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I'm building a "smart garden" - which is really nothing more than moisture and temperature sensors on each of my garden beds / planters hooked up to Raspberry Pis. Each Pi will be connected to a switch and powered by that switch (using PoE), so I need to connect the switch to the Pi with ethernet cable carrying between 48 and 57 VDC.

To try to shorten the story, I need to run conduit between the central switch location and the garden beds / planters. It will mostly be alongside the house; I intend to bury it instead of having the conduit run along the outside. Can I use EMT conduit for this? Can I use PVC? If both, which one would be the better solution?

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  • EMT is allowed but can be problematic, as it can rust out underground. Now 57V? You know, just because the PoE spec allows a voltage, doesn't mean NEC allows it. – Harper - Reinstate Monica Sep 11 '20 at 19:42
  • aside: make sure your moisture sensors are only powered on to do a reading; leave them running and they will corrode through in weeks. – dandavis Sep 11 '20 at 20:36
  • To echo Ed's answer, either type will work, it just comes down to cost vs ease of assembly and personal preference. If I were you, I'd probably do it in PVC. – Nate S. Sep 11 '20 at 20:53
  • The moisture sensors are the non-corrosive capacitance sensors, so I'm good there. They'll also be easily replaceable, just like the other sensors, so even if they do corrode or get damaged otherwise it won't be a big deal. I prefer the PVC for ease of assembly, but I prefer the EMT because it's a smaller tube for the same number of ethernet cables. – John Sep 11 '20 at 21:32
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Going back to finger safe voltages I use the contact limits in article 680 , 15v rms 30 for DC ,

However you are not talking about a body of water/pool In chapter 9 of the NEC there are 2 tables 11a AC &11b DC. These show the classifications based on the available voltage and current Inherently limited power supplies 30-60v and under 100 va are class 2.

Class 2 do not propose a hazard and the wiring methods are just about whatever you want if your wiring is rated for running in walls no conduit is needed (even speaker wire run in walls needs to be listed for use in walls). The wiring method used out side can be either pvc or emt. If you don’t think it’s going in the ground for 10-15 years I find emt less expensive because you don’t need a fitting you bend it. If you do use emt fittings They are reusable where once conduit is glued it is solid. So it is really up to what you want to use.

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  • +1, though I'm not sure how reusable EMT fittings will be after being buried 10-15 years -- I'd consider either type of conduit to be single use if it's getting buried. – Nate S. Sep 11 '20 at 20:51
  • @Nate s. I am not sure either because this was a new change in 2017 code but I have reused emt fittings & pipe much older that were in wet locations. – Ed Beal Sep 11 '20 at 22:32
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    Interesting. Perhaps local soil chemistry also plays a role in how long it'll last buried. – Nate S. Sep 11 '20 at 22:38

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