Removing a socket from a ring main

[stillp]

Well spotted John.
However, although those words are in the Scope, the requirements of the standard seem to apply to connectors intended for use in applications other than telecoms or electronics. Would telecom applications need 3.6mm diameter?

 

[JohnW2]

Well spotted John.
However, although those words are in the Scope, the requirements of the standard seem to apply to connectors intended for use in applications other than telecoms or electronics. Would telecom applications need 3.6mm diameter?

At first sight, one probably wouldn't have thought so! However, having said that, in the pre-optical days, I imagine that long-distance telecoms cables (e.g. submarine), and possibly other comms network applications, will have had conductor CSAs at least as great as that (about 10mm²), quite possibly far larger. Indeed, although I realise that one would not use crimping for such cable, I see that the diameters of inner cores of large low-loss coaxial cables (for telecoms) go up to way over 10mm (i.e. CSAs over 80mm²).

I have to say that the view expressed by EFLI (that solid conductors should not be crimped) corresponds with what I was taught in my youth. As you will be aware, the issue has often been discussed here, and people often wheel out a NASA document which appears to forbid the crimping of solid conductors.

Kind Regards, John

 

[stillp]

In my defence, the new edition of the standard popped into my inbox just as I was reading the thread, and it seemed so appropriate that I didn't read it first...
It goes on to state that "Stranded conductors s hall b e used, solid round conductors o f 0,25 mm to 3 ,6 mm diameter
may be used provided their suitability has been proven."
I believe the NASA document you mention is quite specific about where/which solid conductors shall not be used.

 

[JohnW2]

It goes on to state that "Stranded conductors s hall b e used, solid round conductors o f 0,25 mm to 3 ,6 mm diameter may be used provided their suitability has been proven."

... which obviously leaves some answered questions!

I believe the NASA document you mention is quite specific about where/which solid conductors shall not be used.

Indeed so. The scope of the NASA Standard which I think is the one which usually gets cited is "...the manufacture of space flight hardware or mission critical ground support equipment....". It can be found here , and you are undoubtedly much better/quicker at reading these things than I am, but I think the part in question is 4.3.4 which says:

4.3.4 Crimping. Stranded wire shall be used for crimping (Requirement). Crimping of solid wire is prohibited. Crimping of solder tinned wire is prohibited.

Although this obviously refers to highly specialised and very critical applications, I presume that the view of those who cite this Standard is that if NASA see a problem with crimping solid conductors in their mission-critical aerospace applications, why do such joints not also represent a problem in a domestic electrical installation. Before you mention vibration etc. as making a difference, as you can see above, NASA's standard also applies to critical 'ground support equipment'.

Kind Regards, John

 

[bernardgreen]

if NASA see a problem with crimping solid conductors in their mission-critical aerospace applications, why do such joints not also represent a problem in a domestic electrical installation

Not much hope of getting an electrician or the fire brigade out to attend when in space. Failed joints are not an option in space.

 

[JohnW2]

I would argue that given the reason why accessories create safe zones for concealed cables to run in, if you obscure an accessory behind something permanently fixed, like a stove, you no longer have a safe zone. Remove the cables from the wall.

There is no doubt that removal of the cables is the most desirable course. However, as regards what you say, we have not been told that the accessory will be 'obscured', merely that it will not be 'accessible' for use - which may well not amount to 'obscured'.

Kind Regards, John

 

[JohnW2]

Not much hope of getting an electrician or the fire brigade out to attend when in space. Failed joints are not an option in space.

You perhaps should have also quoted my next sentence, which included:

NASA's standard also applies to critical 'ground support equipment'.

... which is presumably located somewhere accesible to electricians and fire brigades.

In the final analysis, if crimped joints of solid conductors are not deemed to be reliable, then they are not deemed to be reliable - regardless of the context. Whilst the financial implications may be different, the human ones probably aren't - unless you believe that loss of a life in a spacecraft due to failure of ground support equipment is in some way worse than loss of a life in a house fire.

Kind Regards, John

 

[stillp]

Thanks John. That wasn't the document I was thinking of; I've used a NASA document in the distant past that was very much more specific about where crimping solid cores was forbidden. In the one you linked it is certainly a general prohibition. I suspect that a clue to their reasoning is in 12.3.4 e), which states "The crimp tool setting which produces the maximum number of fray breaks and breaks outside the contact shall be used for assembly". A fray break, where the strands break at different locations, is obviously not possible with a solid core.
The document doesn't seem very logical though. I was surprised to see that they allow soldered lap splices, whereas we were always taught that soldered joints should be capable of remaining together before they are soldered, so that no mechanical stress is carried by the solder. There are also other techniques that would not be accepted in, say, the automotive industry.

 

[stillp]

In the final analysis, if crimped joints of solid conductors are not deemed to be reliable, then they are not deemed to be reliable - regardless of the context.

I supect, having glanced through the document, that the issue is not so much reliability as 'inspectability'.

 

[JohnW2]

Thanks John. That wasn't the document I was thinking of; I've used a NASA document in the distant past that was very much more specific about where crimping solid cores was forbidden. In the one you linked it is certainly a general prohibition. I suspect that a clue to their reasoning is in 12.3.4 e), which states "The crimp tool setting which produces the maximum number of fray breaks and breaks outside the contact shall be used for assembly". A fray break, where the strands break at different locations, is obviously not possible with a solid core.

Is there a typo in there somewhere? They surely aren't insisting on a tool setting which maximises the number of 'fray breaks', are they? !

The document doesn't seem very logical though. I was surprised to see that they allow soldered lap splices, whereas we were always taught that soldered joints should be capable of remaining together before they are soldered, so that no mechanical stress is carried by the solder.

That's certainly one of the first things I was taught about (electrical/electronic) soldering, some 50 years ago - that solder should merely be used to prevent a mechanically (and electrically) satisfactory joint 'coming apart', not as the primary means of achieving a mechanical and electrical joint.

Kind Regards, John

 

[stillp]

Thanks John. That wasn't the document I was thinking of; I've used a NASA document in the distant past that was very much more specific about where crimping solid cores was forbidden. In the one you linked it is certainly a general prohibition. I suspect that a clue to their reasoning is in 12.3.4 e), which states "The crimp tool setting which produces the maximum number of fray breaks and breaks outside the contact shall be used for assembly". A fray break, where the strands break at different locations, is obviously not possible with a solid core.

Is there a typo in there somewhere? They surely aren't insisting on a tool setting which maximises the number of 'fray breaks', are they? !

No, but the context is missing. What they mean is the maximum number as a proportion of total breaks.

 

[JohnW2]

I supect, having glanced through the document, that the issue is not so much reliability as 'inspectability'.

You may be right, since you've obviously looked at more of the document than I have. However, as Bernard has sort-of pointed out, whilst that may be relevent to ground equipment, it's probably fairly moot in the case of a spacecraft!

In any event, if reliability were in no way in doubt, why would 'inspectability' be an issue? As is the case with current BS7671, if (rightly or not) they deemed a type of joint to be 'totally reliable', they would presumably allow it to be 'uninspectable', wouldn't they? ... and, furthermore, why should a crimped joint of a solid conductor be any less inspectable than a crimped joint of a stranded one?

Kind Regards, John

 

[JohnW2]

Is there a typo in there somewhere? They surely aren't insisting on a tool setting which maximises the number of 'fray breaks', are they? !

No, but the context is missing. What they mean is the maximum number as a proportion of total breaks.

Fair enough - but even that still sounds very odd to me. I suspect I'd have to read the whole section to understand!

Kind Regards, John

 

[stillp]

The NASA document is a mixture of requirements for workmanship and instructions for inspection. I suspect its main use is for inspection of incoming wiring harnesses. I wasn't referring only to the crimping requirements, but I was thinking that if they specified crimp connectors with inbuilt insulation grip, then the integrity of the electrical connection would be difficult to inspect.

 

[riveralt]

Thanks for all the input folks. The stove installers have given instructions that "any electrical sockets/TV sockets in the vicinity of the installation must be removed prior to our arrival." We certainly wouldn't be able to access the socket and I'm guessing there may be a concern about heat affecting the socket.

Hello Andy - if you're still there and not lost the will to live with all these side bar discussions. Last I read we were heading for outer space with NASA.
As I understand it the removal of the socket may breach the safe zone conditions which cannot easily be rectified. Yet that is a requirement of the installers.

..... put a blank plate on where the socket was. Job done.

I would speak to the installers again. Explain the predicament regarding the safe zone and ask them if a blanking plate is acceptable.
If it is then use appropriately sized Wago or connector strips or whatever to continue the ring final circuit.