Welcome to my J.A.M. (Just Ask Mike) Session, a weekly column where I answer your basic electrical questions. If you’re a newbie who’s never plugged in a shore power cord (or ask – what’s a shore power cord?), or wonder why your daughter’s hair dryer keeps tripping the circuit breaker, this column is for you. Send your questions to Mike Sokol at mike (at) noshockzone.org with the subject line – JAM. This week I discuss torque and torque screwdrivers.
I really liked the “Mike’s Gadget” Torque Screwdriver in your RVelectricity™ Newsletter last week, but I can’t find a chart showing proper torque values. Please help!!! —Larry the DIY Guy
Dear Larry the DIY Guy,
I’m so glad you’re taking this problem seriously. I get email every week from readers who have burned up Generator Transfer Switches and Shore Power Plugs. One thing to remind you is to make sure ALL power is off. So unplug from shore power, turn off your generator, and power off your inverter.
But first, make sure there’s no possibility of 120-volt power. And if you’re going to re-torque any of your 12-volt DC screws, be sure to disconnect the batteries so you can’t create a shore circuit and melt a wrench, or get your wedding ring or metal bracelet trapped in the fault current path.
What are the numbers?
Just remember these are all in inch-lbs of torque, NOT foot-lbs like your wheel lugs. You’ll want a torque-limiting screwdriver that can be set from 20 in-lbs to 60 in-lbs, and have the proper bits for each type of screw you need to re-torque. Also, back off each screw a little, and then retighten them until the torque screwdriver clicks. You can get this torque screwdriver on Amazon HERE.
Loosen the torque driver when you’re done
After you’ve finished your yearly re-torque maintenance, you’ll want to back off the torque setting on the screwdriver to as low as it will go. This will prevent accuracy drift from the spring being under tension for months at a time.
Chart 1 on WFCO power centers
Chart 2 on standard circuit breakers
Chart 3 on a Southwire Generator Transfer Switch
That’s a wrap!
OK, everyone. Remember that electricity is a useful and powerful force, so we all need to pay attention to safety precautions while using it.
Let’s play (and stay) safe out there….
Mike Sokol is an electrical and professional sound expert with 50+ years in the industry. His excellent book RV Electrical Safety is available at Amazon.com. For more info on Mike’s qualifications as an electrical expert, click here.
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Interesting article, but it’s been a while since I’ve read the NEC. I don’t remember ever reading about torquing terminals. Has that changed? (Retired for 12 years)
If I were still working, I’d buy one of those. Good idea.
Every listed connector has a torque requirement included in their installation documents.
Looks like a great tool. Wondering if it comes with a certified torque calibration? I have a buddy electrical contractor who was getting an inspection & was asked what were torques on the service panel screws. Well they are tight, the inspector said they need to be torqued to the proper specs. My buddy went out & bought the necessary torque wrench. The inspector came back & saw the tool & then asked for the calibration certification date for the tool! True story!
Ok just re read the specs & indeed it does come with one. “Each Shipped Wrench Units Includes A Calibration Certificate of Conformance in Accordance with ISO 6789-1:2017”.
Great article. Much, much better than the usual instructions to “not overtighten”.
My dad used to tighten wiring screws until snug, and then give them an “extra twist” to make sure they were tight. I replaced a lot of his stripped and broken-off screws.
You’re articles are so (electrifying). Thanks for the info.