# 1/4" threaded post shear strength



## BBQ (Nov 16, 2010)

Are you really looking for the sheer strength or the tensile strength?

http://www.powerstrut.com/psjan2005/fibergl189.jpg

I imagine you are talking working load which is about 220 pounds


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## MDShunk (Jan 7, 2007)

I guess this was a sidewall fixture, if you're asking about shear strength? The shear strength of 1/4-20 threaded rod is 1,590 pounds.


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## Davethewave (Jan 6, 2012)

Since it is a chandelier, I am guessing I am looking for tinsel strength. What would it take to separate the nuts on the top of the canopy from the threaded post.


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## MDShunk (Jan 7, 2007)

The "pullout strength" of ordinary steel 1/4-20 rod and nuts with standard thread engagement is 220 pounds. You double nutted it, but that doesn't double it. It's closer to 345 pounds when double nutted. The tensile strength of the rod is something like 1900 pounds, but the threads will pullout well before that.


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## Davethewave (Jan 6, 2012)

Thanks for that. Looks like I will be cutting it close with this one. 230 lb One post double nutted. Totally nutts!


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## dronai (Apr 11, 2011)

How was the box supported ?


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## al13nw4r3LC76 (Apr 6, 2009)

I'd sleep better at night with 3/8


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## MDShunk (Jan 7, 2007)

Davethewave said:


> View attachment 13066
> 
> 
> Thanks for that. Looks like I will be cutting it close with this one. 230 lb One post double nutted. Totally nutts!


That is a cool fixture, by the way.


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## Davethewave (Jan 6, 2012)

It is cool and bazar. Very similar to the artist who built it. 18K ! . The canopy is 1/4" brass and is secured to the ceiling with four 3/8" lag bolts. The hardware was supplied by the artist, so I am hoping this isn't her first rodeo. I could hang a piano from the canopy, the threaded post has me up at night. I hung a similar fixture which was supported by 3 1/4" threaded posts and felt good about that one. :-/


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## MDShunk (Jan 7, 2007)

Davethewave said:


> It is cool and bazar. Very similar to the artist who built it. 18K ! . The canopy is 1/4" brass and is secured to the ceiling with four 3/8" lag bolts. The hardware was supplied by the artist, so I am hoping this isn't her first rodeo. I could hang a piano from the canopy, the threaded post has me up at night. I hung a similar fixture which was supported by 3 1/4" threaded posts and felt good about that one. :-/


Since you might have a rapport with this artist, it might be a decent idea to inform him or her that you believe that the 1/4-20 was on the hairy edge of it's pullout strength. That way, if they design a fixture of similar weight like that in the future, they can make the beauty parts to accommodate a more substantial rod, like maybe a 3/8". My guess is that this fixture you installed had a painted down tube that would only accommodate a 1/4" rod max.


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## leland (Dec 28, 2007)

So, your threaded post, how exactly was it secured- the post-?
Thru a timber- a 'sammy' threaded bolt-?

please expand on the mechanics of it.

I did 1 300# fixture- 20 yrs ago. 
3 guys 12 hrs just to hang the Chrystal medallions on it. Then the price of the riggers whom set up and took down the staging.

That was hung with unistrut lagged thru the floor joists,3/8".
To the best of my memory.


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## Davethewave (Jan 6, 2012)

Correct. After "sleeping on it for a night. I think a more secure connection would have been to cut the bronze cover 1 " shorter, extended the post through the canopy tripple nutted it and drilled a small hole through the top of the post for a pin. Bad scene with the owners 5 year old kid under my feet digging through my bags and my parts. Distractions are the MOAFU's.


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## Davethewave (Jan 6, 2012)

There is a decorative threaded nut below a flat brass canopy and double nutted on the top. Since the 1/4" post is threaded into a hub at the bottom of the post, there will always be the risk of shearing of the threads. Beautiful fixture, not engineered very well.


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## 360max (Jun 10, 2011)

I don't think I'd hang a 18k fixture with 1/4" rod, but you have to work with what they give you. I do agree with Mark, I would suggest to artist or whoever to run 3/8 if possible in future.


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## macmikeman (Jan 23, 2007)

Anybody remember how the "War of the Roses" ended?....


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## BBQ (Nov 16, 2010)

Davethewave said:


> It is cool and bazar. Very similar to the artist who built it. 18K ! . The canopy is 1/4" brass and is secured to the ceiling with four 3/8" lag bolts. The hardware was supplied by the artist, so I am hoping this isn't her first rodeo. I could hang a piano from the canopy, the threaded post has me up at night. I hung a similar fixture which was supported by 3 1/4" threaded posts and felt good about that one. :-/


For what it is worth the Artist is required to follow some standards while constructing the fixture



> *ARTICLE 410
> Luminaires, Lampholders, and Lamps
> 
> I. General
> ...





> *410.6 Listing Required. *All luminaires and lampholders
> shall be listed.


Is the fixture listed by an approved agency?

If so the hardware should be correct.

If not all bets are off and you could get screwed for installing an unlisted fixture.


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## Southeast Power (Jan 18, 2009)

BBQ said:


> For what it is worth the Artist is required to follow some standards while constructing the fixture
> 
> 
> 
> ...


Ok but, "listed" is defined by the AHJ. The list could be written on the back of a $20 bill.


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## BBQ (Nov 16, 2010)

jrannis said:


> Ok but, "listed" is defined by the AHJ. The list could be written on the back of a $20 bill.


Ah no, listed is defined by the NEC, any greenbacks changing hands is between you and the lord.


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## RandyM (Apr 5, 2012)

BBQ said:


> Ah no, listed is defined by the NEC, any greenbacks changing hands is between you and the lord.


For an18K fixture the artist could have UL do a field evaluation!


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## Davethewave (Jan 6, 2012)

The fixture has no listing. I brought the topic up with the owner and explained my concerns to the artist, the contractor. Unfortunately, it is hard to get these " important " people to take your concerns seriously. I am going to submit a formal letter to the GC if the fixture doesn't crash to floor first. Since there will always be a weak link at the hub connecting the rod to the fixture, I am going to suggest two aircraft cables from the canopy to the fixture. Does anyone know the pull strength of a 3/8" threaded post? I want to have my facts straight when I address the owner.


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## Cletis (Aug 20, 2010)

Is the fixture grounded?


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## CanadianSparky (May 10, 2011)

Cletis said:


> Is the fixture grounded?


No it's on the ceiling


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## Big John (May 23, 2010)

Davethewave said:


> The fixture has no listing. I brought the topic up with the owner and explained my concerns to the artist, the contractor. Unfortunately, it is hard to get these " important " people to take your concerns seriously....


 You may have made a mistake.

I know the goal is to please the customer and keep his business, but I'm not sure that all the written letters in the world will reduce culpability if the fixture fails and you knew you weren't supposed to install it because it wasn't listed.

-John


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## Tiger (Jan 3, 2008)

A little late but stainless steel rod has greater strength than std or galv. steel. I'm a fan of massive overkill in situations like this (sister joists, adhesive, lag bolts) and I sleep like a baby.


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## Big John (May 23, 2010)

Tiger, I've never looked at the specs on stainless rod, but we use a lot of stainless hardware and in my experience, it's almost always mechanically weaker than carbon steel.

-John


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## Tiger (Jan 3, 2008)

Big John said:


> Tiger, I've never looked at the specs on stainless rod, but we use a lot of stainless hardware and in my experience, it's almost always mechanically weaker than carbon steel.
> 
> -John


You have the experience. I just did a quick check online. Personally, I'd be thinking about something other than the rod for support. I was just thinking of this in a legal situation with a lawyer asking why the electrician chose that material rod instead of a stronger material rod, whatever that may be.

This links to a table of bolt strength:
http://www.derose.net/steve/resources/engtables/bolts.html


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## Davethewave (Jan 6, 2012)

Sure wouldn't want it to come down to a lawyer. If someone decided that it was my fault for hanging a fixture that was constructed and furnished by someone else, I will write a check and be done with it. My recommendation will be to run a couple of aircraft cables parallel to the rod. It would have been nice to have the fixture a couple weeks in advance to brain storm but hind site is 20/20


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## Jlarson (Jun 28, 2009)

I'm still trying to figure out why just about every electrician out there always skips 5/16" hardware, everybody always goes from 1/4" straight to 3/8".


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## BBQ (Nov 16, 2010)

Jlarson said:


> I'm still trying to figure out why just about every electrician out there always skips 5/16" hardware, everybody always goes from 1/4" straight to 3/8".


LOL, 

I don't know if the local electrical supply houses carry 5/16" or 7/16".


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## davis9 (Mar 21, 2009)

Only time I've ever used 5/16" is on my 72 Dodge. Was a pita since all I had on the truck was 1/4 and 3/8 stock.LOL

Tom

Last big Chandelier I hung was about 6' tall x 4' wide and used 3/8 hardware. Used a 16' step rented from HD with an 8' for someone to hold the bottom. I didn't think the hardware was big enough(was UL though). We had it through solid blocking and a 4" sq to wire it up since the wiring was inside the hardware.


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## NY ELECTRIC (Sep 27, 2009)

How about some steel "airplane" cable as back up fastened to the box then down the fixture like the ground wire this helps me sleep at night


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## Davethewave (Jan 6, 2012)

I have made the suggestion. We will see if it sticks? :-/


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