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Temperature rating of C.B's, cables and conduits

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Question 1: All PVC conduits in market to BS:61386 are rated for 60C operating temp while CU/PVC single core wires to IEC 60228 are rated for 70C. what is the BS 7671 point of view.
Question 2: BS 7671 section 512.1.5 states that :Switchgear, protective devices, accessories and other types of equipment shall not be connected to conductors

intended to operate at a temperature exceeding 70°C at the equipment in normal service unless the equipment manufacturer has confirmed that the equipment is suitable for such conditions, or the conductor size shall be chosen based on the current ratings for 70° C cables of a similar construction. where as NEC 110.14(c): “Conductors with temperature ratings higher than specified for terminations shall be permitted to be used for ampacity adjustment,correction, or both.” Derating factors may be required because of the number of conductors in a conduit, higher ambient temperatures, or internal design requirements for a facility. By beginning the derating process at the ampacity of the conductor based on the higher insulation value, you may not be required to upsize the conductor to compensate for the derating.is there a similar way to apply the exception of NEC using the BS 7671.
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    AJJewsbury:


    On the face of it that sounds inconsistent, but I think the difference is accounted for by PVC  having a higher thermal insulation value than XLPE 


    Andy,

    You are making a big assumption here - that there is logic behind the cable rating figures. I know of various standards where the cable current ratings would not stand up to a rigorous scrutiny as to their basis. However having been around for decades and no-one questioning them does mean that they are accepted as valid, and after all if they have not given any problems then who is to say that they shouldn't continue to be used.

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    AJJewsbury:


    On the face of it that sounds inconsistent, but I think the difference is accounted for by PVC  having a higher thermal insulation value than XLPE 


    Andy,

    You are making a big assumption here - that there is logic behind the cable rating figures. I know of various standards where the cable current ratings would not stand up to a rigorous scrutiny as to their basis. However having been around for decades and no-one questioning them does mean that they are accepted as valid, and after all if they have not given any problems then who is to say that they shouldn't continue to be used.

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