the underground loop passes through the transformer and any one unit can be isolated for maintenance while the rest of the loop stays energised from the other direction — the standard choice for utility and campus networks.

Dead-front vs. live-front

Dead-front equipment keeps every energised part behind insulated, separable elbow connectors (IEEE 386) so no live metal is exposed when the cabinet is opened; live-front equipment uses exposed porcelain bushings. Dead-front construction is the North-American norm for pad-mounted transformers, sectionalizing cabinets and pad-mounted switchgear because it allows loadbreak switching and elbow-to-bushing testing with hot sticks at a safer working distance.

Unit substation (compact secondary substation)

Also: packaged substation, CSS, unitized substation

A factory-assembled package that close-couples an incoming medium-voltage section (load-interrupter switch and fuses or a breaker), a transformer and a low-voltage switchgear or switchboard section through solid bus, built to IEEE C37.121. Because the whole assembly is wired and tested in the factory, a unit substation shortens site work from weeks to days — the format Entogo uses for its pad-mounted compact secondary and 36 kV outdoor unit substations.

Step-up (collector) transformer

Also: inverter-duty transformer, GSU

In a solar, wind or battery plant, the transformer that raises inverter output (typically 480–800 V) to the collection-system voltage, most often 34.5 kV, before the plant’s main step-up to transmission. Inverter-duty units are designed to IEEE C57.159 for harmonic content, cyclic loading and the DC offset inverters can impose. Entogo packages them on skids with the medium-voltage switchgear as a solar / storage unit substation.

K-factor

A rating (K-4, K-13, K-20 …) that states how much harmonic current a dry-type transformer can carry without exceeding its temperature limit, calculated by the UL 1561 method from the harmonic spectrum of the load. Non-linear loads such as UPS systems, variable-frequency drives and switch-mode power supplies raise eddy-current loss in the windings; a K-13 rating is a common specification for data-centre and industrial-drive transformers.

Taps (de-energized tap changer)

Also: DETC, tap changer

Extra connections on the high-voltage winding that change the turns ratio in small steps so a transformer can deliver nominal secondary voltage when the supply runs persistently high or low. The North-American standard is four 2.5 % taps — two above and two below nominal (±5 %) — selected with the transformer de-energised. On-load tap changers (OLTC) that switch under load are reserved for large power transformers.

Switchgear & distribution

Medium- and low-voltage assemblies, the UL and ANSI/IEEE C37 standards that define them, and the ratings that must match the available fault current.

Metal-clad switchgear

Medium-voltage switchgear built to ANSI/IEEE C37.20.2 (4.76–38 kV) with drawout vacuum circuit breakers, grounded metal barriers between every major primary compartment, insulated bus and automatic shutters that cover the live stabs when a breaker is withdrawn. It is the top tier of MV gear, used wherever feeders need breaker protection and relaying — utility and industrial substations, data-centre MV rooms and renewable interconnections. Entogo builds metal-clad lineups to 4000 A and 50 kA.

Metal-enclosed (load-interrupter) switchgear

Also: interrupter switchgear, switch-and-fuse gear

Medium-voltage switchgear built to ANSI/IEEE C37.20.3 in which fixed-mounted load-interrupter switches (600 or 1200 A) and power fuses, rather than drawout breakers, switch and protect the circuit, and compartments are not required to be barriered from each other. It costs less and needs less floor space than metal-clad gear, which makes it the usual choice for transformer primaries, feeder taps and unit-substation incoming sections.

Switchboard (UL 891)

Also: dead-front switchboard, LV switchboard

A low-voltage (up to 600 V) dead-front assembly in which fixed or group-mounted molded-case and insulated-case circuit breakers share a common bus, certified to UL 891 (Canada: CSA C22.2 No. 244). Short-circuit ratings are established with a 3-cycle test and rely on the breakers’ instantaneous trip. Front-accessible, compact and economical, switchboards are the default service-entrance and distribution equipment for commercial buildings up to about 6000 A.

Low-voltage switchgear (UL 1558 / ANSI C37.20.1)

Also: LV power circuit breaker switchgear, drawout LV switchgear

Metal-enclosed low-voltage power-circuit-breaker switchgear: drawout air or vacuum power breakers (UL 1066 / ANSI C37.13) in individually compartmented cells, certified to UL 1558 and ANSI/IEEE C37.20.1 (Canada: CSA C22.2 No. 31). Its 30-cycle (0.5 s) short-time withstand lets upstream breakers delay tripping so only the device nearest a fault opens — the basis of selective coordination in hospitals, data centres and process plants.

Panelboard (UL 67)

A wall- or surface-mounted low-voltage distribution assembly, certified to UL 67 (Canada: CSA C22.2 No. 29), in which branch circuit breakers plug onto a common bus behind a dead-front trim. Panelboards are limited to 1200 A and to front access, and feed lighting, receptacle and small-motor branch circuits downstream of a switchboard or switchgear.

Motor control center (MCC, UL 845)

A low-voltage assembly of motor starters, variable-frequency drives, soft starters and feeder breakers in plug-in “buckets” on a common vertical and horizontal bus, certified to UL 845 (Canada: CSA C22.2 No. 254) and built to NEMA ICS 18. An MCC centralises motor protection and control for pumps, fans, compressors and conveyors, and is specified by its bus rating, short-circuit rating and the NEMA class and type of wiring.

Ring main unit (RMU)

Also: pad-mounted switchgear

Compact, sealed medium-voltage switchgear — gas-insulated, dry-air or solid-insulated — that combines two load-break switches for the incoming and outgoing loop cables with a fused or breaker-protected tee-off to a transformer. An RMU lets a distribution loop be sectionalised and a transformer isolated without interrupting the ring. In North America it is packaged as dead-front pad-mounted switchgear per IEEE C37.74 and ANSI C57.12.28 enclosure rules.

Sectionalizing (junction) cabinet

Also: cable junction cabinet, pad-mounted junction box

A dead-front pad-mounted cabinet with bushings — and optionally loadbreak switches or fuses — used to split, tap, loop and isolate underground primary cable runs without a transformer. Cables land on IEEE 386 separable elbow connectors inside an ANSI C57.12.28 tamper-resistant enclosure, so a crew can reconfigure a 15 / 25 / 35 kV class loop with hot sticks instead of excavating splices.

Arc-resistant switchgear (IEEE C37.20.7)

Also: arc-flash resistant gear, Type 2B

Switchgear tested to IEEE C37.20.7 to contain and vent an internal arcing fault so that operators standing in front of (Type 1) or on all sides of (Type 2) the lineup are protected for the rated fault current and duration; suffix B means the low-voltage control compartment may be open during the event. Arc-resistant construction adds plenums and pressure-relief flaps and is increasingly specified for occupied electrical rooms in data centres and industrial plants.

Interrupting rating vs. short-circuit current rating (SCCR)

Also: AIC rating, kA rating

Interrupting rating is the highest fault current, in kA symmetrical, that a circuit breaker or fuse can safely interrupt. Short-circuit current rating (SCCR) is the fault current an entire assembly — switchboard, panelboard, MCC or unit substation — can withstand with its overcurrent protection. Both must equal or exceed the available fault current at the installation point (NEC 110.9 and 110.10; CEC Rule 14-012), which is why the utility’s fault study is needed before equipment is ordered.

Short-time withstand rating

Also: short-time current

The fault current an assembly or breaker can carry for a defined time — 30 cycles (0.5 s) for UL 1558 low-voltage switchgear and typically 2 s for ANSI/IEEE C37.20.2 metal-clad gear — without damage, so that an upstream breaker can intentionally delay tripping while a downstream device clears the fault. Equipment without a short-time rating, such as most UL 891 switchboards, must rely on instantaneous tripping instead.

Selective coordination

Setting overcurrent protective devices so that only the device immediately upstream of a fault opens, keeping the rest of the facility energised. The NEC requires it for emergency (700.32), legally required standby (701.32), critical operations (708.54) and elevator (620.62) circuits. It is achieved with short-time-delay trip units on power circuit breakers, current-limiting fuses, or both — a primary reason projects specify UL 1558 switchgear over UL 891 switchboards.

NEMA enclosure types (1, 3R, 4X, 12)

Also: NEMA 250, UL 50E

Enclosure ratings from NEMA 250 / UL 50E that describe what an electrical cabinet keeps out. Type 1 is indoor general purpose; Type 3R is outdoor, rain- and sleet-resistant with drainage; Type 4 is watertight against hose-directed water and Type 4X adds corrosion resistance (stainless or fibreglass) for coastal and chemical sites; Type 12 is indoor dust- and drip-tight. Outdoor pad-mounted equipment is normally Type 3R; meter and CT cabinets often Type 3R or 4X.

Power-factor-correction capacitor bank

Also: PFC, automatic capacitor bank, detuned capacitor bank

Switched capacitor stages, usually with detuning reactors when the site has harmonics, that supply reactive power locally so the utility sees a higher power factor — typically above the 0.90 threshold at which many North-American utilities bill penalties. Correction also releases transformer and feeder capacity that was carrying reactive current. Banks are built to IEEE 18, UL 810 and NEMA CP-1 and are sized in kvar from the utility bill.

Gas-insulated switchgear (GIS) and SF6-free gear

Also: eco-gas switchgear

Medium-voltage switchgear whose primary circuit is sealed in an insulating-gas tank, giving a very compact footprint and immunity to dust, humidity and salt. Sulphur hexafluoride (SF6) has a global-warming potential about 23,500 times that of CO₂, so new designs use fluoronitrile or fluoroketone mixtures, dry air or vacuum interrupters instead; regulators in the EU, California and several Canadian provinces are phasing SF6 out. Entogo’s MV GIS is offered in SF6-free eco-gas versions per IEEE C37.20.9.

Energy storage

Battery energy storage terms, the UL 9540 / NFPA 855 safety framework and the tariff mechanics that make commercial storage pay.

Battery energy storage system (BESS)

An integrated system of battery modules (today mostly lithium iron phosphate, LFP), a battery management system (BMS), a power conversion system (PCS), thermal management and an energy management system (EMS), packaged as a cabinet, container or skid. A BESS is rated in power (kW / MW) and energy (kWh / MWh); the ratio gives its duration, e.g. a 500 kW / 1000 kWh system is a 2-hour battery. Entogo builds air- and liquid-cooled cabinets and containerised systems.

Commercial & industrial (C&I) storage

Also: behind-the-meter storage, BTM storage

Battery storage installed behind a customer’s utility meter — typically 100 kW to several MW — to cut demand charges, shift consumption away from peak time-of-use rates, ride through outages and absorb on-site solar. C&I systems are usually outdoor cabinets with integrated PCS and are dispatched by an EMS against the site’s tariff; payback depends mainly on the demand-charge rate ($/kW) and the site’s load shape.

Air-cooled vs. liquid-cooled BESS

The two ways of managing battery temperature. Air-cooled cabinets circulate conditioned air through the racks — simpler and cheaper for small or mild-duty systems. Liquid-cooled systems pump coolant through cold plates in contact with the cells, holding cell-to-cell temperature spread to a few degrees, which extends cycle life, allows higher charge/discharge rates and denser containers, and is now the norm above a few hundred kWh.

UL 9540 and UL 9540A

UL 9540 is the product-safety standard for a complete energy storage system (batteries, PCS and controls as a unit) — the listing an AHJ looks for. UL 9540A is not a listing but a large-scale fire test method that measures whether thermal runaway propagates from cell to module to unit to installation; its results are what NFPA 855 and the fire codes use to allow closer spacing, larger groups or indoor installation than the default limits.

NFPA 855

Also: Standard for the Installation of Stationary Energy Storage Systems

The NFPA installation standard for stationary energy storage, adopted through the International Fire Code and many Canadian jurisdictions alongside CEC Section 64. It sets siting and separation distances, maximum energy per unit and per group, fire detection and suppression, ventilation and explosion control, signage, and the hazard mitigation analysis that a project must submit — with UL 9540A test data as the main route to relaxed limits.

Demand charge and peak shaving

A demand charge is the part of a commercial electricity bill based on the highest average power drawn in any 15- or 30-minute interval of the billing period, priced in dollars per kW. Peak shaving uses a battery (or load control) to discharge during those peaks so the recorded maximum stays below a target. Because one short peak sets the charge for the whole month, even a 1- or 2-hour battery can remove a large share of it.

Grid-forming vs. grid-following inverter

A grid-following inverter synchronises to the voltage and frequency it measures and injects current; if the grid disappears it must shut down. A grid-forming inverter establishes its own voltage and frequency reference, so it can black-start a site, run an islanded microgrid with solar, storage and generators, and provide inertia-like frequency response. Grid-forming capability is what turns a BESS into a resilience asset rather than only a tariff tool.

Power conversion system (PCS)

Also: battery inverter, bidirectional inverter

The bidirectional inverter/converter between the DC battery bus and the AC grid or load, rated in kW. It controls charge and discharge, power factor and — in grid-forming products — voltage and frequency. DC-coupled designs add a DC-DC converter so PV can charge the battery without a second AC conversion, raising round-trip efficiency and letting one PCS serve solar, storage and EV charging.

Round-trip efficiency

The AC energy a storage system returns divided by the AC energy it absorbed over a full charge–discharge cycle, including PCS, transformer and auxiliary (cooling, controls) losses. Lithium iron phosphate systems typically achieve 85–92 % at the AC terminals. Round-trip efficiency, together with depth of discharge and cycle life, determines how many usable kWh a project actually gets per dollar over its life.

EV charging

Charging levels, connector standards and the code terms — NEC Article 625, CEC Section 86, EVEMS — that decide how much service capacity a charging site needs.

Level 2 (AC) charging

Also: L2 charger, AC charger

AC charging at 208 or 240 V single-phase in North America (400 V three-phase with a Type 2 connector in IEC markets), in which the vehicle’s onboard charger converts AC to DC. Output ranges from about 7 kW (32 A) to 19.2 kW (80 A) per SAE J1772; 7.2–11.5 kW is typical for workplaces, multi-unit residential and fleet depots that charge for hours rather than minutes.

DC fast charging (DCFC)

Also: Level 3, DC charger, ultra-fast charger

Charging in which an off-board rectifier delivers DC directly to the vehicle battery, bypassing the onboard charger, at 30 kW to 400 kW and above through a CCS1, NACS (SAE J3400) or CHAdeMO connector. DCFC sites need three-phase service — usually 480 V — and often a dedicated transformer, which is why service capacity is checked before chargers are chosen. Entogo’s Mobox, Turbo and Rocket lines span compact 40 kW to dual-outlet 300 kW.

SAE J1772, CCS1, NACS (SAE J3400) and CHAdeMO

Also: EV connector standards

The North-American charging connectors. SAE J1772 is the AC (Level 1–2) plug. CCS1 adds two DC pins beneath a J1772 for fast charging. NACS is the former Tesla connector, standardised as SAE J3400 in 2023–24 and adopted by most automakers selling in North America from 2025, so new public DC chargers are typically ordered with NACS and CCS1 cables. CHAdeMO is the legacy DC connector used mainly by earlier Nissan and Mitsubishi models.

Related: Rocket DC Ultra-Fast Charger

OCPP (Open Charge Point Protocol)

The open protocol from the Open Charge Alliance that connects a charger to any charging-network back end for authorisation, metering, pricing, remote diagnostics and smart-charging set-points. OCPP 1.6J is still the most deployed version; OCPP 2.0.1 adds ISO 15118 plug-and-charge, stronger security and device management. Entogo’s AC and DC chargers are OCPP-certified, so site owners can choose or change their network operator without replacing hardware.

EVEMS / EV load management

Also: electric vehicle energy management system, ALM, dynamic load management

A control system that monitors the site or feeder and throttles charger output so that total EV demand never exceeds an allocated capacity. Both the NEC (625.42) and the Canadian Electrical Code (Section 8 and Section 86 rules for EV energy management systems) let the managed maximum, rather than the chargers’ nameplate sum, be used in the service load calculation — often the difference between adding chargers to an existing service and paying for an upgrade.

NEC Article 625 and CEC Section 86

The code articles that govern EV charging installations. NEC Article 625 (Electric Vehicle Power Transfer System) treats charging equipment as a continuous load — counted at nameplate, with the 125 % continuous factor for conductors and overcurrent devices — unless an EVEMS limits it. The Canadian Electrical Code covers EV supply equipment in Section 86, with Ontario’s ESA and the provincial codes adding local rules. Always confirm the adopted edition with the AHJ.

Demand factor

The ratio of a system’s maximum demand to its total connected load, used by the codes to size services realistically for loads that never all run at once. Most EV charging is excluded from that relief: chargers are treated as continuous loads at 100 % of nameplate unless an approved load-management system enforces a lower maximum, which is why a 10-charger site can drive a larger service upgrade than its average draw suggests.

Standards & certification

The standards families and certification terms that appear on North-American specifications — and what Entogo means when it says “designed and built to”.

ANSI/IEEE C57 series

The IEEE transformer standards used across the United States and Canada: C57.12.00 (general requirements for liquid-immersed transformers), C57.12.90 (test code), C57.12.10 (power transformers), C57.12.20 (overhead distribution), C57.12.34 and C57.12.38 (three- and single-phase pad-mounted), C57.12.28/.29 (pad-mount enclosure integrity), C57.12.01 (dry-type) and C57.159 (inverter-duty). Entogo designs and builds its North-American transformers to these documents.

ANSI/IEEE C37 series

The IEEE switchgear standards: C37.20.1 (low-voltage power circuit breaker switchgear), C37.20.2 (metal-clad), C37.20.3 (metal-enclosed interrupter switchgear), C37.20.7 (arc-resistant testing), C37.04/.06/.09 (medium-voltage circuit breakers), C37.74 (pad-mounted switchgear), C37.20.9 (medium-voltage gas-insulated switchgear) and C37.121 (unit substations). A specification names the relevant C37 document together with the UL or CSA certification required.

UL Listed, cULus and CSA Certified

Certification marks accepted by North-American inspectors. “UL Listed” means UL certified the product to a UL standard for the United States; “cULus” means UL certified it to both Canadian and U.S. requirements; “CSA Certified” means CSA Group did so, and CSA is accredited in both countries. Entogo’s catalogue is European-standard (IEC/CE); North-American units are designed and built to the ANSI/IEEE and UL standards, with UL (cULus) or CSA certification obtained on request for the specific order.

NRTL (Nationally Recognized Testing Laboratory)

A laboratory recognised by the U.S. Occupational Safety and Health Administration to test and certify products to U.S. safety standards — UL, CSA Group, Intertek (ETL), TÜV and others. An NRTL mark is what the NEC (110.3) and most AHJs expect on installed electrical equipment. In Canada the equivalent is a certification body accredited by the Standards Council of Canada, such as CSA Group or UL (cUL).

Field evaluation (field labelling)

Also: special inspection, SPE-1000

The route to inspector approval for equipment that carries no NRTL listing — custom-built, imported or modified switchgear, for example. A field evaluation body inspects and tests the equipment in place to NFPA 790/791 (U.S.) or the SPE-1000 model code (Canada) and applies a field label the AHJ can accept. It is a one-off approval for that installation, not a product listing.

CE marking and IEC standards

CE marking is the manufacturer’s declaration that a product meets the applicable European Union directives; the technical basis is the IEC standards — IEC 60076 for transformers, IEC 62271 for switchgear, IEC 61439 for low-voltage assemblies. CE is not recognised by North-American inspectors, so IEC-catalogue equipment sold into the U.S. or Canada is re-engineered for 60 Hz and ANSI/IEEE ratings and certified by an NRTL or field evaluated.

Related: Manufacturing & lead times

60 Hz vs. 50 Hz

North America runs at 60 Hz; Europe, most of Asia and Africa at 50 Hz. Frequency sets core flux for a given voltage and turns, so a 50 Hz transformer operated at 60 Hz runs at lower flux and is safe (with slightly different losses), while a 60 Hz design connected to 50 Hz saturates and overheats. Motors, switchgear relays and metering are also frequency-specific, which is why Entogo builds dedicated 60 Hz units for North-American orders.

Lead time (transformers and switchgear)

The elapsed time from purchase order to shipment. In 2026 the North-American merchant market commonly quotes one to four years for power transformers and many months for distribution units and medium-voltage switchgear. Entogo manufactures in its own factory with a vertically integrated supply chain: catalogue equipment ships in about 12 weeks on average, with a guaranteed worst case of 36 weeks even when a product needs new UL or other North-American certification.

Manufacturer warranty

The manufacturer’s commitment to repair or replace equipment that fails from defects in materials or workmanship within a stated period. One to two years is the common baseline for electrical equipment in the industry; Entogo backs every product with a minimum 36-month warranty, extending up to 10 years on major power equipment such as transformers and distribution cabinets, with the exact term, coverage and start point (delivery or commissioning) confirmed in each contract.

Related: Warranty & returns

A–Z

All terms

60 Hz vs. 50 Hz
Air-cooled vs. liquid-cooled BESS
Amorphous-core transformer
ANSI/IEEE C37 series
ANSI/IEEE C57 series
Arc-resistant switchgear (IEEE C37.20.7)
Basic impulse insulation level (BIL)
Battery energy storage system (BESS)
CE marking and IEC standards
Commercial & industrial (C&I) storage
DC fast charging (DCFC)
Dead-front vs. live-front
Demand charge and peak shaving
Demand factor
DOE 10 CFR 431 efficiency (DOE 2016 / 2029)
Dry-type transformer
EVEMS / EV load management
Field evaluation (field labelling)
Gas-insulated switchgear (GIS) and SF6-free gear
Grid-forming vs. grid-following inverter
Interrupting rating vs. short-circuit current rating (SCCR)
K-factor
kVA rating (apparent power)
Lead time (transformers and switchgear)
Level 2 (AC) charging
Liquid-filled (oil-immersed) transformer
Loop-feed vs. radial-feed
Low-voltage switchgear (UL 1558 / ANSI C37.20.1)
Manufacturer warranty
Metal-clad switchgear
Metal-enclosed (load-interrupter) switchgear
Motor control center (MCC, UL 845)
NEC Article 625 and CEC Section 86
NEMA enclosure types (1, 3R, 4X, 12)
NFPA 855
NRTL (Nationally Recognized Testing Laboratory)
OCPP (Open Charge Point Protocol)
Pad-mounted transformer
Panelboard (UL 67)
Percent impedance (%Z)
Pole-mounted (overhead) transformer
Power conversion system (PCS)
Power-factor-correction capacitor bank
Ring main unit (RMU)
Round-trip efficiency
SAE J1772, CCS1, NACS (SAE J3400) and CHAdeMO
Sectionalizing (junction) cabinet
Selective coordination
Short-time withstand rating
Step-up (collector) transformer
Switchboard (UL 891)
Taps (de-energized tap changer)
Temperature rise (55 / 65 / 80 / 115 / 150 °C)
UL 9540 and UL 9540A
UL Listed, cULus and CSA Certified
Unit substation (compact secondary substation)
Voltage class (15 kV / 25 kV / 35 kV)
Wound-core (3-D triangular core) transformer

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