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The hole diameter is 8mm or 0.31" how long should be the screws inside the concrete wall with tux? and what has more break resistance, stainless steel or GI (Galvanized Iron)?

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Original message:

What screws are the strongest? Is it Stainless steel? Pure iron? GI? Bronze? What else available?

I need to attach the Siemens Load Center panel to the concrete flat wall.. but they are just so heavy, for example, the smallest 12 space alone weights 20 lbs.. or 30 lbs with the breakers... and the 30 space weights 30 lbs or 40 lbs with breakers. And it only needs 4 screws to attach flat to concrete wall.

It's very dangerous for power panel to fall down because the open main feed big wires can become hazardous if it touches other objects or people.

For the 12 space Siemens load center with 30 lbs total weight with breakers. How long should be the screws and should it be stainless or GI? How do you compute for it?

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    I think the concrete anchor is going to be be more limiting than the strength of the bolt itself. I don't know what size bolts you're using, but a 1/4" steel bolt will have a shear strength and tensile strength of over 1000 lbs. Some nail-in drywall picture hanger anchors are rated at 25 - 50 lbs, so any reasonable bolt should be more than strong enough for a 30 lb panel. – Johnny Nov 17 '18 at 0:38
  • the hole is 8mm or 0.31".. see imagizer.imageshack.com/v2/800x600q90/922/FX7r2d.jpg I'm worried the screw head may break. To be sure it won't happen. Is the Stainless steel stronerg than GI? What material must I get to be sure it will last a hundred years or more? and important how long must it be? – Samzun Nov 17 '18 at 1:52
  • No such thing as iron bolts unless you have some research source. SS is either 304 or 316 , usually cold worked /hardened at only the surface. So, not as strong as steel = galvanized ( if it has been proper heat-treated). The typical hardware steel or galvanized bolt has a moderate strength level , better than any other named material . Automotive bolts are stronger , depending on the grade. Check SAE for strength and markings. – blacksmith37 Nov 17 '18 at 17:39
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I'd probably go with something simple like a tapcon anchor. Just be sure to drill deep enough and do not over tighten it, just get it snug and then stop. Over tightening will reduce or eliminate your pullout strength.

https://m.lowes.com/pd/Tapcon-4-Pack-3-in-x-5-16-in-Concrete-Anchors-Drill-Bit-Included/4686259

Here is a nice resource for other options for securing to concrete.

https://www.concretefasteners.com/diy-articles-fastening-electrical-junction-boxes-to-concrete-brick-block

  • What is the technical reason tightening will reduce or eliminate the pullout strength? – Samzun Nov 17 '18 at 5:01
  • What is your opnion about this plastic tux? imagizer.imageshack.com/v2/640x480q90/922/H5sj6R.jpg They are what we commonly use.. – Samzun Nov 17 '18 at 6:23
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    @Samzun - Tapcon fasteners have a special sharp thread that is designed to cut into the grain of the concrete. To make them work properly you have to drill a hole of precise dimensions. And then when you thread the Tapcon fastener in you need to apply steady pressure to advance the screw into its hole at the the rate prescribed out by the fastener threads without any slipping. If you over tighten a Tapcon fastener it basically strips out the thread that has been created in the concrete. If installed properly they have high straight pull out strength. – Michael Karas Nov 17 '18 at 10:05
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I'd use quarter inch lag screws and lag shields. These are far stronger than necessary, they are easy to remove and reinstall, and they leave the surface flush if you ever need to remove the panel.

lags

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