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Topic Title: Consumer Unit Earth Cable Size Enquiry
Topic Summary: What size is required for consumer unit connected via 25 mm2 tails
Created On: 31 August 2005 02:00 PM
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 31 August 2005 02:00 PM
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azteck

Posts: 40
Joined: 09 November 2001

A spot of quick help please.


I am buying materials for a new consumer unit installation.
The unit will be on 25 mm2 tails with a main fuse of 60A.
The cable length will be 12 m.

What mm2 is required for the earth cable (mains incomer to consumer unit)?


Thank you,

All the best,

Nic Williamson

Azteck
Troubleshooting, Innovation and Project Management for Technology
phone: 07000 298325 email: nw@azteck.com

-------------------------
Thanks

SparksFly
 31 August 2005 03:17 PM
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harryhatchet

Posts: 106
Joined: 15 July 2005

Jesus buddy if you don't know the answer to that then you are probably not aware of the fact that you meter tails can be no longer than 3m in length.Are you sure you know what you are doing???
 31 August 2005 03:27 PM
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Jimoldham

Posts: 1754
Joined: 29 November 2004

16mm 6491-X Green/Yellow. Meter tails will have to be fused on the consumer side of the meter if they are to be of that length

-------------------------
Regards

Jim Oldham
 31 August 2005 04:38 PM
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azteck

Posts: 40
Joined: 09 November 2001

Thank you.

"Are you sure you know what you are doing???" I am sure I do not know what I am doing, but I am sure that when I do it, I will.


Interesting.

To clarify, the distances are:
external wall mounted meter to indoor consumer unit 12 m.

As the fuses will be on the consumer side of the meter, (utility side of the consumer unit) are they provided by the SWEB as part of the meter unit ?


All the best,

Nic Williamson

Azteck
Troubleshooting, Innovation and Project Management for Technology
phone: 07000 298325 email: nw@azteck.com

-------------------------
Thanks

SparksFly

Edited: 31 August 2005 at 04:45 PM by azteck
 31 August 2005 05:09 PM
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deleted_beenthere

Posts: 111
Joined: 24 May 2005

In that case I would sugest that you put a 16mm earth
 31 August 2005 09:09 PM
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Jimoldham

Posts: 1754
Joined: 29 November 2004

The maximum permitted length of meter tails is determined by the Electricity Distributor. Different distributors have different requirements. Normally, the Electricity Distributor will decide on the position of the cutout and meter and will state the maximum length permitted for meter tails, such as 2 or 3 metres. In the event that the Distributor’s requirements cannot be met, the electrical installation designer will be obliged to design a suitable distribution circuit, (sub-main), to connect the distribution board to the origin of the installation. This will normally be accomplished by providing, close to the origin, a device such as a switch-fuse to permit the requirements for isolation, overcurrent protection and discrimination to be met for the distribution circuit.

Explanation: ‘Meter tails’ is the term generally used to describe the conductors connecting between the electricity supply meter at the origin of an installation and an item of switchgear or controlgear, or a distribution board such as a consumer unit. As such, meter tails are simply a particular form of distribution circuit. Like all conductors, meter tails are required to be protected against overcurrent and to be provided with a means of isolation.

Protection: Devices for protection against overload and fault current for meter tails at the origin of an installation may be omitted provided the Electricity Distributor agrees that the protection at the supply cutout is suitable and can be so used (Regulations 473-01-04 and 473-02-04 refer). A condition of the Electricity Distributor’s agreement may be a restriction on the length of the meter tails. It is essential that this and any other pre-conditions are complied with.

Discrimination: Where necessary to prevent danger, any intended discrimination between the protective device for the distribution circuit and the Electricity Distributor’s protective device must be achieved.

Isolation: The Electricity Distributor’s equipment may be used to isolate meter tails and other equipment immediately downstream, subject to the Distributor’s express agreement (Regulation 476-01-01 refers).

Concealed cables: Where meter tails are concealed under plaster or other building fabric at a depth of less than 50 mm from any surface of the wall or partition, the requirements of Regulation 522-06-06 must be met (see Amendment 2 to BS 7671). There are a number of options available to meet these requirements, including running the meter tails in designated ‘safe’ zones or providing mechanical protection sufficient to prevent penetration by nails, screws and the like.

-------------------------
Regards

Jim Oldham
 31 August 2005 09:43 PM
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Jimoldham

Posts: 1754
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Nic

You will need to instal your own set of 60A fuses on the consumer side of the installation and then install your tails the 12 m to your CCU complete with a 16mm 6491-X Green Yellow to the MET

-------------------------
Regards

Jim Oldham
 31 August 2005 09:56 PM
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deleted_bos2

Posts: 22
Joined: 05 April 2005

quote:

Originally posted by: Jimoldham
. In the event that the Distributor’s requirements cannot be met, the electrical installation designer will be obliged to design a suitable distribution circuit, (sub-main), to connect the distribution board to the origin of the installation. This will normally be accomplished by providing, close to the origin, a device such as a switch-fuse to permit the requirements for isolation, overcurrent protection and discrimination to be met for the distribution circuit.


No type of switch fuse/ switch is permitted to be installed before the meters (unmetered side) Ryefield / Red cap fuses and the like are accepted NOT SWITCHES
 31 August 2005 09:57 PM
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Jimoldham

Posts: 1754
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who has said before the meters?

-------------------------
Regards

Jim Oldham
 01 September 2005 02:05 AM
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davyn1

Posts: 2845
Joined: 01 August 2004

quote:

Originally posted by: Jimoldham
Nic

You will need to instal your own set of 60A fuses on the consumer side of the installation and then install your tails the 12 m to your CCU complete with a 16mm 6491-X Green Yellow to the MET



do you not mean a 60a fused switch rather than a set of fuses . I read the above as having a fuse in the neutral ?
as i've just recieved drawings for a barn conversion in which i have the same situation and all i was going to do was a 100 A fused switch then my tails clipped at high level along the wall to the new c/u position inside the barn only about 8 mtrs away if i'm wrong tell me as its 2 in the morning and my brain hurts

davy

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just because i'm paranoid doesn't mean theyre not out to get me
 01 September 2005 06:47 AM
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normcall

Posts: 8124
Joined: 15 January 2005

Exactly what I would do, for what it's worth.
Although plan B would be 25mm 3 core SWA

-------------------------
Norman


Edited: 01 September 2005 at 06:48 AM by normcall
 01 September 2005 09:07 AM
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davyn1

Posts: 2845
Joined: 01 August 2004

it means alot norn thanks i may go the 3 core route ,will look neater i think even though you probably wont see it unless your looking but its my rep after all

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just because i'm paranoid doesn't mean theyre not out to get me
 01 September 2005 12:07 PM
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John Peckham

Posts: 7423
Joined: 23 April 2005

Sorry in my view 8/9 metres is a sub main not meter tails. I would suggest that the meter tails should feed a means of switching and cable protection at the origin of the installation and then a sub main would feed the consumer unit.


Regards


John Peckham

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John Peckham

http://www.astutetechnicalservices.co.uk/
 01 September 2005 01:42 PM
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davyn1

Posts: 2845
Joined: 01 August 2004

But it is ,i go from rec incomer to 100A fused switch then run my swa to c/u ?
does your brain hurt ?
davy

-------------------------
just because i'm paranoid doesn't mean theyre not out to get me
 01 September 2005 03:58 PM
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John Peckham

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Joined: 23 April 2005

Davyn1

Spot on that is the correct way.


Regards


John Peckham

-------------------------
John Peckham

http://www.astutetechnicalservices.co.uk/
 01 September 2005 04:53 PM
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azteck

Posts: 40
Joined: 09 November 2001

Thank you to all for your advice and especially Jim for his informative missive.

I am awaiting SWEBs comments. Their original surveyor (for the incomer change and meter move) did not bat an eyelid.

There did seem to be some mixing of threads.


-------------------------
Thanks

SparksFly

Edited: 01 September 2005 at 04:54 PM by azteck
 01 September 2005 07:39 PM
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davyn1

Posts: 2845
Joined: 01 August 2004

quote:

Originally posted by: azteck

There did seem to be some mixing of threads.


nothing is ever striaght forard on here

-------------------------
just because i'm paranoid doesn't mean theyre not out to get me
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