Do Firestop Putty Pads Affect Box Fill?

[vpritchard]

Electrical outlet boxes are stamped with the volume inside, in cubic inches. The NEC provides us with a method of calculating box fill (314.16). Conductors, loops, splices, clamps, yokes... there is an allowance made for actual wires as well as physical items in the box that do take up space...... how about firestop insert pads? Technically they consume space within the box. Hilti and a few other companies make these. I think the intent was if you have to firestop after walls have been closed, there is this wonderful product that you can stick INSIDE the box. But it takes up physical space, and would reduce the available volume for calculating fill. The very helpful technical engineers at Hilti have sent me all kinds of paperwork regarding UL testing and approvals for the "system" of having this pad inside an electrical outlet box. But they had no real answer for me when I mentioned allowances for box fill. I could imagine a scenario where an electrical inspector comes across an outlet box at max fill...lets say a 4-11/16" x 2-1/8" square box (42cu in) with 18 'conductors' in it plus one of these pads, and issues a violation. Although no one I have asked has comes across (or even thought of) this issue. To me it seems very plausible. I was curious to know if anyone has encountered this scenario and/or had any input on the topic.

 

[gadfly56]

Electrical outlet boxes are stamped with the volume inside, in cubic inches. The NEC provides us with a method of calculating box fill (314.16). Conductors, loops, splices, clamps, yokes... there is an allowance made for actual wires as well as physical items in the box that do take up space...... how about firestop insert pads? Technically they consume space within the box. Hilti and a few other companies make these. I think the intent was if you have to firestop after walls have been closed, there is this wonderful product that you can stick INSIDE the box. But it takes up physical space, and would reduce the available volume for calculating fill. The very helpful technical engineers at Hilti have sent me all kinds of paperwork regarding UL testing and approvals for the "system" of having this pad inside an electrical outlet box. But they had no real answer for me when I mentioned allowances for box fill. I could imagine a scenario where an electrical inspector comes across an outlet box at max fill...lets say a 4-11/16" x 2-1/8" square box (42cu in) with 18 'conductors' in it plus one of these pads, and issues a violation. Although no one I have asked has comes across (or even thought of) this issue. To me it seems very plausible. I was curious to know if anyone has encountered this scenario and/or had any input on the topic.

It sounds reasonable that the box capacity has been reduced and that you should calculate accordingly. Measure the width, height, and thickness of the pad and deduct accordingly. Or use the product for the outside of the box.

 

[infinity]

Locknuts, bushings, connectors, wirenuts, mounting screws, nails, pigtails that do not leave the box, etc. all take up space and are not included in the fill calculation. This could be something that the NEC hasn't caught up to but as it stands no there is no requirement to count the space used by the putty pad.

 

[texie]

Putty pads go on the outside of the box. Not the inside.

 

[infinity]

Putty pads go on the outside of the box. Not the inside.

They actually make two types, the smaller square ones fit perfectly on the inside of the box and cover only the back. They even have a cut out for the ground screw. We only use the ones that go on the inside.

 

[texie]

They actually make two types, the smaller square ones fit perfectly on the inside of the box and cover only the back. They even have a cut out for the ground screw. We only use the ones that go on the inside.

Guess we learn something every day. I've never seen inside pads.

 

[infinity]

Guess we learn something every day. I've never seen inside pads.

Me neither until we started our last job. They had something in the spec about using the inside pads. They're actually much easier to use than the ones that go over the entire outside of the box.

 

[Hv&Lv]

They actually make two types, the smaller square ones fit perfectly on the inside of the box and cover only the back. They even have a cut out for the ground screw. We only use the ones that go on the inside.

It would seem that the ones that fit the inside on the back only defeat the acoustical and fire-stop purpose. Like Texie, I had no clue they had these available. Would they still be as good?

 

[hbiss]

It would seem that the ones that fit the inside on the back only defeat the acoustical and fire-stop purpose. Like Texie, I had no clue they had these available. Would they still be as good?

I agree. I can't see how they would be as effective as the ones that are on the outside.

-Hal

 

[infinity]

Not sure how they work maybe they expand slightly during a fire? They are approved as an alternative to puddy pads on the outside.

https://www.hilti.com/c/CLS_FIRESTOP_PROTECTION_7131/CLS_FIRESTOP_PUTTIES_7131/r1575891

 

[Dennis Alwon]

The pad info says to refer to 314.16. I wonder if they give a cu.in number on the pads

 

[vpritchard]

Dennis Alwon, thanks for pointing that out. I never noticed that.

gadfly56, I guess I could do the math myself, but I was looking to see if anyone that has used these pads already has encountered any problems during an inspection.

I worked for 22 years in various roles in the electrical industry in NYC. Some of the electrical inspectors I have dealt with were very tough. I have encountered situations where an inspector's narrow interpretation of the code resulted in very expensive remedial work. I imagined that if this issue were to ever come up.... on a high rise residential project where the EC opted to use these internal pads instead of the ones that go outside the box... in many hundreds of locations, an inspector could be justified in asking the EC to prove box fill. The largest pad that would be used for a 4-11/16" square box is a 1/4" thick, and a little under 5 cubic inches. So putting one inside a 4-11/16" x 1-1/2" square box (29.5 in3) effectively reduces it to the volume of a 4-11/16" x 1-1/4" square box (25.5 in3). We are allowed 13 #12 in the 1-1/2" box but only 11 #12 in the 1-1/4" box. So this EC has 12 #12 in some of his 1-1/2" boxes, the inspector cries foul, and a debate ensues.
In new construction, I have always opted for the moldable pads that go on the outside of the box. But, if you consider the labor savings by just sticking a pad inside the box versus molding outside... I can see many contractors choosing the inserts.

 

[gadfly56]

The pad info says to refer to 314.16. I wonder if they give a cu.in number on the pads

I did a look-see at 314.16 in the 2014 edition, and it's not clear to me how or if you would need to make an allowance. Can you step me through your thinking?

 

[infinity]

Dennis Alwon, thanks for pointing that out. I never noticed that.

gadfly56, I guess I could do the math myself, but I was looking to see if anyone that has used these pads already has encountered any problems during an inspection.

I worked for 22 years in various roles in the electrical industry in NYC. Some of the electrical inspectors I have dealt with were very tough. I have encountered situations where an inspector's narrow interpretation of the code resulted in very expensive remedial work. I imagined that if this issue were to ever come up.... on a high rise residential project where the EC opted to use these internal pads instead of the ones that go outside the box... in many hundreds of locations, an inspector could be justified in asking the EC to prove box fill. The largest pad that would be used for a 4-11/16" square box is a 1/4" thick, and a little under 5 cubic inches. So putting one inside a 4-11/16" x 1-1/2" square box (29.5 in3) effectively reduces it to the volume of a 4-11/16" x 1-1/4" square box (25.5 in3). We are allowed 13 #12 in the 1-1/2" box but only 11 #12 in the 1-1/4" box. So this EC has 12 #12 in some of his 1-1/2" boxes, the inspector cries foul, and a debate ensues.
In new construction, I have always opted for the moldable pads that go on the outside of the box. But, if you consider the labor savings by just sticking a pad inside the box versus molding outside... I can see many contractors choosing the inserts.

What code article would anyone cite to say that the pad has to be figured into the box fill calculation?

 

[bkludecke]

Funny how we all get tied up on this stuff. Devices (receptacles, switches, dimmers, timers, etc.) come in all different shapes & sizes but are all counted as equivalent to two conductors in the box fill calculations. Never made much sense to me. Fortunately we had a chief inspector around here for years who looked at the box make-up and if it was done clean and careful, and it looked liked there was plenty of room to device it, it was good to go. Wish more inspectors were like that.

 

[Dennis Alwon]

What code article would anyone cite to say that the pad has to be figured into the box fill calculation?

The section I quoted 314.16...It is not that section that states the pad must be figured in but the pad itself says to refer to 314.16. I assume that means you must consider the cu.in of the pad.

 

[MAC702]

... I think the intent was if you have to firestop after walls have been closed, there is this wonderful product that you can stick INSIDE the box....

That would mean trying to install it with all the wires in it, unless it's just conduit and the wires are being pulled in after the walls are closed.

I might guess that the inside and outside pads have different performance characteristics, and there are times the inside is sufficient, and times the outside is required.

 

[vpritchard]

I might guess that the inside and outside pads have different performance characteristics, and there are times the inside is sufficient, and times the outside is required.

I do know that the outside pads are moldable, so that you can cover a surface (box, panel, etc) around a corner. The inside ads are flat and made to just stick to the back of the box.


I am wondering if Hilti's reference to 314.16 is just a way for them to cover themselves about the code. I get what everyone else is saying... devices come in all different shapes and sizes. But we make the same allowance whether its a switch or a receptacle. The point is that we do make an allowance. Whereas with the pad we have no make an allowance besides deducting the volume for the pad. Allowances seem to be made for items in the box that are conductive. The pad material is non-conductive and obviously fire-rated AND UL listed, so maybe this is all just a useless discussion.