Radial Circuit in Garage - Change to Ring?

[EFLImpudence]

Varies

Thanks.

I have read several comments lately about presumably small terminals that I never seemed to encounter, so I have been looking into the required size for different cable sizes.

There is a difference of less than three quarters of a millimetre in diameter between only accepting 3 @ 2.5mm² and 2 @ 6mm² T&E.

I think I did all the sums correctly.

 

[JohnW2]

... I have seen various 'unusual' circuit designs over the years and I'll absolutely and totally expect EICR % fails of this sort of circuit: ... to be into the high 90's. ... You know and I know it's fully compliant but I imagine some of the regular good posters on here may struggle with accepting it.

If you are right then, as EFLI has said, that is an indictment of those 90%+ of EICR inspectors.

It is surely ridiculous (and a situation which we should not accept) that something which (you, I and EFLI know) is fully compliant with BS7671 should be reported as "potentially dangerous - urgent remedial action required" (C2, aka 'fail') by an EICR inspector, isn't it?

It will invariably be described a a ring with one socket and 3 sockets on a spur, or a ring with forbidden links etc.

Assuming that you are talking of 2.5mm² cable, as you imply, a ring with one socket together with an unfused spur wired with what is effectively 5mm² cable supplying three (or 30) further sockets is perfectly compliant.

You know and I know it's fully compliant but I imagine some of the regular good posters on here may struggle with accepting it. Not least of which may be due to the difficulty of getting 4x 2.5mm² T&E's into a BS1363 acceessory or even the backbox.

That is a valid (practical) reservation, and they might also (for some reason) just have a personal uneasiness about such an arrangement - which is fair enough. However, if they claimed that it was 'non-compliant' they would probably be no better than the 90% of EICR inspectors which you believe exist.

Having said all that, as I've said before, I can think of very few reasons why anyone should even consider such a circuit (rather than 'the alternatives).the hypothetical 54/50A radial being only something I mentioned to explain a point..

Kind Regards, John

 

[crappy]

Don't most compressors include an unloader valve

I don't think this one does. It's a laboured start for sure. After the first compression (I assume) it spins freely but there is effort there. I will check again over the weekend.

Link

 

[Harry Bloomfield]

I don't think this one does. It's a laboured start for sure. After the first compression (I assume) it spins freely but there is effort there. I will check again over the weekend.

I guess you could buy an add on unloader valve maybe Thorite Pneumatics, to go on the air output. All it needs to do is close off the receiver and open the output to just vent, for a few seconds whilst the motor and compressor get up to speed via a delay timer.

 

[JohnW2]

... I have read several comments lately about presumably small terminals that I never seemed to encounter, so I have been looking into the required size for different cable sizes. There is a difference of less than three quarters of a millimetre in diameter between only accepting 3 @ 2.5mm² and 2 @ 6mm² T&E. ... I think I did all the sums correctly.

You may have done your calculations correctly, but I think your conclusions are extremely 'modest'.....

There is, in practice, a complication in that conductors get distorted (cease to be circular in cross-section) when the terminal screw is tightened. However, if one considers the situation before one tightens the screw, with all conductors remaining circular in cross section, then one could, in theory 'just' get SEVEN 2.5mm² conductors into a circular terminal hole that could accommodate 2 x 6 mm² conductors (without distortion). On that basis, getting four in really should not be too much of a problem ...

Kind Regards, John

 

[EFLImpudence]

You are forgetting that 6mm² T&E has seven strands (14 for 2); each of which is 1.045mm. in diameter.

Your seven 2.5mm² wires; diam. 1.784; would fit in a terminal of 3 x that - 5.352mm.

Admittedly, this is the minimum geometric size so slightly larger might be required for practical purposes, but a 5% larger diameter results in 10% larger c.s.a.

 

[EFLImpudence]

For 14 strands of diameter 1.045mm., the minimum is a circle of 4.523mm.

 

[SUNRAY]

Thanks.

I have read several comments lately about presumably small terminals that I never seemed to encounter, so I have been looking into the required size for different cable sizes.

There is a difference of less than three quarters of a millimetre in diameter between only accepting 3 @ 2.5mm² and 2 @ 6mm² T&E.

I think I did all the sums correctly.

That does not sound correct to me, I haven't done the calcs but experience of fitting those combinations... plus... says wrong.
Basically 2x 6mm² will usually take a 2.5mm² too.
Have you allowed for 6mm² being stranded?

EDIT: Apologies I didn't see the following posts before my reply.
EDIT 2: Edit 1 crossed in the post with #54.

 

[EFLImpudence]

Basically 2x 6mm² will usually take a 2.5mm² too.

That must mean the terminal is bigger than the minimum required for 2 x 6mm².

Have you allowed for 6mm² being stranded?

Yes, see above.

 

[SUNRAY]

That does not sound correct to me, I haven't done the calcs but experience of fitting those combinations... plus... says wrong.
Basically 2x 6mm² will usually take a 2.5mm² too.
Have you allowed for 6mm² being stranded?

EDIT: Apologies I didn't see the following posts before my reply.
EDIT 2: Edit 1 crossed in the post with #54.

And to ammend the statement, I may be thinking more about 4mm² than 6mm².

I'll try and have a little play tomorrow.

 

[SUNRAY]

As above, I was in no way advocating such a hypothetical circuit (even if it would probably be technically compliant with BS7671), but was merely using it to explain a point.

Kind Regards, John

Whether hypothetical or not it was certainly considered as a solution for this incorrectly switched ring:

To this parallel fed parallel fed radial:

But we settled on this parallel fed ring circuit (lollipop circuit):

 

[JohnW2]

You are forgetting that 6mm² T&E has seven strands (14 for 2); each of which is 1.045mm. in diameter.

Good point - I totally overlooked that!

Your seven 2.5mm² wires; diam. 1.784; would fit in a terminal of 3 x that - 5.352mm.

Yep, slightly less than the 5.53mm I was quoting for two (solid) 6mm² conductors.

Admittedly, this is the minimum geometric size so slightly larger might be required for practical purposes, but a 5% larger diameter results in 10% larger c.s.a.

It does, roughly (as I'm sure you know, actually 10.25%)..

For 14 strands of diameter 1.045mm., the minimum is a circle of 4.523mm.

It's obviously the case that, when correctly remembering that 6mm² conductors are stranded, the minimum terminal size will be less than the 5.52 mm I indicated for a solid 6mm² conductor [and apologies for incorrectly typing "mm²" for the diameters in the diagram I previously posted!].

However, even if your figure is correct (it may be, but see discussion below), if I've done things right this time -) ), I think that 4 x 2.5mm² (solid) conductors only require a terminal diameter of 4.30mm - so presumably should easily fit into what you state as the minimum size for the 14 strands of 2 x 6mm² conductors, as illustrated by:

However, I wonder how you came up with your 4.523 mm figure? Unlike the situation with, say, 3, 4, 7 or 13 strands, I don't think that there is any obvious 'fully-symmetrical' optimal arrangement for 14 strands and, if there is a general theoretical solution to such a question, I must have at least temporarily forgotten it However, in the first diagram below I have examined, graphically the case of 13 strands (fully symmetrical and hence, I presume, 'optimal') and it seems that your 4.523 mm diameter hole is probably not quite (but very nearly) big enough for that, let alone 14 strands.

In the second diagram below, I have looked at what seems to be the 'most symmetrical' arrangement of 14 strands I can think of, and, although I have so far only done this graphically, it wood look as if the minimum required hole size is probably about 4.75 mm, again just a little larger than your 4.523 mm figure.

I may well be going wrong again, but I'd be interested to know how to came to that figure and, in particular, what arrangement of 14 strands you were assuming.

Mind you, the bottom line of all this is that the amount of space to 'comfortably' take 2 x 6mm (stranded) and 4 x 2.5mm (solid) conductors is extremely similar. I have certainly put 4 x 2.5 mm conductors into a socket terminal in my time, and I suspect that, in practice, space for everything in a backbox is probably more often a difficulty than the terminal capacity.

Kind Regards, John

 

[JohnW2]

Whether hypothetical or not it was certainly considered as a solution for this incorrectly switched ring: .... To this parallel fed parallel fed radial: .... But we settled on this parallel fed ring circuit (lollipop circuit): ...

Fair enough, and that's certainly what I would have suggested (unlike some, I personally have no particular problem with 'lollipop' circuits - and, indeed, have some in my house). Quite part from the fact that it may represent the 'contentious in some people's eyes" circuit we have been discussing, the 'middle option' would have required a lot more work.

In any event, even if you had gone with 'the middle option', I suspect that you would not have gone as far as the hypothetical example I mentioned - since (assuming it was all 2.5mm² cable), I imagine that you would have left the OPD as 32A there, rather than 'upgrade' it to 50A, wouldn't you?

Kind Regards, John

 

[SUNRAY]

Fair enough, and that's certainly what I would have suggested (unlike some, I personally have no particular problem with 'lollipop' circuits - and, indeed, have some in my house). Quite part from the fact that it may represent the 'contentious in some people's eyes" circuit we have been discussing, the 'middle option.

In any event, even if you had gone with 'the middle option', I suspect that you would not have gone as far as the hypothetical example I mentioned - since (assuming it was all 2.5mm² cable), I imagine that you would have left the OPD as 32A there, rather than 'upgrade' it to 50A, wouldn't you?

Kind Regards, John

There was no thoughs at all about upgrading, only fixing the non conforming installation,

 

[JohnW2]

There was no thoughs at all about upgrading, only fixing the non conforming installation,

As I said, that's what I presumed - so I think that what I mentioned probably does remain 'hypothetical' (I certainly can't imagine anyone doing it!)

P.S. I've just noticed that I didn't finish the sentence at the end of the first paragraph in my previous post - I've now added the missing few words!

Kind Regards, John