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Torque settings

Jam
Hi all,


Obviously, where available we use manufacturer's torque settings for connections. But where do they get them from?


I ask this not least because it's not always easy to obtain, at least in a timely fashion, but also because I appear to have conflicting instructions on some OEM'd equipment (comparing the original manufacturer with the wrapped supplier) or notably different settings when using the same lug onto a very similar terminal bar from a different supplier. It would also be helpful to be able to sense-check the answers for misplaced decimal points.


Jam
  • 0

    Jam:

    But where do they get them from?




    Probably by calculation, but could be experimental.


    Clearly a great deal depends upon the materials. Also, pinching a copper conductor is rather different from, for example, taking the varying load of a con-rod's big end, but there are some guidelines here.

  • 0

    Jam:

    Hi all,


    Obviously, where available we use manufacturer's torque settings for connections. But where do they get them from?


    I ask this not least because it's not always easy to obtain, at least in a timely fashion, but also because I appear to have conflicting instructions on some OEM'd equipment (comparing the original manufacturer with the wrapped supplier) or notably different settings when using the same lug onto a very similar terminal bar from a different supplier. It would also be helpful to be able to sense-check the answers for misplaced decimal points.


    Jam




    I never use a torque screwdriver when tightening electrical terminal screws or torque wrench bus-bar bolts and have never had any trouble. It is all down to experience. Some may say that I am wrong. Experience teaches that if you tighten up a screw too much it may strip the thread or break the part involved. So if you do that once you don't do it again. I have a torque wrench for my car repair work as that is very important. I don't want to break a stud or camshaft bolt and have difficulty in removing it afterwards, or strip a thread.  That would be a very expensive mistake.


    If electrical terminal screws are too loose then the conductor may run hot under load. I tighten and then do the wiggle test to see if the conductor is well secured in the terminal, then I re-tighten a little bit more, just a bit. M.C.B. clamp terminals are never to be over tightened as they can distort. I double over single solid conductor ends, but leave stranded conductors untwisted and then  let the clamp terminal grip the strands evenly.


    With new consumer  units I tighten all screws well. Sometimes I wire up R.C.B.O.s before positioning them in their final locations. When I have installed all M.C.B.s and R.C.B.O.s I then finally check EVERY terminal screw for tightness, as I may have disturbed a cable termination whist working. I check ALL screws before replacing the consumer unit cover.


    Z.

  • 0

    Zoomup:

    I double over single solid conductor ends, but leave stranded conductors untwisted and then  let the clamp terminal grip the strands evenly.




    I am not at all sure about doubling over solid conductors (or twisting them together) but I do agree that it helps to prevent the conductor slipping beside the screw in poor quality accessories.


    As for fine stranded conductors, on the basis of the advice in here, I bootlace them (or use other crimped connector).

  • Former Community Member
    0 Former Community Member
    on the basis of the advice in here


    Or even 526.9.1?


    Regards


    BOD
  • 0
    Call me old but back in the day every electrician knew just how much to tighten terminals, no torque wrench, it was down to practice, practice, practice.

    Engineers similarly were taught to feel the micrometer and not need to use the ratchet.

    Back in those days terminals were round, screws had slightly dommed ends and terminal quality, both in screw-threads size and metal composition was such that they did not screech as you were tightening them. Living is cheaper these days but quality is a race to the bottom.


    They don`t make things like they used to do (there again, they never did! ?)
  • 0

    Chris Pearson:




    Zoomup:

    I double over single solid conductor ends, but leave stranded conductors untwisted and then  let the clamp terminal grip the strands evenly.




    I am not at all sure about doubling over solid conductors (or twisting them together) but I do agree that it helps to prevent the conductor slipping beside the screw in poor quality accessories.


    As for fine stranded conductors, on the basis of the advice in here, I bootlace them (or use other crimped connector).


     




    Hello Chris. I double over single solid copper wires at terminals as any twisting action after installation can loosen a single wire due to the high torque forces involved. This is the case with clamp terminals and screw terminals. It increases the terminal conductor surface area.


    Where two 2.5mm2 copper wires enter a terminal, say at a socket on a ring final circuit, I just leave the copper wire ends single and parallel. The screw holds very well in that situation as rotation of the wire is not so likely. I gently twist the 1.5mm2 C.P.C.s together.


    I do NOT twist together 2.5mm2 solid conductors.


    I may gently twist together 1.0 or 1.5mm2 C.P.C.s. It makes for a reliable connection and reduces the risk of one C.P.C. of two not being reliably gripped in a terminal. And as we know C.P.C.s are important.


    Fine stranded wire should be treated carefully as you say, and normally have a ferrule installed.


    Z.

  • 0
    In many accessories such as those made by Hager and Schneider, particularly SFCU you have to do something to try and stop the small conductors from going up the side of the terminal screw.


    Andy Betteridge
  • 0
    Ditto what Sparking chip said, plus, in an ideal world, the termination hole would be filled with conductor to ensure large point of contact area, doubling helps to go some way achieve this idea, I never twist, except perhaps cpc in switch back box connections and rose earth terminal
  • 0
    This week I was installing an M.K. switched fused connection unit with the neon light in the switch. A very neat design, BUT the terminal screws are very well gripped in the terminals from new, BEFORE you start to tighten them down. I imagine that some torque screwdrivers would indicate a full tightness even BEFORE the screw secures the conductor. I really struggled to get the screws to initially start rotating.


    Z.
  • 0
    Thanks for all the thoughts so far everyone.

     

    Probably by calculation, but could be experimental.

    Clearly a great deal depends upon the materials. Also, pinching a copper conductor is rather different from, for example, taking the varying load of a con-rod's big end, but there are some guidelines here.



    Thanks for the link Chris, one to keep to hand. This is the kind of thing I was looking for and it'd be great to have a similar table for copper / tinned copper / alu / tinned alu etc.


    I've found the Copper Development Association's guidance document which has typical torque settings for various sizes but manufacturer's recommendations don't always fall particularly close... for an M10 bolted termination I can be quoted anything from 13Nm at the device at one end of a cable to 60Nm on the device at the other! Maybe it really is that it's calculated in detail and there's a wide range of sensible answers without detailed analysis, which I'll not have the data for.


    Jam

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