"Approved" filling material- 300.7
NEC 300.7 Sealing. Where portions of a raceway or sleeve are known to be subjected to different temps and where condensation is known to be a problem, as in cold storage areas of buildings or where passing from the interior to the exterior of a building, the raceway or sleeve shall be filled with an approved material to prevent the circulation of warm air to a colder section of the raceway or sleeve. An explosion proof seal shall not be required for this purpose.
What is approved for this? I would think silicone would be ok, but they don't have a designation code or anything in this book. Thanks
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