The IET is carrying out some important updates between 17-30 April and all of our websites will be view only. For more information, read this Announcement

This discussion is locked.
You cannot post a reply to this discussion. If you have a question start a new discussion

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

Former Community Member
Former Community Member
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.
Parents
  • Former Community Member
    0 Former Community Member

    AJJewsbury:

    There's a formula relating the derating of a cable to its conductor temperature (I don't have it to hand but should be able to dig it out if needs be) - from memory it's similar to the one for adjusting voltage drop when a cable isn't fully loaded. I'm sure I've seen it used to justify the use of 1.5mm² MICC cable on ring circuits in one of the IET books - showing that the 70 degree terminal temperature isn't exceeded.



    You mean Formulas such as Neher-Magrath or that which are found in IEC-60287 or is there another formula in BS-7671.

    I usually use ETAP to find actual operating temperatures of cables for Under ground systems but I can't find easy equation for another mode of installations.
Reply
  • Former Community Member
    0 Former Community Member

    AJJewsbury:

    There's a formula relating the derating of a cable to its conductor temperature (I don't have it to hand but should be able to dig it out if needs be) - from memory it's similar to the one for adjusting voltage drop when a cable isn't fully loaded. I'm sure I've seen it used to justify the use of 1.5mm² MICC cable on ring circuits in one of the IET books - showing that the 70 degree terminal temperature isn't exceeded.



    You mean Formulas such as Neher-Magrath or that which are found in IEC-60287 or is there another formula in BS-7671.

    I usually use ETAP to find actual operating temperatures of cables for Under ground systems but I can't find easy equation for another mode of installations.
Children
No Data