Crimps

[sprocketflup]

Deke,Grub screws have always undone themselves, it is a phenomenon known IMHO incorrectly in this situation as hysteresis.

It is more evident in highly loaded conductors where significant heat cycles occur and it is based on the fundamental laws of physics.

Thing is see the same can happen with crimps even if made with the correct "compression" tool.

Same physical phenomenon will occur unfortunately.

IMHO again crimps and small solid conductors are not a good mix if they are under high load, bigger conductors will deform in the crimp and offer multiple facets, small ones will not.

The "best" maintenance free connectors are spring loaded with springs that do not change mechanical properties until above the design temperature that they will reach in service no matter how many heat cycles they are submitted to, again IMHO.

However, I can back my opinions up with the science, the physics the chemistry and the engineering to explain my opinions and I can even demonstrate some, ask KME I blasphemed on the phone to him last week when I missed one of these and had a VERY minor "accident" I dropped a component out of a vice.

Ill be honest straight up front and say that I do not have enough sciencey qualifications to argue on a level dias with you Sidey, so please be gentle with me

You say its to do with heat cycles and I see you mention that the 'hysterisis' is more apparent in high load conductors and joins, surely that is what correct cable selection is all about - i.e. ensuring that the equipment installed is capable of taking the loads and heat cycles thrown at it and doesnt overheat? So if a large enough rated cable and crimp/connector are employed then surely they wouldnt suffer the phenomenon and stay tight throughout thier working lives?

 

[Sidewinder]

Sprock,

A heat cycle would say take the cable from room temp up to operating temp and then back again, now this could be a temp change of 60 deg C say from 10 to 70 yeh?

This would all be within the cable parameters would it not?

Get my drift?

 

[Steve3948]

Are Red Blue Yellow in-line crimps even designed for solid copper cables ??

I was under the impression they were for stranded copper not solid and if solid copper was used then an indent crimp was required.

 

[Sidewinder]

Steve,

This is one of my concerns with all this!

I agree with you that the deformation is insufficient, however, it seems that the "powers that be" disagree!

 

[Andy™]

push fit V crimps

 

[Sidewinder]

Only one answer Andy, in the immortal words of Harry Hill.......

FIGHT!!!!!!!!

 

[apprentice87]

Hi all,

So far as i am concerned, there is, [in general] only one thing that crimps are good for.... fitting foglights on your car......

Cheap and nasty.... No, i think they are fine for stranded cables, that is for fitting terminals to the ends, but as for using them to join cables, and then plaster over them.... No thanks....

Do not care what the makers say about solid cables. I should sit down with a calculator and work out what the expansion and contraction of a typical cable would be and then using youngs modulus [the ratio between stress and strain, don't ask!] work out what the variation in clamping force would be over a heat cycle.

For me?? Wagos in the little box thing they make for them, or din rail terminals in an enclosure. If not possible, then renew the cable back to the fitting it connects to. A customer might not like this, and of course it would be expensive, but look at it like this;

When an MOT tester tests your car, he does not say to himself "i had better not fail his power steering rack, cos they are expensive and he will not like it"

If he thinks it is not "to the regs" it fails, simple as!!

If i fit stranded cables to a screw connector or JB then i ALWAYS fit bootlace ferrules first. I do believe that there is a reg which covers this too...

I wonder about the resistivity of wagos versus crimps though??? Perhaps one of us should string about ten of each together and measure the resistance of them all in series.

That would be interesting!!!

john..

 

[sw1970]

"If i fit stranded cables to a screw connector or JB then i ALWAYS fit bootlace ferrules first. I do believe that there is a reg which covers this too..."

Appentice87 - can you point out the specific reg that addresses this? Thanks.

 

[Riggy]

I understand the theory, has anyone ever seen this particular failure mode? I haven't (and I've seen a good few electrical failures over the years).

 

[Sidewinder]

Which one are you referring to Riggy?

 

[Riggy]

Sidewinder,

I was talking about insulated splice crimps on solid conductors.

I've seen them fail when they have been melted by an external heat source, and I've seen them pulled off the end of the cable by a forklift but I've never seen one fail due to becoming loose due to heat cycling.

 

[Dan007]

Ok so in the BRB reg 526 Electrical connections- this covers all of what's being mentioned in this thread but the way it's interpreted by each individual obviously differs. Someone mentioned earlier about crimps not being suitable for solid core cables but in 526.2 note 2 it states "terminals without the marking R (only rigid conductor), F (only flexible conductor), S or Sol (only solid conductor) are suitable for the connection of all types of conductors". I don't recall seeing crimps with any of these markings. Saying this I'm still not sure if I'd be happy with a crimp, heat shrink, capping and plaster, although 526.5 seems to cover this ok. Personally I tend to put my crimps in an enclosure (Chocbox) before hiding them away but that's just me.

 

[arthur]

Have been using Wago for ages now, won't use anything else

 

[Doc Hudson]

Modern connector blocks / terminal strip have very poor quality, the screrws either strip their threads or the metal snaps. Crimp joints are very dependant upon a decent quality crimp tool. I have found many lose screw connectors in both j/bs and connector blocks, either never tightened originally or worked lose over time.

Doc H.

 

[MarkieSparkie]

Sorry to through a spanner in the works of all you guys that are heat shrink sleeving crimped joints and then plastering over, but you seem to have forgotten about:

526.5 Every termination and joint in a live conductor or PEN conductor shall be made within one of the following or a combination thereof:

1) A suitable accessory complying with the appropriate product standard.

2) An equipment enclosure complying with the appropriate product standard.

3) An enclosure partially formed or completed with building material which is non-combustible when tested to BS476-4

 

[Riggy]

Markie, point 3 covers it surely?

 

[Andy™]

heatshrink encloses the connection, therefore is an an enclosure.

 

[Nicky Tesla]

I use crimps for extending cables all the time, but you have to use the right colour crimp for the conductor size. This can be a problem when crimping 2.5 to 1.5 as the 2.5 requires the blue and the 1.5 requires the red crimps. This may be required when a previous electrician has used an usual cable for the circuit, but if that is what cable has been used then thats what we have to work with sometimes, unless we start ripping everything out.

Another thing with crimps is that they are not really designed for fitting more than one conductor. They can often become loose or the crimp gets too tight, but everybody has tried im sure. This is the great bonus with choc block and wagos.

I have looked at the manufacturers data sheet for some crimps, and there were figures for stranded and solid wiring, so both can be used.

When i crimp i dont generally use heat shrink, just use insulation tape, and sometimes i have used self amalgamating tape.

Wagos can often take quite a lot of room up in an enclosure, and the wiring has to all go to the same side of the connector, not like choc blocks, so wiring may need extending to fit when fitting to old existing wiring.

 

[apprentice87]

Hi sw1970,

You say that, [referring to my comment about stranded cables]:

"If i fit stranded cables to a screw connector or JB then i ALWAYS fit bootlace ferrules first. I do believe that there is a reg which covers this too..."

"Apprentice87 - can you point out the specific reg that addresses this? Thanks"

Here we are;

526.8 CONNECTION OF MULTIWIRE, FINE WIRE AND VERY FINE WIRE CONDUCTORS.

526.8.1 In order to avoid inappropriate separation or spreading of individual wires of multiwire, fine wire or very fine wire, suitable terminals shall be used or the conductor ends shall be suitably treated.

526.8.2 Soldering [tinning] of the whole conductor end of multiwire fine wire and very fine wire conductors is not permitted if screw terminals are used.

Which kind of just leaves ferrules!!

John...

 

[Nicky Tesla]

This is because the turning of the screw can rip the strands off.