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

  • Replies 35 replies
  • Subscribers 39 subscribers
  • Views 2713 views
  • Users 0 members are here
Options
You may also be interested in

Long meter tail upgrade, no nice solution comes to mind.

Russell Edwards

Hi All.

Thought I'd open this one up for discussion as I'm sure some of you can come up with a nice solution.

I've been given a friendly notice that i need to do something about the meter tails in my house by my DNO following the installation of a smart meter. They're the wrong gauge for the master fuse (16mm2 on a 100A fuse) and too long, about 4m. I'm having a job coming up with a solution I like. The current installation is original from when my house was built in 1996 and has gone unnoticed until now.

The meter is in a box on the front wall of the house and the tails exit this, run up the inside of the wall and over the ceiling of what was originally a bin cupboard in an uninsulated roof space before entering the distribution board directly though the hallway wall. The logical thing to do would be to protect the tails by replacing them with SWA but I have two problems with that. 1 that I have no way of terminating the SWA in the meter box without invading the DNO's space and 2 I'm not confident in brining in SWA from behind the board, as I'd effectively have to terminate it long and push some excess back into the roof space, and end up with the SWA termination in the wall screwed to the back of the board. So I can see this option needing me to bring the SWA in from above or below the board which would be ugly as sin in my hallway, doubly so as it'll have a bend radius easily measured in miles.

So I've considered using Steel Conduit instead, as that should be as tough as SWA. However unless I've missed something the largest I can get is 32mm OD which has an ID of circa 27mm. As I'm expecting some quite high temperatures in the roof space during the summer 25mm2 (rated to 101A if I'm reading Appendix 4 properly) could well end up under rated in the summer, so I'd be best to use 35mm2. This has a max OD of 13.5mm according to Doncaster cables meaning it'll be tight getting 2 down it.

I considered using XLPE Insulated 25mm as that can run hotter but of cause there's the 70 degC conductor limit of the board so it's not a help.

Bringing my back to SWA again.

I don't want to put joints in above the bin cupboard as there's no way of inspecting them.

So any other ideas of what I could do to protect the cables sufficiently to ignore the limits?

Thanks in advance.

Parents

  • Downrate the fuse. (1) I am surprised that the DNO has not done that already. (2) Just how much power are you going to draw? At most we have an 80 A fuse, but it may be 60 A - I forget. In any event, if I ever finish the new supply, it will be on a 63 A MCB.

    Strictly, 4 m tails are a bit long, but I don't quite see the problem. Would you cut off the first metre or the last?

    Any bends if you use conduit?

Reply

  • Downrate the fuse. (1) I am surprised that the DNO has not done that already. (2) Just how much power are you going to draw? At most we have an 80 A fuse, but it may be 60 A - I forget. In any event, if I ever finish the new supply, it will be on a 63 A MCB.

    Strictly, 4 m tails are a bit long, but I don't quite see the problem. Would you cut off the first metre or the last?

    Any bends if you use conduit?

Children
  • in reply to Chris Pearson

    Hi  

    Thanks

    Like you I was surprised i wasn't just given a 60A fuse. But it was a third party did the work and I suspect he didn't have one on the van / wasn't authorised to make changes like that. But I am glad they didn't. Why...

    Because over the next couple of years I'm going to ditch the gas (for multiple practical and personal reasons) and I'll be fitting EV charging. The combination means that 60+ amps will be perfectly possible. Having just done the paperwork for a mates EV charger I can vouch DNO's want to know if you're fitting them to a property with a 60A main fuse.

    I've never seen a supply with its own dedicated MCB before but that's probably just my lack of knowledge / experience. what are you hoping to achieve that the master fuse doesn't dare I ask?

    Yes there would be a single right angle bend. My plan would have been to put an inspection box in at that point and use that to make the earth connection. That said I suspect the bend would have been tight.

  • in reply to Russell Edwards
    Russell Edwards said:
    I've never seen a supply with its own dedicated MCB before but that's probably just my lack of knowledge / experience. what are you hoping to achieve that the master fuse doesn't dare I ask?

    My new house supply will be from the 3-phase intake in the garage, so I have little choice. Any EVCP will be supplied from the main DB and the kitchen will have its own supply, so I don't have to allow for a cooker either.

    With only one bend, you might just get 2 x 25 mm² + 1 x 16 mm² down some (25 mm) conduit. I include the CPC because I would want a certain earth continuity path.

    Again with only one bend, you don't need a bender - you can buy pre-formed ones which screw on.

    How about flexible galvanized conduit?

  • in reply to Chris Pearson
    Chris Pearson said:
    My new house supply will be from the 3-phase intake in the garage, so I have little choice. Any EVCP will be supplied from the main DB and the kitchen will have its own supply, so I don't have to allow for a cooker either.

    That makes a lot more sense now. I did something similar with an Annex a few years ago, As I'm OCD about things I chose to add a selective / Time delay RCD to the situation to make sure I'd got most edge cases that pure current based protection might not catch if the earth connection was poor.

    according to Doncaster 6181Y in 25mm has an OD of 12.5mm so no way you're getting 2 of them down some 25mm OD conduit. If I go single insulated then they might just fit but it'd be making a lot of work for myself in routing the conduit.

    I agree about not using conduit as the earth that and you've read my mind on that front.

  • in reply to Russell Edwards
    Russell Edwards said:
    according to Doncaster 6181Y in 25mm has an OD of 12.5mm so no way you're getting 2 of them down some 25mm OD conduit. If I go single insulated then they might just fit but it'd be making a lot of work for myself in routing the conduit.

    Quite so. I have just measured some 6491 (B or X) at 8.8 mm diameter.

    I think that you have answered your own question concerning conduit.

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