Wire nut ampacity

Tulsa Electrician

Senior Member
Location
Tulsa
Occupation
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.
Interesting
Have any current or voltage drop info
 

Another C10

Electrical Contractor 1987 - present
Location
Southern Cal
Occupation
Electrician NEC 2020
In my world, the wire nut simply insulates and helps lock tight the already tight solid wire twist, stranded on the other hand does need help from the wirenut to assure the joining of the conductors stay snuggly pressed upon each other. The majority of current is easily transferred onto the clustered wire/s, the wire nut should not be the determining factor of current flow.
 

ElectriPat

Member
Location
USA
Occupation
Electrical Contractor
6 or 8 awg really can't be twisted and then have wire nut put on. We use split bolts without issues. Now that we have the md7 it's crimp time...
 

Fred B

Senior Member
Location
Upstate, NY
Occupation
Electrician
The melted down wirenut I don't think is strictly an amperage issue but more likely an issue with temperature rating. Never looked but what are the temperature rating of a typlical wirenut? A welder can develop a significant load that might exceed the temperature listing of the connector but not the wire. (Just a thought).
Seen a lot of plug in welders that the owner would simply plug into the xx amperage receptacle just because "it will fit in", but no knowledge or consideration of duty rating impact on temperature rating of the components of the electrical system being plugged into.
 

Tulsa Electrician

Senior Member
Location
Tulsa
Occupation
Electrician
There no doubt the wire nut had a connection issue with the conductors or it would not have gotten hot enough to dis form the shell.
If it was just one and not both them I would access the connection as the issue. If both did one create enough heat to damage the other.
One way to tell is look at the spring. One will be discolored and one may not. With any spring heat is bad for there constant. Once a spring is over heated it is rendered ineffective.
So wonder what that spring is made of.
Also if only one had an issue then I would say your have a resister at that point. Good old series circuit stuff. KCL and KVL. Even if both had an issue. This why I ask about voltage drop at the welder/ cook top under load.
Taking measurement at given point along the circuit will help tell a story.
If the connection had enough R at joint it would become a resistive load and produce heat. So was it's the wire nuts fault?
The spring can not become weak from heat unless it was there first.
The plastic can not become distorted from heat unless the connection had enough R.
I would also look at the time between install and failure.
 
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