Screw connections: How tight is too tight?

grandmumAugust 12, 2013

I put on a new dryer cord the other day and really torqued down those screws, almost to point of stripping the screw... so I stopped.

Got me to thinking how tight is too tight in regards to electrical connection on screws?

Could over torqueing actually cause them to become loose if that even makes any sense?

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jreagan_gw

In theory, most of the connections have recommended torque values for the screws. You can see this on breakers, etc. Not so much on the whip cords. You almost never see a torque wrench in a residential installation, but you will in commercial settings.

If you over-tighten a screw, you end up stretching the threads on the screw or on the connector. The end result is that you will make it looser. Even if you stopped "before" you stripped the screw, you still might have excessive force being applied to the threads. Subsequent vibration, thermal cycles, etc. might eventually loosen the connection.

    Bookmark   August 12, 2013 at 10:02AM
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inox

I spoke with a few physicists about this topic last year, and none could think of a reference, but they all agreed that putting too much torque or too little torque both cause the resistance at the connection to be increased compared to the resistance with the specified torque. It is not just a matter of the mechanical aspects of the connection.

    Bookmark   August 13, 2013 at 12:33AM
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