A question about torque screwdrivers

[HappyHippyDad]

I have been umming and arghing about a torque screwdriver for some time but have not yet bought one.

My fears are the following:

1. There are set torque settings that conductors in a consumer unit should adhere to. However, in the neutral bar which are screw terminals I tend to screw a 6mm in tighter than a 1mm (for example), as if you screw in a 1mm too tight it can shear. You can screw in a 6mm pretty much as tight as you can without fear of it going through the copper. I cant see how a torque screwdriver distinguishes between a 1mm and 6mm. Does it? Does it need to?

2. Are torque screwdrivers always accurate? If I use my normal screwdriver I have a 'fairly', if not 'very' precise feel for how tight I have made the connection. This experience will only improve over the years and you will make varying degrees of tightness as required. You lose this with a torque screwdriver and put all your trust in the mechanism.

I wonder if a torque screwdriver may not be a good option for someone who knows how to use a screwdriver properly? However, I am very much open to persuasion hence the post.

 

[Moley]

In a domestic situation I really don't see the need for torquing (hmmm.. spell checker wanted to change that to torturing). Anyone who has been in this game should be able to work out if a screw is tight.

 

[davesparks]

I don't believe the terminals are of a good enough quality these days to achieve a properly torqued question.

 

[pc1966]

From my own (limited) experience of torque screwdrivers I found the recommended setting for some of the bigger screws sort of matched my hand-experience setting, and for some of the smaller screws it was about 1/8 to 1/4 turn more than I would normally do, but not a massive difference.

I think the major advantage is to reduce seriously wrong values for folk without a lot of experience (or for unusual devices) and for that precise calibration is not needed, just a sanity check on its functionality. Of course, one you get in to insurance/liability/etc then you might find it becomes another routine expense to have provable current calibration certificates for torque tools.

 

[Midwest]

Ommph. I'm out.

 

[ipf]

Anybody use 'em for fixing back boxes??????

 

[Mike Johnson]

I use hammer screws.

 

[Moley]

I use hammer screws.

I hope your hammer is calibrated.

 

[Mike Johnson]

My hammer is, but my hands aren't.

 

[billyblade]

On your annual inspection from whichever regulatory body you belong to you should, in theory, be asked to produce your torque screwdriver and a valid calibration certificate. I know from talking to electricians that this doesn't happen all the time.

However, taking it to the nth degree, what if an installation you have worked on catches fire and gets investigated? And the investigators ask to see your screwdriver and certificate as incorrectly tightened terminals are a common cause of hot spots? far-fetched?

I have spoken to many electricians who have a torque screwdriver with a valid calibration certificate just to cover their own backs. Many of them don't even use them, instead trusting their judgement after many years of installing

 

[Mike Johnson]

Taking this even further a neighbour is a Forensic investigator for the Fire Brigade and when questioned he had no idea that torque screwdrivers where available for electrical installations, I have also asked the same question to a relative who is an Insurance Assessor, same response, I have, now it would seem, unfortunately opened a can of worms with both of these investigators.

 

[pc1966]

The use of torque tools, and forensic investigation of torque used, has been a thing in the USA for many years. Just search of "Inspecting Electrical Connections for Proper Torque" for an article on it by the IAEI Magazine (again, seems I can't post a usable link).

I don't know why. Maybe it is down to litigation being the USA's national sport, or the lower voltage/higher current arrangement, or the common use of aluminium conductors (and the issues of galvanic corrosion and compressive strength). Whatever the reason, the fact their electrical code is actually published by the National Fire Protection Association (NFPA) says something about the risks they worry more about.

 

[Mike Johnson]

All seems a bit implausible to me, if the DB has caught fire the heat could have loosened or even tightened the terminals, that would be my argument in the case of investigation if it was found to be out of specification, plus the DB would probably be destroyed.

 

[ipf]

Torque drivers have been around for a good while. There must have been plenty of situations where investigations have taken place.

It would be interesting to know if there has ever been a 'fire' case, involving a contractor, where torque drivers (or lack of) has been taken into account, resulting in any sort of prosecution?
If so, I'm sure the trade in general would be pretty rattled.

 

[pc1966]

It would be interesting to know the stats for that sort of issue.

From what I have heard, the biggest problems has been a deskilling of the industry as a whole, and imposing requirements such as torque screwdrivers is trying to paste over a lack of proper training/experience being used.

While I have seen figures quoted for the percentage of hand-tightened terminals being within 20% of the manufacturer's specification, I have never seen anything on how critical that is. E.g. if you are, say, 50% above or below specified torque, what does that do the the contact resistance over the expected system lifetime?

 

[Mike Johnson]

With the constant heating and cooling of terminals surely the torque they where done up to can't stay constant.