Soldered wire tails and screw terminals

[Mike Tomlinson]

A cautionary tale...

A couple of regular posters to uk.d-i-y occasionally warn against soldering wire tails where said tail is to enter a screw terminal. The usual reason given is "solder creep" and eventual development of a poor connection.

I have a washing machine plugged into a home-made extension lead. This lead has been in use for many years and is constructed using good quality materials (Duraplug 4-way strip, 2.5mm2 PVC cable etc.) I soldered the wire tails before fitting the plug; this was before I'd seen any of the warnings on uk.d-i-y.

The washing machine is plugged into this lead (no other appliances because of the load) as a temporary solution while I wait for my bathroom to be refurbished.

For some time I'd noticed an occasional faint "hot bakelite" smell but had not been able to trace it to a specific device. I've just had the kitchen refurbished, and had GU10 halogen spots fitted in the ceiling as part of that work. I assumed that one of those was failing, or that the smell was the lamp housing simply getting hot.

Today the smell was particularly strong and I traced it to the plug of the extension lead feeding the washing machine. The plug and first two inches of cable were hot, but the washing machine plug was cool, as was the 4-way block itself.

Opening the plug and checking showed that all three screws had worked loose, and that the live connection had begun to burn up. Photos at:

you don't want to browse the album, this shows the burnt connection:

I cut the plug off, disposed of it and replaced it with a MK Safetyplug, where the wire tails wrap around the terminals instead of being held by a screw.

[Dave Osborne]

Thanks for posting this - all we need now is someone to add to the DIY Wiki (and nick your photo's if that's ok)...

[PCPaul]

(tinned wires in screw terminals considered harmful)

When I were an Electronics Engineering apprentice with the MOD we were taught to wrap a strand of thin steel wire round the stranded stuff then tin the lot, before clamping it in a screw terminal.

I wonder if it made much difference...?

[Mike Tomlinson]

In article , Dave Osborne writes

No problem, feel free to use the photos (and the text too if it's of any use.)

[The Natural Philosopher]

WE were taught to use a proper eye terminal soldered non, sleeved and then supported.

[stevelup]

I don't think you took enough pictures :)

Steve

[Mike Tomlinson]

In article , stevelup writes

:) had intended to pick out the best half-dozen but couldn't be arsed and uploaded the lot.

[PCPaul]

Well, it depended on the exact connector you were using at the time. The wrapped and tinned stranded wire was a very early exercise in 'wiring a mains plug'.

I still shudder at the thought of the 'Advanced wiring test' - a defined layout with every kind of soldered wire wrapped and crimped connectors that stores had in stock, mostly laid out with single strand wire that had to be laid out very neatly and flat to the baseboard. There were about 400 joints to do in all.

If just one joint had any problem (a bit of flux left on the surface, the sheath easing away from the wire because it got slightly too hot, the wire not being crimped firmly enough to a post before soldering, wires not laying flat on the board etc. etc. etc.) then you got it back to do again.

Any cheating (such as the ingenious use of clear nail varnish to lightly tack wires in to each other at tricky corners) resulted in a large part of the wiring being roughly pulled off, to be redone. I got it through after about three attempts. Some people would still be there now except it was the last thing done in the training workshops before heading out into the 'real' labs, so they ran out of time.