Torque Talk

[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?