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Student & Learning Zone - City & Guilds
Is Your Selected Cable Suitable?
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<blockquote data-quote="Manator" data-source="post: 345485" data-attributes="member: 9561"><p>Good post John, and a very good informed question.The cpd and cable should be calculated hand in hand. It is of no use selecting a cable to find that the cpd will not operate as expected.The size of the MCB, RCD or RCBO has to be used at the start of calculations, this would give you negative results when using cables not suitable.</p><p></p><p>Say we choose a 32amp type B breaker, we calculate the cable given all the de-rating values, the load, and the volt drop and distance. We still need to know if the breaker will break the load under any fault or overload. Sometimes cables are installed given all the factors and still fail because the cpd is not sized accordingly.</p><p></p><p>In my example I think the load is around 37amps, so the cpd would be chosen as 40amp. The cable must be able to withstand any extremes until the cpd disconnects from service. 4mm could do this but would you want to push a cable to its limits on a family home on a daily basis?</p></blockquote><p></p>
[QUOTE="Manator, post: 345485, member: 9561"] Good post John, and a very good informed question.The cpd and cable should be calculated hand in hand. It is of no use selecting a cable to find that the cpd will not operate as expected.The size of the MCB, RCD or RCBO has to be used at the start of calculations, this would give you negative results when using cables not suitable. Say we choose a 32amp type B breaker, we calculate the cable given all the de-rating values, the load, and the volt drop and distance. We still need to know if the breaker will break the load under any fault or overload. Sometimes cables are installed given all the factors and still fail because the cpd is not sized accordingly. In my example I think the load is around 37amps, so the cpd would be chosen as 40amp. The cable must be able to withstand any extremes until the cpd disconnects from service. 4mm could do this but would you want to push a cable to its limits on a family home on a daily basis? [/QUOTE]
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Student & Learning Zone - City & Guilds
Is Your Selected Cable Suitable?
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