Our Voltimum Experts answer your questions on a daily basis in our Technical Expertise area. This one, concerning, circuit breakers and fuses and ACB breaking capacities, is answered by ABB:
Answer: ACBs generally have very high short circuit breaking capacities because of the fact that they have high current ratings and are used very close to the source of the low voltage supply where the prospective fault level is at it's highest.
The UK normally requires a minimum short circuit capacity of 50kA at 400V for ACBs, but ABB can offer lower versions - such as our X1B, E1B and E2B devices, which have a breaking capacity of 42kA. I have attached a link to the technical catalogue for Emax.
AMTECH has noted the ABB response to the question and has this to say: 'AMTECH software contains extensive ranges of protective devices. Most of the protective devices in the software are manufacturer specific (for example Merlin Gerin, Eaton, Square D etc). Generic devices are also provided to assist designers during the early stages of a project.When a device from one of AMTECH's supported suppliers is selected, the data you are using has been checked and accepted by the manufacturer, so the software will be using manufacturer's data for parameters such as the device's breaking capacity (Icu). It appears that this question is based on the generic ACBs listed in AMTECH's range of design software (for the purpose of non-manufacture specification). The generic ACBs in AMTECH are listed at 50kA, 70kA and 100kA. If an ACB with a lower breaking capacity is required, then a specific manufacturer's device should be selected'.
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