Wire Nut temp. rise with "dryer" circuit?

[john374]

What is a normal temp rise, on a brown wire nut, for a 30A circuit? A friend of mine hired a new contractor to install a bunch of appliances. She asked me to observe the installation. I did. The newly minted contractor used brown wire nuts to connect together the wires of two 1 ph. 30A 3+one 10AWG cables, running from the service panel to a junction box. Why he split the cable, he had enough new cable, I don't know. Said he didn't like the crowed service panel.
Anyway, when the owner of the residence turned on the second floor close dryer I measured the temp. rise on the wire nuts in the junction box and noticed a 5 degree F rise.
Now, as an ex engineer I think that a perfect connection would have no resistance, thus no tenp. rise. But, the world is not perfect. So, I ask; how much of a temp. rise, in a 1 ph. 30A circuit, would you expect at a wire nut join?

 

[zbang]

. So, I ask; how much of a temp. rise, in a 1 ph. 30A circuit, would you expect at a wire nut join?

very little above none - unless the entire conductor heats up, then I'd expect it to pretty much match. A joint that even gets warm on it's own is not good.

 

[don_resqcapt19]

A good connection will have almost the same temperature rise as the conductor itself. Did you check the temperature rise of the conductor away from the connection.

 

[templdl]

In my opinion heating is not acceptable because if there is heating it only get worse. The heating cooling cycle cause expansion nd contracting which works to losen the connecting further.

 

[john374]

Thanks for replies

Thanks for replies

Well, I guess I forgot one item. How much do the wires themselves increase in temp. I guess I'll have to go back to her residence and make that measurement.
I'd think a 5 degree F rise in the wires would be too much; but, what do I know.
I still think that rise at the wire nuts is too much; but may be I'm just nuts
May be I'll ask her if I can redo the connections. But then I'm responsible. Or may be she just get him back; but that would mean making him angry.
What a conundrum.
Again, thanks for your replies.

 

[winnie]

A 5F temperature rise in the wires when carrying current is IMHO totally reasonable.

Unless you use superconducting wires, there has to be some resistance and thus some temperature rise.

If you look at the definitions of conductor ampacity for NEC 310.16, most residential installations have wires installations that are based on the expectation of a 40C temperature rise. The calculations used to arrive at the 'ampacity' numbers hava a bunch of fudge and safety factors built in, and most circuits are never used at their ampacity, so that sort of temperature rise would be very uncommon...but a 5F (3C) rise is totally reasonable!

-Jon

 

[john374]

Thanks Winnie

Thanks Winnie

Guess I'll have to look at the NEC again. thanks for the reference.

wow, 40 degrees C rise. Looks like a lot to me; but if the insulation and box can handle it then I guess I'll just let it go.
Thanks

 

[PetrosA]

If you want to check the connections, there are two things I'd check for:

1) is there at least 1/2-inch of twisted, stripped conductors under the wirenut
2) are either of the conductors nicked deeply from stripping with pliers or ringed from using the incorrect hole on wire strippers

Dryers typically draw about 22A, so well within the rating of a 10 AWG CU conductor. Unless the connection is above the temp of the conductors themselves (as measured some distance from the splice), you're probably fine.

 

[john374]

Thanks PetrosA

Thanks PetrosA

The wires were not pretwisted; i.e., just straight.
Didn't see if they were stripped 1/2 inch. As to nicking, he eyeballed the distance and just cut with a knife.
I really was appalled by his technique; but who am I to tell someone they are not doing it correctly.

 

[templdl]

Would be approprete

Would be approprete

The wires were not pretwisted; i.e., just straight.
Didn't see if they were stripped 1/2 inch. As to nicking, he eyeballed the distance and just cut with a knife.
I really was appalled by his technique; but who am I to tell someone they are not doing it correctly.

Thee is a technique to strip he wire with s knife without damaging the wire. If done haphazardly damage can occur. Even when done with a wire stripper if used incorrectly the wire can be damaged.
I wouldn't anticipate that to be the cause of your issue but nevertheless it would be appropriate to eliminate the possibility.
And someone who does this all the time isn't going to take the time to measure each time he strips a wire.
If you are qualified I wouldn't find it to be an issue to redo the connection to you satisfaction.

 

[john374]

Thanks templdl,
Since he is just starting his business and was a Marine security person before this I'm not sure just how much experience he's had. Don't even know if he's apprenticed with anyone.
Just the same, it seems like I over reacted and will just let it drop. After all, the nuts are in a metal box so probably little chance of heat/fire damage.
Sorry for taking up everyone's time with this.:roll:
Sincerely, John374

 

[rt66electric]

Brown wire-nut ?? do you mean Tan??

Brown wire-nut ?? do you mean Tan??

Brown wire-nut ?? do you mean Tan??

 

[templdl]

Thanks templdl,
Since he is just starting his business and was a Marine security person before this I'm not sure just how much experience he's had. Don't even know if he's apprenticed with anyone.
Just the same, it seems like I over reacted and will just let it drop. After all, the nuts are in a metal box so probably little chance of heat/fire damage.
Sorry for taking up everyone's time with this.:roll:
Sincerely, John374

Thanks John374,
I caution you with just letting this go as there was something that caught your attention and concern. If the individual has sufficient knowledge of safe electrical practices and procedures there shoud be no concern. But you are not sure as to how much experience he has and being a Marine (thank him for his service) isn't quite enough to be qualified.

 

[PetrosA]

I don't normally use tan twisters, but my guess is that two 10s, not pretwisted, hand tightened under a tan is not going to create a good connection. There aren't many guys with enough strength in their fingers to twist that bad boy enough to actually get the wires to twist around each other without using a drill and attachment or a nut driver. So the only real mechanical connection making the splice is the spring in the wire nut. If the wires are not laying perfectly flat against each other, there is likely only a tiny little spot where they're making actual copper-to-copper contact. I would not be happy with that splice.

 

[john374]

Brown wire-nut ?? do you mean Tan??

Yes, just couldn't tell the difference in the dim light with my old eyes.

 

[iwire]

I don't normally use tan twisters, but my guess is that two 10s, not pretwisted,

Warming up the close thread button .....

 

[john374]

Thanks PetrosA for the insitefull post.

Thanks PetrosA for the insitefull post.

I don't normally use tan twisters, but my guess is that two 10s, not pretwisted, hand tightened under a tan is not going to create a good connection. There aren't many guys with enough strength in their fingers to twist that bad boy enough to actually get the wires to twist around each other without using a drill and attachment or a nut driver. So the only real mechanical connection making the splice is the spring in the wire nut. If the wires are not laying perfectly flat against each other, there is likely only a tiny little spot where they're making actual copper-to-copper contact. I would not be happy with that splice.

Actually, that's what I thought. In 2002 there was a lot of controversy about pretwisting. Don't know if that was ever settled. I think you hit the nail-on-the-head with the strength required to twist. The angle was not the best and he had just smashed his index finger, with a hammer, the day before and had two finger-long splints on it. Thus, he complained about not being able to use his right hand very well. May be the nuts were not tightened very well. I don't think I saw a twist in the wires. You're correct I think; the spring in the nut is the only connection.
Again, thanks for the good analysis.
I'll have the check the tightness; or may be just redo the connections he made.

 

[Strathead]

Warming up the close thread button .....

Then I will resist the urge to blast his opinion that UL obviously doesn't share.

 

[iwire]

Actully if you guys want to go down that road I will not close it, another mod might.

But it seems like arguing what color of a rainbow is best.

 

[john374]

Change of thread

Change of thread

Actully if you guys want to go down that road I will not close it, another mod might.

But it seems like arguing what color of a rainbow is best.

Are you telling me that after 15 years the pretwist or not question still has not been been answered?