UNC Grade 5 Bolts Torque Settings

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barrymac20

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Hi,
Would anyone have any information on torque settings for UNC Grade 5 1/2 inch bolts?
Connecting two Burndy lugs to a copper bus and need to recommend torque settings.
Thanks in advance.
 
barrymac20 said:
Hi,
Would anyone have any information on torque settings for UNC Grade 5 1/2 inch bolts?
Connecting two Burndy lugs to a copper bus and need to recommend torque settings.
Thanks in advance.
Click to expand...

Usually you can find a chart on the switch gear with recommended torques.

Are you using bellevue washers?
 
iwire said:
Usually you can find a chart on the switch gear with recommended torques.

Are you using bellevue washers?
Click to expand...

Its our own switchgear. But we normally use metric bolts so I'm looking for a bit of help on the imperial.
Yes we are using Belleville washers.

E.g. We would normally use M12 bolts and recommend a torque setting of 55NM for cable lug connections, approx. 40 lb-ft. The 1/2 inch bolt isn't to different from the M12 but any torque setting I've found seems very high, like 75 lb-ft. So I'm a bit confused.
I've asked our bolt supplier for this info but have yet to get anything from them.
 
barrymac20 said:
Its our own switchgear. But we normally use metric bolts so I'm looking for a bit of help on the imperial.
Yes we are using Belleville washers.

E.g. We would normally use M12 bolts and recommend a torque setting of 55NM for cable lug connections, approx. 40 lb-ft. The 1/2 inch bolt isn't to different from the M12 but any torque setting I've found seems very high, like 75 lb-ft. So I'm a bit confused.
I've asked our bolt supplier for this info but have yet to get anything from them.
Click to expand...

But my understanding of the concepts is that your torque values in this case would be generated by the properties of the Belleville washer not the bolt. The need is to give the Belleville washer the ability to spring and unspring to maintain proper connection between the bus plates.
 
Right.
When using Belleville washers, you get the correct contact pressure by selecting the right pair of washers and you get the right expansion tolerance by using the right number of pairs. Then you torque the bolt to get the right degree of compression, either visually or by measurement.

The only time the torque would depend on the bolt grade rather the connection specs would be if all you are trying to get is the maximum possible tension.

Tapatalk!
 
Remember that the tension/torque (friction not considered) has thread pitch as a term as well as diameter ... 1/2-20 creates 20/13 the tension of 1/2-13 at the same torque. Your M12 are what, m12x1.75 coarse, or M12x1 fine? The coarse is about 14.5 tpi, the fine 25.4 tpi. SO ... assuming coarse metric and imperial, the "same" diameter, and same friction surfaces, you'd need about 10% more with a 1/2-13 than for a M12x1.75.

Thread friction will be far more significant than these calculations.
 
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