Tri Rated 35mm Earth - Johns adventures of tin tin - or not...

[John-]

Hi. I have some TP supply SPD and JB to re wire in 25mm TRI rated cable this weekend. For the Iine conductors i am using 35mm DIN connectors with manufacturers links between - it is all being housed in a Hager Din Extension box with window.

For the earth, I have 5 x terminations at 25mm. But if i ferule the 25mm earths they do not fit in the 25mm terminations on the brass earthing blocks as they create a square profile, that will not fit into the circular hole of the termination. They fit fine n the in the 35mm, but the terminal blocks themselves only come with 35mm on either end - i need 5.

I really want to avoid using 35mm Earth DIN connectors and rely on the DIN rail as the link between the earths.

If I was to tin the termination with solder, would that be suitable?

I can shape the cable to the size of the hole (without cutting strands off obviously) then tin it up with my torch.

Any reasons why i should not do this? I will take some isopropyl Alcohol to clean of any flux residue - shouldn't be much anyway.

There is no significant vibration in the area by the way. Could be a concern maybe if there was.

Cheers

John

 

[Rockingit]

The only problem, and it's a largely theoretical one, is that under fault conditions the heat generated can melt the solder again. I'd be tempted to shop around for some different ferrules or different shaped crimper. At a push you could drill out a mil or so on the earthing block to make the holes slightly bigger.

Also, if your calcs allow then, 25mm to 16mm reducing ferrules?

 

[John-]

Yep good point about the heating effects. the solder could melt allowing the conductors to re shape and perhaps, loosen and reduce contact with the termination. To be fair though, if it is going to get that hot, i would expect more serious issues than that on the installation that would warrant a visual check anyway. So I think I will file that under a very low likelihood, but if did occur a visual check should pick it it up.

 

[SJD]

If the end terminations have slightly larger holes to take 35mm, likely you can just enlarge the other 3 holes to the same size? I'd expect the screws for all 5 holes are identical. [I'm assuming the brass block can just be put in a vice to aid doing this.]

Actually I sometimes wonder why some of these brass earth blocks come with larger holes at the end and less-useful smaller holes in the middle.

 

[David Prosser]

Can you put lugs on and bolt them to a 35mm bar?

 

[John-]

Reading up some more even with tined solder you can still get some 'creep' where the solder will move a little with time and pressure, creating a loose joint. Oh well...

Speaking of 'time and pressure', it reminded me of the Only Fools and Horses episode where Dell boy had a money spinning idea to make coal by burying wood...

 

[Rockingit]

Yep good point about the heating effects. the solder could melt allowing the conductors to re shape and perhaps, loosen and reduce contact with the termination. To be fair though, if it is going to get that hot, i would expect more serious issues than that on the installation that would warrant a visual check anyway. So I think I will file that under a very low likelihood, but if did occur a visual check should pick it it up.

Total aside and not hoping to derail the thread, I had this on a light fixture in parts very foreign some years back - instead of replacing the ceramic base to a 1000W lamp, it had been bodged and soldered straight onto the tag. Turn light on.....

 

[Lucien Nunes]

Agreed - do not tin cable ends for use in screw terminals. We have seen this done countless times and invariably the terminal is slack, or the screw has been tightened repeatedly and progressively cut through the conductor because there's no springiness in the solid lump.

Can you crimp the ferrule and then gently reshape it with pliers squashing the corners in so that it fits? It doesn't matter if it slackens the crimping a little as ultimately it is the terminal screws that clamp the ferrule to the conductor once tightened. Better still, use pin terminals.

There are all sorts of commoning terminals available including DIN-rail mountable ones, that don't rely on continuity through the rails. Search '25mm distribution block' and look at the offerings from Weidmueller, Entrelec, Phoenix et al.

 

[Strima]

The ferrule only stops the strands from poking out everywhere, once you clamp down on them they deform to suit the termination. We often have this problem on larger CSA cables and cheap MCBs where they are a struggle to get in, we deform the ferrule to fit, clamp the termination, torque it up, leave for ten minutes, re-torque then energise after the appropriate testing etc.

If possible after the circuit has been in use for a couple of hours we try and re-torque the terminations again as often the cables will 'settle' once they've warmed up but this isn't always possible in my line of work.

 

[Rockingit]

You can actually get 25mm 'barrels' (cord end ferrule) to do this job - they just deform as Strima said but keep the strands all together.

That pic's lifted from Cablecraft, btw

 

[John-]

Agreed - do not tin cable ends for use in screw terminals. We have seen this done countless times and invariably the terminal is slack, or the screw has been tightened repeatedly and progressively cut through the conductor because there's no springiness in the solid lump.

Can you crimp the ferrule and then gently reshape it with pliers squashing the corners in so that it fits? It doesn't matter if it slackens the crimping a little as ultimately it is the terminal screws that clamp the ferrule to the conductor once tightened. Better still, use pin terminals.

There are all sorts of commoning terminals available including DIN-rail mountable ones, that don't rely on continuity through the rails. Search '25mm distribution block' and look at the offerings from Weidmueller, Entrelec, Phoenix et al.

Thanks. Looking on line i can find someting close in Weidmueller.

WPD 305 3X35/6X25+9X16 3XGY

But there are not enough 35mm terminals. and no way to link that i can see - recall 25mm ferules wont fit in 25mm circular screw terminals.

 

[John-]

You can actually get 25mm 'barrels' (cord end ferrule) to do this job - they just deform as Strima said but keep the strands all together.

View attachment 85954

That pic's lifted from Cablecraft, b

You can actually get 25mm 'barrels' (cord end ferrule) to do this job - they just deform as Strima said but keep the strands all together.

View attachment 85954

That pic's lifted from Cablecraft, btw

Mine are circular too, but the crimp tool former squares them off. I don't want to have to purchase yet another crimp tool

 

[Vortigern]

So why not get a reducer?
Edit: Just seen already suggested by @westward10