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Underground power / network cabling to observatory

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#1 Tom Gwilym

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Posted 21 July 2014 - 10:29 PM

I'm currently working on building a new observatory at our new house. I have a 6 foot dome that I'm planning on building on a cement slab. Before I get that far, I need to figure out how to run the power and network cable from the house in a trench. We have about 65 feet out to the observatory from the house and will probably pull power off an outlet (with a junction box in the crawlspace, then out the foundation). I'm looking for ideas/tips about how to run the cable. I'm thinking at least 12 inches deep on the trench, then use underground resistant conduit for the power cable. I'm also going to run some kind of cat5 network out there too. I hear some say that they don't have problems running it next to the power, but I'm just not sure. If I could run it all through a single conduit that would be great, but thinking I should have two of them and run the network a few inches apart?
I'm sure people here have done similar, looking for some good ideas!

Thanks,
Tom

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#2 hbastro

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Posted 21 July 2014 - 10:49 PM

Hi Tom,
I ran separate power and data in 2" conduit 18" below ground. The spans were ~40 feet to a dome on a tower and ~60 feet to a ground level dome on a pad. It is important to keep the bend angles gentle as each bend adds considerable resistance when pulling large cable bundles, or pulling a single additional cable later. I wish that I had run 3" conduit for the data lines. Also if you run a rope in the conduit as its being laid, be sure not to glue it, pulling the first bundle will be easier.
Regards,
Dave

#3 TCW

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Posted 21 July 2014 - 11:13 PM

Code requires 18" of cover for your conduit. Run the power and data in separate conduits.

#4 GJJim

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Posted 21 July 2014 - 11:35 PM

Consider UF wire for the power feed and skip the conduit. Buried conduits eventually get waterlogged at some point and that is why you dont want to mix high and low voltage cables in the same pipe.

Last year an indirect lightning strike on my CAT5 network cost me over $1K in damaged equipment. You may want to look at wireless or fiber optic for the data link.
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#5 Tom Gwilym

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Posted 21 July 2014 - 11:49 PM

Hi Tom,
I ran separate power and data in 2" conduit 18" below ground. The spans were ~40 feet to a dome on a tower and ~60 feet to a ground level dome on a pad. It is important to keep the bend angles gentle as each bend adds considerable resistance when pulling large cable bundles, or pulling a single additional cable later. I wish that I had run 3" conduit for the data lines. Also if you run a rope in the conduit as its being laid, be sure not to glue it, pulling the first bundle will be easier.
Regards,
Dave


Thanks for the reply. I should comment that I was thinking 18 inches at least. Did you run both the power and the network in the same conduit?
I have pretty rocky ground about 6 inches down which the sod was unrolled over the gravel when the house was built. I have dug the pier hole so far, but that took a long time. It's probably about 2.5 feet deep into VERY solid ground. That's another forum topic though!

#6 TCW

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Posted 22 July 2014 - 01:07 AM

Code requires that low voltage (data) be run in a separate conduit from power for safety reasons.

#7 Tom Gwilym

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Posted 22 July 2014 - 10:25 AM

Is there a minimum distance apart that the data / power conduits should be separated?

#8 hbastro

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Posted 22 July 2014 - 10:48 AM

I run power and data in separate conduits that are spaced 6 inches apart. My area is a high desert at 6300feet with less than 7 inches of rain per year. The ground is decomposed granite and rocky. So the trench was dug in spring when the ground was softer. My Pier is 4x4x4 feet of reenforced concrete separated from the 10x10foot slab on which the 6 foot dome rests. The tower rests on a 4x4x4foot base and rises 16feet for the small RoboDome.

#9 MJB87

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Posted 22 July 2014 - 12:05 PM

I just had coax, ethernet and power run to my observatory from a distance of about 175 feet. The electricians -- who are very aware of the codes and very fastidious -- put the power cable alone in one conduit and the (shielded) coax and (shielded) Ethernet cable together in a separate conduit. The conduits were laid side by side -- not separated.

#10 Brian P

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Posted 25 July 2014 - 03:29 PM

I ran direct burial line to the observatory (about 30 feet). For data I used a 2" PVC conduit. Dug 18 inches down, laid the power line, laid a red warning tape with some dirt to bury, then the low voltage conduit. I made sure to leave a tag line in place so I can pull cables through in the future as well.

Been in place four years with no problems or issues.






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