Meter Tail Length

[enlighting]

Afternoon all,

Carried out an EICR yesterday, on the job I doscovered the consumer unit to be located in the kitchen and the incoming supply under the stairs. The tails feeding the board look to me to be just over 3 meters perhaps 3.5. But it is difficult to tell as they are ran in an internal wall.

What coding is recommended and what remedial action required.

Im thinking C2 with a fuse fited between the isolator and the consumer unit.

Cheers

Dave

 

[Guest55]

A number of people believe that 433.2 and 434 do not apply in these instances.
I do not understand why people have this belief, as they must be aware that the distribution network does not fall within the parameters of BS7671?
I believe that this has promted the network distributors to now insist oversized conductors of 25mm be installed.
There does appear to be a misconception that the network operators protective device is intended to provide protection for the installation, however in fact it is there to protect the network operator's equipment.
It is very rare that the network operators will agree for their device to be used to protect an installation, when they do allow such, they impose quite severe restrictions and conditions.
From BS7671's view point the installation begins at the Meter, and any protective device upstream from the Meter is of no consequence.
As such, if the Meter Tails are longer than 3m, a protective device is required along that run.
The OP has also indicated that the tails are run in a cavity wall, which is something the network distributors do not allow.

i still dont get where your C2 comes from ?

if 3mtr tails are considered safe / acceptable , where does the risk / danger come from if they are 3.5mtrs ?

have they suddenly become a threat to the installation user for being 0.5 mtr longer ?

 

[Deleted member 26818]

A code C1 is applied for when there is an immediate danger.
A code C2 is applied where there is a potential for danger.
A code C3 is applied in instances where the Regulations were complied with at the time of design/construction, but due to changes in the requirements, no longer comply.

As far as I am aware this situation has never complied with any Regulations.
As such codes C1 and C3 are not applicable, leaving only code C2 as an option.

Not certain which DNO you are referring to Andy?
However any DNO have a statutory obligation to allow connection for installations which comply with BS7671.
However, that said the DNOs do not work under BS7671, so there is no reason for anyone to have any knowledge of the requirements of BS7671.
I do know that individual DNOs and the association of meter operators produce guidelines indicating the maximum length they allow. Most of which can probably be found onLine.

Here is a link to the FAQs page for the association of Meter Operators:
http://www.meteroperators.org.uk/faqs

At the end of the day compliance with the Regulations is not statutory.
If you want to interpret the Regulations, as you see fit, that is your option, I cannot force you to comply, or to not misinterpret the Regulations. I can only offer advice and my considered opinion, based on my limited knowledge and experience.

 

[Guest55]

that was absolutely no answer at all to my question.

and your definition of C3 is incorrect , it is referred to as "improvement recommended" , there is no particular tie in with any edition of the regs for it to be used.

which seems a considerably more suitable defect code for the length of tails that have not been confirmed to be actually longer than 3 mtrs.........

 

[Gavin A]

Yes, when it is agreed.
If it has been agreed then there will be a written agreement with a list of conditions and stipulations as long as your arm.
I doubt very much that such an agreement would be made for a domestic installation, where there are no statutory requirements for who has control of the installation.

I thought the point of the 3m rule was that it was automatically agreed by the DNOs up to 3m.

 

[Deleted member 26818]

Sorry Biff, I edited my post to include the link whilst you were posting.

 

[Guest55]

no worries.

 

[Deleted member 26818]

I thought the point of the 3m rule was that it was automatically agreed by the DNOs up to 3m.

No, there is no automatic agreement that the DNO protective device is there to protect the installation.
If there was, then you as the person in control of that installation would automatically be legally entitled to remove or replace the protective device.

 

[andyelectric]

I thought the 3m rule was simply the DNO not wishing for their cut-out fuse to be used for protection of the installation. Their has to be some cable between meter and next protective device hence a convenient 3m allowance which can allow a consumer unit to be attached. However a lengthy run over 3m would require a switch fuse.

So for the purpose of the EICR we are not particularly concerned if tails are 3m or 3.5m, but merely whether there is potential danger through tails in the internal wall. Either code 2 or no code depending on whether the OP sees any potential danger.

 

[Gavin A]

No, there is no automatic agreement that the DNO protective device is there to protect the installation.
If there was, then you as the person in control of that installation would automatically be legally entitled to remove or replace the protective device.

of course there is, otherwise it'd be impossible for anyone to run any length of tails to the first protective device.

if the DNO is giving permission to run tails up to 3m without the use of an additional protective device, then they are at the same time giving permission for their fuse to be used as the only protective device for that length of tails.

How else could that possibly work?

 

[Andy78]

A code C1 is applied for when there is an immediate danger.
A code C2 is applied where there is a potential for danger.
A code C3 is applied in instances where the Regulations were complied with at the time of design/construction, but due to changes in the requirements, no longer comply.

As far as I am aware this situation has never complied with any Regulations.
As such codes C1 and C3 are not applicable, leaving only code C2 as an option.

Not certain which DNO you are referring to Andy?
However any DNO have a statutory obligation to allow connection for installations which comply with BS7671.
However, that said the DNOs do not work under BS7671, so there is no reason for anyone to have any knowledge of the requirements of BS7671.
I do know that individual DNOs and the association of meter operators produce guidelines indicating the maximum length they allow. Most of which can probably be found onLine.

Here is a link to the FAQs page for the association of Meter Operators:
Association of Meter Operators - FAQs

At the end of the day compliance with the Regulations is not statutory.
If you want to interpret the Regulations, as you see fit, that is your option, I cannot force you to comply, or to not misinterpret the Regulations. I can only offer advice and my considered opinion, based on my limited knowledge and experience.

I am referring to Northern powergrid.

Thanks for the link spin... very helpful ....
From that link:

[h=3]How long can meter tails be?[/h]

---

The meter tails should be as short as possible. Different metering companies have different policies but the length should always be less than 3 metres of cable from the cut-out through the metering equipment to the consumer unit. A example may be 1m of cable from the cut-out to the meter, then 1.5m from the meter to the consumer unit. The meter tail cable size must be consistent. BS7671 Reg. 434.2.1 gives some guidance. If the consumer unit is required to be further away, then a switch-fuse unit should be installed close to the meter and a sub-main compliant with BS7671.




Reg 434.2.1 deals with fusing down for fault current for changes in CCC. What if there is no change in CCC ?

I have been working this week in an area (whole streets newly renovated) where each house has been supplied with 10m of unfused split con from an isolator in the meter cabinet through to the CU. Surely this breaches the rules from the link above too ?

 

[trev]

I understand what people are saying about does that extra half a metre somehow make it dangerous but there has to be a line drawn somewhere.
If the extra half a metre doesn't make it dangerous, how about an extra 5 metres?
Or an extra 1 amp on the loading of that 1mm cable?

 

[andyelectric]

I understand what people are saying about does that extra half a metre somehow make it dangerous but there has to be a line drawn somewhere.
If the extra half a metre doesn't make it dangerous, how about an extra 5 metres?
Or an extra 1 amp on the loading of that 1mm cable?

My thinking is, it is the dno that imposes the 3m rule.

For the purposes of the EICR, is the cable an immediate danger, potential danger or does it require improvement irrespective of the length. Here, the fact the cable is run through an internal wall makes it a probable C2(as unlikely to be more than 50mm, no rcd and as tails no mechanical protection) , but only the OP can see the actual run so possibly no coding.

 

[Deleted member 26818]

I am referring to Northern powergrid.

Thanks for the link spin... very helpful ....
From that link:

How long can meter tails be?

---

The meter tails should be as short as possible. Different metering companies have different policies but the length should always be less than 3 metres of cable from the cut-out through the metering equipment to the consumer unit. A example may be 1m of cable from the cut-out to the meter, then 1.5m from the meter to the consumer unit. The meter tail cable size must be consistent. BS7671 Reg. 434.2.1 gives some guidance. If the consumer unit is required to be further away, then a switch-fuse unit should be installed close to the meter and a sub-main compliant with BS7671.




Reg 434.2.1 deals with fusing down for fault current for changes in CCC. What if there is no change in CCC ?

I have been working this week in an area (whole streets newly renovated) where each house has been supplied with 10m of unfused split con from an isolator in the meter cabinet through to the CU. Surely this breaches the rules from the link above too ?

BS7671 does not cover the distribution network.
As such the DNO protective device and the CCC of the DNO cable should be disregarded, although I would expect the DNO to use a cable with a greater CCC than is required for the supply and would always assume that a cable on the installation side would have a lower CCC than the DNO's side.
As for the 10m of unfused split con, how do you know that it is unfused?
Does it require fusing, even under the requirements of BS7671?

 

[Guest55]

I understand what people are saying about does that extra half a metre somehow make it dangerous but there has to be a line drawn somewhere.
If the extra half a metre doesn't make it dangerous, how about an extra 5 metres?
Or an extra 1 amp on the loading of that 1mm cable?

but at that point the debate goes 2 ways........

1. does the length of the tails strictly comply to the letter of the rules governing their length ?

in this case , maybe not.

2. does that additional 0.5mtr make the installation dangerous enough to warrent a C2 , thereby failing the inspection as a whole ?

again , in this case probably not.


whats written in this thread is neither here nor there , its how the inspector views the situation , on site , on that day.

;-)

 

[Gavin A]

the length of the cable doesn't make it dangerous, what it does is to put it in breach of the DNO guidance, making the entire installation technically non-compliant.

That guidance is really there to minimise the chances of the DNO fuse getting blown by a fault on the meter tails, but that fuse will protect 10m tails just as well as it will 3m tails.

Is how I understand it.

Must admit I'd always thought the 3m started at the suppliers meter, not the fuse carrier as stated in that AMO guidance.

Personally I'd work on the basis that anything that can be rounded down to 3m would be ok, anything that would be rounded up to 4m wouldn't. Got to have a bit of leeway on these things.

ps there also seem to be a fair few installs out there that treat a main switch as if it was also providing overload and fault protection when running extended lengths of tails.