Is twisted and taped splice on cable, objectively any less stable than wire-nuts or terminal blocks?

Question

In Brazil, electrical connections are almost always done splicing electrical cables by twisting the strands together and insulating them with electrical tape. Here is a video showing some of the connections the way they are done in Brazil. Terminal blocks are only used on some specific applications and wire-nuts are nonexistent here.

Here on DIY.StackExchange and elsewhere, I've seen criticism of that method and statements that wire-nuts are the way to go.

Is a stranded cable connection, twisted and taped as shown in the video, objectively any better or worse than wire-nuts/terminal blocks?

Answer 1

Splice connectors such as US-style wirenuts and UK style terminal blocks are demonstrably better in nearly every way to the twist-and-tape method you describe.

1. Wirenuts and terminal blocks are more resistant to mechanical failure due to heating/cooling cycles and the mechanical stress of installation.
2. Wirenuts and terminal blocks are easier to inspect and test, even long after initial installation.
3. Wirenuts and terminal blocks are easier to install CORRECTLY and require less training to do so.
4. Wirenuts and terminal blocks can be quickly removed, and can be re-used without shortening the wire.
   1. Tape can be removed and the wires reused, but the process is labor intensive and messy because of the adhesive. It's easier to cut the wires before the splice, thereby shortening the wires.

So why are wirenuts not more common everywhere? Cultural bias and intertia. For example, wirenuts are not commonly used in the UK because an early wirenut product in the UK market had a design flaw and frequently failed, spoiling the reputation of the product. Terminal blocks became the standard by default. Because of this history, wirenuts are seen as inferior in the UK, when they are empirically not. They are just different than the commonly used terminal block.

I would argue the same is true for twist-and-tape joints in Brazil: it's how it was done in the past, and anything different is strange and therefore must be wrong. The only difference is that, at least for household wiring, wirenuts and terminal block are empirically superior to twist-and-tape splices.

Answer 2

Is a stranded wire connection, properly twisted and taped, objectively any worse/better than wire-nuts?

I have not found any objective studies that compare a properly-made twisted splice of stranded cable with joins made using a US wire-nut, a UK terminal block or other systems such as the Wago 222 lever connector (and other makers equivalents).

Various similar types of twisted connections are used in specialized cases. For example NASA use a "linemans splice" in some situations. But they have very strict rules about how the connection is made. I imagine they are rigorous about inspecting and checking the quality of these connections before they are permitted to be used.

The main reasons that the type of connection preferred in homes in Brazil are not permitted in homes in other countries probably include:

• It takes skill and regular practice to do properly.
• It is very time consuming to do properly.
• It takes dedication to scrap and redo connections that end up done poorly.
• It is difficult to do properly in many real-life situations. For example in a dark area where space in a junction box is limited and the available wire length is short.
• It is likely that some untrained people, perhaps householders, copying this type of professional connection, will do it carelessly and very badly and produce a weak and unsafe electrical connection.
• It is relatively difficult to undo this join in a way that the wires can be included in another subsequent join.
• The insulating tape may make it slightly more difficult to trace electrical faults to failures in the joins.
• Poorly made joins will be concealed behind tape.

In the US, UK and similar high-wage countries, it probably costs less for an electrician to use faster techniques and tools than to spend time carefully making this kind of splice. This may not yet be the general case in Brazil.

Answer 3

There are a few cons to using tape: I think the most imperitive factor is that a good tape-job is difficult or impossible to verify (an inspector couldn't tell if 3 wraps or 4 were used). Also working on the wires later is often a goey mess, because tape breaks down. And tape is slower to install than wire nuts (time is more expensive than material).

Electrical tape cannot be used in USA as the only thing holding wires together; they must be connected by another means. A primary factor for instituting that law, is that workers or safety inspectors would be liable for failure to apply the tape correctly, which is hard to prove, and laborers/people are harder to collect restitution from than corporations (that have money). Also, having money allows corporations to push/influence laws. But, while I'm kind of cynical, I also appreciate the pros for wire nuts. I would prefer to see wire nuts in my home because they are (almost) fool-proof and any error/fault can be attributred to the manufacturer (part of the reason that manufacturers are abandoning this country, but that's another issue).

Also, having a good electrical system is not just a matter of having something that works- it's about organization and utility of the finished product; so that anyone who comes along behind the original electrician can easily modify or repair the system.

The only pro that I can think of for tape would be versatility. One product for any connection.

With regard to the twisted and interlaced connection (from the youtube video: https://youtu.be/Y9TrJhAGcoA), the tensile strength of this connection is good, but superfluous for conduction.

Answer 4

While i am a communications engineer [MSEE], i have wired a few houses, as well as done quite a bit of field engineering. What i would question with the twisted/taped connection, is whether the joint is "gas tight". Merely twisting the wires allows moisture and oxygen into the joint. Over time, particularly in a moist environment, this can lead to corrosion, resulting in a high resistance joint, and a potential fire (if it's power wiring). A "wire nut" tends to prevent this by screwing down on the wires, thereby tending to eliminate oxygen + water (and the resulting corrosion) from the joint. For something in a moist environment (possibly outside), as well as something carrying significant current (over 5 amps or so), my preference would be to solder the conductors together, and then either tape them - with the "fusing" type tape that melts together with itself - or, pot it in epoxy, with one of the 3M [Minnesota Mining & Mfg] or a competitor's product. Properly done, this should survive under water immersion over a long time. Cheers.

Answer 5

A 7 twist solid copper wire has fair strength but over time especially with just tape the connection can loosen with big loads as the wires jump around. Wire nuts are normally used in the US on 10, 12 & 14 AWG wire.

Stranded wire will not hold up with out some kind of pressure connector a wire nut works great on stranded. With larger wire sizes Split bolts and compression fittings that are bolted together then insulated with Cambric, Liner less (rubber tape) and black tape (I use super 88).

The second problem with just tape it breaks down over time and or heat, Have you ever seen the black goo in the wires from the tape breaking down? Wire nuts allow more secure connections in a smaller area where you may have many connections coming in a box I would feel much better with a wire nut than several wires twisted and taped.

If the wires were also soldered maybe it could be a better way but solder melts and causes additional paths to ground so it is not allowed.

Much of the world uses the NEC national electric code as a wiring standard so I would say someone without a superior method is more of a hobbyist.

The only better way than wire nuts that I have seen is screw terminals but these take a lot of room and are normally only used in industrial control panels.

Answer 6

The main advantages to twist-on wire connectors are ease of use, and time required to make a splice.

Making a reliable connection with twist-on wire connectors is easy, only requiring three simple steps.

1. Strip the wires
2. Put the connector on the wires
3. Twist until secure.

A twisted splice is a bit more difficult, requires a bit of practice to get right, and may require multiple types of tape.

Since making a splice with twist-on wire connectors only requires three simple steps, splices can be made quickly.

Twisted splices are a more complex, and so require longer to make up.

One additional advantage to twist-on wire connectors, is that you can use them to connect more than just two wires. Most twist-on wire connectors allow you to connect four or five wires together, whereas a twisted splice only allows two.

Answer 7

I use "butt connectors" for every application. Tape eventually wears out like other have mentioned. Butt connectors are those that get crimped through a little metal tube (usually) making the connection very secure. I have never had a problem with them coming out. Good luck!

Answer 8

Hm. Different strokes for different folks... In my country, terminal blocks are mandatory. So, to me, THAT'S normal.

However, a 'butt connector' or other crimped connection is fairly solid. I´d like to point out that a proper lineman's splice works fine for solid copper wire, as far as I'm concerned, insulated with a couple layers of heat shrink tubing.

As for stranded, same thing, but soldered so it doesn't unwind. And I've found wire nuts (found inside US manufactured equipment) broken (overtightened?) or had them break apart as I respliced wiring.

You can prolong the life of plastic tape insulated splices by rubbing them all over with a hot soldering iron. The bits tend to fuse together, and don't come undone when the adhesive dries up. However, I prefer heat shrink tubing.

BTW, are wire nuts good for 40 Amps? I use terminal blocks for that current regularly, and, if properly tightened, they work just fine.

Cheers, staqUUR