Fuses and cable CCC

[JohnW2]

I'm starting to get a bit annoyed about this new phenomenon of curtailment of discussions which, although protracted, are well mannered, 'of interest' and (at least in this case) at least partially related to the topic of a thread. Maybe it's time for me to take another rest from the forum!

Is it? Why?

For the reasons I went on to explain...

I do not see why. If 433.1.1(iii) is NOT satisfied then then (i) and (ii) are irrelevant. It must satisfy all three - 'and' not 'or'.

I think you may be missing my point. In the case of a BS 3036, 433.1.202 supersedes 433.1.1(ii), but 433.1.1(iii) still also has to be satisfied (as you say, "and"). However, as I explained, given a 'fusing factor' of 2, if 433.1.202 is satisfied (by a 3036), then 433.1.1(iii) is automatically also satisfied - that's an arithmetical inevitability (for any 'fusing factor' above 1.45).

As I said, the equivalent is not true of other fuses which do not necessarily satisfy 433.1.1(iii) even though they satisfy 433.1.1(ii).

Why then are BS3036 fuses singled out as they are only 5% 'worse' than BS1362 fuses?

I think the real question is why they bothered to single out BS 3036s. Given the existence of 433.1.1(iii), I can't see that the situation (for 3036s) would be any different if 433.1.202 didn't exist, would it? Satisfaction of 433.1.1(iii) would effectively involve use of the 'de-rating factor' (which is implicit in the determination of I2) - and if (iii) were satisfied, then (ii) would be satisfied as well.

Why not?

As explained above.

For a 3A fuse and 3A cable, it isn't. Therefore the derating factor applies.

Exactly - hence the 'F' in what I wrote. For a 3A cable, the In of the fuse would have to be no greater than 3A x (1.45/F).

They are, so perhaps 3A flex (0.5mm²) is alright with a 6A MCB

I don't doubt that it would be 'alright' (particularly given that the CCC of a non-flexible 0.5mm² cable {in free air} would {if we were allowed to use it} presumably be considerably more than 6A). However, I'm not sure how you could read BS7671 as saying that it was 'alright'!

Kind Regards, John

 

[EFLImpudence]

Thank you for the original comment regarding the locking of the other thread.

Very strange.

I think you may be missing my point. In the case of a BS 3036, 433.1.202 supersedes 433.1.1(ii), but 433.1.1(iii) still also has to be satisfied (as you say, "and"). However, as I explained, given a 'fusing factor' of 2, if 433.1.202 is satisfied (by a 3036), then 433.1.1(iii) is automatically also satisfied - that's an arithmetical inevitability (for any 'fusing factor' above 1.45).

Yes, I don't have any trouble accepting the conditions for BS3036s.

As I said, the equivalent is not true of other fuses which do not necessarily satisfy 433.1.1(iii) even though they satisfy 433.1.1(ii).
I think the real question is why they bothered to single out BS 3036s. Given the existence of 433.1.1(iii), I can't see that the situation (for 3036s) would be any different if 433.1.202 didn't exist, would it?

No, but I thought it was your view that the same - or equivalent - did not apply to other fuses.

Was I mistaken?

Satisfaction of 433.1.1(iii) would effectively involve use of the 'de-rating factor' (which is implicit in the determination of I2) - and if (iii) were satisfied, then (ii) would have to be as well.

Well, yes, but I just meant if (iii) is not satisfied then it doesn't matter if (i) or (ii) are or not; it's not compliant.

Exactly - hence the 'F' in what I wrote. For a 3A cable, the In of the fuse would have to be no greater than 3A x (1.45/F).

Yes, or the other way round, the cable must have a CCC of 3A / (1.45/F)

Isn't that what I have been arguing for and saying what should happen - but doesn't?

I don't doubt that it would be 'alright' (particularly given that the CCC of a non-flexible 0.5mm² cable {in free air} would {if we were allowed to use it} presumably be considerably more than 6A). However, I'm not sure how you could read BS7671 as saying that it was 'alright'!

No, I wasn't saying it would be compliant; just saying it probably would be 'alright'.

 

[bernardgreen]

I'm starting to get a bit annoyed about this new phenomenon of curtailment of discussions which,

Maybe winston is a Mod

 

[JohnW2]

Thank you for the original comment regarding the locking of the other thread. Very strange.

Quite so - unless, of course, someone slipped in a diabolic post or three that got deleted before we saw it. However, there have been a few recent cases of threads being locked seemingly only because of their length (and/or because they had evolved into just a dialogue between two people) - which seems very odd.

Yes, I don't have any trouble accepting the conditions for BS3036s.

Fair enough - so you agree that if 433.1.202 [the BS 3036's equivalent of 433.1.1(ii)] is satisfied that, then, 433.1.1(iii) is also inevitably satisfied?

No, but I thought it was your view that the same - or equivalent - did not apply to other fuses. Was I mistaken?

Slightly mistaken, I think. My point was that if the "In requirement" [433.1.202 for 3036s, 433.1.1.(ii) for everything else] was satisfied then, the "I2 requirement" [433.1.1.(iii) for everything] would also automatically be satisfied for 3036s, but not necessarily for any other fuse.

Well, yes, but I just meant if (iii) is not satisfied then it doesn't matter if (i) or (ii) are or not; it's not compliant.

Well, yes, we're agreed about the "and". However, I've explained above the differences between 3036s and other fuses.

Yes, or the other way round, the cable must have a CCC of 3A / (1.45/F)

Exactly.

Isn't that what I have been arguing for and saying what should happen - but doesn't?

I think it is and, more than once, I've agreed that it's something which probably never gets considered (other than for 3036's - which perhaps illustrates the folly of having {unnecessarily, I think} 'singled it out' for a reg of its own.

No, I wasn't saying it would be compliant; just saying it probably would be 'alright'.

Fair enough. As I said, I'm sure that it would be (more than) alright.

It seems as if we are agreed about most of this.

Kind Regards, John

 

[JohnW2]

Maybe winston is a Mod

If he is, he's doing a pretty poor job of moderating himself

Kind Regards, John

 

[winston1]

Maybe winston is a Mod

No.

 

[EFLImpudence]

Fair enough - so you agree that if 433.1.202 [the BS 3036's equivalent of 433.1.1(ii)] is satisfied that, then, 433.1.1(iii) is also inevitably satisfied?

Is this where I was confused about your view?
Compliance with (ii) does not ensure compliance with (iii).
Surely the equivalent of 433.1.202 is 433.1.1(iii); not (ii)

(i) and (ii) apply to every OPD. In ≥ Ib and In ≤ Iz respectively.
(ii) being satisfied does not mean (iii) is satisfied for fuses because their I2 does exceed 1.45 x the Iz of a cable with the same CCC as the OPD's In.
(iii) compliance has to be met by using a larger cable.

Let me demonstrate.
Ib 15A; 3036 15A fuse; 1mm² T&E, 16A CCC.
(i) 15A In ≥ 15A Ib - ok
(ii) 15A In ≤ 16A Iz - ok
(iii) I2 (of 15A ) fuse > 1.45 In - not ok, so larger cable required.

Slightly mistaken, I think. My point was that if the "In requirement" [433.1.202 for 3036s, 433.1.1.(ii) for everything else] was satisfied then, the "I2 requirement" [433.1.1.(iii) for everything] would also automatically be satisfied for 3036s, but not necessarily for any other fuse.

Have I covered that above?

I think I got all that right.
Edit - I didn't, error corrected.

 

[JohnW2]

Is this where I was confused about your view?

It seems as if that is the case.

Compliance with (ii) does not ensure compliance with (iii).

Agreed - it definitely doesn't. That's my whole point about fuses other than 3036s.

Surely the equivalent of 433.1.202 is 433.1.1(iii); not (ii)

No. 433.1.202 is the 3036 'replacement' for 433.1.1(ii), both being about In. 433.1.1(III) [which applies to everything, including 3036s] is about I2.

(i) and (ii) apply to every OPD. In ≥ Ib and In ≥ Iz respectively.

I presume you mean In ≤ Iz.

I've been ignoring (i), assuming that it is always satisfied. As above, (ii) applies to everything other than 3036s (it being 'replaced' by 433.1.202 for 3036s). I suppose that, if you want, you could say that it also applies to 3036s, but, as you say, it only requires that In ≤ Iz (which certainly has to be satisfied, by anything). However, in the case of a 3036, 433.1.202 requires that In ≤ ( 0.725 x Iz) - so that obviously supersedes/over-rules/trumps/'replaces' 433.1.1(ii) in the case of a 3036.

... (ii) being satisfied does not mean (iii) is satisfied for fuses ...

As above, that is exactly the point I keep making about fuses other than 3036s.

However, in the case of 3036's, they have to go beyond the requirement of 433.1.1(ii) and also satisfy 433.1.202 - i.e. In ≤ ( 0.725 x Iz). For a 3036, I2 = 2 * In, so, if In ≤ ( 0.725 x Iz) [i.e. if 433.1.202 is satisfied], then I2 ≤ (2 x 0.725 x Iz). In other words...

I2 ≤ (1.45 x Iz)

... which is precisely what 433.1.1(iii) requires (of any device). Hence, if a 3036 satisfies 433.1.202 then it also inevitably (simple arithmetic) satisfies 433.1.1(iii).

The same is not true for any other fuse because, for them, there is no equivalent of 433.1.202. They merely have to satisfy 433.1.1(ii) (i.e. In ≤ Iz) and that will not necessarily (in fact, never, assuming that 'fusing factor' is >1.45) be enough to ensure compliance with 433.1.1(iii)

Do you disagree?

Kind Regards, John

 

[EFLImpudence]

Agreed - it definitely doesn't. That's my whole point about fuses other than 3036s.

...but it doesn't apply to 3036s either.

No. 433.1.202 is the 3036 'replacement' for 433.1.1(ii), both being about In. 433.1.1(III) [which applies to everything, including 3036s] is about I2.

433.1.202 is about In as well.
It says a derating factor is to be applied. The same could be written about other fuses with different values.

I presume you mean In ≤ Iz.

Yes, thanks. Sorry.

I've been ignoring (i), assuming that it is always satisfied.

Ok.

As above, (ii) applies to everything other than 3036s (it being 'replaced' by 433.1.202 for 3036s).

...but (ii) still applies to 3036s; 3036s just happens to be specifically mentioned in 202 which is the same as (iii).

I suppose that, if you want, you could say that it also applies to 3036s, but, as you say, it only requires that In ≤ Iz (which certainly has to be satisfied, by anything).

...but then (iii) has to be considered.

However, in the case of a 3036, 433.1.202 requires that In ≤ ( 0.725 x Iz) - so that obviously supersedes/over-rules/trumps/'replaces' 433.1.1(ii) in the case of a 3036.

Only because it is additionally mentioned for some reason - otherwise you would have to do the calculation to satisfy (iii) and having done that 202 is just a repitition.

As above, that is exactly the point I keep making about fuses other than 3036s.

Yes, but without 202, they would all be covered by (iii).
You said:
My point was that if the "In requirement" [433.1.202 for 3036s, 433.1.1.(ii) for everything else] was satisfied then, the "I2 requirement" [433.1.1.(iii) for everything] would also automatically be satisfied for 3036s, but not necessarily for any other fuse.
which is not the case. It is the same for all.

However, in the case of 3036's, they have to go beyond the requirement of 433.1.1(ii)

Yes, but not beyond (iii) - the same as all the others.

and also satisfy 433.1.202

Yes, but that is the same in different words.

i.e. In ≤ ( 0.725 x Iz). For a 3036, I2 = 2 * In, so, if In ≤ ( 0.725 x Iz) [i.e. if 433.1.202 is satisfied], then I2 ≤ (2 x 0.725 x Iz). In other words...I2 ≤ (1.45 x Iz)

There could be clauses for every other fuse beginning with:
In ≤ ( 0.763 x Iz). For a 1362, I2 = 1.9 * In, so, if In ≤ ( 0.763 x Iz) [i.e. if 433.1.202 is satisfied], then I2 ≤ (1.9 x 0.763 x Iz). In other words...I2 ≤ (1.45 x Iz)
I do not see why you think it different for 3036s just because it is unnecessarily specifically mentioned elsewhere.

... which is precisely what 433.1.1(iii) requires (of any device).

Exactly.

Hence, if a 3036 satisfies 433.1.202 then it also inevitably (simple arithmetic) satisfies 433.1.1(iii).

Of course it does; so do all the other fuses using their values.

The same is not true for any other fuse because, for them, there is no equivalent of 433.1.202.

There doesn't have to be.
There doesn't have to be for 3036s but there just happens to be a another clause which says the same thing.

They merely have to satisfy 433.1.1(ii) (i.e. In ≤ Iz) and that will not necessarily (in fact, never, assuming that 'fusing factor' is >1.45) be enough to ensure compliance with 433.1.1(iii)

Precisely.

Do you disagree?

I don't disagree. I just don't understand why you think 202 is different than 1.1(iii).
If 202 were not there, nothing would change.

 

[ban-all-sheds]

All devices with an I2 > 1.45In have to go beyond the requirement of 433.1.1(ii).

433.1.202 does not override/supersede/trump anything, it is just, for some reason, the explicit example of 433.1.1 (iii) when applied to 3036s

I2 ≤ 1.45 Iz
2In ≤ 1.45 Iz
In ≤ 0.725 Iz

In theory that same calculation has to be done no matter what the device. In Step 2 it won't always be 2In, that's all.

But it's only with 1362s and non-general purpose (gG) BS 88s that you also get a different outcome for 433.1.1 (ii) (if we assume that the fusing factor of 1.5 for 1361s and small 3871 MCBs is so close to 1.45 that it makes no difference). But even using BS 88s with a factor of 1.6 you end up with In ≤ 0.9 Iz.

The question is not what does 433.1.202 mean wrt 433.1.1, but why they felt it necessary to have it at all. Maybe because it's the most onerous (although 1362s run it a close second), and they wanted to make sure people didn't fail to do it?

 

[JohnW2]

... It says a derating factor is to be applied. The same could be written about other fuses with different values.
... but (ii) still applies to 3036s; 3036s just happens to be specifically mentioned in 202 which is the same as (iii).
... Only because it is additionally mentioned for some reason - otherwise you would have to do the calculation to satisfy (iii) and having done that 202 is just a repitition.
... Yes, but without 202, they would all be covered by (iii).
... Yes, but that is the same in different words.
... There doesn't have to be for 3036s but there just happens to be a another clause which says the same thing

I think that you and BAS are saying exactly the same thing I said early in this discussion....

I think the real question is why they bothered to single out BS 3036s. Given the existence of 433.1.1(iii), I can't see that the situation (for 3036s) would be any different if 433.1.202 didn't exist, would it? Satisfaction of 433.1.1(iii) would effectively involve use of the 'de-rating factor' (which is implicit in the determination of I2) - and if (iii) were satisfied, then (ii) would be satisfied as well.

I do not see why you think it different for 3036s just because it is unnecessarily specifically mentioned elsewhere. .... I just don't understand why you think 202 is different than 1.1(iii). If 202 were not there, nothing would change.

I think you are reading too much into what I have written. The only thing I have said is different about 3036s is that 433.1.202 exists ('unnecessarily', which I think we all now agree). That means that for 3036's, there is an explicit regulation which 'does the thinking (or 'calculation') for you', in determining whether or not 433.1.1(iii) will be satisfied. With any other fuse (any other device with a 'fusing factor' above 1.45), one has to do one's own thinking to determine whether that reg is satisfied.

In a literal sense, I disagree with BAS's view that 431.1.202 "does not override/supersede/trump anything" (for a 3036). Just like 433.1.1(ii) it is written in terms of In - and it requires a lower In (for a 3036) than would be required to satisfy 433.1.1(ii) alone. To cite an analogy, if one 'regulation' said that "the maximum speed on this road is 60mph" and another regulation said "the maximum speed of an HGV is 50mph", then the latter clearly 'over-rides' the former in the case of an HGV.

Maybe what has confused the discussion is the fact that, in practice, "it does not matter". Although, at first sight, it might appear that 433.1.1(ii) allows an 'unacceptably' high In for any fuse (other than a 3036, for which that reg is 'over-ridden' by 202), since, for example, In=Iz would not be acceptable for anything with a fusing factor >1.45 [although it would satisfy 433.1.1(ii)], the mathematical reality is that if one complies with 433.1.1(iii) in terms of I2, that the In will then also be 'appropriate' [and less than CCC, as required by (ii)]

Kind Regards, John

 

[EFLImpudence]

I think that you and BAS are saying exactly the same thing I said early in this discussion....

I am sure you have changed from what you wrote earlier.

In a literal sense, I disagree with BAS's view that 431.1.202 "does not override/supersede/trump anything" (for a 3036). Just like 433.1.1(ii) it is written in terms of In - and it requires a lower In (for a 3036) than would be required to satisfy 433.1.1(ii) alone.

I also think you are looking at it the wrong way round. I know it's only arithmatic here but in practice the outcome of this is not that it requires a lower In but a larger cable.
After designing the circuit a lower In is not a choice that can be applied.

To cite an analogy, if one 'regulation' said that "the maximum speed on this road is 60mph" and another regulation said "the maximum speed of an HGV is 50mph", then the latter clearly 'over-rides' the former in the case of an HGV.

Yes, but that is not a good analogy nor what it says.
In fact, one says "the maximum speed limit on this road is 60mph unless the vehicle is subject to a lower limit" and then another unnecessarily says "the maximum speed of an HGV is 50mph".

Maybe what has confused the discussion

I think you have caused my confusion by saying 3036s are treated differently than other devices.

is the fact that, in practice, "it does not matter". Although, at first sight, it might appear that 433.1.1(ii) allows an 'unacceptably' high In for any fuse (other than a 3036, for which that reg is 'over-ridden' by 202)

No, it doesn't because after (ii) you have to read (iii). This is the case for ALL devices; not just fuses and definitely not just 3036s.

since, for example, In=Iz would not be acceptable for anything with a fusing factor >1.45 [although it would satisfy 433.1.1(ii)], the mathematical reality is that if one complies with 433.1.1(iii) in terms of I2, that the In will then also be 'appropriate' [and less than CCC, as required by (ii)]

Well, of course. That's why (iii) is there - and all three have to be satisfied.

 

[JohnW2]

I am sure you have changed from what you wrote earlier.

Certainly not intentionally - my thoughts and views (and the facts and arithmetic) have not changed. Maybe I haven't expressed myself clearly enough - in which case I apologise.

I also think you are looking at it the wrong way round. I know it's only arithmatic here but in practice the outcome of this is not that it requires a lower In but a larger cable. After designing the circuit a lower In is not a choice that can be applied.

Strictly speaking, that does not have to be the case. 431.1.1(i) merely requires that In≥Ib. One might initially have been over-generous in considering an In which was markedly greater than Iz (maybe through 'habit'). If one then found that this would require a large cable than one would 'like' to use, one might then consider changing to a lower In (but still ≥Ib)

Yes, but that is not a good analogy nor what it says. In fact, one says "the maximum speed limit on this road is 60mph unless the vehicle is subject to a lower limit" ...

Is that not precisely what 433.1.1(ii) is (implicitly) saying ... "The maximum permissible In is Iz unless the 'fusing factor' of the OPD is such (i.e. >1.45) that the limit becomes lower".

This has got me thinking. Is it not 433.1.1(ii) [as well as 433.1.202] also 'unnecessary'? If one satisfies 433.1.1(iii) in relation to I2 [which, after all, is merely (In x F), F being the 'fusing factor'], then 433.1.1(ii) will surely also be satisfied. If one divides the I2 [which satisfies 433.1.1(iii)] by F, one will get the maximum permissible In. In the case of an MCB (F=1.45), that maximum In will be equal to Iz and for any device with F>1.45, it will be less than Iz - hence, in all cases, compliant with 433.1.1(ii) [if 433.1.1(iii) was satisfied].

Hence, unless my thinking has gone wrong, I therefore think that we could get rid of 433.1.1(ii) and 433.1.202 without changing anything. Indeed, if one got used to thinking in terms of the I2, rather than In, of OPDs, then design might get just a little bit simpler.

Kind Regards, John

 

[ban-all-sheds]

In a literal sense, I disagree with BAS's view that 431.1.202 "does not override/supersede/trump anything" (for a 3036). Just like 433.1.1(ii) it is written in terms of In - and it requires a lower In (for a 3036) than would be required to satisfy 433.1.1(ii) alone. To cite an analogy, if one 'regulation' said that "the maximum speed on this road is 60mph" and another regulation said "the maximum speed of an HGV is 50mph", then the latter clearly 'over-rides' the former in the case of an HGV.

If 431.1.202 were not there then absolutely nothing would be different regarding the In-I2-Iz relationships of cables and 3036s. You would still end up, by virtue of 433.1.1 (iii), needing In to be ≤ 0.725 Iz. So truly nothing is overridden, superseded or trumped. Please bear in mind that "required to satisfy 433.1.1(ii) alone" is a pointless consideration - 433.1.1 has (i), (ii) and (iii) linked by and - they are all required to be complied with. 431.1.202 does not produce a requirement which is any different from the one already introduced by 433.1.1 (iii).

Your analogy is flawed - the one that should be used if you want to imagine speed limits and vehicle class/weights would be a regulation which said "the maximum speed on this road is {a function which involves vehicle class and/or weight}" and which when the function is evaluated produces a limit of 50mph for HGVs. If another regulation said "the maximum speed of an HGV is 50mph" it would add nothing to the evaluation of the function, it would not override/supersede/trump anything.

It would merely be as superfluous as 431.1.202 is.

Maybe what has confused the discussion is the fact that, in practice, "it does not matter". Although, at first sight, it might appear that 433.1.1(ii) allows an 'unacceptably' high In for any fuse (other than a 3036, for which that reg is 'over-ridden' by 202), since, for example, In=Iz would not be acceptable for anything with a fusing factor >1.45 [although it would satisfy 433.1.1(ii)], the mathematical reality is that if one complies with 433.1.1(iii) in terms of I2, that the In will then also be 'appropriate' [and less than CCC, as required by (ii)]

"If"?

There is no "if". It is not optional.

433.1.1 The operating characteristics of a device protecting a conductor against overload shall satisfy the following conditions:
(i) ... AND
(ii) ... AND
(iii)

The "mathematical reality" which exists is that when 433.1.1(iii) is complied with an "appropriate" degree of ≤ in In ≤ Iz results.

433.1.1 does not allow an unacceptably high In for any fuse, and 431.1.202 is not needed in order to prevent an "unacceptably" high In vs Iz for 3036s.

 

[ban-all-sheds]

FYI: