Arc Shields or Add a Depth Rings

[winnie]

I don't believe that the _mounting screw_ is considered to provide an effective ground fault path for a self grounding device. I always thought that the little metal spring that holds the screw and gets wedged against the box was considered the required grounding connection. In this case, a plastic box extender would interrupt the connection.

However beyond this, I don't see using a plastic box extender as being any more or less permissible than using a plastic device cover plate, and something that may or may not be permissible depending upon circumstances. If the reason for using a metal box has to do with fire resistance, then IMHO iwire is correct, a plastic box extender won't do. But if the metal box is being used for other reasons, and fire resistance is not an additional requirement, then the plastic box extender might be just fine.

When using a metallic wiring method, at a minimum, you have to bond all of the metallic conduit or cable armor. This can be accomplished with plastic boxes with suitable bonding wiring, but a metallic box simply makes more sense. If the only reason for using the metal boxes was to provide bonding, then IMHO a plastic box extender would be sufficient.

-Jon

 

[JohnE]

If the reason for using a metal box has to do with fire resistance, then IMHO iwire is correct, a plastic box extender won't do. .

-Jon

I"m not sure about this. What if you are using the spark guard because box is set back just over 1/4"? And you are in a 2 hour wall consisting of double 5/8. Your spark guard doesn't need to provide fire resistance. The box and the gypsum do that.

 

[iwire]

I"m not sure about this. What if you are using the spark guard because box is set back just over 1/4"? And you are in a 2 hour wall consisting of double 5/8. Your spark guard doesn't need to provide fire resistance. The box and the gypsum do that.

If the wall is firerated and there is a fire the 'spark guard' will melt out long before the rating of the wall alowing a place for the fire to spread.

Again this would be no different than using a plastic old work in a fire rated wall.

The info can be found in the UL orange book, but I do not have one.

 

[mdshunk]

The info can be found in the UL orange book, but I do not have one.

I don't have one either, but it runs in my mind that your box needs to be within 1/8" of the drywall surface in order for the assembly to qualify as fire resistive anyhow. In that case, box extenders would never be needed in the first place. Your box is either within 1/8", or you don't have a fire rated assembly, and you need to move your box somehow. (don't quote me on the 1/8" measurement, but it's some measurement around there)

 

[goldstar]

No one ever really plans to use a box extender. If you set your boxes for the proper depth, under most Utopian conditions you don't need one. Now, here's a scenario : The sheetrock on a particular job is supposed to be 5/8" and you set your boxes in, you rough-in the job and you're off the job for x amount of days. You come back only to find out that the sheetrock contractor couldn't get, couldn't find, couldn't purchase or had no time to locate 5/8" sheetrock so he decided to use two sheets of 1/2" sheetrock.

Now, I can only envision the following possible events occurring :
1) Have the sheetrock contractor rip off the double 1/2" sheets and install the proper size because your boxes are set to 5/8" (like that's going to happen)
2) Use metal extenders because you believe that there should be a metal to metal to metal bond between the receptacle and the box you're attaching to and because the metal extension collar will provide a better fire rating, or
3) use a 3/8" plastic arc shield to make up the difference

My choice (every time) would be # 3 because :
a) the device will already be bonded to the back of the metal box because you installed a green EGC wire (so grounding is not an issue)
b) The plastic ring provides a better mounting surface and is safer than the split metal extension ring and you don't have to tape up the device

This is just my opinion and not based on any codes or reference books.

 

[JohnE]

If the wall is firerated and there is a fire the 'spark guard' will melt out long before the rating of the wall alowing a place for the fire to spread.

Again this would be no different than using a plastic old work in a fire rated wall.

The info can be found in the UL orange book, but I do not have one.

IMO the difference is that once the spark guard melts, the fire is still blocked by the box and the sheetrock. It's not as if the face of the box is behind the sheetrock. I don't know, maybe I'm off base.

 

[JohnE]

Here's another scenario. Say the box was flush with the face of the fire rated wall. Then someone adds wainscotting for whatever reason. I'd say the plastic extenders are ok in this case. My logic is the same in the OP's case.

 

[iwire]

John we have a few options.

1) We can agree to disagree.

2) We can try to find the UL orange book info.

3) We can wait till Roger D. gets back and ask him, he has the orange book and has posted a lot of info from it in the past.

the fire is still blocked by the box and the sheetrock.

Yes, but not blocked by the entire depth of the sheet rock, keep in mind it is not so much a question of what will work it is a question of meeting the UL requirments.

I am sure that UL requirements do not say 1.25" of sheetrock or at least close to that.

 

[JohnE]

Bob,

I'm not sure we exactly disagree. Admittedly I don't know what the orange book says. What are your thoughts on my last scenario?

edit: I meant to elaborate when the doorbell rang and company was early. Had to cut it short. I was going to say that I didn't think that either ring would have a fire rating. I'm still not sure about box set back, and how it affects the rating. Larry has since posted about the 1/8 gap, but I haven't heard anything about depth. Intuitikvely it seems that if a box were wet back somewhat it would reduce the rating, but I'm not sure if that's the case.

 

[iwire]

Here's another scenario. Say the box was flush with the face of the fire rated wall. Then someone adds wainscotting for whatever reason. I'd say the plastic extenders are ok in this case. My logic is the same in the OP's case.

I would have to say I am not sure in that case.

I would assume that the original steel box made it into the sheetrock far enough to meet the fire rating so any addtional depth might be fine with plastic.

 

[sandsnow]

Here's some info for you guys. The UL guide info is silent on the plastic on metal issue. The Arlington spec sheet "appears" to allow use on metal but not specifically.

http://www.aifittings.com/m_9.htm

http://database.ul.com/cgi-bin/XYV/...n=versionless&parent_id=1073991695&sequence=1

http://database.ul.com/cgi-bin/XYV/...n=versionless&parent_id=1073991695&sequence=1

Ithink this is the info you wanted from the orange book:

5. Nonmetallic Electrical Outlet Boxes

Outlet Boxes and Fittings Classified for Fire Resistance (CEYY) includes Classifications for nonmetallic outlet and switch boxes for use in wall or partition assemblies. The information provided for each Classification includes the model numbers for the Classified products, a description of the rated assemblies, the spacing limitations for the boxes and the installation details. Nonmetallic boxes shall not be installed on opposite sides of walls or partitions of staggered stud construction unless Classified for use in such constructions.

6. Metallic Electrical Outlet Boxes

Listed single and double gang metallic outlet and switch boxes with metallic or nonmetallic cover plates may be used in bearing and nonbearing wood stud and steel stud walls with ratings not exceeding 2 h. These walls shall have gypsum wallboard facings similar to those shown in Design Nos. U301, U411 and U425. The metallic outlet or switch boxes shall be securely fastened to the studs and the opening in the wallboard facing shall be cut so that the clearance between the box and the wallboard does not exceed 1/8 in. The surface area of individual metallic outlet or switch boxes shall not exceed 16 sq in. The aggregate surface area of the boxes shall not exceed 100 sq in. per 100 sq ft of wall surface. The aggregate surface area of the boxes may be exceeded when Wall Opening Protective Materials (CLIV) are installed according to the requirements of their Classification.

Metallic boxes located on opposite sides of walls or partitions shall be separated by a minimum horizontal distance of 24 in. This minimum separation distance between metallic boxes may be reduced when Wall Opening Protective Materials (CLIV) are installed according to the requirements of their Classification.

Metallic boxes shall not be installed on opposite side of walls or partitions of staggered stud construction unless Wall Opening Protective Materials are installed with the metallic boxes in accordance with Classification requirements for the protective materials.

And finally here's the guide info on non-metallic boxes in fire resistive construction. I did not find any info on use of box extenders in fire resistive construction.

http://database.ul.com/cgi-bin/XYV/...n=versionless&parent_id=1073984997&sequence=1

 

[JohnE]

I'm thinking that neither the metal or plastic spark guards are rated for fire resistance.