| Rated Voltage (Ue) | Confirm the system voltage, frequency, number of phases, and whether the enclosure is for low-voltage AC or DC distribution. | 230/400 V AC, 480 V AC, 690 V AC
DC ratings must be specified separately. | The switchgear assembly, busbars, protective devices, clearances, and insulation system must be suitable for the actual operating voltage. | Match the equipment rating to the highest continuous system voltage and the applicable local electrical code. |
| Rated Current (In) | Determine the maximum continuous load current, diversity factor, future expansion, and conductor ampacity. | 63 A to 4,000 A+
Common panel ranges include 125 A, 250 A, 630 A, 1,600 A, and 2,500 A. | An undersized rating can cause overheating, nuisance trips, reduced service life, or insulation damage. | Check temperature-rise test data, busbar capacity, terminal ratings, and derating for ambient temperature and grouping. |
| Short-Circuit Withstand | Check prospective fault current at the installation point and the assembly’s short-time withstand current (Icw), peak withstand current (Ipk), or conditional short-circuit rating. | 10 kA to 100 kA
Common values include 25 kA, 36 kA, 50 kA, and 65 kA for defined durations. | The enclosure and internal conductors must withstand thermal and electrodynamic forces until the protective device clears the fault. | Use the utility or engineering fault study. Verify coordination between upstream protection and the switchgear assembly. |
| Breaking Capacity | Verify the interrupting capacity of circuit breakers and fuses, including service short-circuit capacity where applicable. | Icu and Ics values in kA
Ics is normally expressed as a percentage of Icu. | The protective device must safely interrupt the available fault current without catastrophic failure. | Ensure the device rating is not lower than the calculated prospective short-circuit current at its terminals. |
| Ingress Protection (IP) | Select protection against solid objects, dust, and water according to the installation environment. | IP31 Indoor, limited protection
IP54 Dust-limited and splash-resistant
IP65 Dust-tight and water-jet resistant
IP66 Dust-tight and powerful water-jet resistant | A higher IP code can reduce contamination and moisture entry, but it may also restrict natural cooling. | Check the complete assembled enclosure, door seals, cable glands, ventilation openings, and drainage arrangements. |
| Mechanical Impact Protection (IK) | Assess the risk of accidental impact from tools, vehicles, handling equipment, or public access. | IK05 0.7 J
IK08 5 J
IK10 20 J | Impact resistance helps prevent deformation, loss of enclosure integrity, and accidental exposure of live parts. | Specify an IK rating for the complete enclosure and consider the door, viewing windows, locks, and mounting accessories. |
| Insulation Level | Check rated insulation voltage (Ui), rated impulse withstand voltage (Uimp), creepage distances, and clearances. | Ui: commonly 500–1,000 V
Uimp: commonly 4–12 kV, depending on the system and equipment category. | These values address long-term insulation stress and short-duration overvoltage events such as lightning or switching surges. | Confirm values for the assembly, incoming devices, busbars, terminals, and any surge-protection equipment. |
| Overvoltage Category | Identify where the equipment is installed in relation to the electrical supply and transient overvoltage exposure. | Category II, III, or IV
Distribution switchboards commonly involve Category III conditions. | The category influences required impulse withstand capability and insulation coordination. | Apply the category defined by the installation standard and the equipment’s point of connection. |
| Pollution Degree | Evaluate dust, humidity, condensation, chemicals, and conductive contamination at the installation location. | Degree 2: normally non-conductive pollution
Degree 3: conductive pollution or dry non-conductive pollution that becomes conductive | Pollution affects creepage distance, insulation reliability, corrosion resistance, and enclosure sealing requirements. | Use the actual environment rather than selecting a rating only from the indoor or outdoor location. |
| Ambient Temperature | Check minimum and maximum air temperature, solar heating, enclosure heat dissipation, and altitude. | Typical design reference: −5 °C to +40 °C
Special ratings may be required outside this range. | Temperature affects conductor ampacity, breaker trip characteristics, component life, and internal heat accumulation. | Review manufacturer derating data, ventilation, forced cooling, heaters, thermostats, and enclosure solar-load calculations. |
| Altitude | Determine the installation elevation above sea level. | Up to 2,000 m: commonly used reference condition
Above 2,000 m: derating may apply | Lower air density reduces cooling performance and dielectric withstand, especially at higher elevations. | Obtain altitude correction factors for current, insulation, and short-circuit performance. |
| Internal Separation | Decide whether busbars, functional units, terminals, and cable compartments need physical segregation. | Forms 1, 2, 3, or 4
Higher forms provide greater separation between functional sections. | Separation can improve operational safety, fault containment, maintenance access, and continuity of service. | Specify the required form and verify that barriers, shrouds, partitions, and terminal compartments are included. |
| Arc-Fault Protection | Consider internal arc classification, pressure relief, arc-resistant construction, and the expected fault location. | Internal arc testing may specify accessibility types and test duration
Not every low-voltage enclosure is arc-resistant. | Internal arcs can generate extreme heat, pressure, molten metal, and toxic gases within milliseconds. | For high-risk installations, request tested internal-arc performance and define front, lateral, and rear accessibility. |
| Earthing and Bonding | Check protective conductor arrangement, enclosure bonding, earth-fault path, and door bonding. | PE or PEN arrangements
Protective bonding must be continuous and appropriately sized. | A low-impedance fault path enables protective devices to disconnect the supply quickly and reduces touch-voltage risk. | Verify earth continuity, bonding points, conductor sizing, fault-loop impedance, and local requirements. |
| Cable Entry and Termination | Confirm cable type, conductor size, bending radius, gland plate arrangement, entry direction, and sealing method. | Top, bottom, or side entry
Cable glands and terminals must match conductor material and cross-section. | Poor termination can cause loose connections, hot spots, water ingress, mechanical stress, and loss of the declared IP rating. | Check terminal temperature ratings, tightening torque, segregation, strain relief, and spare capacity for future circuits. |
| Standards and Testing | Confirm the applicable assembly, enclosure, breaker, wiring, and installation standards for the project location. | IEC 61439 for low-voltage assemblies
IEC 60529 for IP code
IEC 62262 for IK code | Standards establish design verification, routine verification, performance ratings, and safety requirements. | Request design-verification evidence, routine-test records, type-test information where relevant, and installation documentation. |
