Wire nut ampacity

nizak

Senior Member
Is the ampacity of a wire nut determined by the maximum wire size it's designed for?


Never really thought much of it until recently . I've gone on 2 service calls, one a j box connection feeding an electric welder and the other a j box connection for a fairly high wattage cooktop. Both instances I've found the wire nuts pretty much toast.Both were residential applications, both on 60 amp 2 pole breakers with #6 NM cable on both.
I routinely use Ideal blue wire nuts on all my oven and cooktop installs and have never knowingly had a problem.
Anybody still using split bolts for these connections?
Thoughts.
 

retirede

Senior Member
Location
Illinois
My thought is that when installed properly, the wire nut itself should carry little to no current, and the contact area between the conductors should be sufficient to prevent enough heat to be generated as to cause damage.
 

macmikeman

Senior Member
Side note: I like to use itty bitty split bolts for circuits of #6 joining. Or the butt connectors with the screw lugs they sell in the orange big box store. Big Blue wire nuts are kinda dicey...........
 

Another C10

Electrical Contractor 1987 - present
Location
Southern Cal
Occupation
Electrician NEC 2020
The way I learned and agree with is as long as there is no air gaps or movement between the two or more conductors which inevitably causes excessive heat to occur, The connection is one of the most important aspects of the electrical system.

The wire nut on my profile here is the result of a loose connection, it usually starts off as micro arcing then just gets worse.
As a rule of thumb to myself, I wouldn't use a wire nut on any conductor larger than #6
 

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Semi-Retired Electrician
My thought is that when installed properly, the wire nut itself should carry little to no current, and the contact area between the conductors should be sufficient to prevent enough heat to be generated as to cause damage.
But the spring/wire inside the wire nut would have to carry current as it's contacting the conductors. The heat would come from a poor connection in both the conductors and the contact with the spring.
 

garbo

Senior Member
I worked at two large companies that had both vibrating equipment such as hammer mills, crushers,vibrating screens along with daily high pressure wash downs where water intrusion was a big problem. We always dropped the #14 to #8 guage longer then instructions said then pre twisted them with large linesmen pliers until you had a full twist on insulation, trimmed ends, tightened wire nuts with linesmen pliers then applied several wraps if quality electrical tape. Never had any failures. #6 guage & larger we used split bolt bugs or T&B crimped lugs using grade 5 Hex bolts , flat washers and lock washer's.
 

ActionDave

Chief Moderator
Staff member
Location
Durango, CO, 10 h 20 min without traffic from wing
Occupation
Licensed Electrician
Is the ampacity of a wire nut determined by the maximum wire size it's designed for?


Never really thought much of it until recently . I've gone on 2 service calls, one a j box connection feeding an electric welder and the other a j box connection for a fairly high wattage cooktop. Both instances I've found the wire nuts pretty much toast.Both were residential applications, both on 60 amp 2 pole breakers with #6 NM cable on both.
I routinely use Ideal blue wire nuts on all my oven and cooktop installs and have never knowingly had a problem.
Anybody still using split bolts for these connections?
Thoughts.
Anytime I have come upon a similar circumstance I figured the problem had to do with the nut who wired it, not the wire nut.
 

macmikeman

Senior Member

My thinking is the wire nut spring should never carry amps. The spring compresses the conductor together tightly if installed correctly

Also notice the wire nuts with square wire expanding spring vs round wire fixed spring.
The square wire wil actually cut threads to hold securely
I'm with you. I also say there won't be current on the screwshell until you try to attach a volt meter to it in which case it will then , by virtue of becoming part of the circuit if tested against any ground.
 

wwhitney

Senior Member
Location
Berkeley, CA
Occupation
Retired
My thinking is the wire nut spring should never carry amps. The spring compresses the conductor together tightly if installed correctly
If the spring is in contact with both copper conductors, and the the copper conductors are in contact with each other, then there are two conductive paths. Coper to copper, and copper to spring to copper. They will both carry current, in inverse proportion to their resistances.

Cheers, Wayne
 

Hv&Lv

Senior Member
Location
-
Occupation
Engineer/Technician
If the spring is in contact with both copper conductors, and the the copper conductors are in contact with each other, then there are two conductive paths. Coper to copper, and copper to spring to copper. They will both carry current, in inverse proportion to their resistances.

Cheers, Wayne
Correct.
I guess I should have said the wire nut should never carry any appreciable current.
 

Little Bill

Moderator
Staff member
Location
Tennessee NEC:2017
Occupation
Semi-Retired Electrician
If the spring is in contact with both copper conductors, and the the copper conductors are in contact with each other, then there are two conductive paths. Coper to copper, and copper to spring to copper. They will both carry current, in inverse proportion to their resistances.

Cheers, Wayne
I guess post #6 was invisible!:)
 
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