Widget for joining 3-core mains flex

Coleman · 2007-06-01T08:00:59+00:00

I am in the UK. I want to ask for info about joining 3-core mains flex on an appliance that may have to carry up to 3,000 Watts.I usually extend the mains flex by soldering but the finished join is too bulky when winding the flex or pulling it around a corner.When I make my 3 joints I slightly offset each one so that it is not beside another one. This helps make a slimmer overall joint but it makes for a longer joint (about 2.5 to 3 inches) and with insulating tape it is still too bulky.(A) Is it safe to use heat shrink insulating tubing for each join and have each join beside the other? Then I might use a single layer of insulating tape to bind over and protect the 3 joins.(B) Or is there some widget which can help with this? Perhaps a small moulding which is made up of three very small metal tubes held by moulded plastic to be close together but not touching. I could put a wire into each end of a metal tube and then solder the wires into it. (It's just an idea.)Any info?

Jun 01, 2007 44 Replies

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MikeC 19 years ago

I didn't see the beginning of this thread, but a technique that I frequently use when joining wires is as follows. Look at the diagrams in Courier New font, or they won't make much sense.

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------------------- Cable +---- wire_1 --------------------+ Cable sheath +----------- wire_2 -------------+ sheath +-------------------- wire_3 ----+

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Firstly, strip a piece of the outer cable sheath off and put it to one side to use later. Then cut the wires as shown in the diagram. Bare the ends of the wires, and solder the two ends of wire_1 together, and the same for the other wires. Because the wires were cut to different lengths in this way, the soldered joints are not close to each other, and cannot short together.

Now take the piece of sheath that you put to one side, slit it down the side, and put it over the new joints. At this point, the cable should look almost as if it had never been worked on.

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Now wind some electrician's tape around the full length of the sheath that you have inserted, and an inch or so beyond each end. Better still would be if you had slipped a piece of heat-shrink tubing over the wire before soldering it together. The heat-shrink tubing should be about two inches longer than the piece of sheathing you used to cover the joints. _________________________________________________________________

---------/ / / / / / / /----------- / / / Taped up with electrician's tape / / ----/ / / / / / /____ / / / / / / / /

----------/_________________________________________________________________/------------

I have used the same technique on multi-wire cable - most recently on an Ethernet cable that I had to cut to get through a small hole, then join together again, because I didn't have the tool to put the connector back on. In this case, with 8 wires, the total length of the connection was about 4 inches.

MikeC

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Palindrome 19 years ago

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Fine for signal cables.

Lethal for mains flex.

The method provides virtually no strain relief for the conductors. Which a continuous outer sheath provides as well as insulation.

Subject to even a modest pull, the conductors or soldered joints will fail, potentially leading to a bare live conductor.

Any means of jointing mains flex has to provide strain relief for the conductors comparable to that provided by the outer sheath of the original cable.

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