A question about torque screwdrivers

[billyblade]

So who writes the certificate of calibration if you have the Wiha self test unit, are testing certificates available for you to fill them out yourself?

It's a torque checker, not a calibration tool. It doesn't really measure and record readings rather it indicates that the torque screwdriver is working correctly. It does not remove the need for annual calibration

Green light for safety – check the functionality of torque tools every day with Wiha Torque QuickCheck

It’s a familiar situation for users. After the recommended period of one year or 5,000 couplings, it’s time to send the torque tool off for…

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To produce a calibration certificate you need to follow EN ISO6789:2017. There are extensive checks stipulated (including 5 checks at 3 separate settings with the average values recorded).

 

[davesparks]

One last thing about this..

Do you have to send off your screwdriver to be calibrated or can you buy some sort of calibrating tool to do it yourself?

The proper use, care and calibration of precision torque screwdrivers and wrenches is not as simple as it is for test gear.
Ultimately it relies on a precision spring to get the actual torque setting.

Some key points are having the torque device at the correct temperature, always returning it to its minimum setting for storage, operating it a few times before use if it hasn't been used for a while.
Calibration periods are often set by the number of operations rather than by time period.

Any application where torque is actually critical will already be subject to significant checking and monitoring with ever use of the torque device being properly logged against each specific fastener it is used on.

 

[telectrix]

but don't any of you think this is all overkill. next we'll see plumbers having temp.calibrated blowlamps to stop them burning structures, and wood butchers with their hammers calibrated in foot pounds in case they nail a plumber to the floor too tightly..

 

[Moley]

Any application where torque is actually critical will already be subject to significant checking and monitoring with ever use of the torque device being properly logged against each specific fastener it is used on.

We have to go through that on some our jobs. Usually the reconnection on gen transformers or the connections on the main generator breaker. Very often we have the site engineer watching the torquing and noting down the readings against each braid or connection. Some check the torque setting on the wrench at the start and finish of the reconnecting to make sure it hasn't changed. Then comes the ductoring....

 

[Midwest]

On a domestic setting ( see what I did there), who will actually be asking for you to provide a calibration certificate, for your torque screwdriver?

 

[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.