When was this last done?

[EFLImpudence]

I was not considering mechanical protection as that is not a requirement for earthed metallic coverings.

 

[JohnW2]

I was not considering mechanical protection as that is not a requirement for earthed metallic coverings.

That was my point - that earthed steel capping offers the same protective functionality as the 'earthed metallic coverings' of pyro or ali-tube, but with the additional benefit of a (limited) degree of mechanical protection - hence 'at least as good as' (probably 'a little better than') than those two types of cable with earthed metallic coverings.

Kind Regards, John

 

[seasickstevie]

The good thing about metal capping, is the telltale 'bounce' you get when knocking a nail in, or drilling.

 

[JohnW2]

I guess you meant >50mm

I did, and will correct it. Thanks for noticing!

Kind Regards, John

 

[Iggifer]

The good thing about metal capping, is the telltale 'bounce' you get when knocking a nail in, or drilling

That's all well and good if you know what that's bounce means! Otherwise people just give it another whack

 

[SimonH2]

it cannot be completely buried as the earthing connection must be inspectable

Or the connection can be MF. How about crimping a ring terminal onto the cable and a pop-rivet to attach it to the capping ?

it would be difficult to earth several pieces together for the typical cable runs.

That's true. Or pop-rivet the pieces together with an overlap joint ?

 

[EFLImpudence]

Is a pop-rivet one of the suitable methods for inaccessible joints? I don't know.

You could use the acceptable type of cable.

 

[JohnW2]

Is a pop-rivet one of the suitable methods for inaccessible joints? I don't know.

Well, I suppose one could argue that a pop-riviter was an "appropriate compression tool". Failing that, one could perhaps use a 'rolled/folded joint', created with an "appropriate compression tool" (essentially the same concept as crimping) or could weld, solder or braze (not so sure about brazing steel!) bits of capping together (and use any of those techniques, including crimping, for attaching cables to the capping).

However, as you say, it would be simpler to just use an appropriate cable - which, for most of us, would probably mean SWA (pyro needing skills and equipment, and ali-tube being expensive and difficult to find).

Kind Regards, John

 

[SimonH2]

Well, I suppose one could argue that a pop-riviter was an "appropriate compression tool".

Indeed. If a crimp connection is accepted for solid cores ( I was taught otherwise as an apprentice ) then I fail to see why a pop-rivet shouldn't be permitted. I'd use a steel (or stainless steel) rivet to avoid any electrolytic corrosion issues.

However, as you say, it would be simpler to just use an appropriate cable - which, for most of us, would probably mean SWA (pyro needing skills and equipment, and ali-tube being expensive and difficult to find).

That assumes that the cable under the capping is "most" of the run. What about where it's just part of the run - do you use large amounts of (say) SWA just because a couple of yards needs it, while the other 10, 20, whatever yards could be just T&E ?

 

[JohnW2]

Indeed. If a crimp connection is accepted for solid cores ( I was taught otherwise as an apprentice ) then I fail to see why a pop-rivet shouldn't be permitted. I'd use a steel (or stainless steel) rivet to avoid any electrolytic corrosion issues.

Glad you agree. I, too, was 'taught' that - albeit 'informally'.

That assumes that the cable under the capping is "most" of the run. What about where it's just part of the run - do you use large amounts of (say) SWA just because a couple of yards needs it, while the other 10, 20, whatever yards could be just T&E ?

That's a reasonable point. I suppose that if one used acceptable jointing methods (for inaccessible joints) (albeit the armour would be 'interesting'), one could just use SWA where needed, with T+E for the rest - but that sounds just slightly 'orrible!

Kind Regards, John

 

[EFLImpudence]

If a crimp connection is accepted for solid cores ( I was taught otherwise as an apprentice )

It's not. That others do it because others do it does not alter the fact.

 

[JohnW2]

It's not. That others do it because others do it does not alter the fact.

FWIW, I was also 'taught' that, even with stranded conductors, it was not really very satisfactory to use tools that just did "one-plane squashing" (such as the tools advocated here, and almost universally used by electricians).

Kind Regards, John

 

[SimonH2]

Interesting, because when I've mentioned it before, there's been no comment - so it led me to wonder if what I'd been taught as an apprentice was wrong. BTW - that was in an establishment (primarily) building vehicles for military use so standards could well be different (more stringent) than for domestic electrics where things aren't subject to the levels of vibration (and people trying to blow it up).

As to one plane squashing, I think it's not so much that, as whether there is constraint in the second axis. The cheap "pliers" only squash the terminal to an oval, and leave plenty of room for the strands to move sideways - so a joint with poor integrity (as I remember from the past when I had a few poor joint on a car I'd done a lot of wiring on ). The ratchet crimper I have, while only being a cheap set, constrains the terminal in that plane, so while the result is still an oval there is limiter scope for the strands to move.

Interestingly, the LPGA (now UK LPG) addressed this by prohibiting crimped joints in LPG conversions for vehicles. Well not actually prohibited, but the CoP for conversions states that joints must be soldered. I guess they figured that while the same people who can't make a decent crimp probably can't solder either, there's a better chance of there being a joint that's vaguely reliable when soldered
When doing crimped joints on cars, I generally also put a bit of vaseline on the wires first. As well as using the ratchet tool that seems to do a good crimp, I figure there "belt and braces" approach makes it less likely that damp will get in and cause corrosion - though if adequately crimped, the joint should be "gas tight".

And there are people who should know better doing bad crimps as well.
Back when I had a share in a light aircraft, we had a problem for some time with the alternator tripping. The alternator itself is similar to to a car one, but without the regulator. The regulator is normally an external unit, and includes (either integrated or a separate unit) an over-voltage trip - and the field is supplied from the battery via a switch so the alternator can be turned on/off independently of everything else. After a year (yes a while year) of the engineers charging us ever increasing amounts in the "change everything one component at a time" diagnostics technique, I was advices that it was probably a bad connection. The theory is : if there is a bad connection, when it's high resistance, the (analogue) regulator cranks up the field to compensate, if the joint then goes "good", the output voltage from the alternator spikes until the regulator can turn it down - and so the over-voltage trip operates.
So I told the engineers that I was going to work through the battery/charging system, checking and cleaning every joint. They "weren't happy", told me they'd need to check my work ("no problem" I said), etc. When I got there (1 ½ hour drive) with my tools, they said "can you take it for a test flight, we think we've found the problem". Sure enough, they had magically fixed it.
When I got back, they shows me a crimp terminal they'd removed - from the field connection on the alternator. The last ½ inch of white insulation was grey from heat damage - yet the alternator had only recently been replaced. Seeing as it was obvious that a supposedly intelligent person had changed the alternator (at great expense) but didn't think to act on the signs of an obvious problem had me "a tad excited" and I think I did fairly well not to be making all sorts of comments such as questioning their parentage.
Sadly, I've since heard other stories of dodgy goings on that suggest this was not an isolated incident with them.

 

[securespark]

I'm an old fart, but not that old!!

I'll try and find out.

I have a copy of the 13th Ed. on order.

What it will tell me I'm not sure but I'll let you know.

 

[JohnW2]

As to one plane squashing, I think it's not so much that, as whether there is constraint in the second axis. The cheap "pliers" only squash the terminal to an oval, and leave plenty of room for the strands to move sideways - so a joint with poor integrity (as I remember from the past when I had a few poor joint on a car I'd done a lot of wiring on ). The ratchet crimper I have, while only being a cheap set, constrains the terminal in that plane, so while the result is still an oval there is limiter scope for the strands to move.

That's all true, but passive constraint in the second axis is not the same (or anything like as 'good') as active pressure being applied in two (or, more commonly, three) axes. I may be wrong, but I think you'll find that when, say, DNOs crimp massive cables, they wouldn't dream of using anything less than a 'hex' (i.e. 3-axis) (hydraulic) crimper.

Kind Regards, John