Running 300 feet of 2 1/2 inch pipe across a commercial roof for a 600 amp chiller is a beast if you don't plan for the expansion. Those rooftop temperatures swing wildly and if you don't use expansion couplings correctly, you'll see those parallel runs start to snake and pull right off the supports. I always make sure to set my rooftop blocks every seven feet or so to keep everything rigid, expecially when you're transitioning down a block wall at the end of the run. It makes the pull alot smoother when the pipe isn't bouncing around under the weight of those heavy copper feeders. When you're doing a run this long, gravity and heat are your biggest enemies. Make sure your supports are acutally rated for the weight of the conduit plus the wire, and don't skimp on the strut straps. If you're coming off a membrane roof, double-check that your blocks have the proper pads under them so you don't end up with a leak six months down the road. It's the small details like that which keep you from getting a callback when the building settles or the seasons change. Just take your time with the layout and ensure those parallel lines stay perfectly spaced before you start pulling.
Tips for long rooftop conduit runs that nobody talks about
Aug 29, 2026
Last reply: 2 days ago
4 Replies
I just finished a 280-foot run on a hospital roof using 3-inch EMT, and those expansion couplings are no joke. We had a guy miss one on a previous job and the summer heat literally buckled the strut. Now I always use those O-Z/Gedney expansion fittings every 80 feet. Even if the code says you can go longer, the peace of mind is worth the extra cost when you’re dealing with 500kcmil copper that doesn't want to bend.
One thing I do differently is the spacing on the supports. I prefer the C-Port or Big Foot sleepers over the standard rubber blocks for those heavy 600 amp loads. I found that the standard blocks tend to sink into the insulation under the TPO membrane over time, expecially if the roofers didn't use high-density board. I ussually set mine every five feet instead of seven just to keep the deflection down during the pull. If that pipe starts sagging while the tugger is humming, you’re asking for a nightmare at the 90s.
Whoa, seeing the scale of these 600 amp runs is seriously cool! I’m just getting started in the trade and the thougth of 300 feet of heavy copper is wild. I’m definately taking notes on those support blocks so I don't mess up my first big job.
Speaking of the equipment, have you guys ever had issues with the actual chiller vibration rattling the conduit loose over the years? I’m also curious, what’s the best way to keep the wire reels from tipping over on a hot roof during a pull like that? I’d be terrified of one catching air and causing a disaster!
Don't forget the transition to Liquidtight at the unit. I always swap to 2-inch Sealtite or a heavy-duty Liquatite Type LA for that last 3-4 feet to isolate that chiller vibration the kid mentioned. If you hard-pipe right into the cabinet, you're just begging for a cracked hub in five years.
Also, for a 600A load, I’m usually pulling two sets of 350 kcmil copper. If you're using a Greenlee UT10, make sure your anchor point at that 90 is rock solid. I’ve seen guys rip a strut right off the wall beacuse they didn't lead-anchor into the masonry. Use some Poly-Pull string to start or you'll be fighting friction the whole 300 feet.
Quick update—I finished the run today. I took the advice about using those O-Z/Gedney fittings every 80 feet, and it made a huge difference in keeping the parallel runs straight. I also swapped to the heavy-duty Liquidtight at the chiller to handle the vibration like you guys suggested. everythign is locked down and looking solid. Thanks for the tips!
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