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Topic Title: Meter change
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Created On: 28 December 2012 10:30 PM
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 31 December 2012 09:41 PM
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blokes

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Joined: 28 December 2012

Do you ever wish you hadnt asked??

Let me start again for those that have miss understood, I know the info at the start was a bit vague.

I have been asked to do an installation in an extension, the supply at present is overhead which will need to be moved to complete the build. The owner is aware of this and has agreed with DNO to remove them and to install a new underground service to a new outside meter box in the end of the extension.
The builder has kindly provided a ducting from the new meter box position around the back of the property to the outside wall of the existing building to where the exisitng Consumer Unit is positioned on inside wall. This would mean new sub main would be clipped on outside wall before entering the property.

Details

Approx length of new Sub Main = 25 meters
Route = In 100mm duct, Clipped direct to outside wall
Approx. load = 60amps max
DNO Supply = 100amps

If I have missed anything let me know and I will try to add.

Questions

1, Can I install an SWA cable form the meter box to supply the Consumer Unit?
2, What size cable would you guys suggest? I have done some calcs but Im interested in your thoughts
3, The new supply will be PME, therefore would I need an RCD to protect the cable?

For the record I have not mentioned anything about moving the meter, cutting the seals or tampering with the DNO equipment in anyway.

Thanks

Steve
 31 December 2012 09:58 PM
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JonSteward

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My DNO (UKPN) don't mind switch gear located in top left hand side of meter box with an SWA terminated within switch fuse. Best to ask first though.
 31 December 2012 10:08 PM
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daveparry1

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16.00mm 3 core swa with 60 amp switch-fuse at supply end, no need for rcd at supply end,

Dave.
 31 December 2012 10:10 PM
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blokes

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Thanks Dave
 31 December 2012 10:28 PM
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whjohnson

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blokes - please permit me to apologise - I posted my item in the incorrect thread.

The correct one is here -

http://www.theiet.org/forums/f...d=39265&enterthread=y


Kindly dismiss my earlier comments.

Happy New Year to all.

-------------------------
Political correctness is a doctrine, fostered by a delusional, illogical minority, and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a turd by the clean end.
 03 January 2013 07:04 AM
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colinhaggett

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Originally posted by: daveparry1

16.00mm 3 core swa with 60 amp switch-fuse at supply end, no need for rcd at supply end,



Dave.


Why would you want to lose 40amps of capacity for the Sake of a bigger switch fuse and cable? Unless money was tight.

 03 January 2013 09:25 AM
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AJJewsbury

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Why would you want to lose 40amps of capacity for the Sake of a bigger switch fuse and cable? Unless money was tight.

I can imagine that dragging 16mm² 3C SWA through a duct with a few bends is going to be a bit easier than 25mm² 3C SWA ...
- Andy.
 03 January 2013 09:45 AM
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colinhaggett

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Originally posted by: AJJewsbury

Why would you want to lose 40amps of capacity for the Sake of a bigger switch fuse and cable? Unless money was tight.


I can imagine that dragging 16mm² 3C SWA through a duct with a few bends is going to be a bit easier than 25mm² 3C SWA ...

- Andy.


It is a 100mm duct, so not really a problem. Am just thinking about the furture. Got to be better to install for furture expansion, rather than running a 16mm on a 60 amp fuse. Plus you run the risk of high volt drop before you even reach the consumer unit. Just my thoughts, but got to be easier to put in now rather than later.
 03 January 2013 04:16 PM
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alancapon

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Originally posted by: colinhaggett
Originally posted by: daveparry1
16.00mm 3 core swa with 60 amp switch-fuse at supply end, no need for rcd at supply end,

Why would you want to lose 40amps of capacity for the Sake of a bigger switch fuse and cable? Unless money was tight.

If the supply is fused at 100A by the DNO, then the customer will have paid them based on a 23kVA supply. It seems strange to then design a submain that then restricts the property to 13.8kVA.

Regards,

Alan.
 03 January 2013 07:40 PM
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daveparry1

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So he could use a bigger swa and have a 100 amp switch-fuse but then I suppose you would say there's no discrimination between the two fuses Alan? (could use 80 amp of course)

Dave.
 03 January 2013 07:59 PM
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slittle

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Discrimination isn't a problem in that situation Dave, well not in my book anyway.

We've got loads of 70KVA supplies feeding 100A TPN switchfuses or MCCB's. Ok, ours are three phase but same principle.

The only possible advantage I can see to using a 60A fuse and 16mm is that if the DNO will let you squeeze it in the meter cupboard, then a 60A switch fuse is quite a bit smaller than a 100A one depending on the type you use.

Stu
 03 January 2013 09:37 PM
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alancapon

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Why do you need discrimination? There is no real difference between a submain and having the CU adjacent to the meter. The difference is that the DNO do not have to assess the rating of the submain to see if their cutout fuse will operate for a fault at the far end - this is done by the designing electrician who will rate their overcurrent protection accordingly. It just seems a bit strange to me if you apply for a certain capacity of supply, the submain isn't designed to take the entire capacity to the CU.

Regards,

Alan.
 03 January 2013 09:48 PM
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daveparry1

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Well that's interesting to me Alan as I have some friends with a large house with an outbuilding fed by a 35mm swa submain from a 60 amp switch-fuse preceded by an 80 amp BS1361-11 cutout fuse. (on a seperate phase to the main house)
So are you saying it would be in order for me to up the switch-fuse rating to 80 amps as they want me to add some more circuits and it's already getting rather tight on 60amps!

Dave.
 03 January 2013 09:58 PM
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alancapon

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The electricity company that I work for, state that meter tails can have a maximum length of 2.5m. We guarantee that our cutout fuse will protect this 2.5m of cable. Of course it will go further in terms of cable length, but this requires a possibly time-consuming calculation based on the characteristics of the submain. If we provide a 60A cutout fuse, and the electrican designs their submain to be able to operate a 60A fuse with a fault at the end of it, then they should fuse their submain at this value, even if it is the same size fuse as the cutout.

Regards,

Alan.
 03 January 2013 10:01 PM
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alancapon

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Originally posted by: daveparry1
. . . So are you saying it would be in order for me to up the switch-fuse rating to 80 amps as they want me to add some more circuits and it's already getting rather tight on 60amps!

Yes, if you calculate that the submain is capable of operating at 80A and it is possible to operate your overcurrent fuse with a fault on the far end of it.

Regards,

Alan.
 03 January 2013 10:14 PM
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daveparry1

Posts: 6239
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Thanks for that Alan, as the swa is 35mm with a length of about 20 metres I reckon it's ok then,

Dave.
IET » Wiring and the regulations » Meter change

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