I have never seen any hard statistics. However, in my experience they are
reliable if they are installed properly according to the manufacrturers
instructions... wires stripped to correct length, not exceeding the rated
number of wires, wires in the rated size range, etc. If you remove the wire
nut you will see tightly twisted conductors almost fused together. The
problems I have seen with them are traceable to improper application. I have
seen wire nut connections that were in fires (unrelated to the connector),
and they still had the spring tightly installed, although the plastic burned
Benjamin D Miller, PE
I agree with (almost) everyone that wire nuts are reliable when used as
Some wire nuts have a spring which will expand over the wires.
Others have hard plastic behind the spring and the springs can't deform.
In my experience the expanding ones work much better.
If they are installed correctly they are ok. However you can't use them
on multi-strand cable and are not really suitable for isolating a
They aren't used at all here in Australia; The standard connector is a
BP style connector with one terminal screw for current carrying
conductors and a twin screw type for earthing conductors.
The drawback with this type is with single core. The screw someimes
scars the copper, weakens the conductor and causes it to break.
I guess to answer your question, Wire nuts are safe as long as they are
installed correctly and used in a suitable application.
The same applies to all electrical connectors that meet working
electrical codes and/or stanadrds.
It happens that firstname.lastname@example.org formulated :
Well, if that is the case then I stand corrected.
I have been led to believe that the the twisting motion damaged finer
strands and it made that type of connector unsuitable for use with
Wire nuts reliability is about workmanship. I always twist the wires
together first befors applying the wire nut. I also apply electrical
tape over the wire nut where there is vibration such as motor terminal
housings. It is also important to read the instructions and use the
correct wire nut for the size and number of wires.
At a mine job the engineers speced buchanan connectors that are a
crimped connection. That was a good idea, except there weren't enough
crimpers to go around and some electricians crimped them with their
pliers. I opened one box and these plier crimped connectors fell
off. Wirenuts with tape would have been much better.
Any connector that requires a special tool to install properly has
that risk associated with it. That is why unionized electricians have
a negotiated tool list that they are responsible to have with them on
every single day on the job. If the job requires a particular tool,
and that tool is not on the tool list, it is management's
responsibility to see that no one is given that connector to install
that is not also issued the appropriate installation tool. It is a
management function to match materials to the job to be done AND
provide any unique tool that is for only a single task as well as all
The job I am referring to is the Red Dog Mine Port site concentrate
storage building job 70 milers north of Kotzebue, Alaska in about
1999. It was a union job (IBEW). All deliveries were by air and it
took a week or two to get a tool. The electricians were under the gun
to produce and the job covered a lot of area. A concentrate building
is about 1250 feet long by 300 feet wide and had a catwalk up 90 feet
from end to end It would take about 20 minutes to walk from the cat
walk to the end of the job and another 20 minutes to walk back. I
cannot blame an electrician from crimping the buchanan connectors with
their pliers. I think there were two crimping tools for 18
electricians. Using taped wire nuts would have been much better.
This is the second time you have refered to "taping" the wire nuts. I am not
aware of any manufacturer's instructions or UL listing requirements that
call for tape. In my opinion the tape is useless, and in fact I have removed
tape at times to find shoddy workmanship underneath (ie. exposed conductors
because the insulation was stripped too far). The problem is, you are then
relying on the tape for insulation so the workmanship for applying it comes
into play. For example, according to tape manufacturer's instructions,
proper layering is required and the last wrap is supposed to be stretched
significantly (there is a spec as to how much) to prevent unraveling.
I think the taping is just a habit handed down from generation to generation
of electricians. If you install the wire nut according to instructions, it
is reliable and does not require tape.
Benjamin D Miller, PE
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