surface mounted fluorescents

[k d]

when mounting a surface mount fluorescent fixture to common sheetrock, do I need to use stand-offs or can I mount directly to the sheetrock since it weighs approximatly 40 to 45 pounds per cubic foot and by definition low-density cellulose fiberboard weighs 20 pounds or less per cubic foot?

[ May 29, 2003, 06:08 PM: Message edited by: k d ]

 

[electricmanscott]

Re: surface mounted fluorescents

Huh?

 

[bphgravity]

Re: surface mounted fluorescents

I would mount it directly to the sheetrock, however, I would try to locate the mounting screws into the wood or steel members that the sheet rock is attached to. I would not rely on the sheetrock alone if the fixtures you are using are that heavy.

 

[iwire]

Re: surface mounted fluorescents

I think the weights k d is talking about are of the sheet rock and the low-density cellulose fiberboard not the fixtures.

But I have no idea why that would matter in the mounting of light fixtures.

Bob

 

[BAHTAH]

Re: surface mounted fluorescents

470-76(B) A fixture that contains a ballast must have 1-1/2" clearance from combustible materials such as low-density cellulose fiberboard. You can mount directly against drywall, concrete or wood framing members. You cannot use drywall as the only physical support for the fixtures.

 

[iwire]

Re: surface mounted fluorescents

Originally posted by grant:
470-76(B)

I think you mean 410.76(B)

You cannot use drywall as the only physical support for the fixtures.

Is this a local ordinance as I know of nothing in the NEC that states that.

In my area it is done all the time, the installer uses his judgment on whether or not the fixture is to heavy to hang from sheetrock.

 

[bennie]

Re: surface mounted fluorescents

There is some articles in the building codes dealing with sheetrock as a sole support.

There is a seismic issue, plus sheetrock when damp, dumps everything in the floor or on some pretty girls head.

No structural inspector should approve the attachment of anything on sheetrock.

 

[canadian]

Re: surface mounted fluorescents

Then what are toggle bolts for???

 

[bennie]

Re: surface mounted fluorescents

canadian: I do not know what they are for.

[ May 30, 2003, 12:24 PM: Message edited by: bennie ]

 

[al hildenbrand]

Re: surface mounted fluorescents

So, Bennie,

I guess that you don't have sheetrock in your house, 'cause you will get hit on the head by it?

What does this say about normally dry locations?

 

[bennie]

Re: surface mounted fluorescents

Al: Yes, I have sheetrock in my house. I am not concerned with the sheetrock being a normally dry location, I am concerned when it stops and becomes an abnormally wet location.

 

[iwire]

Re: surface mounted fluorescents

Bennie if the sheetrock gets wet enough to start dropping fixtures the sheetrock itself will be coming down shortly to.

If I have to start doing my all my installations as "wet" locations things are going to get expensive.

An eight foot strip fixture is something we would toggle, a 175 watt HID fixture is something we would put blocking in for on the rough.

 

[curt swartz]

Re: surface mounted fluorescents

In Bennie's defense most building departments in my area including the City of San Jose prohibit using sheetrock to support surface mounted fluorescent fixtures. We always have the framing contractor install blocking between the joists during rough-in so when its time to hang the fixtures we can screw into the blocks.

 

[bennie]

Re: surface mounted fluorescents

Thanks Curt, a strain moment calculation, of a toggle bolt in sheetrock, will show it will barely support it's own weight.

 

[al hildenbrand]

Re: surface mounted fluorescents

That must be one heavy toggle bolt !!

Seismic considerations bring interesting exceptions to otherwise general practice. Most of the country gets to enjoy buildings that aren't shaken. As a result, roof membranes aren't torn, dry locations remain dry and the drywall stays sturdy. Inertial and kinetic energy of flourescent luminaires don't add additional stress to the toggle bolt / drywall support as the building is not shaken.

(Sorry for the double negative)

[ May 30, 2003, 09:46 PM: Message edited by: al hildenbrand ]

 

[hurk27]

Re: surface mounted fluorescents

All though it is allowed in our area we stoped using toggle bolts because of a failure of one fixture the toggle bolts were over tightend and it crushed the sheet rock causing it to fall and since all the fixtures were piped together it brought down every one of them (15)
and it was a mess we were lucky nobody got hurt or we would of been sued.

 

[electricmanscott]

Re: surface mounted fluorescents

That is installer error, which could be applied to any type of installation, not the fault of the toggle bolt. But what a mess that must have neen!

[ May 31, 2003, 07:33 AM: Message edited by: electricmanscott ]

 

[tim]

Re: surface mounted fluorescents

8' strip- toggle bolt on each end and 2x10 screw in the middle next to the junction box going into the ceiling joist. That baby isn't going anywhere.

 

[bennie]

Re: surface mounted fluorescents

One toggle bolt fails entire row falls, my case is made.

I will go into buildings done by Tim.

 

[hurk27]

Re: surface mounted fluorescents

Beenie I carry a stud finder and use #10x2" square drive screws that look like over sized dry wall screws, they shoot right through the metel into the joist. you could hang on these fixtures.