Torque Screwdrivers and Settings

by Editor on July 21, 2012

This article gives some info to electricians about electrical torque screwdrivers and terminal torque setting specs for various manufacturers of MCBs, RCBOs and Consumer Units.

Torque screwdrivers for electricians–  Electrical connections that are loose can cause arcing, whereas over tightening can cause the screw to cut through the wire and damage the connection.  The 17th Edition Wiring Regulations require installers to check torque settings for connection tightness where instructed to do so by the manufacturer. The ideal torque screwdriver for an electrician would need to be 1000 volt insulated (VDE Mark Certified), have an adjustable range from 1 to 8.0 Nm and have a selection of crosshead blades to fit terminals of both breakers and main switch terminals.

The subject of using torque screwdrivers for electrical work has been the cause for some consternation amongst electricians for a while now. We all have our own views of how tight we consider an electrical terminal screw should be (see the forums comments below) but now it seems to be a requirement that we all own and use a calibrated torque tool.

This is especially true with electricians working on consumer units and distribution boards. We all know that over-tightened or loose connections can cause problems of damaging the terminals of electrical devices or overheating, but do we follow the manufacturer’s instructions and torque settings?

In order to comply with the Erection and Initial Verification section of the Regs (BS7671 Regulation 134.1.1) “Electrical equipment shall be installed in accordance with the instructions provided by the manufacturer of the equipment”, the instructions must be followed. Where switch gear and circuit protection devices are concerned this is especially important. If the installation of the equipment is not carried out in accordance with the manufacture’s instructions, the warranty will not be valid and the installer could be held responsible for any fault that may occur and found guilty of non compliance with regs.

Torque Settings Instructions & Specs

Torque settings are specified as Nm (Newton Metre) or as in.Ibf  (Pounds of Force per inch)

To convert-  1 x in.Ibf = 0.112 Nm        1 x Nm = 8.85 in.Ibf

Many electricians may wonder if the torque settings for breakers and main terminals are actually given in the installation instructions which come with the new devices. Well, I’ve carried out an online search and checked some of the circuit breakers and distrubution board manufacture’s websites and it’s not easy to find Nm torque settings for any specific products. As for the instructions that come with MCBs and consumer units, I’ve looked at the data sheets for Hagar, Crabtree and Wylex RCBOs and Consumer  Units and found the following:

Hagar– Please ensure that all connections (that are not factory sealed, or have a label over them) have been correctly torqued in accordance with the appropriate standards for devices, and for other connections at least 2Nm should be applied.

Hagar Torque Settings Info

Crabtree– Torque Specs:

Crabtree Starbreaker and Loadstar MCB Torque Spec

Wylex– The NH Range specify torque settings for the main terminals:

Wylex NH Range Consumer Unit Torque Spec

Consumer Units General  (BTI) It is the responsibility of the installer to ensure that all electrical connections are tight and that satisfactory earthing has been achieved. Guidance for torque settings:

Conductors- 2.1 – 5.3 mm2 (14-10 AWG)    Torque Settings- 2.3 N.m

Conductors- 8.4 mm2 (8 AWG)    Torque Settings- 2.8 N.m

Conductors- 13.3 – 21.2 mm2 (6-4 AWG)     Torque Settings- 3.1 N.m

From my own research it would appear that the general guidelines for electrical terminal torque settings range between 1.7Nm and 3.1Nm depending on the size, type and material of cable and the size of terminal.

Please Note: This information is only taken from my own research and I would recommend you check with the manufacture of any equipment before you install it to find out their recommended torque settings.

Maybe it would be a lot simpler for the recommended torque setting to be stamped on each device. Or would this be too much to ask of the manufacturers, especially as it’s so important?

Torque Electrical Screwdrivers

In the past is was difficult to find a reasonably priced torque screwdriver, especially one suitable for electrical work with less than 20Nm setting and with a 1000 volt insulated handle and shaft.  The Wiha Vario VDE range of torque screwdrivers are aimed at electricians and the electrical installation market. The yellow and red handled insulated version are obviously more expensive than standard but the are a quality tool.

Checkout some of the range of Wiha Torque Screwdrivers.

Please Note- Electricians should always check the voltage rating of torque screw drivers and other insulated tools. This is often inducated next to a VDE Mark.

What Is VDE Mark?
The VDE mark helps in the the selection of certified safe products.

The VDE trademark on tools such as insulated pliers or screwdrivers gives assurance that they have been thoroughly tested and are safe to use. Alongside the VDE mark you’ll normally find a voltage limit which indicates the safe working limits of the tool.

Torque Over Experience?

Do experienced electricians really need to use a torque screwdriver? When you think of all the hundreds of electricians terminating tens of thousands of cables every day, how many actually fail due to poor workmanship and would using a torque screwdriver really improve the failure rate. When I tighten a terminal screw I assess how tight to make it by judging the strain on the cable, the device and the terminal. A torque screwdriver can not take any other factors into account apart from the recommended setting. Can this be any better than my many years of experience of tightening thousands of terminal screws?

Forum Comments

Here is an interesting selection of some of the forum comments I came across on the subject of electrical torque screwdrivers:

  • Another thing to get calibrated another yearly cost, this has been coming for a while suprised the NIC haven’t brought out one with there name on it and then demand you have one. Manufactureres’ instructions do have to be adhered to but all the torque setting i’ve seen seem a bit low, im sure they would have been at or more than that point anyway. Even shear off bolts on mccbs seem to go a easily but they still work ok.
  • I’ll stick with using the ‘torque’ settings built into my wrist….
  • Overly tightened terminations can be just as bad as loose ones.
  • The Electrician I was Apprentice to [35 years ago] reckoned that on small stuff you just ‘ tightened til it felt tight then just nipped it up ‘. Bigger stuff was ‘grunt tight’. Even bigger stuff was ‘grunt tight and a touch’. Never had his arms calibrated. Just stripped out a factory that he did originally, tried undoing some of connections onto busbar and nearly broke my wrist.
  • The global recommended torque settings that have been set for any thread is to tighten it up to the point just before it rings, there you go, argument settled.
  • I used to use torque drivers on mcb and rcbos, didnt like them, you could always get at least another half turn on them. Id rather a termination be over tightened that loose and cause arcing and overheating.
  • Anyone ever seen instructions that state finger tight then half a turn? FFS, depends on whose fingers, and how hot or cold it is…..
  • Any decent tradesman should be able to gauge when its tight enough…..
  • 5 white knuckles 10nm ……..sorted
  • Had a subbie working for us last year finishing 4 houses off, he was using a 10.8 driver to tighten breaker screws and he completely demolished 4 wylex RCD’s with it, so I don’t recommend them for that purpose.
  • I use a 10.8 bosch impact normally dead quick for striping the old board, the elecsa assessor suggested getting a torque driver/wrench if only to cover yourself to show you followed manufac instructions if anything went wrong e.g. if it burnt how could you arrgue u tightened it correctly if u dont even own a torque tool.
  • Specs, Whilst I agree and there may yet be issues with this idea. It is manuf’ specs and thus must be adhered to. As I understand it ELECSA are going to be demanding calibrated torque screwdrivers as of the 1/1/12?…
  • B***** torque drivers indeed , I reckon with most sparks , you’d have to loosen the screws off to bring them to the required settings.
  • The torque screwdriver. When will we see actual torque settings specified in the OSG if in the technical information?

Conclusion- So is that 10/10 for the electrician’s torque screwdriver chaps?

Do you share any of these views?  You can have your say below and at Talk.Electrical Forum

Fire Prevention / Metal CUs

Due to the reported growing number of domestic fires (in plastic CUs) which were started by loose electrical connections, the updated amendment-3 regulation 421-1-200 states that consumer units, switch boards and assemblies in domestic electrical installations are now to be made of non-combustible material such as metal, or enclosed in a fire proof boxing or enclosure. Perhaps these measures and the correctly torqued terminals will help reduce the number of electrical fires. Read more about 421-1-200.

You can also download a general Newey & Eyre Products- Torque Settings Masterfile and the Wiha- Torque Settings for Many Products from the ERA.

Review the range of Wiha Torque Screwdrivers.

Wiha-Vario-VDE-Insulated-Electrical-Torque-Screwdriver1


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{ 2 comments… read them below or add one }

pete September 6, 2012 at 20:35

So if we torque the consumer board. What happens to the rest of the Circuits. Do we have to have two TORQUE screw drivers for every size cable.How many times guys/girls have you found Faults in DBS !/ Wrong cable size/ Wrong Breaker/ Mutiple circuits off same breaker/ mouse chewin cables.Ive been a Electrician 50 Years this will make you youg guys think 3029 stranded we twisted to gether. It changed to 1.00 hard core. thats when we han problems over tightning (solid strand )MANUFACTERS WHO ARE ON THE BOARDS NIECIC/ ECA ETC They over the years are costing us all loss of money for what we all have to find the extra money from our custemers now PART P mine noine cheers

Editor July 24, 2012 at 00:28

SPOT ON rant here from Kerching:
No!!…..we do not need to use a torque screwdriver!! Period, end of, finished, move on!!!

However, if we do not wish to fall foul of some litigous meber of society who [rightly or wrongly] feels he has been wronged because he has ‘a screw loose’ and seeks to engage the services of a be-wigged member of our ambulance chasing legal profession then, alas, we have to use a torque screwdriver as an insurance policy to prevent serious financial losses.

Yes, I do have a torque screwdriver [in fact I have about 4 of them]…I do not actually want them , but I have to have them

I also have calibrated 1000V VDE 1/2″ torque wrench and all the associated gubbins, dibbits and kimpfs

and yes, I do also have a calibrated torque checker.

I have these because

A) my Family is worth it
B) my peace of mind is worth it
C) my [minimal] bank balance is worth it!!!!

I don’t like having to keep buying new Regs Books, I don’t need to keep buying them however, for the reasons stated above I have to

Sorry for the rant [ette]…..but unfortunately we are stuck with the system that we have

….and remember there is always somebody out there that ‘wants a piece of you’ [ I know this from bitter first hand experience ] Read more… http://www.talk.electricianforum.co.uk/electrician-talk-forum/16306-torque-screwdrivers-7.html#post286124

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