Difficult to see how it offers short circuit protection to the service, Martyn - clearly it offers short circuit and overload protection to everything downstream of the cut out however - it's also the fuse that allows (in the UK) the ZA agreement on the consumer unit fault rating - ie it provides back up protection to the consumers first tier protection.

It's effectively what allows simple compliance with Regulation 434.1 in every domestic installation and why the DNO's stipulate maximum length of tails (and usually CSA) to avoid the need for specific calculations in each and every case.

Thje primary purpose of the cut out fuse is principally, nothing to do with the service cable, it's the means of seperating the consumer from the network - ie overload and low IR problems will disconnect automatically

Regards

OMS

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Failure is always an option

It quite obviously as you know offers no short circuit protection to the head or service cable, you other comments are at odds with the major dno's for the UK, I'm not suggesting it does not offer protection just that this is not its primary function, the dno have no interest in consumer installations.

I suspect the 3m / csa rule is to cover their backsides more than anything else.

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

Martyn.

Only a mediocre person is always at their best



www.electrical contractors uk.com

OK then Martyn - lets go back a bit - the 1988 supply regs should do it



The emboldening is my emphasis

I suspect we could deduce from that regulation, that the supplier is responsible for protecting both his own and for that part of the consumers installation over which he has no control (ie cut out, meter tails, meter and consumers tails to the consumer unit).

Note that the protection shall be by means of a fusible cut out or similar

Now lets move on to ESQCR



Almost identical wording I suspect you'll agree


Does that convince you and others that the DNO (and latterly, the MOP)have been and continue to be responsible for that part of the installation not under the consumers control and in the context of domestic or similar installations offer thecut out fuse as a statutory obligation and as a means of consumer compliance with the relevant parts of BS 7671 (without which they would be entitled to deny or withdraw a supply)

Satisfied now

Regards

OMS

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Failure is always an option

No OMS, to the contrary, it suggests (exactly as I have stated) that the DNO's do not provide protection for any part of the consumer's installation, which is under the control of the consumer.
i.e. Anything downstream from the consumer connection terminals.
i.e. The tails.

Mmmm - that's not what we were discussing Spin.

It was your view that the DNO would not have given permission for the cut out fuse to offer protection to those parts of the installation that fall under 434.3 (iv).

You maintained that the DNO would not have given permission based on the long list of erroneous observations you made - it was my (and others) view that the permission was expressly implied (as indicated in, for example, the OSG) - basically because it's what the legislation requires.

The DNO are obliged to provide that protection by staute - therefore permission to use it is expressly given ?

Regards

OMS

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Failure is always an option

What part exactly of a normal domestic installation, is the consumer's but not under the consumer's control?
Yes there are installations where the DNO's have to provide protection for what is effectively part of the consumer's installations, but such installations, have specific agreements. i.e. the DNO agrees that their protective device can be used to protct part of the consumer's installation.

As for the erroneous observations, how about you actually put your money where your mouth is, and provide some argument to show that they are erroneous?

I really don't understand why you have this odd belief that DNO's will provide protection, for something whilst at the same time insist that the consumer also provide protection?
What purpose would doing such serve?

Tails from cut out to meter -DNO

Meter - MOP
Tails from meter to consumer unit - consumer

Consumer main switch and installation terminals (ie the consumer unit) - consumer

Short circuit protection is provided for every item in that list but you'll note the last two don't belong to the DNO or the MOP - they belong to the consumer but they rely on the cut out fuse for protection, under statute law, and relied on in the UK annexe ZA deviation for breaking capacity for domestic consumer units ie backed up by a max 100A BS 1361.

as for erroneous, try these:



They do, under statute



see above



How so - read ESQCR



They'd be breaking the law if they didn't

I guess that's enough to be going on with.



I'm sorry Spin - I don't understand what your saying here ? - the division of responsibility is clear cut, the consumer cannot provide protection to his consumer tails and incoming device on the consumer unit which means he can't comply with BS 7671 unless he invokes 434.3 (iv) - for which the DNO have a legal duty to provide. In short, the consumer needs to comply with BS 7671 and for a typical domestic arrangement, he achieves that by making a demand on the DNO fuse for that part of his installation not under his control.

Regards

OMS

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Failure is always an option

what code would you give tails on a TT supply ??

none but they have no protection :0

I must admit to believing that the supply fuse was there to secure the supply company's equipment only, and that unless specifically stated, that protection, did not extend to the "Tails from meter to consumer unit. But as OMS points out the "parts that form the consumers installation" which "are not under the control of the consumer" (presumably because assess to the termination at the meter is restricted) must be protected, by either the distributor or the meter operator by law. And that "part" would have to be at least, the meter tails. And, to be "protected by a suitable fusible cut-out or circuit breaker which is situated as close as is reasonably practicable to the supply terminals".
Thanks for "nudging the penny"

Regards

Well that's alright then, the next time I have to make an instalation ready for connection, I won't bother installaing any tails, as they're not under my control.
I'll just leave it to the DNO.
All I have to figure out now, is why the DNO are bothering to inform me of the maximum length, when the tails aren't under my control?

Well Spin, they may not be under your control, that doesn't mean to say they aren't supplied by the consumer, in the same fashion as the dist board - didn't you read my last post

As I explained, the limit on tails length is to avoid the DNO undertaking the calculations in each and every case

It's quite simple:

They tell us the fault level won't exceeed 16kA

They tell us thier tails are protected up to 3m

The equipment standards tell us the consumer unit assembly is also protected to 16kA as long as we have a suppliers BS 1361 fuse protecting them - ie the DNO fuse.

Regards

OMS

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Failure is always an option

OMS, get real.
Of course the tails would be under my control.
If they weren't, then there would be no stipulation on their maximum length, and I would not be installing them.

The fact that the DNO would or would not have to make calculations, would not be grounds for refusing a connection.
The only grounds the DNO's have for refusing a connection are:
(a) the consumer's installation, street electrical fixture or other distributor's network fails to comply with British Standard Requirements or these Regulations; or .
(b) the connection itself will not be so constructed, installed, protected and used or arranged for use, so as to prevent as far as is reasonably practicable, danger or interruption of supply.

Are you seriously suggesting that the difference between 3m tails and say 5m tails could cause anyone to believe that (b) above would be applicable?
Are you really suggesting that the DNO's would put themselves in a position where they could be taken to task and perhaps fined or even have their licence taken away, just for the convenience of not having to make calculations, especially as the length they stipulate is so insignificant?

Edited: 06 February 2013 at 07:37 PM by spinlondon

Regards

OMS

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Failure is always an option

My recollection was faulty - it was 4m, not 5m - (see gcottingham's post of 27 July 2006 02:46 PM http://www.theiet.org/forums/f...tid=205&threadid=11404 ) - but still obviously not related BS 7671's 3m.

Then there's UKPN's published document: http://library.ukpowernetworks...ervices+up+to+100A.pdf which states (in 4.1.4) "The maximum length of tails from cut-out to meter is two metres and from meter to the customer equipment is two metres." - which again doesn't seem to tally with BS 7671's 3m limit.

We've got Alan saying that the supplier's themselves do think they have that responsibility.

And the IET (in the OSG) saying we can assume that they have that responsibility.

Seems to satisfy 'the balance of probability' test at least.

- Andy.

They seem protected to me - from L-N faults (perhaps internal to the CU before the MCBs) by the supplier's cutout and from shock by the insulation+sheath with BS 7671 accepts as fulfilling the requirements for double or reinforced insulation where they're installed inn suitable conditions (and the double insulation of the plastic CU enclosure).

- Andy.

Or alternatively, in simple terms, the comprise a "fault free zone" by virtue of the construction and arrangement Andy described above.

Regards

OMS

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Failure is always an option