# Glossary Standards, test methods and terms used on UK utility-scale solar, storage and grid connection projects. Source: https://crestwatt.com/glossary/ Publisher: CrestWatt — Electrical contracting for utility-scale solar, storage and grid connections. Contact: info@crestwatt.com Language: en-GB ## Connections and networks ### Independent Connection Provider (ICP) A company accredited under the National Electricity Registration Scheme to carry out contestable connection works on a distribution network. An ICP designs and builds the connection; the DNO retains the non-contestable works and adopts the completed assets. Related scope: https://crestwatt.com/services/icp-grid-connections/ ### Distribution Network Operator (DNO) The licensed operator of the regional electricity distribution network. The DNO issues the connection offer, defines the technical specification for the connection, witnesses key tests and adopts the connection assets on completion. Related scope: https://crestwatt.com/services/icp-grid-connections/ ### Contestable works The parts of a new connection that a customer may have built by an accredited ICP rather than the DNO. These typically include the HV cable route from the point of connection, the point of connection substation, metering, protection and earthing, and all works on the customer side of the ownership boundary. Related scope: https://crestwatt.com/services/icp-grid-connections/ ### Non-contestable works The parts of a new connection that only the DNO may carry out: the connection to the existing network, any network reinforcement required to accommodate the new load or generation, and the final adoption inspection. Related scope: https://crestwatt.com/services/icp-grid-connections/ ### Point of connection (PoC) The physical point at which a customer installation connects to the distribution network, and the ownership boundary between DNO assets and customer assets. On a generation project the point of connection substation is usually on the critical path to energisation. Related scope: https://crestwatt.com/services/icp-grid-connections/ ### National Electricity Registration Scheme (NERS) The UK accreditation scheme, assessed by Lloyd’s Register, under which companies and individual operatives are registered to carry out contestable connection works. DNOs check the published NERS register before accepting an ICP onto a connection. Related scope: https://crestwatt.com/services/icp-grid-connections/ ### Final Acceptance Certificate (FAC) The document by which the owner or EPC accepts a completed plant, normally issued after provisional acceptance, the defects period and closure of outstanding snags. The commissioning record pack is compiled against the FAC checklist. Related scope: https://crestwatt.com/services/testing-commissioning/ ### Authorised person (AP / SAP) A person formally appointed in writing to carry out or supervise defined high-voltage operations, including switching and the issue of safety documents. A senior authorised person holds a wider appointment covering permits to work on HV systems. Related scope: https://crestwatt.com/services/operations-maintenance/ ## Standards and codes ### ENA EREC G99 The Energy Networks Association Engineering Recommendation governing the connection of generation to distribution networks in Great Britain. It sets the compliance testing, protection settings and grid code performance requirements a generator or storage site must demonstrate before it may export. Related scope: https://crestwatt.com/services/engineering-grid-studies/ ### ENA EREC G81 The Engineering Recommendation covering standard design, materials and construction practice for new LV and HV connections, used by DNOs to specify how contestable works must be designed and built. Related scope: https://crestwatt.com/services/icp-grid-connections/ ### ENA TS 41-24 The Energy Networks Association technical specification for the design and installation of earthing systems at substations, including step and touch potential assessment and earth electrode arrangement. Related scope: https://crestwatt.com/services/engineering-grid-studies/ ### ENA EREC P28 The Engineering Recommendation governing voltage fluctuation and flicker limits for plant connected to public distribution networks, assessed as part of a connection application. Related scope: https://crestwatt.com/services/engineering-grid-studies/ ### BS 7671 The IET Wiring Regulations, the UK national standard for low-voltage electrical installations. LV distribution on a utility-scale plant is inspected, tested and certified to BS 7671. Related scope: https://crestwatt.com/services/testing-commissioning/ ### BS EN 50522 The European standard for the earthing of power installations exceeding 1 kV AC, applied alongside ENA TS 41-24 in UK substation earthing design and verification. Related scope: https://crestwatt.com/services/hv-substation-cable-works/ ### IEC 62446-1 The international standard for the documentation, commissioning tests and inspection of grid-connected photovoltaic systems. It defines Category 1 tests, applied to every string, and Category 2 tests such as IV curve tracing and thermographic survey where specified. Related scope: https://crestwatt.com/services/testing-commissioning/ ### IEC 62852 The standard covering DC connectors for photovoltaic systems, including the safety and interoperability requirements that govern MC4-type connector assembly and cross-mating. Related scope: https://crestwatt.com/services/cable-termination-testing/ ### IEC 60352-2 The standard for solderless crimped connections, defining crimp quality, tooling and the pull-test acceptance criteria used to verify DC cable crimps on a sample plan. Related scope: https://crestwatt.com/services/cable-termination-testing/ ### IEC 60502-2 The standard for extruded-insulation power cables rated 6 kV to 30 kV, covering the 33 kV XLPE cable and accessories used on UK solar and storage collector systems. Related scope: https://crestwatt.com/services/hv-substation-cable-works/ ### IEC 60840 The standard for extruded-insulation power cables and accessories rated above 30 kV up to 150 kV, covering 66 kV and 132 kV XLPE cable, joints and sealing ends. Related scope: https://crestwatt.com/services/hv-substation-cable-works/ ### IEC 61439 The standard for low-voltage switchgear and controlgear assemblies, covering the design verification and routine testing of LVAC distribution boards and control panels. Related scope: https://crestwatt.com/services/hv-substation-cable-works/ ### IEC 60287 The standard method for calculating the continuous current rating of cables, used in cable sizing alongside BS 7671 where installation conditions, grouping and soil thermal resistivity govern. Related scope: https://crestwatt.com/services/engineering-grid-studies/ ### ISO/IEC 11801 and EN 50173 The standards for generic structured cabling, defining the permanent link and channel performance classes against which CAT5e to CAT7 installations are certified. Related scope: https://crestwatt.com/services/cable-termination-testing/ ### EN 50174 The standard covering information technology cabling installation planning, practice and separation from power circuits, applied to control and communications routing on site. Related scope: https://crestwatt.com/services/cable-termination-testing/ ### Distribution Code The code setting out the technical requirements governing the relationship between DNOs and the users connected to their networks, including planning, operation and connection conditions. Related scope: https://crestwatt.com/services/icp-grid-connections/ ## Testing methods ### Insulation resistance test (IR) A DC test measuring the resistance between conductors, and between conductors and earth, to confirm insulation integrity before energisation. Applied across DC strings, LV circuits and HV cable systems. Related scope: https://crestwatt.com/services/testing-commissioning/ ### VLF withstand test (VLF) A very low frequency AC withstand test, normally at 0.1 Hz, used to prove the insulation of installed MV and HV cable systems after termination. Test voltages and durations follow IEEE 400.2. Related scope: https://crestwatt.com/services/cable-termination-testing/ ### IEEE 400.2 The IEEE guide for field testing shielded power cable systems using very low frequency, setting the voltage levels, waveforms and durations for VLF withstand testing. Related scope: https://crestwatt.com/services/cable-termination-testing/ ### Sheath integrity test A DC test applied between the cable metallic screen and earth to prove the outer sheath is undamaged after installation and backfill. Voltage and duration follow IEC 60229 and the manufacturer requirement. Related scope: https://crestwatt.com/services/cable-termination-testing/ ### Tan delta measurement A dielectric loss measurement that indicates the overall condition and water-tree ageing of cable insulation. Specified by some clients and DNOs in addition to a withstand test. Related scope: https://crestwatt.com/services/cable-termination-testing/ ### Partial discharge test (PD) A measurement that detects localised breakdown within insulation, joints or terminations before it develops into a fault. Used to verify workmanship on HV accessories where specified. Related scope: https://crestwatt.com/services/cable-termination-testing/ ### Time domain reflectometry (TDR) A pulse-echo method used to measure cable length and locate joints, open circuits and faults along a cable route, both before termination and during fault location. Related scope: https://crestwatt.com/services/cable-termination-testing/ ### Optical time domain reflectometry (OTDR) The fibre equivalent of TDR: a backscatter trace that shows splice loss, connector loss and breaks along an optical link. Traces are recorded bidirectionally and delivered as part of the link certification. Related scope: https://crestwatt.com/services/cable-termination-testing/ ### IEC 61280-4-1 The standard for measuring attenuation of installed multimode and single-mode fibre links, defining the insertion loss method used to certify each link. Related scope: https://crestwatt.com/services/cable-termination-testing/ ### IEC 61300-3-35 The standard defining visual acceptance criteria for fibre optic connector end-faces, applied during inspection and cleaning before mating. Related scope: https://crestwatt.com/services/cable-termination-testing/ ### Secondary injection A protection test in which currents and voltages are injected directly into the relay inputs to verify settings, characteristics and tripping logic without energising the primary plant. Related scope: https://crestwatt.com/services/protection-control-switchgear/ ### Primary injection A protection test in which current is injected through the primary conductor, proving current transformer ratio, polarity and the complete secondary wiring path through to the relay. Related scope: https://crestwatt.com/services/protection-control-switchgear/ ### IV curve tracing A Category 2 photovoltaic test that plots the current-voltage characteristic of a string and compares it against the expected curve, revealing mismatch, shading, degradation and connection faults. Related scope: https://crestwatt.com/services/testing-commissioning/ ### Thermographic survey An infrared survey carried out under load to find hot joints, loose terminations, failed connectors and unbalanced circuits in switchgear, transformer stations, combiner boxes and DC connectors. Related scope: https://crestwatt.com/services/operations-maintenance/ ### Step and touch potential The voltages that can appear across a person’s feet, or between hand and foot, during an earth fault. Measured and assessed against the limits in ENA TS 41-24 and BS EN 50522 to verify an earthing design. Related scope: https://crestwatt.com/services/engineering-grid-studies/ ## Plant and equipment ### String combiner box The enclosure at which multiple photovoltaic strings are paralleled onto a single DC feeder, containing string fuses, a disconnector and, usually, string current monitoring reported over Modbus. Related scope: https://crestwatt.com/services/testing-commissioning/ ### Transformer station The skid or containerised unit on a solar or storage plant housing the inverter, the LV/MV transformer, MV switchgear and auxiliary supplies, connecting the array to the collector network. Related scope: https://crestwatt.com/services/testing-commissioning/ ### Sealing end An HV cable termination that transitions the cable to an air-insulated or gas-insulated connection, providing stress control and environmental sealing. Used at 66 kV and 132 kV on outdoor structures and at GIS bays. Related scope: https://crestwatt.com/services/hv-substation-cable-works/ ### Separable connector A plug-in MV cable termination, in elbow or T-body form, that can be disconnected for testing without cutting back the cable. Common at 11 kV and 33 kV on transformer and switchgear bushings. Related scope: https://crestwatt.com/services/cable-termination-testing/ ### XLPE cable Cross-linked polyethylene insulated power cable, the standard insulation system for modern MV and HV distribution, manufactured to IEC 60502-2 at 33 kV and IEC 60840 at 66 kV and above. Related scope: https://crestwatt.com/services/hv-substation-cable-works/ ### Current and voltage transformers (CT / VT) Instrument transformers that scale primary current and voltage to standard secondary values for protection and metering. Ratio, accuracy class and burden must be verified against the protection scheme they serve. Related scope: https://crestwatt.com/services/protection-control-switchgear/ ### Battery energy storage system (BESS) A grid-connected battery installation, either AC-coupled through its own inverters or DC-coupled behind a shared inverter with generation. Connection, protection coordination and G99 compliance testing follow the same framework as generation. Related scope: https://crestwatt.com/services/testing-commissioning/ ### MC4 connector The prevailing photovoltaic DC connector family used on module leads, string harnesses and combiner box inputs. Cross-mating between manufacturers is a recognised failure mode, so compatibility is verified against module and combiner types. Related scope: https://crestwatt.com/services/cable-termination-testing/ ## Communications and control ### IEC 61850 The international standard for substation automation communications. It defines the data model, the SCD configuration description, and the GOOSE and MMS services used for protection signalling and supervisory data. Related scope: https://crestwatt.com/services/protection-control-switchgear/ ### GOOSE Generic Object Oriented Substation Event: the fast, publisher-subscriber multicast messaging service in IEC 61850 used for protection interlocking and trip signalling between devices over the substation network. Related scope: https://crestwatt.com/services/protection-control-switchgear/ ### Modbus RTU over RS-485 The serial protocol and physical layer most widely used for string monitoring, inverter data and field device polling on solar plants. Correct daisy-chain topology, 120 Ω line termination, bias resistors and single-point shield earthing govern whether a loop is reliable. Related scope: https://crestwatt.com/services/cable-termination-testing/ ### SCADA Supervisory Control and Data Acquisition: the plant-level system that collects data from field devices and presents control and alarming to the operator. Point to point verification proves every signal from field device to HMI against the signal list. Related scope: https://crestwatt.com/services/testing-commissioning/ ### Power plant controller (PPC) The controller that regulates a plant’s active and reactive power at the point of connection to meet grid code requirements, including voltage and frequency response modes and ramp rate limits tested under ENA EREC G99. Related scope: https://crestwatt.com/services/engineering-grid-studies/