Securing conduit for roof penetration

[pls2000]

I need to redo a badly done roof penetration for an air conditioner. Since there is an existing penetration, there will be very little rewiring needed.

I'm intending to install a vertical piece of 3/4 or 1" EMT secured to a roof joist. Put a service junction box on the top to transition to flexible NMT to the A/C.

My question is how to secure the EMT to the joist. In particular, I want it secured so that if someone on the roof steps on the top, the tubing won't just slide down. The normal 2-hold clamps don't hold against forces along the length of the tube.

Are there clamps that do?

Thanks

 

[WorthFlorida]

Add a electrical box and screw that to the joist. Wires only need to past through the box.