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CarlByrns
07-14-2014, 07:36 PM
I have an extension cord that needs a new plug and I'm wondering if I should tin the bare wires before clamping them or not. This cord is pretty heavy-duty- I use it for my air compressor and as a lead for the generator.

Thoughts?

IdahoJim
07-14-2014, 07:51 PM
Heavy gauge cords, I tin. Light gauge cords, I don't.
Jim

J Tiers
07-14-2014, 08:28 PM
Tinning is a bad idea.

While it may cut corrosion, it allows the connection to loosen.

The solder is "squeezable", and it will slowly relax (cold flow) away from the screwhead. You do not want that. You want a good solid connection to the copper strands alone.

If you want to prevent the strands from "brooming out", you CAN just tin the very end, to hold them. But you need to strip a long enough length that the tinned end will not be under the screw.

The effect was really bad with lead solder, the newer solders may in some cases be as subject to that, or more so, and in other cases less subject to it.

Paul Alciatore
07-14-2014, 08:33 PM
I have done it in the past primarily to control loose strands. Some of the older, cheap plugs and sockets made keeping the strands in control very problematic. But I have had problems with such connections. With modern plugs and sockets I would not recommend it. Just be sure all the strands are inside the clamp or hole.

Ohio Mike
07-14-2014, 09:03 PM
No, just buy good quality cord ends that have good clamp hardware.

IdahoJim
07-14-2014, 09:04 PM
Tinning is a bad idea.

While it may cut corrosion, it allows the connection to loosen.

The solder is "squeezable", and it will slowly relax (cold flow) away from the screwhead. You do not want that. You want a good solid connection to the copper strands alone.

If you want to prevent the strands from "brooming out", you CAN just tin the very end, to hold them. But you need to strip a long enough length that the tinned end will not be under the screw.

The effect was really bad with lead solder, the newer solders may in some cases be as subject to that, or more so, and in other cases less subject to it.
Interesting....I've never seen that. Maybe I should check my heavy duty cords.
Jim

Jon Heron
07-14-2014, 09:22 PM
What JT and OM said, avoid tinning. Besides the good reasoning given by JT the tinning will also make the end more brittle than without the tin.
Cheers,
Jon

CarlByrns
07-14-2014, 09:37 PM
Thanks, guys.
The cold flow effect is something I would have never thought of.

mickeyf
07-15-2014, 12:03 AM
Or, you could solder or crimp fork (or better yet ring) type connectors onto the ends of the wires and screw those down. For a serious heavy duty connection this is what I would do.

RichR
07-15-2014, 01:51 AM
Just twist the strands together. Get a decent plug. They have a hole that the wire goes into, tightening the screw squeezes the wire between two plates.

Benta
07-15-2014, 03:25 AM
Do not tin. As J Tiers say, tin will cold flow. Additionally, you'll experience that the cable will break in the section where tinned/non-tinned strands meet.

The correct way of doing it is to slip a ferrule over the cable end and then just tighten the screw.

Like these: http://www.heidemann-handel.de/aderendhuelsen-blank.html

Benta.

EVguru
07-15-2014, 04:40 AM
Copper cold flows too. We have a contractor who goes around all the electrical panels at work re-torquing the connections. The ones in the glasshouses in particular give trouble due to the wide temperature swings.

DR
07-15-2014, 08:12 AM
Do not tin. As J Tiers say, tin will cold flow. Additionally, you'll experience that the cable will break in the section where tinned/non-tinned strands meet.

The correct way of doing it is to slip a ferrule over the cable end and then just tighten the screw.

Like these: http://www.heidemann-handel.de/aderendhuelsen-blank.html

Benta.

I haven't tried the ferrule method. My first thought was the ferrule might be too large diameter to fit into the wire-hole in the cord end, especially with a "heavy-duty" cord's large strands. What about if the locking screw flattens the ferrule so much that you can't pull the ferrule'd section out of the wire-hole?

I have noticed on most older power tools the strands are tinned from the factory, old Delta stationary machines for example. It sure makes it easier to change a switch or cord end when the wires are tinned. Breaking of tinned ends is not something I've noticed, IME the more common problem with old machine cords is the insulation deteriorating.

J Tiers
07-15-2014, 08:34 AM
You'll mostly notice the old tinned ends are also very flattened. Obviously they "flowed" under pressure.

The breaking will not happen unless there is flexing. The break occurs at the end of the tinned area, where there is a stress-riser created between the stiff solidified strands plus solder, and the free strands just past the solder. Since solder alloys (dissolves) into the copper, there may be an added effect from that, but largely it is the stress riser.

The ferrule is a good plan, it keeps the strands together. That's what is mostly wanted anyhow. If the screws do not have some sort of "cup" or other method to keep the wires from brooming out, it may be best to use a crimped-on ring or fork terminal.

otherwise, wrap the wire around the screw in the tightening direction, and screw it down solidly.

browne92
07-15-2014, 09:40 AM
It's been a VERY long time, but it seems I read somewhere "official" (connector instructions? NEC?) not to tin.

Also, if I have enough room in the connector, I like to leave the ground wire an inch longer than the hot and neutral. That way, when someone yanks the cord out of the plug, the ground wire will be the last to disconnect. We did this a lot in the hospital because the nurses were notorious for forgetting to unplug the Life Pak when they took off with the crash cart for a code. We went through a lot of hospital grade plugs and outlets.

ikdor
07-15-2014, 09:57 AM
I know that the solder flows and that it's a definite no-no in mil spec and automotive. However, if the amount of solder is kept to a minimum, I would suspect that there will be little flowing in most (non vibrating) household applications. One could use their own judgement in such cases where tinning makes life easier.
Personally I'm a big fan of the ferrules, especially using square crimping pliers. What you stick the wire into also matters, with cage clamps being much nicer than the screw directly onto the wire variant.

http://cdn3.volusion.com/ucbgd.syjxw/v/vspfiles/photos/975304-2.jpg?1372170811

Igor

Benta
07-15-2014, 12:53 PM
First, thanks to J Tiers for a very good explanation of the cable break mechanism. I can only add that not only flexing, but also vibrations cause the break, which is why soldered connections are an absolute no-no in automotive and similar applications. Crimping is the way to go.

EVGuru: no, copper does not cold flow, it simply deforms. Cold flow (which means that the deformation happens over time) is a problem with tin and aluminium.

Using ferrules for stranded cable is mandatory in Europe, not necessary by law, but because if you have a fire due to bad connections you'll have a serious problem with insurance coverage.

The ferrules are (in Europe) available for all cable sizes in any DIY mart and used as a matter of course.

They are extremely easy to use and slip over the cable end with no problem due to the swaged end. If you want to make it absolutely perfect, special pliers that crimp the ferrules onto the cable are available.

Benta.

Rosco-P
07-15-2014, 02:41 PM
Since we have gone to dead front plugs in the USA, the possibility of strands of copper escaping from under the screw head has been all but eliminated. If you pre-twist the strands before pushing them into the clamp that should be sufficient. Can't quote the reg., but the NEC doesn't recognize soldering/tinning as acceptable for terminations. For fine strand wire like type W or SC in #6 or larger, yes I'd use ferrules, but that requires the approved hex crimper.

J Tiers
07-15-2014, 09:49 PM
I absolutely HATE the usual ferrules..... many crimp with large indents in them, which form a place for the ferrule to break, as well as catch on screw-down connectors.

A few crimpers (usually NOT the "hex" types) crimp with "flats" and those are acceptable to me, they don't break as easily.

Black Forest
07-16-2014, 02:58 AM
I absolutely HATE the usual ferrules..... many crimp with large indents in them, which form a place for the ferrule to break, as well as catch on screw-down connectors.

A few crimpers (usually NOT the "hex" types) crimp with "flats" and those are acceptable to me, they don't break as easily.

Would you name a brand that crimps with "flats"? I need to buy a crimping tool.