30A terminal blocks on 32A circuut

[JohnW2]

This is the only place in your complete word salad that you even attempt to respond logically.

That's certainly not true. Everything I wrote was "an attempt top respond logically", even if your view is that my attempt failed!

Once again you are saying that overloading the cable is acceptable, but not overloading the connector. How can you justify this?

I wrote no such thing. I did not say that the overloading of some of the cable was 'acceptable' but, rather, that it was an inevitable theoretical possibility with many/most BS7671-compliant ring finals. As for "....but not overloading the connector", I surely made it explicitly clear enough for even you to understand that my view is that no (appropriate) connector will get 'overloaded', no matter how low it's 'current rating', didn't I?

A corollary of your position is that, if you had to replace a section of the ring cable, it would have to be with 4mm² cable.

Nonsense. We are talking about a BS7671-compliant ring final, which is allowed to use a cable with a CCC of only 20A, even though that means that (with many/most implementations of such a ring final) there is inevitably a theoretical risk of more than 20A flowing in some of the cable, due to the pattern of usage.

 

[Harry Bloomfield]

Once again you are saying that overloading the cable is acceptable, but not overloading the connector. How can you justify this?

As I suggested, the current rating of a connector, is only a guide to suitability for the sizes of cables which should fit in it - it is not a maximum current rating. If underrated, it will not get hot, melt, or anything else, unless the original termination was inadequate. The priority in choosing a connector, is one of ensuring a snug, low resistance connection between two or more wires, rather than a current rating.

Overloading of one leg the cable of a ring, is only possible if the load is both extreme, and very close to one end, and for a long period - all, occurring at the same time, highly unlikely.

 

[BS3036]

even if your view is that my attempt failed!

It's like arguing with Karoline Leavitt. You use lots of convincing words but they're all slightly off-topic. I'm done.

 

[pete01]

 

[plugwash]

In the video he essentially states two things. One of which he backs up with a reference and one of which he doesn't.

He states that according BS7671 the cable for a ring should be rated at at-least 20A and gives a reference to back it up.

He then goes on to state that the same rule should be applied to rating junction boxes but does not give any citation for this statement. I personally think that in the absence of an explicit rule saying otherwise, is a reasonable and defensible position, but I would not consider efixx to have a "position of authority".

 

[JohnW2]

You use lots of convincing words but they're all slightly off-topic. I'm done.

Fair enough, and I'm pleased to hear that you find my words convincing.

However, it is you who started all this by seemingly implying that the minimum permissible CCC of a cable in a particular situation determines the required 'current rating' of a connector in that cable. You used that assumption to imply that a 20A connector was adequate for a ring final cable (protected by a 32A OPD) only because BS7671 requires a minimum cable CCC of 20A, despite the fact that very many ring finals are wired with Method C 2.5mm² T+T, with a CCC of 27A

 

[JohnW2]

In the video he essentially states two things. One of which he backs up with a reference and one of which he doesn't. ... He states that according BS7671 the cable for a ring should be rated at at-least 20A and gives a reference to back it up.

Indeed - and, as we all know, that is what BS7671 says.

He then goes on to state that the same rule should be applied to rating junction boxes but does not give any citation for this statement. I personally think that in the absence of an explicit rule saying otherwise, is a reasonable and defensible position, but I would not consider efixx to have a "position of authority".

It's not really 'the same rule'. For a start, as I've just written, despite the 'minimum CCC' specified by BS7671, very many ring finals are wired with cable which, with the installation method used, has a CCC of 27A. If he actually believes that the 'current ratings' of screwed terminals need to be taken seriously, it would surely not be very logical for him to suggest that (because of what BS7671 says about the 'minimum CCC') it would be acceptable to use a '20A-rated' connector on a cable which could 'legitimately' be carrying 27A, would it?

All of this discussion is obviously specific to connectors which have screwed terminals, with the vast majority of the 'connection' being between the two conductors themselves. Connectors with 'sprung' terminals (e.g. Wagos) are obviously a totally different kettle of fish, since there is no conductor-to-conductor contact, hence all of the current in the conductors does have to travel through internal parts of the connector - so that one then presumably has to take the 'rated current' of the connector much more seriously?

 

[plugwash]

it would be acceptable to use a '20A-rated' connector on a cable which could 'legitimately' be carrying 27A, would it?

I don't see how installing a ring circuit with a '20A-rated' connector is fundamentally different from installing a ring circuit where part of the cable is installed with a more restrictive installion method than the rest such that the CCC of that particular section is only 20A.

 

[JohnW2]

I don't see how installing a ring circuit with a '20A-rated' connector is fundamentally different from installing a ring circuit where part of the cable is installed with a more restrictive installion method than the rest such that the CCC of that particular section is only 20A.

I suppose those two situations are essentially the same, in that in both cases there is a part of the circuit (a connector or a bit of cable) 'rated at' only 20A, so I suppose BS3036's initial comment would have been fair enough IF he had been talking only of ring finals in which at least some of the cable had a CCC of only 20A.

However, he didn't say that, and he seemed to be missing the point that BS7671's "20A" is the minimum CCC acceptable for a ring final.

There is obviously nothing in BS7671 which forbids a ring final from being wired with cable which has a higher CCC than that minimum and, as I've said, it's very common to have ring finals in which all (or most) of the ring cable, as installed, has a CCC of 27A. In that situation, there will usually be parts of the cable which could legitimately, acceptably and compliantly carry 27A for an indefinite period - so it would seem rather strange for anyone who believed that we need to take notice of the 'current rating' of (screwed) terminals forming joints in that part of the cable (i.e. in a "JB") to say that it would be acceptable for the JB to be 'rated' for only 20A, wouldn't it?

 

[plugwash]

There is obviously nothing in BS7671 which forbids a ring final from being wired with cable which has a higher CCC than that minimum and, as I've said, it's very common to have ring finals in which all (or most) of the ring cable, as installed, has a CCC of 27A. In that situation, there will usually be parts of the cable which could legitimately, acceptably and compliantly carry 27A for an indefinite period

I guess ultimately this brings us to the other requirement, that sustained overloading should be unlikely.

Would/should you as an installer do more to convince yourself that sustained overloading was unlikely if you were installing a ring with an installation method that resulted in a 20A current rating than if you were installing a ring using an installation method that resulted in a 27A current rating?

 

[JohnW2]

I guess ultimately this brings us to the other requirement, that sustained overloading should be unlikely.

Indeed it does.

Would/should you as an installer do more to convince yourself that sustained overloading was unlikely if you were installing a ring with an installation method that resulted in a 20A current rating than if you were installing a ring using an installation method that resulted in a 27A current rating?

Interesting question.

The designer of any sockets circuit obviously can do nothing (other than limit the circuit to one socket!) to guarantee that a user cannot plug in loads totalling more than the 'design current' of the circuit (In of OPD).

However, for total loads up to, and including, that design current (usually 32A for a ring final), the designer can make it unlikley (or, ultimately, impossible) for the current in any part of the wiring of the ring to exceed the CCC of the cable - simply by reducing the number (or eliminating) any sockets within X% of one end of the ring [if one eliminates sockets within X% of an end of the ring, overloading of any of the cable becomes impossible for total loads up to the 'design current'].

The value of that X% depends upon the CCC of the cable - so that is the answer to your question as to 'what the designer can do differently' (for cable with CCC of 20A vs 27A).

 

[EFLImpudence]

You are all forgetting that while the ring circuit regulation separately states that the conductors (except MICC) must have a minimum CCC of 20A, it actually prohibits using conductors with a CCC of les than 27A.

What relevance such nonsense has to any connector used is anyone's guess.

 

[JohnW2]

You are all forgetting that while the ring circuit regulation separately states that the conductors (except MICC) must have a minimum CCC of 20A

Not quite right. The minimum CCC is also 20A for MICC - the difference is that MICC need only have a CSA of 1.5mm² (provided that, as installed, it has a CCC of at least 20A) whereas for other cable types the minimum CSA is 2.5mm.

, it actually prohibits using conductors with a CCC of les than 27A.

Where does that (that which you think we are 'all forgetting') come from??

What relevance such nonsense has to any connector used is anyone's guess.

As I've been saying, absolutely no relevance that I can see!