Anyone seen this before

[martygturner]

As I said, I can personally think of no assumptions that would result in their 'regulation' making sense.

Again, I've never heard of bends in cables being considered in relation to current-carrying capacity (hence 'protection requirements').

It doesn't really matter whether the cable is visible or buried, armoured or not armoured, of whatever length or even if 'bends' are somehow relevant because, regardless of all that, it still makes no sense to suggest that their fuse might not give adequate protection to a particular cable (any cable, installed in any way) but that a consumer's identical fuse immediately adjacent (electrically) to theirs would.

As I keep pointing out we do not know what assumptions they made or who asked them to make use of an assumption they provided. Or if they made a mistake....reverse engineering it is not cool.

I agree with Morq, regulations are just that either must or should, if it says you must then you do and then have the argument about if its relevant. If its should , have the argument if its relevant and then do.

 

[morqthana]

Again, I've never heard of bends in cables being considered in relation to current-carrying capacity (hence 'protection requirements').

Maybe the electrons struggle to get round sharp bends?

 

[morqthana]

No, I'm not

 

[JohnW2]

I agree with everything you say about the general principle of it being desirable for laws/rules/regulations to make sense, as that tends to get the most, and least resentful, compliance, and tends to avoid laws/rules/regulations which have no beneficial effects,

I'm glad you agree.

But re all I've been trying to say here, all I can do is to give this example, of two people talking ...

As I've said, I fully understand what you've been saying, and agree with it, but it has nothing to do with the point I've been making (and with which you also agree), as above - so, if you have any argument, it';s not with me!

 

[JohnW2]

As I keep pointing out we do not know what assumptions they made or who asked them to make use of an assumption they provided.

You are repeatedly ignoring my comment that I cannot think of ANY 'assumption' that would result in the 'regulation' in question making sense. If you can't, either, then you are simply talking about something hypothetical which probably doesn't exist.

I agree with Morq, regulations are just that either must or should, if it says you must then you do and then have the argument about if its relevant. If its should , have the argument if its relevant and then do.

Has anyone disagreed with that, as the only 'advice'one can (should) give? I certainly haven't.

 

[martygturner]

Oh by the way, its the DNO that has made the assumption on meter tail length and the IET has written is regulation with regard to their instruction.

They made it for a variety of reasons apparently, ageing service heads, non reliance on the correct fuse in the service head being fitted which suggest records not kept, a change from their service contract, protecting the meter not the house, others included variations in the breaking capacity of fuses and times.Protection of meter tails from mechanical damage, I said that earlier - so some form of risk analysis has been done. all seem pretty valid.

How old is the fuse in your service head ? 70's, 50's ???

Of course in a perfect universe that regulation would not be needed but here we are.

 

[JohnW2]

Oh by the way, its the DNO that has made the assumption on meter tail length and the IET has written is regulation with regard to their instruction.

Eh? As far as I am aware, BS 7671 says nothing specific about metre tail length - what am I missing?

All I'm aware of BS 7671 saying is that the DNOs fuses can be the sole protector of the meter tails "if the DNO agrees" - but the DNOs don't seem to agree (at least, for tails beyond 2m/3m), for unknown reasons which make no apparent sense.

 

[morqthana]

Eh? As far as I am aware, BS 7671 says nothing specific about metre tail length - what am I missing?

I remember (I think) a comment about what someone said about >3m lengths in general - is there anything like that?

All I'm aware of BS 7671 saying is that the DNOs fuses can be the sole protector of the meter tails "if the DNO agrees" - but the DNOs don't seem to agree (at least, for tails beyond 2m/3m), for unknown reasons which make no apparent sense.

Again, not making sense makes no difference to the need to comply. Argue all you like about the philosophy, but until those arguments are taken on board and they change the regulations, everyone is stuck with what they say.

So back to this...

2... Tell them that what they say is fine - since you do not wish your cables to have any such 'protection'.

there are probably all sorts of ways in which one could contravene the regulations if one didn't like what they said. Would that one be a C1, C2, or C3?

What does an electrician do? If he knows via asking, or already knowing, that the network operator in that area does not agree for his fuse to be used, and he sees that someone is, what does he do?

Unless he, as a responsible, conscientious, qualified professional really believes that the way the regulatory environment should work is that if he believes a regulation to be unjustifiable/unscientific/nonsensical then it's OK for him to say "F... that, I'm going to ignore that explicit contravention", what does he do?

 

[morqthana]

I agree with Morq, regulations are just that either must or should, if it says you must then you do and then have the argument about if its relevant. If its should , have the argument if its relevant and then do.

Has anyone disagreed with that, as the only 'advice'one can (should) give? I certainly haven't.

If an electricity distributor says to you

"You may NOT use OUR fuse to protect YOUR cables", what do you do?

2... Tell them that what they say is fine - since you do not wish your cables to have any such 'protection'.

 

[JohnW2]

I remember (I think) a comment about what someone said about >3m lengths in general - is there anything like that?

Indeed there is, and I've discussed that above. In terms of both overload and fault protection, BS 7671 says that a downstream OPD is acceptable if a number of conditions are satisfied, one of which being that the downstream OPD be no more than 3m from the origin of the cable (or point of CSA reduction).

However, as I said when discussing this, that is irrelevant to the matter under discussion, since the DNO fuse is upstream of the meter tails (which it therefore inevitably 'protects', unless Mt Kirchoff 'got it all wrong'!).

 

[ebee]

I look on it as a one size fits all situation. Making it very easy, relatively, for their engineers to accept a very finite rule of thumb.

2 or 3m or whatever we decide can easily be checked)inspected with a cursory glance). We know the fuse size and characteristics we know the cable csa hence resistance:impedance and we know therefore that a fault of x magnitude should clear within a certain time and protect the tails etc.

Anything else that may or may not work perfectly well we not concern ourselves with and that is down to the customer to take responsibility for or their contractor if they have one.
Simple’s

 

[morqthana]

However, as I said when discussing this, that is irrelevant to the matter under discussion, since the DNO fuse is upstream of the meter tails (which it therefore inevitably 'protects', unless Mt Kirchoff 'got it all wrong'!).

And as I've said when discussing this, that is all irrelevant to the fact that the DNO do have such a rule, and the regulations do have such a requirement.

 

[JohnW2]

2 or 3m or whatever we decide can easily be checked)inspected with a cursory glance). We know the fuse size and characteristics we know the cable csa hence resistance:impedance and we know therefore that a fault of x magnitude should clear within a certain time and protect the tails etc.

I don't really get that (as an explanation for the 2m/3m/whatever) since we also know (or should know) that what you say about the protection remains true regardless of the length of the cable (or how many bends it has ).

Kind Regards, John

 

[JohnW2]

And as I've said when discussing this, that is all irrelevant to the fact that the DNO do have such a rule, and the regulations do have such a requirement.

Why do you keep saying that? As I've said numerous times, I have never suggested that it is relevant to the fact that such rules/regulations do exist.

 

[EFLImpudence]

and the regulations do have such a requirement.

Only if there is no protection against fault current - but even that does not apply to meter tails in the situation being discussed.

Plus of course - the wiring regulations are not the law as you keep stating.