Radial Circuit in Garage - Change to Ring?

[ericmark]

As to de-loader valves, yes there is some method used, three phase normally linked to star/delta starter, but single phase often simple time, converting a reciprocating compressor to inverter drive was not simple, as to vain compressors not so sure.

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.

What matters is cooling, so 2 x 2.5 mm² does not equal 1 x 5 mm² as it is the surface area around the cable that matters. Permissible to use 1.5 mm² mineral cable for a ring final, but not ali-tube as the ali-tube cables does not transmit the heat to the outer casing as well as mineral cable.

As to EICR inspectors, when the MOT was introduced we had a book telling us what was and was not permitted, there was a little leeway, but all singing from same song sheet.

But 230 volt is potentially dangerous, what a silly phrase, so to have a type AC RCD on a circuit where you could get DC could be seen as potentially dangerous. Not seen as yet anyone award a code C2 for wrong type of RCD, but if they did then hard to say wrong, however the electrical safety council seems to think like many, if it complied in 1950 and nothing has changed then it still complies.

OK very unlikely nothing has changed, but it means if an electrician recommends improvement i.e. he has not totally missed faults while doing his drive by, i.e. a list of code C3's, then again hard to say he is wrong.

The EICR is designed to tell the owner the condition of the installation, i.e. cables which have insulation crumbling etc. It was never designed as a home MOT. However the person commissioning the inspection is free to say to what extent they want the inspector to go, so the LABC may tell an inspector to do it as close to an electrical installation certificate as he can, showing all non compliances. Or a prospective buyer may decide the home buyer report is good enough.

Love to know more about Pembrokeshire County Council Trading Standards v Mark Cummins trading as M C Electrics as this case seems to be far reaching, as it was vendor of a Milford Haven property who commissioned the inspection, but the current owner Nia Evans who got local electrician John Morley who in turn said the electrics were unsatisfactory which advised contacting STROMA, but it was Matthew Williams, a Council electrician, who carried out an inspection of the electrics at the property for Pembrokeshire County Council Trading Standards. But the report fails to say what was found, and why a report for the vendor was taken up by Pembrokeshire County Council Trading Standards. I could see the conveyancing solicitors raising a court case, but not Pembrokeshire County Council Trading Standards?

This house I had an EIC which was passed off as being for whole house, but was for the flat under the house, and I see no reason why I should be able to claim from the electricians working on the flat for errors in the main house, had it been an EICR for flat same would have applied.

 

[EFLImpudence]

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

Actually to three decimal places 4.307; so 4.31.

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:

Yes.

However, I wonder how you came up with your 4.523 mm figure?

https://en.wikipedia.org/wiki/Circle_packing_in_a_circle

http://hydra.nat.uni-magdeburg.de/packing/cci/

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

It is not necessarily a symmetrical arrangement but 14 is:

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,

Yes, and 2 x 2.5mm² with the ends doubled over, which is why I am surprised that so many seem to say that (some) socket terminals will not take 3 x 4mm².

 

[EFLImpudence]

Here are the sizes in order of the common T&E cables used:

2 x 2.5 sq.mm. requires terminal diameter of:-3.568 (2 x 1.784)
2 x 4 sq.mm. requires terminal diameter of:---3.692 (4.328 x 0.853)
3 x 2.5 sq.mm. requires terminal diameter of:-3.845 (2.155 x 1.784)
4 x 2.5 sq.mm. requires terminal diameter of:-4.307 (2.414 x 1.784)
3 x 4 sq.mm. requires terminal diameter of:---4.480 (5.252 x 0.853)
2 x 6 sq.mm. requires terminal diameter of:---4.523 (4.328 x 1.045)
5 x 2.5 sq.mm. requires terminal diameter of:-4.819 (2.701 x 1.784)

 

[davelx]

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

Yes it does. What looks like a 90 deg. coupler where the line from the compressor is connected to the receiver is actually a non-return valve with a dump outlet. If you look the other side of it, there will be a thin tube from the dump outlet going into the pressure switch.

https://www.ebay.co.uk/itm/30425421...AajCvBVHEw%3D%3D|clp:2334524|tkp:BFBMwJrIudNf

There is a dump valve inside the pressure switch which is mechanically opened when the switch turns the motor off. This dumps the line pressure to atmosphere. Inside that non-return valve there is a rubber piston which forms a non-return valve allowing air from the compressor into the receiver. When the dump valve in the pressure switch opens, this stops the air from the receiver venting via the dump. Thus the pressure in the lie from the compressor is released to that the compressor is unloaded when the pressure switch turns it back on - at the same time closing the dump valve so that air can be pumped into the receiver.

I know this because the rubber piston in the non-return valve in my compressor (same type) jammed so that pressure in the line was not released After the initial fill, the overload trip operated immediately the pressure switch turned the compressor back on. I had to work out what the problem was, so I stripped the pressure switch and dump valve down to see how they worked. Simply replacing the rubber piston in the NR valve did the trick. You may have a similar problem.

 

[JohnW2]

.... I think that 4 x 2.5mm² (solid) conductors only require a terminal diameter of 4.30mm

Actually to three decimal places 4.307; so 4.31.

It's obviously a trivial matter of detail but, yes, I agree. There is no doubt that, for four circles of diameter D, the smallest circle into which they will fit simplifies to:

(1 + √2) x D

I was, for convenience, using 1.78 mm as the diameter of a 2.5mm² conductor, and that gives an answer (to 10dp) of 4.2973001141.... ,which I rounded to 4.30. However, if one takes the conductor more accurately as 1.7841241161.. then, as you say, the answer becomes 4.307,, (to 3dp), hence 4.31 to 2 dp.

https://en.wikipedia.org/wiki/Circle_packing_in_a_circle

Thanks. As I said, if there is a (mathematical) "general solution", I would probably have once known about it and must have forgotten. However, the more I think about it, the more I come to the view that such a (mathematical) "general solution" is not possible, since one cannot mathematically model, in a general sense, the space taken up by a number of circles in an 'unknown' geometrical arrangement.

That view seems to be confirmed by the Wikipedia article. Other than for the 'trivial' cases (for 1 to 7 circles), the article just gives the answers, which have (individually) been "proved to be optimal" or "conjectured to be optimal" by various people.

It is not necessarily a symmetrical arrangement but 14 is: ...

Indeed - but, as you will have seen, that is a 'solution' which has been "conjectured to be optimal by Goldberg (1971)" - so not even 'proven' to be optimal.

In any event, going back to the actual issue, I don't really know why I wrote ...

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!

... since I didn't actually 'overlook' it in my thinking. I suspect that, when I wrote that (in the middle of the night) I had been 'panicked' by your comment into accepting that I had made a mistake, without recalling the thinking that had been behind what I had done!

My actual thinking had been this. I suspect that what most people do (hence what there are thinking of, when they talk about the capacity of terminals) is to simply 'strip the conductor and then insert it into the terminal'. If they do that, then a 7-stranded 6mm conductor is actually appreciably 'worse' (larger) than a 'solid' 6mm² conductor - about 2.764 mm diameter with the solid core, but an 'effective diameter' of about 3.135 mm (3 x 1.045 mm) for the 7-stranded one.

To reduce the chance of arguments, I presented (admittedly, without adequate explanation!) figures assuming the solid conductor, and on that basis illustrated that you could get 7 x 2.5mm² (solid) conductors into a terminal that could accommodate 2 x 6mm² (solid-core) ones. However, if I had been less conservative, and worked with the 'as stripped' effective diameter of a 7-stranded 6mm² conductor, I would quite probably have found that a terminal which could take two of them 'as stripped' could accommodate appreciably more than 7 x 2.5mm² ones!

I do think the 'as stripped' assumption is the most reasonable one. To achieve the theoretical 'circles within a circle' figures you are talking about would require that one untwisted the strands and re-arranged them, straight, so that they adopted the required pattern - in the case we are discussing, re-arranging them so that they occupied the semi-circle represented by half of the terminal aperture. When a manufacturer says that a terminal can accommodate 2 x 6mm² conductors, I find it hard to believe that they mean that is only the case if one undertakes that fairly tedious process!

Yes, and 2 x 2.5mm² with the ends doubled over, which is why I am surprised that so many seem to say that (some) socket terminals will not take 3 x 4mm².

I agree - particularly in view of my comments above about the effective 'as stripped' diameters of stranded conductors'.

Kind Regards, John

 

[EFLImpudence]

However, the more I think about it, the more I come to the view that such a (mathematical) "general solution" is not possible, since one cannot mathematically model, in a general sense, the space taken up by a number of circles in an 'unknown' geometrical arrangement.

I don't see why not. It can't be beyond the wit of man.
Presumably you don't think 'they' make a socket and then see what will fit in the terminals.

The diameter of one 6mm² T&E, as it comes, is 3.135mm. so, to take two 'they' are not just going to make the terminal 6.270mm. diameter.

The diameter of my minimum 2 x 6mm² terminal being 4.523mm. has a c.s.a. of 16.067mm².
Perhaps someone has worked out that the diameter should be 5% more for ease of insertion; this would result in a c.s.a. of 17.714mm².

To reduce the chance of arguments, I presented (admittedly, without adequate explanation!) figures assuming the solid conductor, and on that basis illustrated that you could get 7 x 2.5mm² (solid) conductors into a terminal that could accommodate 2 x 6mm² (solid-core) ones. However, if I had been less conservative, and worked with the 'as stripped' effective diameter of a 7-stranded 6mm² conductor, I would quite probably have found that a terminal which could take two of them 'as stripped' could accommodate appreciably more than 7 x 2.5mm² ones!

I haven't work it out but if correct then - exactly.

When a manufacturer says that a terminal can accommodate 2 x 6mm² conductors, I find it hard to believe that they mean that is only the case if one undertakes that fairly tedious process!

O.k. but I don't think it that tedius.

MK state:

However, that clearly must allow 4 x 2.5mm².

I was reading elsewhere that when the capacity is stated as 3 x 2.5mm², it was thought that one must not use the socket for more than than that as if it were stated for some current related reason.


Anyway, I did not raise the subject to determine the very minimum size that was required but because I keep reading that some sockets won't take 3 x 4mm² - which I have never come across.

I initially asked if someone could measure the diameter of a socket terminal as I don't have any UK sockets here.
If you could do that with an MK one which takes 2 x 6mm², it would be interesting to find out how much bigger than my minimum it is.
I would think it might be 5mm - 19.635mm² c.s.a.

 

[JohnW2]

I don't see why not. It can't be beyond the wit of man.

I think it is. One cannot have a single mathematical process which models a situation (N little circles arranged in some way) without knowing what that arrangement is.

If there were such a single mathematical process possible, it would give a definite answer for any value on N. However, as you can see from the evidence you have prevented, if one ignores the 'trivial' cases (N=1 to N=7), of the 13 other cases they consider (N=8 to N=20), the result has only be 'proven' in 7 cases, the figures quoted for the other 6 being 'conjectured'.

Presumably you don't think 'they' make a socket and then see what will fit in the terminals.

Of course not. However, as I've said, I might well expect them to make the terminal large enough to accommodate the (real-world) conductors they wanted to claim, without the need to 'distort' the conductors before the claimed number of conductors could be got into the terminal..

The diameter of one 6mm² T&E, as it comes, is 3.135mm. so, to take two 'they' are not just going to make the terminal 6.270mm. diameter.

Why not? As above, they would have to if they wanted their claimed terminal capacity to be correct without the need to 'distort' the cables before insertion.

O.k. but I don't think it that tedius.

As above, I don't think that they should really expect people to modify the cross-sectional shape of the conductors for their claimed capacities to be achieved but, if they did, it would, to my mind, be pretty tedious to do so accurately enough for one to get the claimed number of conductors into a terminal which was anywhere near as small as the 'theoretical minimum'-sized terminals you are considering.

I was reading elsewhere that when the capacity is stated as 3 x 2.5mm², it was thought that one must not use the socket for more than than that as if it were stated for some current related reason.

I can well believe that you 'read that somewhere', but I think I would struggle to make any electrical sense of such a suggestion!

Anyway, I did not raise the subject to determine the very minimum size that was required but because I keep reading that some sockets won't take 3 x 4mm² - which I have never come across.

Nor have I - although I admit that I have probably not often had to do it. Similarly, I have never personally had any problem getting 4 x 2.5mm² conductors into a socket terminal - although, again, it's not often that I've had to do it. What can be quite difficult (because of the thickness of the insulation) is getting 4 x 2.5mm² conductors in without leaving some 'exposed copper'.

I initially asked if someone could measure the diameter of a socket terminal as I don't have any UK sockets here. If you could do that with an MK one which takes 2 x 6mm², it would be interesting to find out how much bigger than my minimum it is. I would think it might be 5mm - 19.635mm² c.s.a.

I don't have any not-in-service MK ones to hand, but I have a few other makes. I've determined a lower bound for the size of the terminal by determining the largest drill shank that I can get in, and then measuring it with a micrometer (as you can see, I ended up using 4.5, 5.0 and 5.5 mm drills):

Volex (double socket): ≥4.94 mm
Contactum (double socket: ≥4.44 mm
Contactum (single Socket): ≥5.44 mm
Philix (double socket): ≥4.94 mm

... make of that what you wish! As you can see, only the Contacted double socket failed to achieve at least your speculated ~5 mm and, for whatever reason, the largest of all (about 5.5 mm) is the Contactum single socket.

Kind Regards, John

 

[EFLImpudence]

Thanks for measurements.

I note Volex state their capacity as only 3 x 2.5mm² & 2 x 4mm² and

this from Contactum makes no sense:

and if people think more conductors are not allowed even if they fit...


Obviously the sizes measured show there is no standard or even logic.

 

[SUNRAY]

Thanks for measurements.

I note Volex state their capacity as only 3 x 2.5mm² & 2 x 4mm² and

this from Contactum makes no sense:
View attachment 259054

and if people think more conductors are not allowed even if they fit...


Obviously the sizes measured show there is no standard or even logic.

One of the things I'll comment on is, we have shown the various dimensions but positioning 4 or 5 conductors and ensuring they are all clamped securely and then repeating for 2 more sets is a very different thing to whether they fit in t'hole. Another aspect is whether the multiple sets of insulation will fit in the recess.

 

[EFLImpudence]

Surely the more conductors there are in a terminal - less empty space - increases the likelihood that they will clamped securely.

 

[SUNRAY]

Surely the more conductors there are in a terminal - less empty space - increases the likelihood that they will clamped securely.

intuitively yes, however looking back at

View attachment 258953

we see gaps and if each of those circles are a solid insulated wire it's not hard to imagine a wire may move after the screw it tightened or alternatively wedged by the insulation rather than its copper.
I do of course know the soft copper will distort to accomodate the space.

 

[EFLImpudence]

intuitively yes,

Ok.

however looking back at we see gaps and if each of those circles are a solid insulated wire it's not hard to imagine a wire may move after the screw it tightened or alternatively wedged by the insulation rather than its copper.
I do of course know the soft copper will distort to accomodate the space.

Don't forget that they are two seven-strand wires.

I am not sure where you would need to connect fourteen separate insulated wires to a socket.


Edit - seven-strand.

 

[SUNRAY]

however looking back at
we see gaps and if each of those circles are a solid insulated wire it's not hard to imagine a wire may move after the screw it tightened or alternatively wedged by the insulation rather than its copper.
I do of course know the soft copper will distort to accomodate the space.

Don't forget that they are two seven-strand wires.

I am not sure where you would need to connect fourteen separate insulated wires to a socket.


Edit - seven-strand.

Just used it as an example why a wire may not be secure.

 

[JohnW2]

Thanks for measurements. I note Volex state their capacity as only 3 x 2.5mm² & 2 x 4mm²

Indeed.

.. and this from Contactum makes no sense: ...

Indeed not. If it can accommodate 2 x 6mm² conductors if it can also accommodate a lot more than three 2.5mm² ones, and more than two 4mm² ones!

and if people think more conductors are not allowed even if they fit...

Quite so.

Looking at my measurements, in terms of the theoretical calculations (and ignoring the potential practical complication of the insulation), any of the sockets I measured could ('easily') accommodate 4 x 2.5mm², all but one of them (the Contactum double socket) could accommodate 5 x 2.5mm² and the Contactum single socket could accommodate 7 x 2.5mm².

Obviously the sizes measured show there is no standard or even logic.

So it would seem The two different Contactum ones (the smallest and largest terminals I measured) is particularly odd!

Kind Regards, John

 

[JohnW2]

One of the things I'll comment on is, we have shown the various dimensions but positioning 4 or 5 conductors and ensuring they are all clamped securely and then repeating for 2 more sets is a very different thing to whether they fit in t'hole.

As EFLI has said/implied, I think there is probably more uncertainly as to whether conductor(s) are 'clamped securely' if there are fewer 'small' conductors in a 'large' hole. That's why people often 'double over' single conductors, isn't it?

Another aspect is whether the multiple sets of insulation will fit in the recess.

That's certainly a potential issue with large numbers of conductors. As I wrote ...

... What can be quite difficult (because of the thickness of the insulation) is getting 4 x 2.5mm² conductors in without leaving some 'exposed copper'.

Kind Regards, John