Torque Talk

[Marvo]

Long time no see and I hope you're all doing well.

I see that torque screwdrivers have become the height of fashion in the UK over the last couple of years. I wondered what general practice has been adopted regarding their use.

Are electricians expected to;
Have a torque screwdriver on site at all times?
Check torque of all terminations in CU's / DB's they open or just any new terminations they make?
Check the torque of all terminations in any accessories they open?

Also;
Is acceptable to do torque testing live in a CU (assuming a VDE screwdriver)? Is a risk assessment required for live torque testing?
If torque testing is performed in a DB/CU do you just check screws for tightness or do you loosen off all terminations first then re-torque to the correct figure to eliminate overtightened connections as well as loose ones?

 

[James]

All very good questions.

I do not own a torque screwdriver and have never used one.

I still rely on my wrist although I don’t have any calibration certificate for it.

 

[Marvo]

I'm sure you could borrow someones torque screwdriver and self calibrate your wrist against it

I don't carry a torque screwdriver on site either but I have a range of very accurate versions in our workshop that are about 15 years old and too expensive to carry around. I'm thinking about getting one of these new snazzy looking red and yellow plastic ones although I wouldn't use it very often with the type of work I do. I'm just interested how they're used in the UK and what the recognised usage practices are now they've been popular for a while.

 

[SparkySy]

I have and use a torque driver for a few years now.
I have found more and more manufacturers listing required torque either in the instructions or on the product next to the terminals (that's if they aren't push in) so that it's obvious.
As to whether or not I agree with that setting is another matter as some of them seem to be extremely low.
So I do if there are settings listed anything else is down to the torque elbow!
Sy

 

[nicebutdim]

I have and use a torque driver for a few years now.
I have found more and more manufacturers listing required torque either in the instructions or on the product next to the terminals (that's if they aren't push in) so that it's obvious.
As to whether or not I agree with that setting is another matter as some of them seem to be extremely low.
So I do if there are settings listed anything else is down to the torque elbow!
Sy

Just over 1Nm on outgoing side of certain breakers seems a tad low for higher ratings with stranded cables, but likewise I (mostly) tend to set torque where manufacturer has clearly requested it.

 

[davesparks]

what the recognised usage practices are now they've been popular for a while.

I suspect a common usage practice is to dig it out and brush the dust off once a year, just in time for the annual visit from the NICEIC.

 

[SJD]

If you don't have one in your tool bag, and you ever find yourself in court defending an installation such as a consumer unit that has e.g. overheated or caught fire, how do you explain how you did the terminals up to manufacturer's instructions. My college tutor used to tell a story about this, of someone being cross examined about the contents of their tool bag after such an occurence, they didn't see where the questioning was leading.

 

[Dustydazzler]

I have 2 vde versions and the only time that they ever see the light of day is on a board change , I do all the connections up by hand then go round at the very end and torque everything up.
To be fair its just another one of those items you shell out £100+ for an it lives in a box for 99% of its days.
I probably did 500 boards before I ever got a torque screwdriver and as far as I know none of them caught fire ( yet )

 

[IAmSparkytus!]

As above, only use mine on distribution boards.

3.5nm on some terminals seems a lot and I quite often find the screwdriver slipping and starting to round the screw head before the driver clicks to confirm torque.

On the flipside, one board I’ve worked on asks for all connections on the earth bar to be 2.0 or 2.5nm (can’t remember which) and the main earth pops right out

being honest I much prefer the old fashioned DIY way of going with your gut instinct

 

[Dustydazzler]

Quite often I find my self doing the torque up and still checking again afterwards by hand as I don't trust the torque screwdriver

I honestly don't think you can beat an experienced hand/arm when it comes to making good connections

 

[Marvo]

Quite often I find my self doing the torque up and still checking again afterwards by hand as I don't trust the torque screwdriver

I honestly don't think you can beat an experienced hand/arm when it comes to making good connections

Is that a lack of trust in the accuracy of the screwdriver or lack of trust in the manufacturers published torque spec?

When you say you recheck by hand afterwards do you mean you 'tug test' the wires or you go again with a normal screwdriver?

 

[davesparks]

Howany electricians using torque screwdrivers actually know how to use them properly?

 

[LukeD]

If you don't have one in your tool bag, and you ever find yourself in court defending an installation such as a consumer unit that has e.g. overheated or caught fire, how do you explain how you did the terminals up to manufacturer's instructions. My college tutor used to tell a story about this, of someone being cross examined about the contents of their tool bag after such an occurence, they didn't see where the questioning was leading.

Always have whats legally required. Down to you if you want to use it , But have it

 

[littlespark]

I’ve got a torque driver, only gets used on boards though. I don’t go back and retighten with a regular screwdriver…. That’s just pointless.
I will, however, check every terminal in a board even if I’m just working on one circuit… although that only finds loose connections, not over-tightened ones.

Someone else on here has my ones twin.

It came with a #1 and a #2 +/- bit which I manage to break the tip off the smaller one on an RCBO at not very much N/m setting (warranty replacement, got both sizes in return)

Also the one I have doesn’t fit any other brand of driver bit. Just slightly too small.

And final gripe, the increments go up in .2 so 1.0, 1.2, 1.4 etc
When most published torque settings for MCBs and the like end in .5


In a response to some other comments….

“I’ve done loads of boards without a torque driver, and none have gone on fire”……
That you know of. Maybe further work has been done, which has been blamed.

“Always have what’s legally required. Down to you if you use it”
This is sadly true. How many instances of drive by EICRs have we seen where the £1000 MFT has never left its box.

 

[Dustydazzler]

Is that a lack of trust in the accuracy of the screwdriver or lack of trust in the manufacturers published torque spec?

When you say you recheck by hand afterwards do you mean you 'tug test' the wires or you go again with a normal screwdriver?

Go back round checking with a normal Screwdriver

 

[Rockingit]

Hey Stranger! Good to see you - was beginning to wonder if all was OK.

As for Torque screwdrivers..... I've got one, bottom on the toolbag, never been asked to show it on any inspection ever! It's not VDE and it's also never been calibrated, but it does do a really good job of holding my extra-wide flat bit for doing up tray bolts

 

[slartybartfast]

The wiring regulations (Regs) themselves do not mandate the use of torque screwdrivers.

However they state at 134.1.1 that "the installation shall take account of manufacturers' instructions".

The word "Shall" in British Standards means a requirement, or in plain English a MUST.

So the Regs state that you MUST take manufacturers instructions into account.

However it is odd that the Regs do not explicitly mandate that the manufacturers' instructions are adhered to.

Even if you MUST adhere to manufacturers' instructions, they do tend to be rather vague and very poorly written. Very few state categorically that connections MUST be set to specified torque.

Quite why this is so vague is beyond me, rather inexcusable of British Standards in my book.

Read into that what you will. I read into all this that torque screwdrivers are optional but can see that in some cases use of them is good professional practice; maybe that is the real intent behind the vague language from British Standards.

 

[DPG]

The wiring regulations (Regs) themselves do not mandate the use of torque screwdrivers.

However they state at 134.1.1 that "the installation shall take account of manufacturers' instructions".

The word "Shall" in British Standards means a requirement, or in plain English a MUST.

So the Regs state that you MUST take manufacturers instructions into account.

However it is odd that the Regs do not explicitly mandate that the manufacturers' instructions are adhered to.

Even if you MUST adhere to manufacturers' instructions, they do tend to be rather vague and very poorly written. Very few state categorically that connections MUST be set to specified torque.

Quite why this is so vague is beyond me, rather inexcusable of British Standards in my book.

Read into that what you will. I read into all this that torque screwdrivers are optional but can see that in some cases use of them is good professional practice; maybe that is the real intent behind the vague language from British Standards.

You've answered your own point about why the regs say that manufacturer's instructions do not have to be strictly adhered to - if we did that with some of the badly written/translated rubbish that often comes with items these days then it wouldn't go well !

 

[slartybartfast]

You've answered your own point about why the regs say that manufacturer's instructions do not have to be strictly adhered to - if we did that with some of the badly written/translated rubbish that often comes with items these days then it wouldn't go well !

Quite why this is so confusing is mind boggling....

 

[DPG]

Quite why this is so confusing is mind boggling....

What's confusing? The regs say manufacturer's instructions should be taken account of. That's not confusing.

 

[slartybartfast]

What's confusing? The regs say manufacturer's instructions should be taken account of. That's not confusing.

Well it is. Very confusing. Read my post of a few minutes ago. In summary, "taking account of" does not mean "must be complied with" and also instructions are generally crap....hence the confusion.

 

[DPG]

Well it is. Very confusing. Read my post of a few minutes ago. In summary, "taking account of" does not mean "must be complied with" and also instructions are generally crap....hence the confusion.

I think I'm missing your point here.

We should take account of manufacturer's instructions, but not necessarily rigidly follow them.

That's straightforward to me. Look at them, but if they are incorrect, badly translated, or geared towards another country's electrical system then adapt as appropriate. A competent electrician will be able to do this.

Let me know if I've missed something

 

[slartybartfast]

I think I'm missing your point here.

We should take account of manufacturer's instructions, but not necessarily rigidly follow them.

That's straightforward to me. Look at them, but if they are incorrect, badly translated, or geared towards another country's electrical system then adapt as appropriate. A competent electrician will be able to do this.

Let me know if I've missed something

You are missing the OP's opening gambit - asking if Torque screwdrivers are mandated....and think it is fair to say that they are not !

 

[DPG]

You are missing the OP's opening gambit - asking if Torque screwdrivers are mandated....and think it is fair to say that they are not !

No, they are not. The regs don't mandate which specific tools to use, only that things are installed correctly and tested correctly.

 

[Lucien Nunes]

The manufacturers' instructions have to allow for the situation where a newly qualified installer wishes to fit their component to the highest standard. It might be the first real installation work in their career, with very little experience to guide them on how terminals behave. By providing torque figures the manufacturers can help ensure them achieve a good installation and begin to learn what is appropriate for each of 101 different types of terminal, based on factory tested torques instead of guesswork.

An experienced installer whose approach combines craftsmanship and engineering, takes the time to examine and test their finished work and that of others, reads up on how devices are made, analyses failures etc. might have as good an idea of the appropriate torque as the manufacturers themselves. They will account for factors that are excluded from the sterile lab environment in which the published figures are devised and fine tune according to variables that cannot be included in a one-figure-fits-all torque setting printed on the side of an MCB.

I am interested to know the correct torque and will test it to decide whether I think it is appropriate. Sometimes, as mentioned above, I find recommended torques somewhat low. I trust my own judgement and would happily defend a departure from the published figure because I consider myself sufficiently competent in the craft and science of termination, and believe I could demonstrate that competence if required.

 

[littlespark]

Here's an example... tyre fitters.

They run up the wheel nuts on your very expensive alloy wheels... Then finish them with a torque wrench, set at the correct value.
This ensures that its not too loose, that the vibration of driving loosens them more, and they fall out... nor too tight, as they would damage your alloys.

Its the same type of forces on the screw terminals within a consumer unit. Not too loose, not too tight...You dont want the cable wiggling out... nor do you want the circuit breaker cracking apart because someone turned the driver too much.
Luckily the manufacturers helpfully give you the optimum values.

I would rather see a tyre fitter use a torque wrench on my wheels, that im going to drive away in.... rather than him doing it by 'feel' alone.... using a manual wrench, and him saying "Aye, that'll do"



Don't tell me.... you change your own tyres.....
As we tend to say around here: Get a professional to do it!

 

[timhoward]

I think both arguments carry some weight.
Fitting to the specified torque will avoid damage and usually provide an adequate connection and peace of mind.
However I'm a firm opponent to the general erosion of common sense and responsibility, and I'd want any sparks to be happy they had made a good connection too. Sometimes, especially with larger conductors, the recommended torque doesn't feel quite enough.

Don't tell me.... you change your own tyres.....

Actually I used to, and I had a torque wrench and hosted a wheel balancing machine that various like minded folk were free to use any time. (Citroen BX owners used to struggle to get big-name firms to change their tyres as the engine needed to be kept running to keep the suspension up and health and safety didn't allow this when on a ramp. )
However I'm regularly told by my wife and children that I'm abnormal so I'm probably not a good case study.

 

[LukeD]

Ive seen breakers where they have been done up too tight and you see the casing "splitting open" :-(

 

[IAmSparkytus!]

Ive seen breakers where they have been done up too tight and you see the casing "splitting open" :-(

I’ve actually had this happen on distribution equipment where I’ve followed manufacturers torque recommendations.

Another reason why ultimately I prefer the gut instinct method.

 

[OnlQQker]

It's a bit like plumbing, you get a feel for it.

I use the same method, tighten up gently making sure no cross threading is taking place, then give it another tweak, and a final tweak before fixing in place.

Usually the third tweak produces nothing in the tightening procedure but gives peace of mind.

I wouldn't trust torque screwdrivers, you might think it's tight because it's torqued to the correct reading, but everything can be faulty.

Good old fashioned feeling can never be wrong, unless you get arthritis.

 

[Rockingit]

It's a bit like plumbing, you get a feel for it.

I use the same method, tighten up gently making sure no cross threading is taking place, then give it another tweak, and a final tweak before fixing in place.

Usually the third tweak produces nothing in the tightening procedure but gives peace of mind.

I wouldn't trust torque screwdrivers, you might think it's tight because it's torqued to the correct reading, but everything can be faulty.

Good old fashioned feeling can never be wrong, unless you get arthritis.

"When it's white, it's tight"...... (knuckle, for anyone not familiar with the saying!)

 

[SJD]

A related comment about stranded cables.

If you tighten a 6 or 10mm2 conductor as found in twin & earth, if you leave it a while, likely as the strands settle, it will become a bit loose. I'd expect someone used to working with these cables would be aware of that, and recheck tightness after (for example) 10 or 15 mins. But I often see loose connections in shower or cooker isolators, either on an EICR, or after one has failed, and suspect the connections were never checked properly, someone in too much of a hurry to finish.

 

[nicebutdim]

A related comment about stranded cables.

If you tighten a 6 or 10mm2 conductor as found in twin & earth, if you leave it a while, likely as the strands settle, it will become a bit loose. I'd expect someone used to working with these cables would be aware of that, and recheck tightness after (for example) 10 or 15 mins. But I often see loose connections in shower or cooker isolators, either on an EICR, or after one has failed, and suspect the connections were never checked properly, someone in too much of a hurry to finish.

I like to hasten the bedding of stranded conductors, by giving them a wiggle and retightening a few times until there's no more movement.

 

[davesparks]

Here's an example... tyre fitters.

They run up the wheel nuts on your very expensive alloy wheels... Then finish them with a torque wrench, set at the correct value.
This ensures that its not too loose, that the vibration of driving loosens them more, and they fall out... nor too tight, as they would damage your alloys.

Its the same type of forces on the screw terminals within a consumer unit. Not too loose, not too tight...You dont want the cable wiggling out... nor do you want the circuit breaker cracking apart because someone turned the driver too much.
Luckily the manufacturers helpfully give you the optimum values.

I would rather see a tyre fitter use a torque wrench on my wheels, that im going to drive away in.... rather than him doing it by 'feel' alone.... using a manual wrench, and him saying "Aye, that'll do"



Don't tell me.... you change your own tyres.....
As we tend to say around here: Get a professional to do it!

Wheel nuts and electrical terminals are different situations.

The torque value for the wheel nuts is set knowing exactly what is being fitted, what its made of etc etc.

Electrical terminals could have a range of types and sizes of conductor put in them, there may even be multiple conductors in there. I can't see how one universal torque setting can be correct for all sizes and types of conductor.

 

[davesparks]

A related comment about stranded cables.

If you tighten a 6 or 10mm2 conductor as found in twin & earth, if you leave it a while, likely as the strands settle, it will become a bit loose. I'd expect someone used to working with these cables would be aware of that, and recheck tightness after (for example) 10 or 15 mins. But I often see loose connections in shower or cooker isolators, either on an EICR, or after one has failed, and suspect the connections were never checked properly, someone in too much of a hurry to finish.

The same is true for any fixing which is being tightened to a specified torque setting, it should be torqued, allowed time to relax, and then re-torqued.

For example when tightening down a cylinder head on an engine it's normal practice to tighten to the specified torque, go and have a tea break and then re-torqued to that same setting.

 

[littlespark]

Electrical terminals could have a range of types and sizes of conductor put in them, there may even be multiple conductors in there. I can't see how one universal torque setting can be correct for all sizes and types of conductor.

So the torque values published by the manufacturers mean nothing?

I’m sure they’ve done their research and whatever value they state will cover any size, quantity or material of conductor.

 

[nicebutdim]

So the torque values published by the manufacturers mean nothing?

I’m sure they’ve done their research and whatever value they state will cover any size, quantity or material of conductor.

I don't see any claim that torque settings suppled by manufacturers mean nothing.

What has been stated, several times by people who are familiar with the phenomena, is that there are variables which may render those recommendations less than ideal. I'd be amazed if you were to tell me that you'd never had such an experience, that you never check how secure a termination is or that you'd never rechecked a termination and found that it was no longer at the required torque.

Edit: To clarify; my background is originally mechanical and involved regular torquing of components and assemblies which were subjected to fairly extreme pressures. The main variable in those situations were bolts and tie rods, which tended to stretch a little. When clamping several, soft strands of copper it comes as no surprise to me that torquing once and walking away is not an option and that clamping soft copper by various different means may yield variable results.

 

[Dustydazzler]

I'm with DS on this one when it come s to torquing up and there is an element of twist back / slackening when you first torque up something, and it is good practice to re-torque especially with bigger cores

 

[davesparks]

So the torque values published by the manufacturers mean nothing?

No, and that's not what I said!

I said I can't see that one universal torque value could be right for all possible situations.

I’m sure they’ve done their research and whatever value they state will cover any size, quantity or material of conductor.

I doubt that it will, and I suspect that if you asked the manufacturer for further information on this you may find that those torque values are intended for a single copper conductor not doubled back or a fine stranded conductor fitted with a ferrule.

 

[SparkySy]

25mm tails are a prime example of the torque, tea break, torque, tug test and torque again scenario!
Manufacturer's should have tested all manor of types and sizes of conductor in their device, weather that is the case or not, the entry position and any pressure or bends in the cable will to some degree all have an effect on the final termination, especially with larger cables.
I would rather have some idea of how tight it should be than either trashing the device / terminal or coming loose.
As with most of our work a lot of it is still down to knowledge and experience. If something doesn't feel tight at the required manufacturers setting would you give it a bit more or say that is it that's how tight it should be so f-it?

 

[Dustydazzler]

Perhaps there needs to be several ranges based on cable type , bare , ferruled , bent , multi or single etc

 

[davesparks]

Perhaps there needs to be several ranges based on cable type , bare , ferruled , bent , multi or single etc

That won't happen, if pushed on the issue manufacturers will start declaring that terminals are only suitable for one conductor in their instructions.

We'd end up like the USA where they are not allowed to put more than one conductor in a terminal unless the manufacturer specifically states it is OK.

 

[slartybartfast]

Wheel nuts and electrical terminals are different situations.

The torque value for the wheel nuts is set knowing exactly what is being fitted, what its made of etc etc.

Electrical terminals could have a range of types and sizes of conductor put in them, there may even be multiple conductors in there. I can't see how one universal torque setting can be correct for all sizes and types of conductor.

Spot on.

Also wheel nuts are subject to significant forces and vibration making torque settings important. Whereas Domestic Electrical installations are (generally) not subject to these forces & vibrations, and so terminal screws, if nipped up, are highly unlikely to work loose.

I guess the intent to using torque screwdrivers is a catch all to ensure that "nipping up" is done, which explains the vagueness in the regs and manufacturer instructions.

You simply cannot have a universal torque setting that caters for all cable types.

 

[Dustydazzler]

Also to mention some electricians torque screwdrivers only range from 1-3 NM like the Wera , which is a bit naff from a £175 tool when some makes of main switches ask for 3.2-3.4NM

 

[slartybartfast]

Also to mention some electricians torque screwdrivers only range from 1-3 NM like the Wera , which is a bit naff from a £175 tool when some makes of main switches ask for 3.2-3.4NM

There are plenty of mini-torque wrenches out that that can take screwdriver bits, but fully accept space constraints in some cases.

 

[Dustydazzler]

I used to have a torque wrench , I be danged if I know what happened to it thou

One a bit like this

https://www.amazon.co.uk/Draper-30357-Square-Drive-22-1-154-9lb-ft/dp/B0001K9S52/ref=asc_df_B0001K9S52?tag=bingshoppinga-21&linkCode=df0&hvadid=79920808416455&hvnetw=o&hvqmt=e&hvbmt=be&hvdev=c&hvlocint=&hvlocphy=&hvtargid=pla-4583520383274666&psc=1

 

[pc1966]

I think most of the key points have been said.

Terminals should be correctly tightened but the regs don't specify how that is done, however, nobody can argue that using the manufacturer's torque setting is not a good way of doing so and thus meeting the fundamental requirement of a sound connection. To avoid liability then proving you have the tool to do so than comes along.

As an aside, wheel nuts and terminals both have forces making them come apart, in the case of electrical stuff though it is usually thermal cycling and not heavy vibration. What is very different is the general condition of them with terminals generally clean & dry and wheel nut varying a lot in terms of surface condition (rust through to well-greased).

Tightening by torque is not that precise as while the tool may be accurate to a few percent, the thread and fastener head friction can vary a lot depending on its finish (machining / plating quality, etc) and state of lubrication. From memory to around 30% or so. That is why high stress bolts like car cylinder heads, etc, now have other methods of final tightening such as going to a set torque to bed them down and then a given final turn angle so the bolt/stud has a certain degree of elongation and thus preload.

Another approach that is good is to observe the torque versus angle do determine how much yield there is, oddly enough that is basically the traditional craftsman's method found out by years of experience (and often a couple of failures along the way)! More summary here:

Methods of Tightening Threaded Fasteners

Personally I use a torque tool for anything critical, but for small DIN screws, etc, usually just hand feel of experience. I have a VDE screwdriver for doing MCBs, etc, and also a few non-insulated tools left over from DIY on car's etc over my lifetime that get used for the occasional big lug bolts, etc.

In my own very limited experience, Hager, Wylex, and Schneider stuff survived fine at their stated torque, one CPN device started to come apart at the seams so lesson learned - don't use them or take it slightly easier!

 

[nicebutdim]

Spot on.

Also wheel nuts are subject to significant forces and vibration making torque settings important. Whereas Domestic Electrical installations are (generally) not subject to these forces & vibrations, and so terminal screws, if nipped up, are highly unlikely to work loose.

Screw terminals are subject to thermal creep, through which they can become loose, although that's not going to be much of an issue at the time of installation.

 

[slartybartfast]

Screw terminals are subject to thermal creep, through which they can become loose, although that's not going to be much of an issue at the time of installation.

hmmm....if temperatures are getting high enough to that then cable is likely undersized

 

[DPG]

hmmm....if temperatures are getting high enough to that then cable is likely undersized

Happens at moderate temperatures, especially when stranded cables have been tinned with solder. That is why they shouldn't be tinned.

Doesn't necessarily need such high temperatures for it occur.