Additionally, any commercial, industrial, or public building that is supplied by overhead lines requires surge protection – so the majority of buildings will require surge protection. Residential properties will depend on use and occupancy levels. Now, imagine that I start delaying phase W more and more. As I do so, it gets more and more different from phase A. The sine wave that is the difference between phase A and phase W gets larger and larger. Eventually this resultant sine wave is actually _greater_ than phase A. This difference sine wave reaches its peak when phase W is exactly 1/2 cycle from phase A, meaning that the +peak of A corresponds to the -peak of W. At this point, the amplitude of the _difference_ between the two phases is twice the amplitude of each phase alone. This is to say that if phase A is 277V relative to neutral, and phase W is 277V relative to neutral, and 180degrees out of phase with phase A, then the voltage A to W is 534V.

Max Zs is the maximum permissible values of earth fault loop impedance (Ω), some maximum Zs values are listed in BS 7671, the maximum earth loop impedance values listed in the Zs tables are used to compare against the actual measured earth loop impedance values to ensure compliance with BS 7671. OC or 40 OC,the purpose of the latter value being to avoid the necessity of de-iating thermally sensitive circuit- K~ 145 for rubbers and 115 for PVC insulation , with certain assumptions about starting temperature.Before delving into the detail of this change, as ever it pays to start at the beginning – namely the Fundamental Principles of Part 1. If you are looking for reason to keep the existing despite the mains upgrade, then you will need more data, but don't be surprised if it doesn't help much - do you know for example if it was compliant before the upgrade took place (ie at the previous fault level) - have you tried a random MCB is say Amtech (or data from a different supplier) So I2t is actually a function of the prospective fault current, and is either depicted graphically, or listed as spot values . For mcbs made to the IEC standards since 1999 or so this is a spec parameter, and guaranteed by design. for earlier devices it isn't Every item of equipment shall comply with the appropriate British or Harmonized Standard.’ For distribution boards, this is the BS EN 61439 series. Part 3 is a specific part of the BS EN 61439 suite and it includes requirements for Distribution Boards intended for use by ‘ordinary persons’.

Section 536 is about ensuring (amongst other aspects) that the performance of devices for protection against faults and overloads are coordinated so that the effectiveness of the operation of individual items of equipment, under both normal and abnormal operating conditions, does not impair the safety or proper functioning of the installation. It includes, for example, the set of regulations that provides requirements for selectivity of protective devices for residual currents, overloads and short-circuits. This is developed in Note 2 to regulation 536.4.203, which states that ‘ If an assembly deviates from its original manufacturer’s instructions, or includes components not included in the original verification, the person introducing the deviation becomes the original manufacturer with the corresponding obligations’. In summary, can you mix devices in distribution boards (including consumer units)? Yes, you can. But you need to seek assurance from the manufacturer of the original assembly that the devices will be compatible, or conduct your own study to ensure the requirements are met. In the words of BEAMA, ‘The installer has responsibility to act “with due care”. If this is not done then there is a probability that, in the event of death, injury, fire or other damage, the installer would be accountable under Health and Safety legislation.’ Let through energy is a bit problematic for breakers - a fuse gets faster as the fault current rises, and tends towards a constant let- through energy (I squared r times time, but the resistance r is a fixed parameter of the fuse, as is the weight of metal to be raised to melting point to start it breaking)The Dorman Smith Loadmaster was very common years ago and because not a din rail mount very hard to replace without whole enclosure replacement but I seem to remember there was only a thermal trip in them and not a magnetic type as well so they would not have a number or letter just a current rating. Protection against transient over-voltages shall be provided where the consequence caused by over-voltage: For this reason, regulation 536.4.203 states that ‘The relevant part of the BS EN 61439 series shall be applied to the integration of mechanical and electrical devices and components, e.g., circuit-breakers, control devices, busbars into an empty enclosure or existing low voltage assembly.’ Type 3 SPDs provide local protection for sensitive equipment. As these have a relatively low discharge capacity, they should always be installed in addition to a Type 1 or 2 device.