Horizontal safe zone with 'dry lining' back boxes

[JohnW2]

Locked up for in years, it was a bad joke

Ah, I see - I suppose I should have thought of that

To be slightly more serious, the problem with these potentially 'creeping' applications of common sense is that one has to decide how much further away from the accessory my blue mark would have to move before your `locked up for 10 years' reduced to 'not locked up at all'!

 

[ebee]

Yes, but you were also seeming concerned that if an 'oversized faceplate' (or maybe a standard size one with a surrounding 'finger plate') were allowed to define a zone, then there would be a risk that it would subsequently would be replaced by a standard-size accessory, leaving cables outside of the zone. That's what I have just illustrated - take away the 'converter pattress' and replace with a single socket attached to the single box, and cables which you accept were previously 'within a zone' no longer would be.

Perhaps you could further clarify your opinion, particularly in the case I have just discussed?

Hah, the converter box, sorry I had not noticed that.
My fault.
Nope , I would not say the faceplate in this respect, I would say the single box could/should/might at anytime be used for a single socket/switch etc so that would define the zone even if a socket converter to 2 or three units is used.
In essence I Iook upon those as a sort of anomaly (usually used as an after thought and not the original plan) and it holds with my often stated "why have a single socket when a twin could be fitted - unless converting storage heater switches to sockets).

 

[ebee]

As an aside, why have the rule regarding ring finals that to have no more spurs than points on the ring?
Not sure I`m convinced with reasons I`ve heard so far and yes I am aware that some have an aversion to the Ring Final Circuit in the first place but I am of the other faith.

 

[JohnW2]

Hah, the converter box, sorry I had not noticed that. ... My fault.

I thought you may have missed that!

Nope , I would not say the faceplate in this respect, I would say the single box could/should/might at anytime be used for a single socket/switch etc so that would define the zone even if a socket converter to 2 or three units is used.

That's what I expected you to say - so that rather puts paid to what was suggested when this little branch of the discussion started (namely that one could 'take advantage' of the fact that the faceplate is usually a bit bigger than the box, doesn't it?

 

[JohnW2]

As an aside, why have the rule regarding ring finals that to have no more spurs than points on the ring? ... Not sure I`m convinced with reasons I`ve heard so far ...

[I presume you mean 'sockets', rather than 'points'?]
That's not actually a 'rule' (regulation in BS 7671), is it, but rather an invention of the OSG.

I can't say that I could think of any sensible justification for such a rule, or even 'guidance'. As bernard might jump in to illustrate, it's by no means unknown to have a ring final which has no sockets on it - just a line of JBs with all of the sockets on spurs from those JBs -and I see nothing electrically wrong with that, do you?

There's an even more intriguing bit in OSG, namely ...

As a rule of thumb for rings, unfused spur lengths should not exceed 1/ 8 the cable length from the spur to the furthest point of the ring.

Do you think you could find a way of 'justifying'that one?

 

[ebee]

[I presume you mean 'sockets', rather than 'points'?]

no I meant points, single, twin

 

[ebee]

That's what I expected you to say - so that rather puts paid to what was suggested when this little branch of the discussion started (namely that one could 'take advantage' of the fact that the faceplate is usually a bit bigger than the box, doesn't it?

No not the way I see it, take the backbox and add a simple typical faceplate that fits and that is the zone, I would find it more than difficult to fault a zone using all of the area a bog standard faceplate should cover.

 

[JohnW2]

no I meant points, single, twin

What do you mean by single and twin 'points'?

The OSG does say (for whatever reason {nothing to do with BS 7671!} !!) that the number of unfused spurs should not exceed the number of 'socket-outlets' (does that perhaps mean that a double socket counts as two?) and hard-wired items of equipment, but I recall nothing about 'the number of points'.

 

[JohnW2]

No not the way I see it, take the backbox and add a simple typical faceplate that fits and that is the zone,

Fair enough.

I would find it more than difficult to fault a zone using all of the area a bog standard faceplate should cover.

I think that most of us would (find it more than difficult to fault such a situation) - hence my original comment about the fact that it seemed to be being suggested that it was 'the box' (not the visible accessory) that dictated the width/height of gthe zones (which seemed rather odd to me).

 

[pete01]

I class a twin as one point

 

[JohnW2]

I class a twin as one point

As I said, even the OSG does not talk about 'points' - it says that one should not have more unfused spurs than the number of 'socket-outlets' - but it is not totally clear to me (certainly not defined by them) as to whether a double socket represents one or two 'socket outlets'.

Mind you, if you (or anyone else) believes that a double socket is "2 socket outlets", then that ought to put to bed the ages-old argument as to the 'total current rating' of an MK double socket. They say "13A per socket outlet" and 2 times 13A is usually 26A (not 20A, as many claim, seemingly based ion the temp-rise test in BS1362)

 

[ebee]

a "point" is a point of utilisation, be it a single socket or a twin socket it is still one point.
Two single sockets is two points, even if those two single sockets are in a dual accessory box (aka a bar box) - well you can not distinguish two single sockets being 100m apart or 2 mm apart.

If MK want to claim that a twin socket is 2 x 13A in their twin socket then fine but a generic twin socket is only good for 13A total, however a type test of 14A one side plus 6A the other side is required.

 

[JohnW2]

a "point" is a point of utilisation, be it a single socket or a twin socket it is still one point.

Where did you get that 'definition' from? Were it the case, why would BS 7671 write, in at least a couple opf places "point OR accessory" ? BS 7671 actually does have a definition ...

Point (in wiring). A termination of the fixed wiring intended for the connection of current-using equipment.

If MK want to claim that a twin socket is 2 x 13A in their twin socket then fine ....

As I said, their "Technical Datasheet" says "13A per socket-outlet" but, as I've reported many times before, when I spoke to their Technical Department, they didn't know what that meant (i.e. whether a double socket was one or two "socket outlets") because, I was told, "the Technical Datasheets are written by the Marketing Dept."

.... but a generic twin socket is only good for 13A total

Where did you get that from?

, however a type test of 14A one side plus 6A the other side is required.

BS1362 specifies many tests but, yes, those are the currents used for the Temperature Rise Test, which is the one that people always cite if they want to argue that double sockets are 'rated' at 20A. They don't seem to understand that BS 1362 merely indicates a minimum requirement, and that there is absolutely nothing stopping someone manufacturing a BS 1362-compliant socket with a 'rating' of 26A if they so wish.

 

[ebee]

BS1362 specifies many tests but, yes, those are the currents used for the Temperature Rise Test, which is the one that people always cite if they want to argue that double sockets are 'rated' at 20A. They don't seem to understand that BS 1362 merely indicates a minimum requirement, and that there is absolutely nothing stopping someone manufacturing a BS 1362-compliant socket with a 'rating' of 26A if they so wish.

Yes I totally agree with you John.

"Point (in wiring). A termination of the fixed wiring intended for the connection of current-using equipment."
I see no conflict there I`m afraid - a twin socket has three terminals basic 9OK it might have an additional E terminal in some but not in others.
The way I see it a twin socket in a twin box yet two single sockets in a dual box (aka Bar Box) one is one point with a 13A total as per BS but the other is virtually the same in practical usage yet is two points and is 2 x 13A total as per BS.
If the particular manufacture at least complies with the ratings then I am sure that the proprietary manufacturers exceed them, often y a great amount and I would have faith in two x 13A simultaneous loads not being an actual problem.
the 13A rating is stamped on the back of the sockets for all to see, if we saw such a label etc on a cooker or hob etc we would understand that it is the full maximum loading of the complete unit and not just one ring of the hob or one oven or grill.
If I saw an electric shower of, for example, 10KW rating with 2 or 3 elements on board the unit I would not be if it had elements of 5KW and 3KW and 2KW accordingly (I am not suggesting the 5,3,2 ratings are in anyway typical by the way).
I don't see a conflict there.

I was told, "the Technical Datasheets are written by the Marketing Dept."

That would not surprise me much

 

[JohnW2]

"Point (in wiring). A termination of the fixed wiring intended for the connection of current-using equipment."
I see no conflict there I`m afraid - a twin socket has three terminals basic

This is all a bit trivial, but .... yes, it has at least three terminals, but it is not intended that any current-using equipment be connected to those terminals. More to the point, as I said, if BS 7671 agreed with you that a socket is 'a point', why would they write "...point OR accessory..."?

the 13A rating is stamped on the back of the sockets for all to see ....

I have seen that occasionally on double sockets, but I think it unusual (i.e. there is usually no 'current marking') - but I agree with you that, if present, such a marking would presumably mean "13A total". However, if that were all that the socket could cope with, it obviously would not be able to pass the BS 1363 temp rise test.

In the absence of a 13A marking, I can understand why some people believe that the total 'rating' of a double socket is 20A (rather than 26A), but I don't really understand why they would think it was 13A - since, in order to be BS1363-compliant, it would have to be able to carry at least 20A total for at least 4 hours without 'overheating'.