Soldered wire connections

[crackle]

I happened to be watching fake Britain today and they were demonstrating what they described as a fake hairdryer. One of the points that was picked up on was the wire ends in the 13 amp plug were soldered and then fitted into the screw terminals and tightened. This they described as illegal and dangerous.
The other aspect of the hairdryer was when tested it had no effective overheat cut out and eventually caught fire when the airflow was blocked.

But what about the soldered wire ends, anyone care to justify what they claimed on the program about them being dangerous, more so than ordinary dry copper multistranded terminations.

Mike

[Terrykc]

Mike, solder is soft and compresses easily.

This deformation continues after the screw in the connector is tightened as, over time, the metal will creep slowly away from the compression point causing the resistance of the joint to increase - it is effectively the same as undoing the screw connection slightly.

Another problem with soldered flexible leads - which should NOT happen in a mains connector! - is that, as the lead flexes, the individual thin wires will break, one by one, at the point where the solder starts because that is the point of maximum flexing.

The correct solution is a crimped brass ferrule on the end of each multi-stranded conductor.

It would probably be OK for your own use to tin the very end of the flexible conductor to stop stray wires separating as you push the wire into the hole provided that the tinned portion passes completely through the hole in the terminal. I doubt such a practice would be acceptable in a production environment, though.

No doubt someone will be along in a minute to quote the official version ...

[Kalee20]

Exactly as Terry says.

I have also seen multistrand wire being tinned with a soldering iron before being crimped in a standars crimp connector. The wire was loose in the crimp, in a matter of a fortnight.

[Alistair D]

Mike, check your mains plugs. If you find one with tinned wires you will almost certainly find the screws are much looser. After a good number of thermal cycles the soldered wires will have deformed more than the untinned ones.

Al

[crackle]

I have learnt something today.
I have wired several boats that I have built new or refitted over the last 30 years and normally always soldered any flexible stranded wires.
Where the atmosphere is heavy with minute droplets of salt water, soldering helped prevent corrosion in the thinner stranded wires. It may sound impossible but thin salt deposits would be found on even the most protected areas in the cabins. The ideal was to use wire with thicker/less strands but that was not always possible when some equipment was supplied with its own cable. Single stranded wire was not recommended for wiring where any degree of movement or vibration may be involved.
I have not noticed any more problems with soldered/screwed joints working loose than with bare copper joints working loose.
To be honest on some ultra thin cables (instrument data wiring) it was sometimes almost impossible to make any reliable connection with screw type terminals with out first folding the copper strands a couple of times and soldering the folds together.

Mike

[alanworland]

Don't think I have ever undone a stranded tinned joint that hasn't been 'loose'!
It's nice to keep the strands tidy but if you have to, as Terry says solder the very tip and pass it through the terminal.
In a lot of respects provided a crimp is deployed with the correct tool and size of termination it will provide a gas tight joint which should be very reliable.

Alan

[Niall]

I have wired several boats that I have built new or refitted over the last 30 years and normally always soldered any flexible stranded wires.

I wonder how this affects "marine grade" cables which are copper stranded with the strands individually tinned? Ordinary copper wire in a marine environment rapidly turns black. I am gradually converting the wiring in my boat to marine grade and while most connections are crimped there are some connectors which have screw terminals.

[Cathovisor]

Certainly when I used to do safety testing, any wires that had been soldered before placing in mains plugs were an automatic fail for all the reasons outlined above - plus of course, under high-current conditions the pin can heat up, soften the solder and then it'll migrate and make the contact between wire and terminal screw even worse.

I always tried to avoid the 'hole and screw' type of termination, preferring the 'MK' style of terminal in plugs.

[Alistair D]

Good point re the safety testing fail.

As far as I am aware no mention is made of checking this during the inspection phase of PAT. It should be.

Al

[sideband]

Mike, solder is soft and compresses easily.

This deformation continues after the screw in the connector is tightened as, over time, the metal will creep slowly away from the compression point causing the resistance of the joint to increase - it is effectively the same as undoing the screw connection slightly.

Another problem with soldered flexible leads - which should NOT happen in a mains connector! - is that, as the lead flexes, the individual thin wires will break, one by one, at the point where the solder starts because that is the point of maximum flexing.

The correct solution is a crimped brass ferrule on the end of each multi-stranded conductor.

Absolutely 100% correct!

We test lots of hairdryers and other domestic products to EN60335 and one thing that is NOT allowed across all products is soldered wire ends on mains leads or any mains connections withing the appliance. As Terry says, brass ferrules are permitted and in addition, the mains lead should be clamped or secured near the connection. This of course is taken care of (or should be) by the lead clamp in the mains plug. Inside the product any other effective means can be used to secure the cable so that there is no movement of the actual connection during use.

[Niall]

As far as I am aware no mention is made of checking this during the inspection phase of PAT. It should be.

It's a long time since I did a PAT course but as far as I remember part of it involved checking rewireable 13A plugs for correct fusing, terminal security and correct wire length. The instructor highlighted it as the most likely source of problems.

[alanworland]

When carrying out some rewiring on my Morris I used bootlace cable ends, kept all the strands in place and could be removed from the terminal if required without fear of losing the odd strand!

Alan

[crackle]

Hi
I take all the points about solder being soft with a low melting point, and the possible effects this can have.
But I have not had any problems with loose or burnt terminals on soldered joints.
If you can get hold of it and justify the expense, tinned wire is better in a marine environment.
Not all chandlers sell it, preferring the cheaper domestic or automotive type cable.
Mike

[Terrykc]

I wonder how this affects "marine grade" cables which are copper stranded with the strands individually tinned?

This is a completely different situation. In the first place, all the strands are completely separate and, in the second place, the thickness of the tin coating is infinitesimally small compared with the diameter of the conductor.

If you consider the amount of solder on a tinned end of bare flex it will make it larger overall than the flexible conductor itself and will also fill all the minute gaps between the individual wires so it will form a considerable portion of the overall cross section. That will not be the case with the individually tinned conductors.

I would expect most migration to take place when the terminal is tightened initially and any difference in contact pressure afterwards to be very small.

After all, there is a difference in the thermal coefficients of expansion of copper and brass, so it could be argued that plugs should only be fitted when the pins are heated to ensure that the contact pressure cannot diminish over the normal range of operating temperatures!

Funny - considering the number of 13A plugs I must have fitted in over half a century, I've never thought of a connection with the way they fit the steel tyres on the wheels of railway vehicles before!

[Cathovisor]

Good point re the safety testing fail.

As far as I am aware no mention is made of checking this during the inspection phase of PAT. It should be.

Al

It's part of the visual inspection regime at the BBC; it also gives you the chance to (a) check that the right fuse is [still] fitted and (b) tighten the terminal screws if they need it.

[Alistair D]

Mike

I have not checked the spec for marine grade cable but it may be the case that the tinning contains no lead and so the tinning material will not suffer the same non elastic deformation that a lead based solder would.

Al