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Old 06-26-2009, 03:19 PM   #1
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Default Code requirements for securing/supporting wires in premanufactured panels

Please assist me with how the NEC would apply to these conditions. Thanks in advance for your assistance.

We finish basements using a wall system that is similar to structural insulated panels. The panels are 3 1/2" thick with a 1/2" cement board panel on the face and 2 1/2" of foam insulation adhered to the cement board. The foam insulation backs up to the concrete basement wall when it is installed. These panels go in very quickly and have many advantages over traditional drywall and stud construction.

Each panel has a 1 1/4" chase bored horizontally through the panel at the height of outlets and switches These chases are to be used to fish wires between the panels. The horizontal chases are more than 1 1/2" behind the face of the panels, so protection for the wires is typically not needed. There is no PVC or metal conduit for these wire chases. NMB wire is typically used for the wiring.

NEC 334.30 states that wires must be supported every 4.5 feet and within 12 inches of boxes. However, 334.30 (B) offers an exception that non-metallic shielded cable will be allowed to be unsupported when the wire "Is fished between access points through concealed spaces in finished buildings or structures and supporting is impracticable." I think that this has been interpreted to apply to premanufactured panels as well.

My questions are:

1. Does exception B apply because these are pre-manufactured panels or because supporting is impracticable?

2. Is there another exception supporting/securing the wiring that I do not know about that could apply to this situation?

3. If an exception does not apply to this situation, can you suggest methods of securing and/or supporting the wiring that would be acceptable under the code.

4. Would the answers to any of the above questions be different if the chase for running the wire was not a 1 1/4" chase completely surrounded by foam, but was a 3/4" deep channel cut horizontally into the back of the foam in which the wire is tucked into and held in place by friction. In this case the top of the channel remains open after the wiring is installed.

Again, thanks for your help.

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Old 06-26-2009, 05:22 PM   #2
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If your fishing the wires you would not need any support for the romex. If your going thru a stud or panel each time it goes thru a stud thats a strap. What are these panels made out of?

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Old 06-26-2009, 05:22 PM   #3
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Welcome to the forum.
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Old 06-26-2009, 05:59 PM   #4
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Thanks for the reply william1978.

The panels are self supporting. They attach to the floor and the ceiling framing using a bracket system and screws. There are no studs or framing, just 4' wide by 8' high panels that are 3 1/2" thick. The panels install next to each other in a line to form a wall. The wires are pulled with string, fished, or pushed through either the 1 1/4" channel that goes horizontally through the foam insulation, or are fit into a channel cut into the back of the foam as described in my initial posting.

Occassionally, electrical inspectors have some reservations about this system because it is new, and they cannot see the wires run through channels or the chases in the foam for the rough inspection, as they can in typical stud framing.

Of course they can see the wire at the electrical and junction boxes on the rough inspection, but some inspectors want to view this as "new work" and they ask about supporting and securing the wire because they view this as a new wall assembly, and others see this as "old work" as if we are fishing in a wall assembly that is already finished.

I'd like to have some exact code references that I have confidence in as ammunition if we are going to challenge the electrical inspector in the field on the issue.

Thanks for giving this some thought!

Last edited by alphabuilder; 06-26-2009 at 06:01 PM.
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Old 06-26-2009, 06:13 PM   #5
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If they are fished in from box to box than you don't need any straps. Do you have any pictures of this system?
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Old 06-26-2009, 06:15 PM   #6
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334.30(B) should take care of any code refference needed.
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Old 06-26-2009, 06:23 PM   #7
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Thanks again for the response.

Regarding some pictures of the systems, here are some web links:

http://www.totalbasementfinishing.co...ment-walls.php

http://www.thebasementtuxedo.com/finishing-overview.php

I hope that this is helpful.
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Old 06-26-2009, 07:03 PM   #8
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How were the boxes mounted on the installs you've done? Mounted to the back wall and then your panel trimmed out to fit? Probably won't shed any light on your wire securing questions but I'm just curious.
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Old 06-29-2009, 09:39 AM   #9
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The electrical boxes that we use are a fire rated old work boxes that attaches to the front mineral board panel of the wall with the tabs that swing out and clamp to the panel. They attach very firmly and we have not had any problems with this.

Thanks.

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