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

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 27 replies
  • Subscribers 38 subscribers
  • Views 7454 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

r1 + r2 for 3 core 10mm XLPE

hertzal123

I,m trying to design a  submain for an outbuilding.The circuit comprises 50m of 3 core 10mm xlpe

on a bs88 40A fuse.Have worked out R1+R2 for the cores as 50x3.66x1.2/1000 =0.0216 ohms

Can the armour be included in the calcs to lower ZS and how would it be done?The supply is TNS 0.8 ohms (understand we have to work on that value)

                                                                                     Thanks for any help,

                                                                                                   Regards,Hz

                                                                         

Parents
  • 0

    The measured ZE was 0.15 ohms,but I thought we had to work on the published value

    of 0.8 in case there was a change in the network.

    I don't think BS 7671 says we have to - it's certainly a good idea in the general case (although I think it unlikely that modern changes to the network would likely raise Ze much above 0.35 Ohms if it's below that already). In some (rare) situation that actual Ze can exceed the published figures - so you can't completely ignore the actual Ze. In others (e.g. sites with own transformers) the chances of significant increases in Ze are extremely unlikely.

       - Andy,

  • 0 in reply to AJJewsbury

    Agreed .  Article here explains the current situation: electrical.theiet.org/.../

Reply 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