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Eaton Glasgow Screw Torque

Will Elec

Hi all,

Just installing a glasgow 104gc switch disconnector. Instructions state 10Nm for terminals, so get torquing and the first screw breaks! As this is a TP+SN unit there is no netural bar but the instructions state 3Nm for neutral, so torque all other terminals to 3Nm and no problem!

Phoned Eaton technical and they insist that the terminals should be 10Nm - which for a small tinned brass flat head screw seems excessive! All the Schneider gear using similiar terminals I have fitted seems to be 3.5Nm and they have a far better combination pozi head.

Anyway, would appreciate some thoughts on this. I must admit I'm happy with 3Nm on the terminals but the regs say to follow the manufactures guidance....

Thanks

Parents
  • 0

    If you tighten to a lower torque, you reduce the pre-load (compressive force on the wire) in direct proportion, minus a loss for thread friction.  The bolt looks flat nosed, so the pre-load will be the force over the area more or less as a flat.
    So at 3nm you are holding the wire with more or less 1/3 the clamping force - if that is enough to  puts a good full area 'flat' onto the cable you are using, then you are on the right side of OK. If the screw force is not enough to flatten the cable to make good contact, then the torque is not enough, or it is the wrong kind of cable.


    I think the regs actually say 'take account of instructions' not 'follow blindly' so if the cable is being well clamped feel free to tell Eaton their advice is incorrect.  And ask them if the can send you some spare screws.

    If you know the thread size on that screw  (or diameter and length  plus  of turns over the length ) I can show you how to calculate the forces on it if you like.
    Mike

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  • 0

    If you tighten to a lower torque, you reduce the pre-load (compressive force on the wire) in direct proportion, minus a loss for thread friction.  The bolt looks flat nosed, so the pre-load will be the force over the area more or less as a flat.
    So at 3nm you are holding the wire with more or less 1/3 the clamping force - if that is enough to  puts a good full area 'flat' onto the cable you are using, then you are on the right side of OK. If the screw force is not enough to flatten the cable to make good contact, then the torque is not enough, or it is the wrong kind of cable.


    I think the regs actually say 'take account of instructions' not 'follow blindly' so if the cable is being well clamped feel free to tell Eaton their advice is incorrect.  And ask them if the can send you some spare screws.

    If you know the thread size on that screw  (or diameter and length  plus  of turns over the length ) I can show you how to calculate the forces on it if you like.
    Mike

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