NEC 300.8 - Raceways or cable trays containing electrical conductors shall not contain any pipe, tube, or equal for steam, water, air, gas, drainage, or any service other than electrical.
Looking for clarification on this. We build machines and often use plastic OPEN ENDED duct along parts of the machine to help organize cable runs as well as pneumatic air lines. I'm wondering if this is not allowed by 300.8? Or is this technically OK because the definition of "raceway" includes the word "enclosed" which means "closed on all sides"? I don't really understand the spirit of this requirement. It seems odd to me that an elect cable and an air line can run right next to each other in the open, but if I put a piece of plastic duct over it, open on both ends, it's no longer allowed.
Anyone have any further clarification to add to this or a better understanding of the intent of this portion of the code?