Rules and Guidelines
Want to participate in the discussions? Please read our Community Rules and Guidelines. Need some help? Visit Support and Answers.

  • State Not Answered
  • Locked Locked
  • Replies 22 replies
  • Subscribers 32 subscribers
  • Views 5979 views
  • Users 0 members are here
Options
You may also be interested in
This discussion is locked.
You cannot post a reply to this discussion. If you have a question start a new discussion

Current carrying capacity of XLPE/SWA cables

M Gilmore
Hi, I keep coming across the same issue in regards to the current carrying capacity of a XLPE/SWA cable. I always use the de-rated current carrying capacity when I am not sure if all associated equipment is rated at  90°c, which is all the time. So as an example, a 4 core 150.0mm² XLPE/SWA cable clipped direct is rated at 386 Amps from table 4E4A column 3 in BS7671:2018. A standard 4 core 150.0mm²  PVC/SWA is rated at 306 Amps from table 4D4A column 3. This is a big difference! If this was protected by a 355 Amp BS 88 I would flag the conductor as being undersized.


There is a note by table 4E4A that points out Regulation 512.1.5. This is regarding compatibility and says equipment should not be connected to conductors intended to operate at a temperature exceeding 70°c unless the equipment manufacturer has confirmed that the equipment is suitable for such conditions. 99% of the time I wouldn't have the available data on site. Most circuit breakers I have checked are rated at 70°c.


Any thoughts? I just want to make sure I'm providing the correct information. I don't want to provide an observation if the conductor is ok to be rated at full capacity. Cheers in advance.


Parents
  • 0

    In what situation would overload not be required? The only thing I can think of is maybe life safety equipment, but I’d still want the cable sized to breaker I think



    or anywhere where overload protection is provided downstream - the common example is industrial motor circuits where the control gear next to the motor provides overload protection so the overcurrent protection at the DB only has to provide fault protection - and is frequently over-sized compared with the cable rating to ensure discrimination with the motor's overload.


    The same principle can even be found in simple domestics - e.g. spurring off a 32A socket circuit using 20A cable to feed one single or one double socket.


      - Andy.
Reply
  • 0

    In what situation would overload not be required? The only thing I can think of is maybe life safety equipment, but I’d still want the cable sized to breaker I think



    or anywhere where overload protection is provided downstream - the common example is industrial motor circuits where the control gear next to the motor provides overload protection so the overcurrent protection at the DB only has to provide fault protection - and is frequently over-sized compared with the cable rating to ensure discrimination with the motor's overload.


    The same principle can even be found in simple domestics - e.g. spurring off a 32A socket circuit using 20A cable to feed one single or one double socket.


      - Andy.
Children
No Data

Join us to get the best from IET EngX.

Joining EngX lets you personalise your experience so you stay up to date on the topics that interest you, plus you’ll be able to make connections who are looking to collaborate, exchange ideas and more.

Join us Not now

Community Rules & Guidelines