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Topic Title: EICR code needed
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Created On: 30 January 2013 05:54 PM
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 31 January 2013 02:47 PM
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Parsley

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OMS

I see what you mean about installing larger conductors between the busbar and the DB's to save on switchfuse costs.

The installation we were looking at had 95mm singles from the 200Amp main switchfuse feeding the adjacent busbar and then several outgoing distribution circuits, including one that fed the TP&N 12 way DB which was fed in 16mm singles in trunking.

So the submain only has an It of 68 Amps according to table 4D1A, no correction factors needed.

Regards
 31 January 2013 03:27 PM
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OMS

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Originally posted by: Parsley

OMS



I see what you mean about installing larger conductors between the busbar and the DB's to save on switchfuse costs.

as engineers we often have to do for a shilling what everyone else can do for a pound !!


The installation we were looking at had 95mm singles from the 200Amp main switchfuse feeding the adjacent busbar and then several outgoing distribution circuits, including one that fed the TP&N 12 way DB which was fed in 16mm singles in trunking.

OK - I suspect 16mm2 may be a bit small for any sensible argument about overload but see below


So the submain only has an It of 68 Amps according to table 4D1A, no correction factors needed.

Depends on the load I guess - I've seen plenty of 12 way TP&N lighting boards pulling 30A flat out

If you were to evaluate on the basis that a 12way board can't handle more than 125A, then using 50mm2 cables would ensure you can't be overloaded - and in practice they could be as small as 16mm2 depending on the load and load type.

Regards


OMS

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Failure is always an option
 31 January 2013 05:37 PM
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spinlondon

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Originally posted by: AJJewsbury
Since when did the DNO fuse start protecting anything other than the distributer's equipment?

433.3.1 (iii) ? - if we're talking about the tails after the meter/isolator.

If they're the DNO's property it's hard to tell. I've seen a couple of most-definitely 100A fused supplies that have what look for all the world to be 16mm tails (with blue/brown sheath) - I can only guess they're 90-degree rated - hence 16mm2 would be good to at least 109A.
- Andy.


Yes as long as the DNO have so agreed.
With the majority of installations, the DNO will not have so agreed.
 31 January 2013 05:48 PM
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gjb747

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Is the 16mm2 tails not to be coded ? Or given a code 3 ?

Thanks ..
 31 January 2013 06:12 PM
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OMS

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In your case I would say no code.

You have an installation MD of 50A, the tails can carry more than that, and despite Spin's post above, the supplier will almost certainly have given agreement to the use of his service fuse to protect the tails and consumer unit up to 16kA fault levels as long as the tails aren't longer than say 3m.

However, you are in the driving seat, and have read all the posts on this thread.

What do you think ?

Regards

OMS

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 31 January 2013 07:49 PM
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gjb747

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I feel that it ought to be mentioned in my report , in section K observations, I shall comment on it but not code it . I shall also ask the client if they could contact their DNO to ask their opinion on the matter .

Regards ... Gary .
 31 January 2013 07:57 PM
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OMS

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OK - sounds like a plan.

If you do code, it's wise to comment against the regulation number(s) - but you'll struggle to find one in this case.

regards

OMS

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 31 January 2013 09:17 PM
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spinlondon

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OMS, you do come out with some crackers.
Do you really believe that a DNO would give permission for their equipment to be used to protect an installation over which they would have absolutely no control and no assurance of who would be using or altering the installation?
If the DNO allow permission for their protective device to be used to provide protection, why the 3m limit?
Do they have special kinds of fuses, that only protect up to 3m?

DNOs have a statutory obligation to ensure that before allowing an installation to be connected to their supply, that the installation complies with either BS7671 or ESQR.
BS7671 just happens to have a 3m limit on the distance a protective device can be from the point of a reduction in CCC of a conductor.
The DNO's are not giving permission, they are ensuring compliance with BS7671, hence the maximum length of 3m for tails.

If a DNO were to give permission for their protective device to be used to protect any part of an installation, if the device failed to provide protection for whatever reason, the DNO could well be considered liable for the damage.
Do you really really believe for one second that any DNO would expose themselve to possible litigation in such a manner?
Why would they do such a thing, when there is no need?
An installation that complies with BS7671 should not need additional protection in the form of the DNO's fuse.

If the DNO give permission for their device to be used to provide protection, then they will also have to allow whomever they have given permission to, access to that device.
Something that we all know the DNOs do not allow.
If they did not allow access then they would have to provide a round the clock replacement service, and if they didn't replace the fuse within a reasonable time, they again could be held liable for any damage, injury, inconvenience, etc.
Again why would they do such, when there is no need?

If a DNO were to give permission for the their device to be used to provide protection, they would be shooting themselves in the foot.
A fuse that is provided to protect your equipment, your installation, is just doing it's job if it blows.
A fuse that is there to protect (as per the statutory requirements) the DNOs' equipment, has been damaged by a fault in the installation, or due to misuse of the supply.
If there's no fault, and the demand exceeds the supply, the DNO can charge to increase the supply.

On the rare occasions that the DNO do allow their fuse to be used to protect any part of an installation, there is a written agreement between the DNO and that particular customer detailling exactly the responsibilities of each party, conditions that have to be met, and invariably the agreement ends when that customer ceases to be a customer, it is not automatically transfered to the next customer.

As for something that complies with BS7671 warrenting a code following an inspection conducted in accordance with BS7671, please don't be silly.
 31 January 2013 10:21 PM
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AJJewsbury

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Nice try Spin, but not convincing!

There's no universal 3m limit from suppliers - some say 2.5m, others 5m, some give different limits for internal and external meters. Although 3m is common, it doesn't seem to be a simple facsimile of BS 7671 requirements.

The 3m limit from BS 7671 for leaving conductors unprotected probably wouldn't work as in most cases conditions (ii) and (iii) of 434.2.1 wouldn't be met. E.g. simple insulated & sheathed tails without further protection in a relatively uncontrolled domestic environment probably wouldn't meet the requirement for reinforcing the wiring system to reduce the risk of faults to a minimum, nor would the traditional cupboard-under-the-stairs (inevitably filled with clutter) do much to reduce the risk of fire.

Clearly where protection is by fuses there needs to be a limitation on Zs, ideally in a form that's easily checked on-site and robust in the case of network alterations. Specifying tails c.s.a. and length, knowing worst-case network characteristics, would be an easy way to achieve that.

There are other precedents to the co-ordination of supplier's fuses and consumers equipment too - annexe ZA of the standard for domestic CUs puts limitations on the size & type of the upstream fuse - which in the majority of cases will be the DNO's cut-out.

- Andy.
 31 January 2013 11:01 PM
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OMS

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OMS, you do come out with some crackers.




Ahhh well - have it your way then - I guess we'll just differ on this.

Just ask yourself one question - there is a section of the system over which the consumer has no control - ie the tails to the meter and the tails from the meter to the consumer unit.

With that in mind why then do you think DNO's impose limits on length and generally dictate both live conductor sizes and earthing conductor sizes.

On for our chums working for DNO's I guess - but having worked in the supply industry, I know what the anwer is going to be.

Congratulations on the post though - impressive

Regards

OMS

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Failure is always an option
 31 January 2013 11:56 PM
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alancapon

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Originally posted by: spinlondon
. . . Do you really believe that a DNO would give permission for their equipment to be used to protect an installation over which they would have absolutely no control and no assurance of who would be using or altering the installation? . . .

Pretty much, which is why each DNO will set out their requirements - For supplies no more than 100A/phase my employer states 25mm² insulated & sheathed meter tails no longer than 2.5m, and a 16mm² Main Earth Conductor. Any difference to this, and overcurrent protection must be provided within the first 2.5m of insulated & sheathed tails.

. . . Do they have special kinds of fuses, that only protect up to 3m? . . .

No, but the LV Distribution Network will be designed such that the stated length of insulated & sheathed tails will be protected by the DNO's main fuse.

. . . DNOs have a statutory obligation to ensure that before allowing an installation to be connected to their supply, that the installation complies with either BS7671 or ESQR. . .

They have to implement the ESQCR regulations, which require that an installation complies with the latest edition of BS7671 before connection.

. . . If a DNO were to give permission for their protective device to be used to protect any part of an installation, if the device failed to provide protection for whatever reason, the DNO could well be considered liable for the damage. . .

Yes, they could. We have two "forensic electricians" who work in conjunction with the Fire & Rescue Service to investigate any fire in the vicinity of the meter position.

. . . If they did not allow access then they would have to provide a round the clock replacement service, and if they didn't replace the fuse within a reasonable time, they again could be held liable for any damage, injury, inconvenience, etc. . .

Again, yes. We provide a round the clock replacement service. Depending on the reason for its operation, attendance may be chargeable. If we discover the fuse is intact, the visit may be chargeable. With the fuses we use, it is usually possible to determine whether a persistent overload or a fault caused the operation.

. . . If there's no fault, and the demand exceeds the supply, the DNO can charge to increase the supply. . .

Yes, and we would hand the customer an application form for an increased supply, certainly on a second visit to the same property.

. . . On the rare occasions that the DNO do allow their fuse to be used to protect any part of an installation, there is a written agreement between the DNO and that particular customer detailling exactly the responsibilities of each party, conditions that have to be met, and invariably the agreement ends when that customer ceases to be a customer, it is not automatically transfered to the next customer. . .

In my employers case, these conditions are included as some of the conditions for applying for / taking over a supply of electricity.


Regards,

Alan.

Edited: 01 February 2013 at 12:13 AM by alancapon
 01 February 2013 12:17 AM
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OMS

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Thanks for the clarification, Alan

regards

OMS

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 01 February 2013 12:22 AM
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gjb747

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Alan , am I correct in requesting that my client contacts their DNO to advise them that the tails need upgrading to 25mm2 or the main fuse replacing with a 60 or 80 amp main fuse .

Thanks .... Gary
 01 February 2013 12:52 AM
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spinlondon

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Sorry Andy, but I'm not aware of any DNO that stipulates a maximum length of 5m for tails.
Yes there are varying lengths, for instance Alan's employer stipulate 2.5m.
This allows 0.5m from the cut out to the meter.
The reduction in CCC in practical terms takes place at the cut out.
However BS7671 doesn't come into force untill the consumer terminals.

With regards 424.2.1 (ii) and (iii), I thought we had been through all this in the discussion regarding tick boxes.
There are a number of installations that are TT and rely on RCDs to provide fault protection.
In the majority of such installations, the RCD protection is provided in the installation, not in the distribution.
However just as with overload protection, fault protection can be omited, if the requirements of 434.3(iv) are met.
I don't know if you have worked on many TT installations Andy, but if you ever find your way to South Wales, you will discover that there are a great number of TT properties in the area. Not just in the sticks, but whole terraces in the towns.
The DNO does not provide as per 434.3(iv) a protective device and agree that it affords protection to any part of the installation.
Are you going to argue that the DNo fuse provides fault protection for TT installations?
Are you going to argue that special tails which satisfy 434.2.1(ii) and (iii) are used?
Are you going to argue that there is some special dispensation for the tails when used in TT installations, that allow them to meet the requirements of 434.2.1(ii) and (iii), but for some reason that dispensation doesn't apply for TN installations?

I really do not understand why you or anyone else believes that the DNOs are that magnamanous that they would agree that their protective devices provide protection for any part of an installation over which they have absolutely no control.

You must be aware that the DNOs do not like anyone tampering with their equipment.
Why do you think that they would consider you using their fuse to protect any part of your installation as anything other than you tampering with their equipment?

There is no reason with the majority of installations, why a DNO should agree that their fuse provides protection to any part of a consumer's installation. There's no practical reason, no statutory requirement, no monetary gain for such an agreement, not even a moral obligation.
Why then do you believe that they as a matter of course agree that their fuse provides protection?
I really don't get it.
 01 February 2013 01:34 AM
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OMS

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Spin - suggest you look at a connection agreement and the underlying documentation - Alan has explained the general position above.

regards

OMS

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 01 February 2013 11:26 AM
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AJJewsbury

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Spin - while I agree that insulated & sheathed tails will provide protection against electric shock - that doesn't help with other faults - e.g. L-N faults internal to the CU (before the MCBs) or L-PE in metalclad CUs on TN systems - or indeed where steel trunking is used before the main DB with single-insulated tails in some commercial/industrial situations. Or indeed with overload where sum of MCB ratings > Iz of tails.

if you ever find your way to South Wales

Funnily enough, all my early experiences with electricity were south of Fishguard and west of Bridgend!

You must be aware that the DNOs do not like anyone tampering with their equipment.
Why do you think that they would consider you using their fuse to protect any part of your installation as anything other than you tampering with their equipment?

They don't like people sticking their fingers in their equipment, but as far as I know they have no objection to consumers drawing electricity through their kit - what more is needed for a fuse to offer protection?

- Andy.
 02 February 2013 07:12 AM
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spinlondon

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I'm not saying that the fuse won't provide protection for the tails, just that that is not it's intended purpose..
It's inteded purpose is to provide protection for the DNO's equipment, as per the statutory requirements.
 02 February 2013 07:22 PM
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AJJewsbury

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I've only got the old reg OSG to hand, but in there - paragraph 2.2.1 it says "..the cut-out me be assumed to provide fault current protection up to the consumer's main switch." I'd expect the current version says something similar.

- Andy.
 03 February 2013 11:41 AM
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OMS

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Originally posted by: spinlondon

I'm not saying that the fuse won't provide protection for the tails, just that that is not it's intended purpose..

It's intended purpose is to provide protection for the DNO's equipment, as per the statutory requirements.


So that would be meter tails, meter and the non contestable aspects of the tails to the installation main switch then Spin - so

which bit of that don't you think the DNO have given permission to the consumer to use for for pretection, up to the point where the consumers protection takes over ?

regards

OMS

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 03 February 2013 08:01 PM
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Martynduerden

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Originally posted by: OMS

Originally posted by: spinlondon

I'm not saying that the fuse won't provide protection for the tails, just that that is not it's intended purpose..

It's intended purpose is to provide protection for the DNO's equipment, as per the statutory requirements.


So that would be meter tails, meter and the non contestable aspects of the tails to the installation main switch then Spin - so

which bit of that don't you think the DNO have given permission to the consumer to use for for pretection, up to the point where the consumers protection takes over ?

regards

OMS


The DNO equipment it the head only, they do not own the meter it belongs to the supplier as do the meter tails connecting to the head, the tails connecting to the meter are the consumers.

Source UKPN

The main fuse is primarily there to protect the head and service cable. Other protection is by agreement - which is common place

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

Martyn.

Only a mediocre person is always at their best



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