Ground rating factor (Cc)
The rating factor Cc = 0.9 is applied to cable sizing calculations for cables installed in the ground (Installation Methods 70 to 73). See BS7671:2018,Appendix 4,Sections3,4 and 5.1.1.
Category: Electrical
Back-up Protection
Circuit-breaker manufacturers publish tables showing combinations of pairs of circuitbreakers, one upstream,one downstream,where the downstream device can be used at a location where the prospective fault current (Ipf) is higher than its breaking capacity (Icu). The Icu of the upstream devicemust equal or exceed Ipf at its point of installation.
Cable k2s2
k2s2 its an Energy withstand of cable in A2s. For example,a cable with a withstand of 12 x 104 A2s, can sustain without permanentdamage,a fault current of 1,000 A for a time of 0.12 s (1,0002 x 0.12 = 12 x 104 A2s).
Ambient temperature rating factor (Ca)
Ambient temperature rating factor used for calculating theminimum required cable size. For cables installed in air, values for this factor are given in BS7671:2018 Table4B1.For ground installations, values are given in Table4B2. Elevating the ambient temperature will result in a lower rating factor Ca.This may result in an increased cable size.
Breaking capacity
The breaking capacity of a circuit-breaker is themaximum level of fault current (kA) it cansafely interrupt. Each circuit-breaker has two breaking capacities: Ultimate BreakingCapacity (Icu) Icu is defined as the ‘Ultimate Breaking Capacity’ of a circuit-breaker – Icn is the ‘Normal Breaking Capacity of an MCB, with the same meaning as Icu. This is the […]
Basic protection
Protection against electric shock under fault-free conditions;use of barriers,placing out of reach,and so forth.
Ambient temperature
The temperature of the free air surrounding a cable,or in the case of cables installed in the ground, the temperature of the surrounding soil.For an enclosed method such as ‘In conduit’ this will be the temperature of the air surrounding the conduit, not the temperature inside it.
Adiabatic
Adiabatic checks are required to determine whether conductorsmight be damaged by the thermal effects resulting from the level of calculated fault conditions.
tertiary power source
A Uninterruptible Power Supply (UPS) or standby generator connected to dedicated final circuits of the distribution infrastructure. Enhance the infrastructure resilience and can improve maintenance opportunities and business continuity for the higher risk areas. Typical tertiary power supplies: batteries for UPS systems, inverter units and generators; HV/LV tripping/closing batteries; UPS systems; inverter units for […]
secondary power supply (SPS)
alternative or supplementary electrical energy sources has become more viable, typical secondary power supply (SPS) Photovoltaic (PV) power Wind turbine power standby generator
