Joining large cables

Do they come with "uninsulated live conductors - do not touch" stickers?

If temporary then screw terminals should be fine:

Do you plan on some form of protection for the 2.5mm cable? Wouldn't a fused/MCB enclosure be the appropriate way forward, temporary or otherwise.

The connection will be there permanently, but the two cables that will be connected will change. (one is 10mm2 T&E, the other will later be exterior grade hi-tuff 10mm2, but will be 2.5mm2 T&E to begin with). Since the above has no indication of tightening torque, I don't want to risk it overheating or loosening under consistent high currents, which is why I'd prefer a screwless connection. It's the best example I managed to find thus far, and if screw terminals are good enough for a Henley block then not completely ruling them out.

What do you mean protection, mechanical or circuit protection? There are MCBs at both ends of this cable run so there's sufficient existing circuit protection. I don't really want a third MCB box. I could put a short length of DIN rail in a plastic box with a bunch of Topjob connectors, but I was hoping there was something neater.

Theo

What about an 831-1103 together with an 831-1203 ?

Insulation? Who wants Insulation? Insulation is for sissies.

Interesting, I'd not come across those. The ratings are a bit marginal:

Ratings per IEC/EN 60664-1 Rated current 41 A

Approvals per UL 1059 Rated current 37 A

Approvals per CSA Rated current 35 A

Not sure what the difference in standards is, but presumably they are being pushed very hard at 40A and there are different ideas of how much 'too hard' is?

Theo

If I'm reading the derating curve correctly, that's at 70°C better if cooler?

What you should use is down to access. If accessible after then screw terminal JBs are ok, otherwise it's crimp or solder for that size of cable.

I meant what current protection will you have for the 2.5mm cable.

Not sure I can see that - the datasheet seems to be about how they are tested rather than the actual specifications. The derating curve doesn't seem to go above 30A.

However, it looks like the MCS Maxi 16 series is suitable for 10mm2 (and

Also it looks like the 2010 series Topjobs are reasonably priced at CPC:

Think about how that termination will be made to the MCB in the CU. There is no reason why a screwed connection can't be made properly as a long term solution.

Part of the issue is heat - less constant heat, and more heat cycling.

A cable that frequently cycles between close to its maximum operating load and significantly lower load, will be subject to more expansion and contraction stress that can work screw connections loose. In cases like that, going for a larger CSA cable can make sense to reduce the thermal cycling.

For your temporary smaller cable install, a conventional high current JB would be fine (high current, for the terminal capacity more than anything).

e.g.

Note that a fairly serious crimp tool will be needed:

This was the graph I was looking at

But there is a similar graph that is "ruled off" above 41A, not sure why they'd show both curves.

Their full catalogue never feels very discoverable ...

Agreed, but MCBs have specific instructions about how to terminate them - there's a specific tightening torque to give a connection at the rated current. Random screw junction boxes don't seem to have that, which means you're at the mercy of doing it 'good enough' by feel. A lot of the time CU loads are intermittent, so you can get away with a substandard termination, but if the load exists for hours then that's the time you have to do it right otherwise you get overheating.

Indeed, which is why we're at 10mm2 rather than 6mm2. More copper, big chunky JB, less heat (and less energy wasted in the connection). But only if the terminals are bearing down on the wire correctly and correctly torqued.

I was planning to keep the JB in place and just swap out the wiring, ie not have a temporary JB, just a temporary cable in it. But that's not set in stone.

Thanks, I'd not considered crimping. It gets used a lot in DC installations, but the usual stud terminations (car batteries and similar) aren't rated for 250V AC. Might need to see if I can find some properly shrouded AC crimp connections.

Theo

Intermittent loads can be harder to deal with than constant ones due to the thermal cycling. An "always" on load will tend to run at a fairly constant temperature.

In which case go for a suitable enclosure and using crimps for both installs - just leave enough spare wire to allow you to cut off the first set and remake the connection later.

Crimping is used widely in AC installs as well for permanent maintenance free joints (and before the advent of "modern" sprung terminal connectors, was one of the few practical approved methods of maintenance free jointing).

You can get insulated crimps, or you can use separate insulation (e.g. heatshrink) on "bare" crimps. You will still need some for of enclosure or second level of insulation though. (the second level could be an overall jacket of heatshrink)

This German company may have a solution

That doesn't appear to be 250V AC rated?

There are lots of high current DC connectors out there, but they're not designed for mains voltage. Not sure what BS7671 would think about them.

Also, I want something that isn't 'a bodge' when an electrician looks at it

- using connections from R/C models would likely fall into that category.

Theo