Behavior of Joule Heating in few contact points terminals and arcing

[kwired]

earlier today i read that overtightening screws has effects of undertightening in long term because when the conductor vibrates it can become damaged and loosen. I couldn't find the information again after searching for half hour so if you know the details, please elaborate how true it is. This was what concerned me that only a torque wrench is worry free to avoid oxidation and burning in future. But there are different models of torque wrench. The good one is one where you can hear an obvious click. So what brand and model is that?

Several manufacturers make a click style torque wrench.

 

[tersh]

Several manufacturers make a click style torque wrench.

According to an inspector:

https://iaeimagazine.org/magazine/2015/01/15/inspecting-electrical-connections-for-proper-torque/

"Torque screwdrivers of different capabilities can look identical but be very different. Once while doing an inspection while the electrician was using a torque screwdriver, I knew something was not quite right by the sound the torque screwdriver made when it reached the set torque. The sound was very faint compared to others I had encountered. After investigating, I discovered the torque screwdriver being used was measured in inch-ounces. There are identical looking torque screwdrivers that have increments given in inch-ounces and inch-pounds. See photo 2. The in-ounces torque screwdrivers will not work for values given in the electrical equipment that you are inspecting — an in-pounds torque screwdriver must be used.

Each brand of torque wrench will make a different sound when reaching the specified torque value. A big difference between the torque screwdriver and the torque wrench when reaching the specified torque value is that a screwdriver will disengage, whereas a torque wrench will continue to tighten if you do not feel or hear the click it makes. If you are not familiar with the sound the torque wrench makes, I suggest lowering the torque value by 25% and torque the termination to verify what the click sounds like; then turn it back up to the specified torque and tighten the rest of the way. Some are so quiet that you practically need to put your ear next to the wrench to hear it click. Sometimes the setscrew will make a sound when turning, making you think that it is the torque wrench clicking as it reaches the correct torque value. It is important that you know the difference."

What torque screwdriver brands and models do the master electricians here uses exactly?
​

 

[kwired]

According to an inspector:

https://iaeimagazine.org/magazine/2015/01/15/inspecting-electrical-connections-for-proper-torque/

"Torque screwdrivers of different capabilities can look identical but be very different. Once while doing an inspection while the electrician was using a torque screwdriver, I knew something was not quite right by the sound the torque screwdriver made when it reached the set torque. The sound was very faint compared to others I had encountered. After investigating, I discovered the torque screwdriver being used was measured in inch-ounces. There are identical looking torque screwdrivers that have increments given in inch-ounces and inch-pounds. See photo 2. The in-ounces torque screwdrivers will not work for values given in the electrical equipment that you are inspecting — an in-pounds torque screwdriver must be used.

Each brand of torque wrench will make a different sound when reaching the specified torque value. A big difference between the torque screwdriver and the torque wrench when reaching the specified torque value is that a screwdriver will disengage, whereas a torque wrench will continue to tighten if you do not feel or hear the click it makes. If you are not familiar with the sound the torque wrench makes, I suggest lowering the torque value by 25% and torque the termination to verify what the click sounds like; then turn it back up to the specified torque and tighten the rest of the way. Some are so quiet that you practically need to put your ear next to the wrench to hear it click. Sometimes the setscrew will make a sound when turning, making you think that it is the torque wrench clicking as it reaches the correct torque value. It is important that you know the difference."

What torque screwdriver brands and models do the master electricians here uses exactly?
​

Yes there are a lot of differences, different ranges being one of them. Same manufacturer will have different but similar models with different ranges. You need to understand what you are using before you use it, though they usually are not all that complicated. If your setting needs to be in in-lb and your tool is marked with ft-lb increments, chance is good it isn't the right tool for the task.

I don't think you will find one common answer to your question, there are many tools out there that are acceptable. What you may get for replies is something to the effect of if it is considerably cheaper than most others, quality is probably not that good. Said cheap tool may still have a use in some applications but maybe not for others.

 

[ptonsparky]

Yes there are a lot of differences, different ranges being one of them. Same manufacturer will have different but similar models with different ranges. You need to understand what you are using before you use it, though they usually are not all that complicated. If your setting needs to be in in-lb and your tool is marked with ft-lb increments, chance is good it isn't the right tool for the task.

I don't think you will find one common answer to your question, there are many tools out there that are acceptable. What you may get for replies is something to the effect of if it is considerably cheaper than most others, quality is probably not that good. Said cheap tool may still have a use in some applications but maybe not for others.

:thumbsup:

 

[tersh]

Yes there are a lot of differences, different ranges being one of them. Same manufacturer will have different but similar models with different ranges. You need to understand what you are using before you use it, though they usually are not all that complicated. If your setting needs to be in in-lb and your tool is marked with ft-lb increments, chance is good it isn't the right tool for the task.

I don't think you will find one common answer to your question, there are many tools out there that are acceptable. What you may get for replies is something to the effect of if it is considerably cheaper than most others, quality is probably not that good. Said cheap tool may still have a use in some applications but maybe not for others.

Ok then I'll wait for something someone has used and can recommend. It must be accurate and reliable. Problem with unreliable torque screwdriver is turning it so hard waiting for the click and destroying the wires or lugs when the calibration is off.. the biggest nightmare.

Our electrician here just make it tight and that's enough. But with torque wrench. One should make it even tighter than tight. So It should be so accurate to avoid risking damage to the panel.

 

[kwired]

Ok then I'll wait for something someone has used and can recommend. It must be accurate and reliable. Problem with unreliable torque screwdriver is turning it so hard waiting for the click and destroying the wires or lugs when the calibration is off.. the biggest nightmare.

Our electrician here just make it tight and that's enough. But with torque wrench. One should make it even tighter than tight. So It should be so accurate to avoid risking damage to the panel.

Think in some instances you will find that they are actually overtightening if not using a torque wrench. This mostly applies to larger lugs like on a 200 amp connector. For your 30 amp and smaller connections that are typically being made with a screwdriver, you are more likely to find many of them are not quite as tight as recommended torque. A breaker that recommends 20 in-lb, about makes you think you are goint to break your wrist if you get that much out of a typical screwdriver one might use. Get a bigger handle or some other leverage and it is easy to overtighten it though.

 

[Russs57]

FWIW, my torque screwdriver brand is Whia. My 1/4" drive torque wrench brand is CDI. Both are capable of being certified and re-calibrated.

I have not seen many electricians use a torque wrench. Much more common for guys like me on the maintenance side. Honestly it is more likely I use one because my dad was a mechanic and I grew up using them. Also I'm in a hospital setting so I tend to be extra cautious.

I use the screwdriver a lot less often and they cost more. So I'd advise a 1/4" drive torque wrench to start with.

Nice thing to have but if all I did was home electrical I wouldn't bother.

 

[hbiss]

Think in some instances you will find that they are actually overtightening if not using a torque wrench. This mostly applies to larger lugs like on a 200 amp connector. For your 30 amp and smaller connections that are typically being made with a screwdriver, you are more likely to find many of them are not quite as tight as recommended torque. A breaker that recommends 20 in-lb, about makes you think you are goint to break your wrist if you get that much out of a typical screwdriver one might use. Get a bigger handle or some other leverage and it is easy to overtighten it though.

I remember many years ago before torque wrenches were required I was tightening the lugs on a 200A meter pan and the threads stripped on the first one I did. Had to scramble to find another top half for that lug. Never had that problem before and I know now, but it just goes to show they don't have to be as tight as you think.

-Hal

 

[kwired]

I remember many years ago before torque wrenches were required I was tightening the lugs on a 200A meter pan and the threads stripped on the first one I did. Had to scramble to find another top half for that lug. Never had that problem before and I know now, but it just goes to show they don't have to be as tight as you think.

-Hal

You were lucky all it did was strip threads. When I was reasonably new Jman back in mid 1990's, was connecting service to a new house. POCO guy watched me torque load side lugs in the meter (200 amp standard meter socket). When I was done with load side he told me he would do the line side, contractor runs pipe and POCO pulls lateral conductors for their services so it kind of was theirs to land in some ways. Just a couple minutes later I heard him out there cussing, overtightened first connection he made and broke something - been along enough ago I don't remember exactly what broke but definitely needed new socket assembly on that side of the meter base.:blink: I told him I would have let him use my torque wrench if he had asked. Unfortunately he didn't come back with replacement parts until the next day so we didn't get energized that first day either like we were expecting.

 

[tersh]

Any connection has a higher possibility of failure if not used properly.

"Wire nuts" have a metallic spring coil inside that is what secures the conductors. Though they are somewhat a simple design, they still have instructions and list of combinations of conductors they are intended to be used with. Improper alignment of conductors before twisting the connector on can result in poor connection on one or more conductors. Experienced users, in particular those that have learned because of call backs because of failed connections, learn to at very least pull on each individual conductor after installing the connector, if any of them pull out - they weren't in very good in the first place and would have possibly failed if you hadn't checked.

The plastic cover is nothing more than an insulator for the connector inside of it, plus it's size and shape help to give some leverage when twisting the entire assembly onto the conductors.

In twisting two AWG 10 in a yellow wire nut. The conductor twists around each other and when you pull out the wire nut. You could see the twisting of the two conductors.

However, in twisting three AWG 10 in a red wire nut. The conductors don't twist around one another. When the electrician unscrewed the red wire nut. The conductors were straight as when it's pushed in. Do you really think three AWG 10 can twist around one another inside in a red wire nut?

Do you have internal schematic of what really goes inside the wire nut and spring that mechanically twists and secures the wires? I couldn't seem to find this in youtube but it should be shown especially when the technology is decades old.

Also do you consider plug-in connectors as more robust than wire nut? Plug-in connectors for 3 wire is like having 3 wire butt splice which is more secure as the wires were pressed down by the butt splice.

 

[peter d]

Wow. Just wow. :slaphead:

 

[kwired]

In twisting two AWG 10 in a yellow wire nut. The conductor twists around each other and when you pull out the wire nut. You could see the twisting of the two conductors.

However, in twisting three AWG 10 in a red wire nut. The conductors don't twist around one another. When the electrician unscrewed the red wire nut. The conductors were straight as when it's pushed in. Do you really think three AWG 10 can twist around one another inside in a red wire nut?

Do you have internal schematic of what really goes inside the wire nut and spring that mechanically twists and secures the wires? I couldn't seem to find this in youtube but it should be shown especially when the technology is decades old.

Also do you consider plug-in connectors as more robust than wire nut? Plug-in connectors for 3 wire is like having 3 wire butt splice which is more secure as the wires were pressed down by the butt splice.

It is a spring compressing against all three conductors, what more detail do you want? Compared to a "push in" connector the spring pressure is from all 360 degrees around it but spring pressure does increase as you twist the connector on further because of the tapered design of the inside of the spring. There are still some limitations, potential misalignment of conductor issues or other failures, installer error and misuse is more of an issue than bad product design.

the "push in" connector is spring pressure from one direction and some sort of fixed object (usually also a conductive object) as a stop on side of conductor opposite the spring so pressure is primarily against two opposite sides at whatever tension the spring delivers. Some are better designed than others, most will probably say properly used "wire nut" is still overall better connection, but the push in can be labor saving and even if you are not on board with exclusive use of them many may still see some applications that they feel they are good for.

 

[tersh]

It is a spring compressing against all three conductors, what more detail do you want? Compared to a "push in" connector the spring pressure is from all 360 degrees around it but spring pressure does increase as you twist the connector on further because of the tapered design of the inside of the spring. There are still some limitations, potential misalignment of conductor issues or other failures, installer error and misuse is more of an issue than bad product design.

the "push in" connector is spring pressure from one direction and some sort of fixed object (usually also a conductive object) as a stop on side of conductor opposite the spring so pressure is primarily against two opposite sides at whatever tension the spring delivers. Some are better designed than others, most will probably say properly used "wire nut" is still overall better connection, but the push in can be labor saving and even if you are not on board with exclusive use of them many may still see some applications that they feel they are good for.

So the wire nut just make the conductors press against themselves and don't actually do twisting like the following?

In two conductors. I saw bits of sign of it, but not three conductors or more. What do you think?

 

[hbiss]

You're really trying our patience with your inept questions and it's getting ridiculous.

I always pre-twist and trim the end before installing my wire nuts. Manufacturer instructions say that pre-twisting is not necessary. A particular wire nut size is suitable for the number and sizes of conductors listed on the box.

If you want to know more Google the instructions!

-Hal

 

[tersh]

You're really trying our patience with your inept questions and it's getting ridiculous.

I always pre-twist and trim the end before installing my wire nuts. Manufacturer instructions say that pre-twisting is not necessary. A particular wire nut size is suitable for the number and sizes of conductors listed on the box.

If you want to know more Google the instructions!

-Hal

I've been googling a lot of times. And it's not ridicuous. For example in https://www.mikeholt.com/forum/Foru...gYTwOA7bG-0dTh8VKaHR_h9yMzEAg8naW0-oofwPi8Q1Q I found this paragraph:

"A few months ago a guy demonstrated to me that could put a wire-nut on with 3 wires and not pre-twist, and it was still twisted when he removed it. That's the only time I saw someone do that successfully. I've found many more occasions where I've removed a wirenut only to have the splice fall apart."

Also I read that the maximum size for wire nut is AWG 10.

But in my place. AWG 10 is 5.5mm^2 instead of your 5.2mm^2. Now imagine you have three 5.5mm^2 in a red wire nut. The conductors are stiffer, the space is less inside the springs. The electrician can't get the wire twisted inside the red wire nut. When he removed it. The wires inside are all straight like original. No sign of twisting. This only works for smaller wires? And it's normal for the conductors to be straight inside with the springs only compressing it at all sides? He removed all wire nuts, but we need to put a couple so we are asking about this behavior. All my questions were not made up but actual applications. Contractors were used to just splicing even AWG 4 without using any connectors. They installed one in the other building where AWG 4 were spliced using just electrical tapes.

 

[ptonsparky]

So the wire nut just make the conductors press against themselves and don't actually do twisting like the following?

In two conductors. I saw bits of sign of it, but not three conductors or more. What do you think?

I was never a twister and don’t really care if they twist as I put the connector on.

Put a red on three pretwisted twelves. Not so far that they distort or come out the end. Stand on one twelve and pull on the other two. If it comes loose easily, you are inept. Try again

Repeat without pretwisting. You may still be inept.

 

[romex jockey]

That receptacle pictured still depends on screw pressure on the clamp to make a secure connection, it is not one where you just push conductor into back of receptacle and the connection is done.

My bad, but hopefully my point is not lost because of it Hal

. A breaker that recommends 20 in-lb, about makes you think you are goint to break your wrist if you get that much out of a typical screwdriver one might use. Get a bigger handle or some other leverage and it is easy to overtighten it though.

I've found the actual bit matters, most breakers and devices are manufactured w/screws that will accept multiple styles

Do you have internal schematic of what really goes inside the wire nut and spring that mechanically twists and secures the wires? I couldn't seem to find this in youtube but it should be shown especially when the technology is decades old.

Also do you consider plug-in connectors as more robust than wire nut? Plug-in connectors for 3 wire is like having 3 wire butt splice which is more secure as the wires were pressed down by the butt splice.

well first the listing/rating of any connector should be addressed....

2ndly, the 'pretwist vs. no pretwist ' debate boils down to the area of contact w/in the wirenut 'spring'.....anecdotally, i find that cutting the very ends the same allows for more contact of all wires introduced.

Just what their failure rate is juxtaposed to other connectables (wago, screw block, backstab) would be an appreciable study......
http://www.ieee-holm.org/h2004/h2004antler.pdf

3rd, there are many tools on the market exclusively for wire nuts>

thus a torque spec must exist....

You're really trying our patience with your inept questions and it's getting ridiculous.

-Hal

Addressing specifics is what engineers do , usually to extents most would not pursue because they've the patience where most do not Hal.

~RJ~

 

[tersh]

The following are tests I am having with electrician (who insisted to just use electrical tape without any wire nut as manual splicing is what they mostly do). .

This is before putting the three 5.5mm^2 AWG 10 inside the red wire nut.

This is when the red wire nut was put over the three 5.5mm^2 AWG 10 wires:

We couldn't pull any of the wires inside the red wire nut:

The following is when the nut was unscrewed:

Look. No difference to the previous wires. They don't come out twisted into one another just like the girl's pony tail hair.

Is it normal to have the wires coming out without any twisting into one another?

 

[romex jockey]

Is it normal to have the wires coming out without any twisting into one another?

Well that's an interesting study Tersh , but i'm unsure as to what answers your Q here..., many varaibles come to mind ,such as solid wire......stranded wire......a combination of both....~RJ~

 

[tersh]

Let's create a teardown of it:

Only the front are compressed. Is this normal?

Please show me images like it with different sizes of wires and wire nuts. I'd like to see how the insides actually look like.