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 2711 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

  • Surface mount SWA through the bin cupboard area, then a small(ish) metal box, above, below or to the side of the CU to terminate the swa into, then into the CU?

    Switch fuse isolator in the meter box will, usually, satisy the DNO, but it doesnt satisfy 7671, as the cables will need to be RCD protected if buried/hidden. The worst solution, but one that will satisfy the DNO and 7671(just/maybe) is to put an isolator in there (has it already got one?) with a 30mA RCD as the isolator switch. Of course, that could trip if anything else down the line trips, so not a good solution.

    I'd be looking at a way to get SWA in there. It isnt the DNOs box, it is yours, and so long as they can get access to their equipment, there should never be a problem.

Reply

  • Surface mount SWA through the bin cupboard area, then a small(ish) metal box, above, below or to the side of the CU to terminate the swa into, then into the CU?

    Switch fuse isolator in the meter box will, usually, satisy the DNO, but it doesnt satisfy 7671, as the cables will need to be RCD protected if buried/hidden. The worst solution, but one that will satisfy the DNO and 7671(just/maybe) is to put an isolator in there (has it already got one?) with a 30mA RCD as the isolator switch. Of course, that could trip if anything else down the line trips, so not a good solution.

    I'd be looking at a way to get SWA in there. It isnt the DNOs box, it is yours, and so long as they can get access to their equipment, there should never be a problem.

Children
  • in reply to alanblaby

    Thanks  

    I'll admit to having not thought about the RCD option. The person who fitted the new meter (a third party contractor) threw me a bone and fitted a switch in there so that I didn't need to pull the master fuse to make the changes. So an RCD could go in there but as you say it's not a nice option and you couldn't uses a selective type to prevent duplicate trips. Thus meaning it isn't a 7671 compliant option because it doesn't provide isolation of faults from adjacent or downstream circuits.

    I considered the box option to terminate SWA next to the board, but concluded it didn't help: As the problem remains the same the SWA is entering the room through the wall the box will be mounted to. Thus making the termination problematic. I suppose one advantage, upon reconsidering the situation, is that at least in the future the board can be removed without disturbing the SWA meaning I don't need to leave slack.

    A final thing that I should have mentioned but didn't is that I'd like to leave the space for current clamps in the future as I'll almost certainly be fitting Solar PV + storage which will need them as do some EV chargers. Again the second box option makes these a lot easier.

    --Edit--

    I believe you're half right on the putting things in the meter box. Yes it's my property but as part of the supply contract you have to guarantee not only access by the DNO but space for any equipment they deem necessary and those boxes are an agreed size, and should be left to them by all accounts I've ever seen. Hence I'm twitchy. But I could, I suppose, loose / replace the switch and call it quits.

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