You'll be Shocked By How Much Torque Changes Electrical Resistance
ฝัง
- เผยแพร่เมื่อ 6 ก.ค. 2024
- How tight your make your electrical connections can have a dramatic effect on their resistance. Higher resistance translates into more power dissipating within the connection as electrical current increases.
Manufacturers of electrical equipment often specify a recommended torque value. What happens when you don't achieve this value or exceeded it.
As part of our eFIXX Talk the Torque series, Dr Robert Weller of Electrical Investigations demonstrates how to measure contact resistance and how it changes within the terminals of a consumer unit main switch.
== AD=================
If you don't use a torque screwdriver you might want to check out the ones we use from Wiha
hub.efixx.co.uk/wiha-torque-se...
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Video Chapters
00:00 Does connector resistance change with torque?
00:15 How can we measure contact resistance?
01:20 Resistance at 1.0 Nm
1:54 What does that equate to as power dissipated?
2:45 Increasing torque what happens to the resistance?
5:00 What happens when a terminal is over torqued?
5:50 Is tighter better?
6:31 Work hardening of copper conductors
7:20 Resistance increasing over time
7:45 Thermal runaway = fires
8:30 Talk the Torque
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❌ This content on this channel is for electrical professionals.❌ ==================================
📹 Presented by
Gary Hayers - Editor eFIXX
with
Dr Robert Weller - Electrical Investigations Ltd
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#efixx #electricians #talkthetorque - วิทยาศาสตร์และเทคโนโลยี
** AD** If you don't use a torque screwdriver you might want to check out the ones we use from Wiha
hub.efixx.co.uk/wiha-torque-set-amz
Which one do you prefer? Wiha, wera, draper? I prefer the Wera.
I have the draper I find it to be a fantastic tool. All the other brands I haven’t seen or used so don’t have much to say about them .
Great video as ever Gaz, I’ve been in the game for 25+ years and always thought my arm was pretty well calibrated 💪. Last week I purchased my first torque screwdriver and it would seem I’ve been slightly under tightening my connections all these years. It’s surprising how tight 2.5Nm actually is!!!
Thanks for the insight chaps 👏
Thanks for the feedback Daddy B 👍🏻
Yes it's much harder to get to with a screwdriver than an Allen key or spanner.
Think I will have to invest in one soon
It would be interesting to see this test done using bootlace ferrules and a fewer standard PVC house wire. How much pressure is applied to the copper strands when a lugs or ferrule is crimped onto a cable, a lot more than 2 - 5 Nm ?
A huge force is applied to the copper causing a cold weld with the ferrule/ lug. The strands are fused together and becoming one solid piece when done properly. Hydraulic crimpers for large wire (300mm^2) can apply up to 16 tonnes of force.
Great video 👍. I wish ALL electricians any anyone that works with electrical connections would watch this.
Great content for all sparks / electricians. Just about nobody does torque specs here in the USA. Crank on it until its tight here.
Perfectly said
We tried. It in real life and caused damaged to screw by not been able to remove or loose and broken.
Great to see you talking the torque
Fantastic video
Regarding tails i always tighten give them a good wriggle & twist & a further tighten & always get a further full turn.
I've seen lots of tail ( coming out of the meter) that come out very easy.
Excellent video thank you 🙏
Great video with proof as if proof were needed that the correct torque is always best. Tightening connectors until your wrists crack is just not good enough and certainly not professional just do the job the right way. Wrenching as tight as it will go and saying click is funny on a youtube video but it puts lives at risk. 😎🐔
Very interesting.
Recently Replaced a shower pull switch that was sticking, it wouldn't switch off. I found out the neutral on the load side had some light burn marks on the insulation near the terminal and the plastic surrounding the neutral terminal had discoloured slightly. The terminal screw itself was difficult to loosen off.
The connections were all tight and the cables couldn't be moved, but perhaps too tight.
The customer never switched it off because the old shower didn't have a light on it, but their new shower does so started to switch it off again until it no longer did so. The new shower is only a few weeks old.
Do you torque the terminal to the same setting with a bootlace ferrule crimped on the wire, would the same setting be used for an indent, hex or other type of crimp?
This isn't actually torque affecting resistance. It's linear force affecting resistance. The screw is just a device for turning torque into linear force. If torque affected resistance, you'd be able to measure changes in resistance in a cylindrical copper rod when you attempted to rotate one end relative to the other.
also came here to say this
wow, that's a lot of watts potentially, ive never considered that before, it would be interesting to know more about this, especially with ferrules and or screw less connections, good shout as always
And it's multiplied by 4 on the double pole switch in the example shown, getting pretty toasty.
Looks like I need to get a tourqe screwdriver
Can't believe the results of this test.
from a mat sci perspective, when you overtighten and work the copper, the new work hardened copper may also exhibit a higher resistance. This is on top of any breaks over time you might get
I was always taught to torque the terminations in a consumer unit and on isolator switches etc.
But why is there no recommendation for accessories like plug sockets, light switches etc?
I’ve done a few EICRs recently and found terminals that have started to melt and fuse into sockets, cooker switches etc due to being too loose.
So I don’t understand why we don’t have a recommendation , especially with things like cooker and shower switches that pull high loads.
Completely agree. Every termination is important. Typical haphazard standards from the IET. If you have any pride in workmanship you check them all. Biggest worry I find is the poor quality of screws in some accessories which I wouldn’t trust above 2.0Nm. Always do the wiggle test afterwards to settle multiple strands in stranded cable, and multiple singles in one terminal. Then torque again. Always follow manufacturers recommendations. All takes longer but I sleep well.
Some accessories now put torque in the instructions
@@KevinOsborne1987 I must admit I haven’t seen any as yet. But will be good to see, especially for cooker and shower switches.
Weakest link in the chain...
It's far less of an issue in lighting circuits because the operating current is a lot less than for other circuits and loads. Remember the power dissipation is P= I*I*R.
Fanatic video guys very interesting
Thanks for watching 👍🏻
What Nm should old breakers be tightened to if you not got or can't find any tension info for?? Came across this problem on a few occasions.
It would be good to test that theory when over tightening the screws, and also testing again a week later when the copper settles in the over tightening connecting.
Would the wire lead sidling up on the driver handle impact the impedance of the path from lead to screwhead? During second test wire loop is closer to handle
Answered just as I asked, negative, what a neat piece of kit
DNO's standard installation process even for a very small tiny 60A incomer is using Torque settings
Would be interesting to do the same comparison with cable lugs and maybe added copper compound
Now here's a twist! I agree with the view that 'every' connection should have a setting (just like engine rebuilds - different materials, sizes and temperature ranges should attract different, and calculated, design torque settings). So I eMailed two of the major manufacturers/providers of fittings such as 2G outlets etc, and so far had only one response... "Further to your recent query there is very little information available in regards to torque settings. Certain product standards reference torque settings for the purposes of testing to the standard but this is not across the board." I'll not embarrass them with their identity (publicly), but it is symptomatic of the non-committal responses we often receive ~but then we can be criticised when we don't.......... Somebody needs to 'get off the pot' and make engineering judgments and decisions and both guide and instruct us; don't they??
What about wetting current ?
We know the surface is microscopically rough, and we have to get the atoms in the two metal parts close enough that they can exchange electrons, either by overlapping of outer orbitals or quantum tunneling.
I have done 4 point tests on other sorts of joints, and can back up that what you show is common , especially if there is inadequate mechanical pressure - for example a twisted wire joint. When first made, the resistance is quite high, as the surfaces make contact only on high spots. However, if there is voltage to drive it, then enough current flows to cause the very tips of the 'microscopic mountain range' that are making contact to soften due to resistive heating, and form a local spot weld - very local sub micron details, not even noticeable when the wire is untwisted except under an electron microscope. Once a high initial current has flowed the resistance falls sharply, and stays down. This might be a good addendum to your film if you still have the kit to hand.
It is also why soft metals like gold make better contacts, but wear away faster. This ''wetting current" effect also is the principle behind the line cleaning current used on the analog phone likes to fix crackles - a current spike to either fuse it shut or blow it open, in one case it is job done, and in the other there is now a clear fault that can be found.
The key really is contact pressure - the area needed is not great but forces need to be adequate.
Thanks for making a film to illustrate this effect.
Hi another great video…But I have a curious question….is the torque setting on your combo drill similar to a torque screwdriver
I don’t think so.
It’s basically a reduction from the drills overall torque is stepped down increments. And it’s not calibrated.
Does your combi drill have Nm settings and do you have a calibration certificate for it? I suspect not.
Would be good to do same test with wago vs screw connection
1.3 W when 100 Amps is passing. Would this not be a negligible value in most domestic installations with far less Amps passing through the main isolator.
So just leave them loose as it’ll probably be alright. Cool.
It looks like the black fly lead was sliding down the shaft of the adjuster at 2.50. Surely that’s having an impact on the readings if your showing a torqued up screw with sliding fly lead. Yes the readings are getting lower but they might be lower still if you’d used a fixed point/probe to test with.
Actually not really; the resistance of the fly lead is not relevant because there is "no" current flowing on that lead and therefore no additional voltage drop.
Doesn’t matter with this 4 wire test method
@@efixx can they prove that it doesn't matter ? looks like a very poor test probe to be trustworthy
How does the meter differentiate between the torqued up terminal and the black fly lead slipping around?? The reading is being taken via that probe.
@@rufusbeard1977 plus who's to say contact at the terminal with the touch probe is the same each time ? I'd at least wanted to have seen 3 back to back tests to rule out spurious readings and prove consistency.
Well,thats the disadvantage off stranded cable.We on the continent dont use stranded cable,and surely not that thick as you are using.Thats the benefit off higher voltages and so less problems with resistance.Even the wires coming into the groupbox as we call it is mostly only 6 mm thick and not stranded! But often 3 fase..
Lads on site swear by the draper torque screwdriver, any good?
Yes it’s a great tool I had mine about a year and it has been fantastic easy to set and nice in the hand .
@@Dog-whisperer7494 thanks mate, it's the only tool I'm on the fence with, not doubting what it does. Just I've never needed to use one. But for £70 I might give it a try.
@@sunshine3187 it was the price that swede me as all the other brands are way overpriced
@@seandempsey7351 the price for the draper one is right, if it's good happy days, I just ordered one off Amazon. Thanks Sean.
Just think of the reduced electric bill by having it torqued up properly lol. Would be really interested to see the power consumption of an AFDD RCBO with no load.
Coming soon
Seems like a very invalid means of testing claiming a screwed connection....is the problem when using a what seems a bodge of a test probe. And testing unloaded circuits is often pointless even though it is the norm.
And any torque numbers should change for the type of conductor being used in any termination. They will not all behave the same way, so generic torque makes little sense.
4 terminal testers are highly accurate
That tester looked mega.
Much like elastic and plastic deformation!
Has the torque screwdriver calibration been checked?
Yes frequently
@@efixx How?
Great watch guys and interesting bit of kit.
Hopefully this video gets spread around to all the TWITTER gang that talk nonsense about not needing the correct kit (you know who you are 😂) and that it some how is just a money spin to make you buy screwdrivers
You have to remember these values from the manufactures are for a reason and not just some made up guff.
They have equipment like shown and even more elaborate testing facilities than just a multifunction tester.
Hello sir, Im your silent viewers on your youtube video from Philippines, thankyou for always teacher and guide with your video sir, I hope i can get some of your second hand tools😁 I hope you can hear this sir, Thankyou and GOD bless stay safe at work
elephant in the room, the connection from the meter to the probe? Seems a bit weak?
Did you say no to doing 2 clicks? I've always done 2 clicks. Should I stop?
AFAIK (glad to be corrected if this is wrong) the target torque is just enough to cause slippage in the screwdriver mechanism, which is when it "clicks". So it shouldn't really matter how many clicks you do. It's just normally pointless to do more than one.
@@nathan87 I normally do 2 as if screwdriver is already half jumped it can click when not tight. Was more curious if there's a detrimental effect to doing more than one click.
Seen high resistance on cheap BG Chinese switches
1.3 watts, damn. It seems negligible but that's about one third of an led bulb that can pretty well light up a room.
It’s a lot of heat to dump into a screw
@@edc1569 true. And we dropped about 0.8 watts or something by tightening it. Which was the resistance between the contact in the breaker and the conductor. The screw itself does not even carry current.
All a means to end trying to solve problems that wasn't there before and then creating more problems if push fits connections and torque is important now. why are we installing arc fault protection. Now we have to pay someone to calibrate all the screwdrivers that .think you understand what I mean by means to an end.
How come we are only concerned with torque tightening in a distribution board, when there are connections everywhere?
Telio.
They're not proper Jelly Babies. How can I trust a man who doesn't use proper Jelly Babies? 😱
haribo jelly babies are number 1 in my house
@@efixx no-no no it has to be Burty Basset’s welly baby’s
If it breakes get a new one 😇 I'm really bad 😆
I had one of those exact same load switches you had.
6mm² needs lots more torque than that gear was build for.