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 7 replies
  • Subscribers 31 subscribers
  • Views 1584 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

falling foul of 'maintenance free' derating

psychicwarrior
Just musing...


I'm probably (as usual) playing catch up, but today I learned that these Wago and other types (with Hager/Ashley MF boxes aside it seems as they do the job whatever I'm told) have a 'maintenance free' installation clause in that, they can be used to the  'full rating' if accessible, but if installed 'maintenance free' and to comply with BS5733,  the current carrying capacity must be derated; quite significantly it seemed to me re:Ideal In-sure offerings. I hadn't realised this.


I found it difficult looking at the 'instructions' to interpret whether it is possible to use one for example, to join some t&e 2.5 ring final conductors protected by a 32A device and it would seem not...but then again, with all the 'aggregate current' splurb, I started to shutdown :-)


Seems daft to me.  If the box is accessible then no fuss, but make it inaccessible and it cant be done !  Bizarre from an electrical point of view to me that is.


I am awaiting some confirmation from Ideal (as their derating figures seem worse than others) on this subject to get a better understanding why and just in case I've misunderstood (likely! )
Parents
  • 0
    I spoke to an engineer (who apparently has something to do with the design of the connectors, etc) about this last year, and he said aggregate thing is really simple, once you know how to apply it (re Wago connectors, that is). Basically, count the load in each L and N conductor in the MF box, and add them together, and ensure they don't exceed 50amps. For example, for a 32amp RFC, if the box had the leg in and the leg out (i.e. you've cut into a leg), assume 16A in each L and N conductor that you're joining together (the other leg would that you've not touched would carry the other half 16/32A), so the total would be 32A in the box; which is below the allowable 50A maximum. That's why you can have one leg through the box (equalling 32A) but not two legs in the box, which would equal 64A.  


    I've attached some documents which detail what you can do with ring and radial ccts, and some other stuff.


    Hope this helps


    F
    attachments.zip
Reply
  • 0
    I spoke to an engineer (who apparently has something to do with the design of the connectors, etc) about this last year, and he said aggregate thing is really simple, once you know how to apply it (re Wago connectors, that is). Basically, count the load in each L and N conductor in the MF box, and add them together, and ensure they don't exceed 50amps. For example, for a 32amp RFC, if the box had the leg in and the leg out (i.e. you've cut into a leg), assume 16A in each L and N conductor that you're joining together (the other leg would that you've not touched would carry the other half 16/32A), so the total would be 32A in the box; which is below the allowable 50A maximum. That's why you can have one leg through the box (equalling 32A) but not two legs in the box, which would equal 64A.  


    I've attached some documents which detail what you can do with ring and radial ccts, and some other stuff.


    Hope this helps


    F
    attachments.zip
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