Push-fits vs Crimps

[Chr!s]

Lanarcaman

Never seen or used any other MV or HV connection, other than crimp connections. Be they in direct buried cable joints, transformer connections, distribution panel connections..... etc etc!!! As i said never seen any other and never used any other connection type

The preferable method for connection of HV MV jointing and terminating is to soft solder into lugs or ferrules and has been used for many years. so im surprised you have only seen a crimped joint. Though i do agree a properly crimped joint will suffice,but where stranded conductors are used inner strands need to be adequately terminated, so soft solder joints are preferable.

 

[Sidewinder]

Plumber,

Quite true, it would seem, and it makes sense, though, you'd be a bit stuffed with Al cable cores would you not!

I have I must hasten to add only ever worked on HV stuff under supervision, dead and that was a LONG time ago, and not much.

As we don't have MV in the UK I can't have ever worked on that!

 

[Chr!s]

Sidewinder

Quite true, it would seem, and it makes sense, though, you'd be a bit stuffed with Al cable cores would you not!

Well there are fluxes and solder for aluminium, but you are right it is more problematic, the aluminium develops a thin oxide layer which makes alloying difficult.

So yes crimps are the preferred method for most when the conductor is aluminium.

 

[Sidewinder]

Plumber,

I am actually aware of the solders and fluxes for Al, my point was merely that you can't soft solder them by conventional means.

I have done quite a lot of Al work in the past including TIG welding, Oxy Acet welding and "brazing", of AL & some of its alloys.

The oxide layer Al2O3, can't do the subscripts on the forum, has a higher melting point than the base pure Al and many of its alloys, the affinity of Al for O is very high thus the oxide layer forms almost immediately on exposing the Al (or alloy) to air, it is also harder than the pure AL base, (though not all of its alloys), hence how Al and its alloys can be "hard anodised" not quite a technically pure explanation but I'm sure you get my drift.

All OK till you get a high magnesium content alloy, obviously not an electrical usage alloy, then it can get interesting!

Also I feel that a suitable crimp into Al will be better than an equal crimp into Cu as the Al core is more ductile thus deforms more under the crimp process, thus offering not only a larger contact area, but also greater deformation increasing the mechanical "wedge" effect & lessening the chance of loosening, also the crimp will be a more similar material will it not (due to electro chemical effects) thus the differential expansion effects during heat cycling will be less.

This then changes when you bolt it to a bus bar though!!! ; \

 

[the_mouse]

I have read this topic with a fair bit of interest and it seems, the use of either method be it crimp or push fit is a personal one both methods being acceptable. I personally prefer to use crimps in a consumer unit and push fits in a junction box although i don

 

[Larnacaman]

LanarcamanThe preferable method for connection of HV MV jointing and terminating is to soft solder into lugs or ferrules and has been used for many years. so im surprised you have only seen a crimped joint. Though i do agree a properly crimped joint will suffice,but where stranded conductors are used inner strands need to be adequately terminated, so soft solder joints are preferable.

Iv'e been working with MV/HV for a good number of years now, and i can honestly say i haven't seen a Soldered type connection of any type for over 30 years now!! That also goes for LV connections/joints too. The compression crimp and hydraulic crimping tool, is the industry standard, and i can't see that changing for a good many more years.

---------- AUTO MERGE Post added at 18:53 ---------- Previous post was at 18:35 ----------

my primary employment is by Prysmian cables and we band voltages differently to BS7671, up to 1000v is referred as low voltage, 1kv to 22kv as medium voltage, 22kv to 132kv as high voltage 132kv and above as super tension, a little off topic just a little bit of info, created a load of confusion for me while doing 2330!!

Thank you Mouse, The above voltage bands are now pretty much Standard around the world. The MV voltage band has been around in Europe and in the UK for a good many years now...

 

[Chr!s]

Larnacaman

Iv'e been working with MV/HV for a good number of years now, and i can honestly say i haven't seen a Soldered type connection of any type for over 30 years now!! That also goes for LV connections/joints too. The compression crimp and hydraulic crimping tool, is the industry standard, and i can't see that changing for a good many more years.

Well that will all come down to the knowledge and experience of the cable jointer, most if not all mv/hv cable jointing courses will cover soldered terminations as part of the course requirements along with compression, welding and bolted terminations.

Compression terminations are one option, and the one in your experience used the most, probably due to the ease of producing an adequate termination.

Though i think most engineers would agree a soldered joint is preferred.

 

[Larnacaman]

LarnacamanWell that will all come down to the knowledge and experience of the cable jointer, most if not all mv/hv cable jointing courses will cover soldered terminations as part of the course requirements along with compression, welding and bolted terminations.

Compression terminations are one option, and the one in your experience used the most, probably due to the ease of producing an adequate termination.

Though i think most engineers would agree a soldered joint is preferred.

Plumber,

Yes there are still MV/HV mechanical type (bolted) connections available. There generally used in site situations where it is physically not feasible to use a hydraulic crimp tool. The Yanks like and use them a lot. They also take a lot of expensive void filling compound.

What type of welding are you suggesting they would use on a cable termination?? ...All welding methods i'm aware of, produce ''s**g'' as a by-product, and that's the last thing you would want at MV/HV termination!!

Personally i can't see any reason why they would still include conducting solder joints and terminations on cable jointing courses these days, ...they just aren't used anymore.

To undertake the jointing, say of a straight forward 150/185mm 3core SWA MV/18KV cable for direct burial, it would take about 3 hours to complete. If the terminations were of the soft solder type, you could easily add another 2 hours. If any mistake was made during the pouring you can add another 1 or 2 hours. Which is another reason why such joints are just not seen in todays industry.

 

[spinlondon]

There are two types of welding, one welds two metals together as a blacksmith would do. The other uses a filler material to fill in between two pieces of metal as in Arc, Mig and Tig.

The method that produces s**g, is Arc, the s**g is produced to prevent Oxygen from reaching the weld during the welding proccess, and is generally chipped off when the welding is done.

Both Mig and Tig use a shielding gas to prevent Oxygen from reaching the weld, and no s**g is produced.

 

[Larnacaman]

Understand, ....but cannot for the life of me see an application for using either for terminating or jointing a cable. I'm sure that both methods are going to produce an excess of heat, that would be detrimental to the cables structure, especially the somewhat delicate termination make-up of MV/HV joint/terminations structure....

 

[Graham Lister]

Just my tuppence worth but the crimps used are not up to the job as larnacaman said. That multipack of cheap crimps may look good value but they aren't up to the standards of reputable companies eg the crimp company. I had the misfortune of trying some from B&Q just a small pack of 10 but they were not up to scratch and could be pulled apart easily. A decent joint made with decent pliers/crimps would not pull apart easily.

If you can retry the experiment with the correct blue crimps from a reputable supplier and use a better quality crimp tool then let us know the results. There is nothing wrong with correctly made crimp connections and all this don't use them on cables under 10mm is hearsay/nonsense pedalled by wago lovers.

 

[Sidewinder]

Graham,

I'm not a "Wago" lover by any means.

However, IMHO there is insufficient compliance in a solid conductor, e.g. 1.0, 1.5 2.5mm sq as seen in T&E for a crimp connector to be correctly applied.

Above this we move to stranded thus there is more compliance and again IMHO a better crimp can be achieved.

Also one needs to consider the difference in the design of a crimp tool for up to 6mm & above and how this deforms the crimp and conductor from a mechanical standpoint.

 

[green-hornet]

If anyone has done any higher electrical examinations/courses like the B(eng) hon degree they will know that all connections will be subject to many different examinations. I have an hydrolic crimp and die tool that crimps single core up to 500mm, never used that size, but have used the 300mm.

All connections I have made in jointing has involved in line screw connectors and bar. Resin sealed, booted and buried. In fact I know the DNO in my area use this type of connection on LV supply lines.

If any of you are interested there are many scientific "style" reports on all types of connections, various stresses encountered and BS or EN numbers given once they pass minimum level requirements.

If you are really old you may remember a way of joining a cable that used no crimps bolts or anything and it never gave way never produced any heat and is sadly a forgotten art.

The method of jointing is over 400 years old maybe more and is still used on high tensile connections.

 

[Sidewinder]

GH,

Its terminology is BEng(Hons) ; ) according to mine, but thats a BSc.(Hons). .

Apache probably also has a BSc.(Hons) amonst his other quals MRCVS etc.

BTW its also Hydraulic!

Sorry bud, just being wicked!

 

[green-hornet]

I know I type faster than I can think I saw the spelling mistakes but could not be bothered to correct them

 

[Sidewinder]

Thank you Mouse, The above voltage bands are now pretty much Standard around the world. The MV voltage band has been around in Europe and in the UK for a good many years now...

Larnacaman,

They may be standard elsewhere in the world, but I have yet to identify a recognised standard in the UK that recognises these values, anyone can call anything whatever they like, and often do!.

However standards and legislation are there to ensure clarity of communications.

I can't find a UK standard referring to MV.

I await to be corrected, sorry buddy.

Here's hoping...

 

[green-hornet]

Larnacaman,They may be standard elsewhere in the world, but I have yet to identify a recognised standard in the UK that recognises these values, anyone can call anything whatever they like, and often do!.

However standards and legislation are there to ensure clarity of communications.

I can't find a UK standard referring to MV.

I await to be corrected, sorry buddy.

Here's hoping...

There is not any mention of MV in the UK its HV or LV.

Thats besides the elv and what have you, before anyone jumps down my neck. So I doubt you will be corrected.

 

[Graham Lister]

Graham,I'm not a "Wago" lover by any means.

However, IMHO there is insufficient compliance in a solid conductor, e.g. 1.0, 1.5 2.5mm sq as seen in T&E for a crimp connector to be correctly applied.

Above this we move to stranded thus there is more compliance and again IMHO a better crimp can be achieved.

Also one needs to consider the difference in the design of a crimp tool for up to 6mm & above and how this deforms the crimp and conductor from a mechanical standpoint.

It is your opinion and I have no problem with that. A decent crimp and tool will make a good connection on a smaller solid cable in my opinion. I have seen no official literature to say crimps cannot be used on smaller solid conductors. If anybody has anything official to back up the theory they cannot be used on smaller conductors then I would be prepared to reconsider my viewpoint.

 

[Sidewinder]

GH,

Yes you are correct with the ELV etc. I just ignored that as we were at the other end of the scale!

Graham,

I don't have any official literature either, I have before and will in the future use them in this situation.

However, when you think about this and how the mechanics of the connection are formed then there is a fundemental flaw in the smaller size solid core wires with crimps.

Please take a few moments to consider this in your own mind and consider the mechanics & the materials science then, I hope you will see my point.

 

[Apache]

UPDATE

I'm glad I started this thread, even if it's just because of the copious discussion that ensued! I spent ten minutes in my shed this evening having a quick play regarding some of the criticism.

1. KME suggested some cheap crimp pliers may not be fit for purpose and have smooth jaws.

That is not the case here. The jaws are clearly ribbed and you can hopefully see from the following close up.

2. It was suggested that the crimp pliers may require adjustment.

I have adjusted them so they are crimping at their maximum tightness. I have quite a collection of tools and although they are at the cheaper end of the market they do 'feel' decent enough quality. It is a reputable company I bought them from, not a DIY shed special.

3. Sidewinder said that the blue crimp is the correct size for 2.5mm cable either single core or stranded.

I made up four more lengths of cable, two stranded and 2 solid core - all 2.5mm2 using blue crimps. Today I didn't heatshrink as it added time, I was cold and I had run out of lighter gas! Furthermore I don't believe it adds anything to the strength of the joint [suppose adhesive lined heat shrink may].

4. Sidewinder and KME pointed out that the crimp was being pulled in a linear manor and the push-fit at 90