When connecting wires to the screw terminals on receptacles or light switches, what torque should they be tightened to if no torque is indicated either on the device itself or in its installation instructions? For example, the instructions for Leviton's receptacles and switches just say to "firmly" tighten them.
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Tight enough so that you could undo it with a firm twist, but your grandmother would have difficulty. – John Canon Mar 23 '21 at 03:34
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1@JohnCanon -- I suspect they're asking because they actually have a torque screwdriver and want to put it to good use :) – ThreePhaseEel Mar 23 '21 at 03:42
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1I believe 2020 NEC amended the torque requirement to send you to a "best practices" torque table somewhere. – Harper - Reinstate Monica Mar 23 '21 at 04:12
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@Harper-ReinstateMonica -- I believe that's only for things that don't have a tightening torque provided already – ThreePhaseEel Mar 23 '21 at 04:12
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Tighten until it just barely starts to hurt your palm or feels like the screw head is about to slip/strip; whichever comes first. – dandavis Mar 23 '21 at 19:10
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Generally, 14 inch-pounds is safe, although you can go somewhat higher if you wish
UL 498 (i.e the standard for receptacles in the US) calls out a tightening torque of 12-14 inch-pounds for wire binding screws (depending on size) in Table 123.3 as part of the Terminal Strength Test, and repeats that 14 inch-pound figure for 12AWG wire in 113.13 for the Terminal Temperature Test. Given that you're generally dealing with duplex receptacles, and those almost always support through-wiring, 14 inch-pounds is a reasonable figure as 113.4 requires their terminals to be temperature tested with 12AWG wire if they aren't based on a 20A design, and most are based on a 20A design anyway.
Likewise, UL 20's terminal retention tests (found in clause 5.30) repeat those figures in Table 16, and Leviton's own specifications for their residential receptacles call out 14-18 inch-pounds of torque.
ThreePhaseEel
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2Interesting that Leviton has a torque spec, but doesn't put it anywhere that an installer would be expected to see it. – Joseph Sible-Reinstate Monica Mar 23 '21 at 22:36
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The best part is when the little paper installation instructions say to check the website for the torque specs. Instead of just printing them on the instructions. – Alexander Riccio Apr 09 '23 at 23:43