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 2 replies
  • Subscribers 34 subscribers
  • Views 1182 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

Aluminium armoring as earthing

Mark Craig

I'm working on an installation in a new shed at the moment. The incoming cables are 95mm single aluminum armored from a 250A MCCB with vigi. The cables will be glanded into an aluminium plate and run through ducting underground with around a 50m run. My question is.....

Am I ok using the aluminium armoring as my main earth or do I need to run in a separate earth? 

I have seen some reports saying not to use the armoring as earth in singles and to only earth one end of the armoring because of circulating currents, but as these cables are aluminium armored they are non-magnetic so I don't believe circulating currents should be a problem

Any help and guidance will be very much appreciated   

Parents
  • 0

    There is no reason not to use the armours of the singles as your earth. If you bond both armours at both ends, yes there will be a one turn transformer effect that will introduce some current in the armour loop. Unless you run the cables very close to their maximum thermal rating, this should not matter. But do use the right glands for aluminum and do ensure that all exposed ends are in places where condensation or other damp are unlikely, Once aluminium starts to corrode it can fail spectacularly.

    You can estimate the voltage round the loop from the load current and the length.

    More on that and a nice graphic  here

    Mike.

Reply
  • 0

    There is no reason not to use the armours of the singles as your earth. If you bond both armours at both ends, yes there will be a one turn transformer effect that will introduce some current in the armour loop. Unless you run the cables very close to their maximum thermal rating, this should not matter. But do use the right glands for aluminum and do ensure that all exposed ends are in places where condensation or other damp are unlikely, Once aluminium starts to corrode it can fail spectacularly.

    You can estimate the voltage round the loop from the load current and the length.

    More on that and a nice graphic  here

    Mike.

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