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  1. Most sprinkler systems directly bury the wire next to the water line. So, this is a big upgrade from that. The main purpose is to protect the wire from being cut if someone digs there.

  2. Why not use 1/2" pcv conduit? b/c it is double the price and the total distance I'm going to is ~600'. So, the cost is significant. PVC conduit is massively overkill as the wire is carrying low voltage and low current.

  3. The voltage is 24 VAC and current is 350 mA. (.35A). The wires are switched by a computer for ~ 10 min on time duration per day. And the supply current will be limited by a 1/2 A fuse. The conductor ampacity is 13A.

The code is sort of ambiguous on sprinkler wiring. I am a Professional Engineer (Electrical), and my site is a rural ranch.

So, interested to hear any viewpoints.

Thanks in advance.

Edit:

In response the thoughtful answer about using some to mark to know where to dig, I place several inches of sand around all buried pipes. The soil here is a rocky, aggressively expansive clay and the sand allows ground shifts to avoid breaking the line as well as serving as a marker, so you know when you're close.

ramblin_wreck1
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    Welcome. You haven't really asked a question here. We're not a discussion forum. Please see [ask] and take the [tour]. – isherwood Sep 19 '22 at 14:00
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    @isherwood Good morning! I have to disagree with your vote to close. While it's not a "how do I do this" question, it's clearly asking for advice before proceeding, thereby avoiding the XY situation. Once the OP decides on an approach, we can help him with the "how to do this" part. ...just my opinion, have a GREAT DAY! – George Anderson Sep 19 '22 at 14:27
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    There's no question up there other than "why shouldn't I do this?" That's both vague and a matter of opinion. – isherwood Sep 19 '22 at 14:29

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There are no code requirements that I know of regarding burying low voltage (IE sprinkler and LV outdoor lighting). PVC conduit is ridiculously expensive right now. Because there are no code requirements, you could protect it in any way you see fit. When I've installed sprinkler systems, I ran the valve control cables underneath the pipes going to the valves to protect the cable. But you could use PVC conduit (expensive), PVC water pipe, funny pipe (yes that's a real term) or just about anything.

It's a good idea to protect it, fixing a break is a PITA.

George Anderson
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    Depending on the depth and concern about accidentally severing either the water or control lines with digging, it might be beneficial to bury some marking tape a few inches above your pipe run, so if someone digs in the future, they'll hit the marking tape first, before going deep enough to hit your lines. – Milwrdfan Sep 19 '22 at 14:36
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Cost and effort, like you said.

Done. Totally valid.

isherwood
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It's a good idea up to about 25 feet.

For 600 feet to save cost I would prioritize. Do it only where the wire is most exposed to damage: parts that are above ground, shallow, near flower beds or anything likely to be dug up by occupants, and a few feet either side of any termination, junction box, valve box, etc.

Elsewhere, if you're just crossing expanses of lawn, I'd bury the raw wire deep enough to avoid typical yard work eg aerators and dethatchers. If you want to be fancy you could add a 3 foot loop in a splice box every 50 feet to allow for easy diagnosis and repair of problems. That would be easier and cheaper than piping the entire 600 feet.

In addition to the cost/effort I'd experiment with the pulling capability of my wire before buying and laying all the pipe. If it's not designed for pulling it may snag and break with just so much as a single 45 degree bend. If you can't pull new wire through your COMPLETED BURIED conduit without breaking it .... it's a bad idea.

jay613
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  • It's a straight run, the trench is already there and shared with another 3/4" PVC electrical conduit containing 2 #8's (15 A dreated due to distance), 2 Cat5e's (one for RS485, One for ethernet, a fire optic pair) – ramblin_wreck1 Sep 19 '22 at 14:58
  • Cool. I'm curious ... 600 feet ... is this so the controller can be in your home (or office or whatever) controlling zones *all of which* are 600 or so feet away? I'm guessing that because of the buried #8 ... ie ... this is all going somewhere, and the things being controlled are "over there". Because if that is the case, you could get a better result with a smart controller. It can be *anywhere* and you do everything from an app. – jay613 Sep 19 '22 at 15:04
  • Fiber optic can be in the electrical conduit. RS485 and ethernet normally can *not* be in the same conduit as regular electrical. However, RS485 and ethernet can go together with your sprinkler wires in the new conduit. End result: 1 conduit for 120V, 1 conduit for for all low voltage cables. As far as the derating, that is a *huge* derate. How much current do you actually need at the end of that run? – manassehkatz-Moving 2 Codidact Sep 19 '22 at 15:08
  • There is a PLC located at the end of the run. It is tied together with other PLC's and host computers at different points(via enet/485). This PLC is also controlling gate actuators and monitoring a dozen prox sensors. A good point about running the 485/enet wires in the electrical conduit but it's already done, nor sure if I want to remove it - convince me - this is why I posted here - this was a design that started out small but grew. I could have used 1/2 for the #8's/fiber and run the 485/enet in yet another 1/2" conduit, I I might well do that if someone convinces me. – ramblin_wreck1 Sep 19 '22 at 15:38
  • Also, on the derating, the derating is for voltage drop - use one of the online calculators - for 15A #8 will have 8% voltage drop but I will put a 13 amp breaker in the panel at the end which will limit drop to 5%. Actually, the only real current draw up there is the intermittent use of some power tools for maintenance and they are maybe 8 - 10A max. – ramblin_wreck1 Sep 19 '22 at 15:43
  • As far as separate conduit, that is a pretty firm rule. Harper talks about it all the time. See a similar answer of mine regarding shared junction boxes at https://electronics.stackexchange.com/questions/635247 The concern is that if anything goes wrong then your low voltage stuff may not be so low voltage anymore. For example, if the hot wire is damaged and has a problem (but not enough to cause an immediate breaker trip) then low voltage stuff could get energized. Not a problem for fiber optic (no conductive materials). Actually fiber optic has another advantage - ethernet has a 100 meter – manassehkatz-Moving 2 Codidact Sep 19 '22 at 16:08
  • limit - you're going almost twice that distance so you could have some issues. As far as voltage drop, it is calculated based on actual usage. So your calculation should be based on 10A (or possibly even 8A) and not 15A. 15A @ 600' @ 12 AWG = 26% drop. But 10A = 17% drop and 8A = 13%. Bump up to 10 AWG and the numbers are 10A = 10% and 8A = 8%. I'd consider that (10 AWG, 8A, 8%) good enough for occasional use, provided you really only need 8A - 10A. But if the wire is already paid for then 8 AWG it is. – manassehkatz-Moving 2 Codidact Sep 19 '22 at 16:12
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    sorry the HV run is only 300' (power pole in middle) and I always plan for more than i intend to use. I never base anything on intended use: that *always* turns out to be inadequate. Paid and pulled. Yes, I know the rule about sharing with the 2, although not all the rules are based on logic. Code is written by politicians, unions, and manufacturers among other ligit sources such as IEEE committees which have their own agendas such as taxing, making more work, or additional product sales (yes, it's corrupt - but I digress). The scope of this has exceeded the original intent, but interesting. – ramblin_wreck1 Sep 19 '22 at 17:08
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    on the ethernet this will be a switch at the power pole (300' mark) that will act as both a repeater and a port for a diagnostic computer. So, it is not twice the distance. I may go back and yank the cat5's out and put them in another pipe. I started this a low budget project but is becoming expensive. If I had to have it done by someone it would probably be in excess of 60k. It now involves 2 storage tanks, 2 pumps, 2 buildings, 8 sprinkler heads 10 SV valves 3 PLC's, a dual gate, HD POE cams and a more in the future - It was going to be a collection of small systems, now a large integrated 1 – ramblin_wreck1 Sep 19 '22 at 17:19
  • Btw, my answer, and probably all of them, are from the perspective of residential DIY. Assumption is lawn sprinklers for a house. Sounds like there might be other factors in your project that might get you better answers. Or might get the question booted :) – jay613 Sep 19 '22 at 17:22
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    @ jay got that; early on I said this was rural ranch which is more like industrial.... Suffice to say ...original question was answered - thank you all – ramblin_wreck1 Sep 19 '22 at 17:23
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    @jay613 ramblin says they're an EE, and seem experienced with industrial control systems. It's no wonder this system seems like an industrial one, because it is designed like one. – jaskij Sep 19 '22 at 18:21
  • @ramblin_wreck1 enet is one thing, 120V will at worst fry the port. But if your RS485 is not isolated, 120V on it will fry anything that's connected to the bus. Might even energize the casings of your control equipment. So a common conduit is a low probability high damage risk which is not up to code as well. Just to underline the point. – jaskij Sep 19 '22 at 18:26
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    @jaskij and manassehkatz thanks, I have been convinced to make that change - it was penny wise/pound foolish; To keep the HV/LV all separate, I guess it's going to mean a separate hole in the bottom of my Hoffman box as well – ramblin_wreck1 Sep 19 '22 at 18:53
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the trench is already there and shared with another 3/4" PVC electrical conduit containing 2 #8's

Clearly you can't put the LV in with the existing cables, but there's nothing stopping you from strapping the LV cable to the outside of the existing conduit.

There's certainly less protection this way, but more than having the LV cable direct-buried. A zip-tie every metre should be sufficient to stop them separating and drifting.

Criggie
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