Safety of twist on wire connectors aka "wire nuts"

retirede

Senior Member
Location
Illinois
If you mean the conductor insulation that was never inside the wirenut (I don't think we can see any of that), that insulation is 5-10 times farther away from the spring in the damaged area than the damaged material of the wirenut. So I could imagine the temperature gradient being high enough that the exposed conductor insulation doesn't get damaged. But it's all speculation on my part.

Cheers, Wayne

I’m speculating as well, and my theory is not one I would defend to the death.

It’s a good discussion nonetheless.
 

ramsy

Roger Ruhle dba NoFixNoPay
Location
LA basin, CA
Occupation
Service Electrician 2017 NEC
Don't many wire nut instruction say to twist the nut until the twist is reflected in one or two twists of the wire outside the nut? The pictures show the wires running straight out of the failed nut.

Cheers, Wayne
Nut1.JPG

In this bell box, burnt nut was pressing against inside edge of metal plate before photo.
Both stranded conductors were tightly twisted together. Seems to me these red wirenuts had softer plastic than others.
Used as DC combiner for resi-solar array. Perhaps 1000.V+ megger test blew thru nut to metal box, before 120v DC eventually burned thru.

Nut3.JPG

The 20A circuit for this J-box was periodically overloaded ~30+ Amps, by 1500-Watt space heaters x 2, and laser printer, among other office computers, before this wirenut burt up & opened the circuit.

There were at least 10 outlets where space heaters & equipment were plugged in with similar wirenuts, albeit further downstream from fuse than this box behind exit sign. If memory serves this #12 wire was solid.
 

ramsy

Roger Ruhle dba NoFixNoPay
Location
LA basin, CA
Occupation
Service Electrician 2017 NEC
Here are a couple where I rubbed a maker over the embossed markings to make them readable. View attachment 2561654 View attachment 2561653
I see similar markings on my photo.

Nut2.JPG
If I'm not the only one encountering failures like this, then the weekest link in building wiring is empirically found at the connectors, or devices for those who wire thru device terminals to avoid connectors, except where prohibited by code.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
I see similar markings on my photo.

View attachment 2561669
If I'm not the only one encountering failures like this, then the weekest link in building wiring is empirically found at the connectors, or devices for those who wire thru device terminals to avoid connectors, except where prohibited by code.
Again, improper installation ....the brand is one that has instructions that require you twist the wire nut until there are at least two full twists of the conductors showing below the skirt of the wire nut. The instructions also recommend, but do not require pretwisting of the conductors before the wire nut is installed.

In addition, you have insisted that these products are not listed. Are you changing that statement?
 

hbiss

EC, Westchester, New York NEC: 2014
Location
Hawthorne, New York NEC: 2014
Occupation
EC
I guess I am "Cheap" ... I have reused a wire nut or two at times., could this be the results ?

VERY good point. I've commented on that practice in the past. Could the spring have been stretched out by previously being installed on a greater number of conductors?

I know a guy who would never throw a wire nut away. Cans and pouches full of used ones on his truck.

-Hal
 

ramsy

Roger Ruhle dba NoFixNoPay
Location
LA basin, CA
Occupation
Service Electrician 2017 NEC
In addition, you have insisted that these products are not listed. Are you changing that statement?
Asking for a mulligan doesn't bother me, but I can't promise the purple wirenut has no counterfeit in circulation, without sending those to IDEAL for analysis.

If listed OEM products encounter failures from reasonable people having difficulty installing them correctly, rather than worry about it, device feed thru or terminals are available to reduce the need for using wirenut connectors, with inferior UL-test requirements.

UL 498 tests punish receptacles at 150% of rated current,1500 Volts, 1000A fault current, and for Mold stress relief: Unwired receptacles are subjected to 70°C for 7 hours, hospital grade @ 90°C..

Qualified persons expect UL listed feed-thru device lugs to handle idiot proof abuse, well beyond UL 486A,B,C ZMVV 300+ Volt standard for wing nuts.
 
Last edited:

Fred B

Senior Member
Location
Upstate, NY
Occupation
Electrician
The purple wirenuts, they are for Aluminium conductors. Is there Aluminum wire there? Is there a mix of Al/Cu present? Could a failure be the result of the difference in capacity? A 14Al would "look close" to a 12Cu in size at a quick glance, and even if correctly sized cannot carry the same amperage and the could be cause of a cascading failure, and meltdown.

If there is no Al, I wouldn't be using these connectors cost way more than Cu wirenuts.
 

kwired

Electron manager
Location
NE Nebraska
I see similar markings on my photo.

View attachment 2561669
If I'm not the only one encountering failures like this, then the weekest link in building wiring is empirically found at the connectors, or devices for those who wire thru device terminals to avoid connectors, except where prohibited by code.
A weak connection is a weak connection, I seen plenty of single devices with failed terminations as well as ones with feed through connections.
 

kwired

Electron manager
Location
NE Nebraska
The purple wirenuts, they are for Aluminium conductors. Is there Aluminum wire there? Is there a mix of Al/Cu present? Could a failure be the result of the difference in capacity? A 14Al would "look close" to a 12Cu in size at a quick glance, and even if correctly sized cannot carry the same amperage and the could be cause of a cascading failure, and meltdown.

If there is no Al, I wouldn't be using these connectors cost way more than Cu wirenuts.
There is no 14 AL conductors - at least not for general usage. Minimum size is 12 AWG, though it's ampacity is similar to 14 AWG copper.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
Asking for a mulligan doesn't bother me, but I can't promise the purple wirenut has no counterfeit in circulation, without sending those to IDEAL for analysis.
...
You can't promise that about any product...there were counterfeit breakers on the market that were really only switches....no tripping device.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
...

UL 498 tests punish receptacles at 150% of rated current,1500 Volts, 1000A fault current, and for Mold stress relief: Unwired receptacles are subjected to 70°C for 7 hours, hospital grade @ 90°C..

....
So you have never seen failures on receptacles that are similar to the ones you are showing us for wire nuts?? There are plenty of those types of failures with receptacles, and for the same reason .... poor installation practices.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
....
Qualified persons expect UL listed feed-thru device lugs to handle idiot proof abuse, well beyond UL 486A,B,C ZMVV 300+ Volt standard for wing nuts.
Table 2 in UL 489C that applies to splicing wire connectors requires that a 300 volt rated wire nut pass a 2200 volt insulation puncture test and a flashover test of 4,000 volts. Those test values rise to 3,400 and 8,000 volts for wire nuts rated at 600 volts.

The static temperature and current cycling tests are made at values that substantially exceed the maximum permitted OCPC for the conductors as found in the NEC. Table 6 shows the static test current for 14 AWG copper 30 amps and the current cycling test current at 33 amps. For 12 copper those numbers rise to 35 and 39, and for 10 copper 50 and 56. For 12 AWG aluminum the currents are 30 and 43, 10 aluminum the currents are 40 and 60 amps. Those values match up with the 150% used for the wiring devices.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
If arcing is possible after a nicked conductor breaks inside the wire nut, arcing temperatures tend to destroy anything they touch.
Again an improper installation....this work requires that the installers know and understand how to make electrical installations.
 

ramsy

Roger Ruhle dba NoFixNoPay
Location
LA basin, CA
Occupation
Service Electrician 2017 NEC
So you have never seen failures on receptacles that are similar to the ones you are showing us for wire nuts?? There are plenty of those types of failures with receptacles, and for the same reason .... poor installation practices.
Yes, loose terminals with fireworks is one example, but I've also documented text-book copper wire hooks around device terminals with non-conductive galvanic reactions.

When both wirenut connector & device suffer miss use or defect, the air gap around mounted device remains a decided advantage.
 

4x4dually

Senior Member
Location
Stillwater, OK
Occupation
Electrical Engineer
I can't believe I just read 57 posts about wire nuts.....quite possibly the most insignificant part every used in the industry....that causes the most significant amount of problems.

I do not pre-twist stranded conductors.
I do pre-twist solid conductors.

What says you experts?
 

retirede

Senior Member
Location
Illinois
I can't believe I just read 57 posts about wire nuts.....quite possibly the most insignificant part every used in the industry....that causes the most significant amount of problems.

I do not pre-twist stranded conductors.
I do pre-twist solid conductors.

What says you experts?

To pre-twist or not is a rabbit hole not worth revisiting.
 
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