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Author: Subject: Best way to connect one mains-voltage wire? [SOLVED]
David Jenkins

posted on 13/10/17 at 02:34 PM Reply With Quote
Best way to connect one mains-voltage wire? [SOLVED]

OK - I know there's a vast amount of knowledge here on stuff that's nothing to do with Locosts, so here's one for the forum's professional electrical equipment builders...

I'm in the process of converting the print-bed heater on my 3D printer from 24v DC to mains 230v AC. I have no problem with the safety issues relating to connecting up 230v (my work ages ago used to involve assessing risks to maintainers of electrical equipment) so the whole business of proper connections, thermal fuses, protective earths and keeping fingers away from live terminals has been addressed.

I have been left with one problem: one leg of the heat-resistant cable attached to the heater is a few inches too short as it has to follow a convoluted path through the printer. The leg connected to mains live is easy - it goes straight to one terminal of an SSR (solid-state relay). The earth connection is also easy - it goes from the heat-bed's metal plate to a nearby chassis point, then off to the central earth point. The one that's bothering me is the mains neutral connection - I have to extend it to get to the best connection point.

Is there anyone in the electrical equipment designing world who can tell me the 'industry standard' or 'best practice' way of joining the two wires together so that it will be safe (and remain safe)? I could solder the wires together and cover the joint with heat-shrink tubing, but I'm not comfortable with that; heat-shrink is fine for lower voltages, but I'm not sure about mains voltage - after all, the neutral wire could easily be at live voltage in some circumstances. I could do a butt crimp joint, but I'm not happy about that either. Finally, I've never seen a 1-terminal connection box!

So - any clues?

[Edited on 13/10/17 by David Jenkins]





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SJ

posted on 13/10/17 at 03:13 PM Reply With Quote
What kind of cable? Wago type connectors - either push fit or lever type are good if you have space. These come in types suitable for one connection.

I'd be tempted to solder and use multiple layers of shrink wrap if you are worried about the insulation properties of just one.

Stu

[Edited on 13/10/17 by SJ]

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David Jenkins

posted on 13/10/17 at 03:16 PM Reply With Quote
Not sure of the exact cable gauge - typical wire extracted from a 10A flex cable, so quite small. I forgot to mention that the current is going to be less than 1A (200W heater).

I'll take a look at those Wago connectors - half the battle in this sort of thing is knowing the correct name to Google!





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gremlin1234

posted on 13/10/17 at 03:21 PM Reply With Quote
I was thinking wago too
these people sell a sample kit about 2.00 plus vat etc
https://www.connexbox.com/shop/wagobox-kits/wago-connector-sample.html

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David Jenkins

posted on 13/10/17 at 03:42 PM Reply With Quote
quote:
Originally posted by gremlin1234
I was thinking wago too
these people sell a sample kit about 2.00 plus vat etc
https://www.connexbox.com/shop/wagobox-kits/wago-connector-sample.html


I had a look at that - the price is right, until you add 3.40 postage and VAT on top!

Never mind - I've ordered a Wago connector off ebay for 1.49 delivered, and I reckon it should do the job nicely.

Many thanks to all.

(The next problem is that I have to wait for 5 or 6 items to arrive from ebay before I can move on... )

[Edited on 13/10/17 by David Jenkins]





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02GF74

posted on 13/10/17 at 04:36 PM Reply With Quote
FYI low voltage heatshrink typically rated at 600V.
IIRC 1mm of air is good for insulating 1kV, not that I recommend having live wires around especially where they can be touched.





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David Jenkins

posted on 13/10/17 at 05:47 PM Reply With Quote
quote:
Originally posted by 02GF74
FYI low voltage heatshrink typically rated at 600V.
IIRC 1mm of air is good for insulating 1kV, not that I recommend having live wires around especially where they can be touched.


I read a spec sheet that said 500v/mil - and I don't reckon the tubing is very thick!

Once the printer's covers are on then any bare wires or terminals would be out of reach, but I often have the covers off to fiddle with something or other so I'd rather not take any risk. Mind you, in my first job I used to do TV repairing, and would often be arms-deep in a switched-on TV...





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v8kid

posted on 13/10/17 at 05:54 PM Reply With Quote
"I could do a butt crimp joint, but I'm not happy about that either"

Crimped joint is the professional way to go about it. It its good enough for NASA it should be good enough for us Click connectors are - to use a technical term - Poo. They depend on spring pressure on a sharp edge and over time loosen and burn. Would you put them on your car?

The old way was to use screwits and although they may seem archaic they worked extremely well without problems. Dunno if you can still but them though.

Heat shrink sleeving is used in the electrical distribution system, to my experience at 33,000 volts without a problem so the principle is sound. Don't see why we should disbelieve the 1,000 volt rating of domestic heat shrink.

Anyhow your RCD will sort out any problems

Cheers!





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David Jenkins

posted on 13/10/17 at 06:37 PM Reply With Quote
quote:
Originally posted by v8kid
"I could do a butt crimp joint, but I'm not happy about that either"

Crimped joint is the professional way to go about it. It its good enough for NASA it should be good enough for us Click connectors are - to use a technical term - Poo. They depend on spring pressure on a sharp edge and over time loosen and burn. Would you put them on your car?

The old way was to use screwits and although they may seem archaic they worked extremely well without problems. Dunno if you can still but them though.

Heat shrink sleeving is used in the electrical distribution system, to my experience at 33,000 volts without a problem so the principle is sound. Don't see why we should disbelieve the 1,000 volt rating of domestic heat shrink.

Anyhow your RCD will sort out any problems

Cheers!


My concern with crimp connectors was that I couldn't find any specification that told me the voltage rating of the PVC insulation, especially after it has been crimped. As for NASA - they do use and recommend crimp connectors, but looking at the specs they don't use anything like our car-type terminals - theirs are far more high-tech and probably far more expensive. The ones we use are fine in a car as there's only roughly 12v under the bonnet (excluding the ignition, of course). Mind you, I have used insulated crimp fork terminals to connect to the printer's power supply (both 24v and 230v) so I can't really object, can I!

My concern with the heat-shrink is its physical properties - I have found it to be quite delicate when compared with the cable's own insulation, especially if the solder joint is a bit lumpy. I would be concerned about it rubbing through against the metal chassis. I suppose that I could always put several layers on!

Maybe I'll have a rethink...





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