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 9 replies
  • Subscribers 32 subscribers
  • Views 1802 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

Meter Tails.

Zoomup
You go to renew an old consumer unit. The Meter is in an outside wall box and the 16.0mm2 tails run in the cavity to a Henley block in the house nearby, where the consumer unit is located at high level. It is impossible to easily install new 25mm2 tails. There is no sign of overheating or damage at all. Do you just run your new 25mm2 tails from your new consumer unit to the Henley block or what? The main fuse must be a 100 Amp fuse as the house has storage heating, also supplied via 16.0mms tails which are in good condition.


Z.
  • 0
    You don't say why you are replacing the tails

    : Is it just a CU change? It's unlikely they will ever overload in a domestic house. It's rare that you couldn't replace them but it might be really involved /expensive if you had to re-route. If you fault it and the customer says that's too expensive, you can't make them, althugh you might consider not changing the board if you don't want to put your name to it.. There doesn't seem a lot of point changing part of them up to a henley block. If there are any issues its likely to be  with the bits you cant see rather than the bit you can. If you advise and record it then you've covered yourself. also you could work out the maximum demand ( unlikely to be more than 80A I'd have thought if the heaters are on their own supply) Measure Ze, do a calculation to prove the fault current would be sufficient- yes they should be 25mm but its unlikely to be a problem. If youre replacing an old board you can argue you are leaving the job safer. But if you are trying to do a full rewire then I'd suggest that you need to think about a way to replace them completely. There's always a way.
  • 0
    16mm² should be fine on 100A fuse for fault protection (after all the 16mm² earthing conductor is) - so that just leaves overload. Is the combined rating of the outgoing ways of the CU and/or a reasonable assessment of actual maximum demand (e.g. a 6A lighting circuit supplying just one or two points isn't ever going to need the full 6A) sufficient to ensure that 16mm² can't be overloaded? For most homes it's likely to be fine, but if it's the type of place that's all-electric and has just had an EV charge point or two installed, it might not be so clear cut.


        - Andy.
  • 0
    It is impossible to easily install new 25mm2 tails.

    You clearly don't own a big enough hammer!


    (After that, it becomes possible, you just have to refine the actual method to something acceptable).


      - Andy.
  • 0
    AJJewsbury:
    It is impossible to easily install new 25mm2 tails.

    You clearly don't own a big enough hammer!




      


    You haven't met the customers wife!


    Z.


  • 0
    You could run them straight  up the outside wall and drill straight though to the board. You shouldn't install them in a cavity anyway, Use SWA, just terminate it properly in a separate enclosure if necessary, with standard tails into the board for ease, but there's usually 25/32mm knockouts in the board anyway
  • 0
    Ah another tale of the tails Lol
  • 0
    Dave Thomas:

    You could run them straight  up the outside wall and drill straight though to the board. You shouldn't install them in a cavity anyway, Use SWA, just terminate it properly in a separate enclosure if necessary, with standard tails into the board for ease, but there's usually 25/32mm knockouts in the board anyway


    What Dave, on a nice Norfolk flint cottage? The customer's wife would go ballistic. The original tails are already in the cavity so not easy to replace.


    Z.


  • 0
    I really don't see why you are worrying Zoom, at 100A the tails on a hot day might reach 80C after a few hours, but then you wouldn't be using the heating. On a cold day, it is very unlikely they will reach anything like 70C. You have evidence that the tails are in good condition, and the install is as before. Is it less safe than previously, no? Flint walls need the chasing machine zoom, and quite possibly a set of new diamond disks as well. Don't go there! I suppose you could fit a new external 25mm SWA for strict adherence to the regs, but I would watch out for the customer, she wouldn't like the snake up the wall and has a handbag with a brick in it ready to go!
  • 0
    davezawadi (David Stone):

    I really don't see why you are worrying Zoom, at 100A the tails on a hot day might reach 80C after a few hours, but then you wouldn't be using the heating. On a cold day, it is very unlikely they will reach anything like 70C. You have evidence that the tails are in good condition, and the install is as before. Is it less safe than previously, no? Flint walls need the chasing machine zoom, and quite possibly a set of new diamond disks as well. Don't go there! I suppose you could fit a new external 25mm SWA for strict adherence to the regs, but I would watch out for the customer, she wouldn't like the snake up the wall and has a handbag with a brick in it ready to go!


    Yep, that is what I thought. Flints are like tool steel, very hard and brittle and they are large  and embedded into the outside walls and cemented in with hardly any gaps between them, so no way through. At least with the tails in the wall cavity they are cool and more than 50mm away from any wall surface so protected from damage. I renewed the last section of tails with 25mm2 from the Henley block to the new consumer unit, slightly repositioned for easier access, to help future sparks in case of upgrades. Modern tails are very hard to bend and we need strong bionic hands. The old tails were lovely bendable softer copper.


    Z.


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