Author Topic: Bad to have cables in outdoor temperatures?  (Read 3286 times)

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Offline Jay112

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Bad to have cables in outdoor temperatures?
« on: June 05, 2016, 03:39:25 pm »
I'm setting up a new indoor garden, and need to bring lots of conductors there for different sensors and other components. I'll mostly be using CAT5 cables.

I have 2 options for bringing the wires there:
1) Keep the wires indoors, but the run will be much longer. Total wire length will be about 50 feet.
2) Take a shortcut by passing the wires outdoors attached to the building walls. Total wire length would be 20 feet instead, with about half of the length being outdoors, where temperatures here (Midwest USA) get hot in summer and -10 F in winter.

Which do you think will be the better method?

I think the longer indoor run might be too long for me to have 2 MCUs communicating reliably via serial, but I think a bonus with using the 20' outdoor run is that I'd be able to use a serial connection at a decent baud rate.

-Do you think the outdoor temperatures would affect the data getting received from the different sensors?
-Do you think the outdoor temperatures would significantly affect serial communications?

Thanks!
 

Online Ian.M

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Re: Bad to have cables in outdoor temperatures?
« Reply #1 on: June 05, 2016, 04:24:58 pm »
The only concerns are physical damage to the cable from mechanical stress, abrasion and impact, grossly excessive temperature extremes causing softening or embrittlement, UV exposure degrading the cable jacket and water penetration.     Ordinary Cat5/Cat5E doesn't have a UV resistant jacket, and with the extreme winter/summer temperature range you are likely to get problems within a few years.  If its only got to last 3 years I might gamble, but otherwise not.   If you run conduit for the full length of the outdoor wiring, above grade, and with a constant fall so any condensation can drain, interior grade wiring can be expected to have a service life >20 years.   Then there's direct burial rated cable, which is resistant to anything except gross mechanical damage, but is considerably more expensive.

You said indoor garden - it doesn't make any sense to have multiple long runs of sensor cabling going outside when you have a semi-protected environment for a control & sensor 'hub' consisting of a SBC with Ethernet connectivity back to your main building.   That would get it down to power + 1 Cat5E data cable, which would vastly reduce the cost of the cabling.  Also a 50' run is no trouble whatsoever for Ethernet.

Also see http://www.howtogeek.com/165097/how-can-i-safely-run-ethernet-cable-outdoors/
 

Offline Simon

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Re: Bad to have cables in outdoor temperatures?
« Reply #2 on: June 05, 2016, 04:34:07 pm »
With cables and temperature it is actually all about the insulation material nothing to do with copper wire. You would need wire designed to work at those temperatures although if the wire is never going to move it will be less of a problem as usually by working temperature manufacturers mean the temperature at which you can flex the cable.
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Offline bitslice

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Re: Bad to have cables in outdoor temperatures?
« Reply #3 on: June 05, 2016, 04:40:00 pm »
-Do you think the outdoor temperatures would affect the data getting received from the different sensors?

Any sensor on the end of a long bit of wire is going to provide variable results,
convert data at source or change it into some form less prone to voltage change (like 4-20ma or frequency)
 

Online Ian.M

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Re: Bad to have cables in outdoor temperatures?
« Reply #4 on: June 05, 2016, 04:42:09 pm »
Its also UV exposure - a non-outdoor rated cable run along a North facing wall is likely to last far longer than one run along a South facing wall.   Once the jacket starts to micro-crack from the UV, moisture penetration + freeze/thaw cycling can do massive damage to the insulation.
 

Offline Simon

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Re: Bad to have cables in outdoor temperatures?
« Reply #5 on: June 05, 2016, 04:47:29 pm »
I'd put any cable in conduit. your other option is a plastic conduit or insulated metal conduit with a heater wire in it if that is not overkill ;)
« Last Edit: June 05, 2016, 04:57:35 pm by Simon »
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Offline coppice

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Re: Bad to have cables in outdoor temperatures?
« Reply #6 on: June 05, 2016, 05:43:10 pm »
Some temporary Cat 5 lines which I put outside crumbled very quickly. Its a good thing they were only temporary. I guess some Cat5 might be made with UV tolerant plastics, but the usual stuff isn't.
 

Offline Simon

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Re: Bad to have cables in outdoor temperatures?
« Reply #7 on: June 05, 2016, 06:05:33 pm »
The standard cable was never meant to go out in the elements. Duct it and you have protected it from sunlight, but the low temperature is another problem. At low temperature plastics go brittle.
« Last Edit: June 05, 2016, 06:19:04 pm by Simon »
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Online Ian.M

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Re: Bad to have cables in outdoor temperatures?
« Reply #8 on: June 05, 2016, 06:11:31 pm »
Don't forget varmits that find interior rated cable jackets to be a tasty chew toy . . . .
 

Offline CatalinaWOW

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Re: Bad to have cables in outdoor temperatures?
« Reply #9 on: June 05, 2016, 07:55:41 pm »
I'm with the others.  For a non- moving cable the temperatures are really not much of an issue.  Be sure not to constrain it so that expansion and contraction doesn't stress it.  A PVC conduit is more than adequate to protect from UV, rats, rain,  ice and the like.  Even if you do it right with boxes, sealed penetrations of walls and so on it will cost less than $30-40 for the distance you are going.  If you don't already have a PVC cutter the $15 expense is well worth it.

Spend a few minutes in the electrical aisle of a Lowes or a Home Depot and you will figure out what you need.  It glues together like Tinker Toys so is really easy to use.
 

Offline Simon

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Re: Bad to have cables in outdoor temperatures?
« Reply #10 on: June 05, 2016, 08:27:46 pm »
if you can get an off the shelf flexible duct on a roll you can do it all in one peice so there is nothing open to the elements. I guess if it's going between two heated rooms you could find a way of moving a small amount of room temperature air through the duct and maybe insulate the duct. I'd suggest you measure the temperature the air comes out the other end at to make sure the whole cable does not fall below temperature. A tiny centrifugal fan will do the job.
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Online Ian.M

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Re: Bad to have cables in outdoor temperatures?
« Reply #11 on: June 05, 2016, 08:45:09 pm »
Flexible conduit is likely to sag and trap water.  Circulating interior air through it guarantees it will get a condensation or even ice buildup in it in the winter.    Use rigid conduit, with a constant fall so any condensation drains and a box at each end to provide access for pulling and make sure the end boxes can drain freely with a mesh screen to keep bugs out.  Seal cable penetrations through the building walls.   Alternatively, direct burial cable can be clipped directly to the wall, and if you have a varmit problem, or in high traffic areas, protected by an open backed cable guard fastened to the wall over it.  This is likely to be significantly cheaper and easier than running conduit if only one Cat5 cable is needed.
 

Offline Simon

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Re: Bad to have cables in outdoor temperatures?
« Reply #12 on: June 05, 2016, 09:03:22 pm »
You are missing my point, if the conduit is kept at above freezing temperature bypassing warm air through it from one of the rooms there will be no condensation buildup or ice. It's only 7 m of conduit we are talking about if it's lagged it will probably hold the temperature quite well so the cable will always be at room temperature as though it was indoors no ice and no brittle plastic sheath.
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Offline SL4P

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Re: Bad to have cables in outdoor temperatures?
« Reply #13 on: June 05, 2016, 11:35:23 pm »
Cat5 gel-filled with UV jacket, and don't forget...
Properly rated outdoor connectors
- will do the job, but are probably not the right way to achieve the best results or reliability.
Don't ask a question if you aren't willing to listen to the answer.
 

Online Ian.M

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Re: Bad to have cables in outdoor temperatures?
« Reply #14 on: June 06, 2016, 12:44:00 am »
You are missing my point, if the conduit is kept at above freezing temperature bypassing warm air through it from one of the rooms there will be no condensation buildup or ice. It's only 7 m of conduit we are talking about if it's lagged it will probably hold the temperature quite well so the cable will always be at room temperature as though it was indoors no ice and no brittle plastic sheath.
ASHRAE standard 55-2013 - "Thermal Environmental Conditions for Human Occupancy" specifies that to decrease the possibility of discomfort in indoor environments due to low humidity, the dew point temperature should not be less than 2.8°C (37°F).  This equals to 30% relative humidity in 21°C. The upper dew point limit is specified to 16.7°C (47°F), which equals to 76% relative humidity in 21°C.

With -10°F exterior temperatures, to maintain the duct walls above the dew point, its going to need extremely thick insulation, have a large interior diameter and a lot of air-flow through it.   *IF* the cable has to be protected against extremely low temperatures, circulating warm humid air from inside the building is *NOT* the way to do it - trace heating tape can easily keep the conduit above freezing with lower energy consumption for the same insulation thickness, and doesn't introduce extra humidity.

Anyway, if the cable is lying slack in the conduit, cooling it to -23°C (-10°F) is unlikely to do any damage or significantly compromise its electrical properties.  Most interior Cat5 cable is rated for operation down to -20°C (-4°F) and going 3°C colder is unlikely to be a major issue.  That's neglecting heat loss through the building wall, which will help keep it within its rated temperature range.
 

Offline Brumby

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Re: Bad to have cables in outdoor temperatures?
« Reply #15 on: June 06, 2016, 05:59:47 am »
... if the conduit is kept at above freezing temperature bypassing warm air through it from one of the rooms there will be no condensation buildup or ice.

Sorry - I have to challenge that.  Over a significant, if not major length of the conduit, it will be cooler than the room air so there will always be the possibility of condensation.  Even if you were able to ensure temperature and relative humidity conditions were controlled so that condensation was unlikely, IMHO it's still bad design to run a conduit any other way than Ian.M has described.  Doing it properly also allows for minimal disruption in unplanned circumstances, such as the failure of a joint or impact damage to the conduit.
 
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Offline coppice

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Re: Bad to have cables in outdoor temperatures?
« Reply #16 on: June 06, 2016, 06:08:52 am »
... if the conduit is kept at above freezing temperature bypassing warm air through it from one of the rooms there will be no condensation buildup or ice.

Sorry - I have to challenge that.  Over a significant, if not major length of the conduit, it will be cooler than the room air so there will always be the possibility of condensation.  Even if you were able to ensure temperature and relative humidity conditions were controlled so that condensation was unlikely, IMHO it's still bad design to run a conduit any other way than Ian.M has described.  Doing it properly also allows for minimal disruption in unplanned circumstances, such as the failure of a joint or impact damage to the conduit.
Conduit with a steady airflow will only have it for a year or two. After that it will be clogged up with dust. :)
 

Offline Simon

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Re: Bad to have cables in outdoor temperatures?
« Reply #17 on: June 06, 2016, 06:24:54 am »
Well then a heating wire as I originally suggested.
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Offline DenzilPenberthy

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Re: Bad to have cables in outdoor temperatures?
« Reply #18 on: June 06, 2016, 09:33:58 am »
Just use cables which are suitable for use outdoors.  External grade UV protected CAT5 is available, and also steel-wire-armoured CAT5 if you want it to be better protected (or bury it in the ground)


https://www.tlc-direct.co.uk/Main_Index/Cable_Index/Network_Cable_External/index.html

 

Offline Jay112

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Re: Bad to have cables in outdoor temperatures?
« Reply #19 on: June 06, 2016, 10:24:35 am »
Thanks everyone, for the information and great ideas! I really appreciate it!

@Ian.M: Considering I had to look up "SBC" (and learned that it doesn't stand for "Southern Baptist Church" :) ), I think that idea is a little too complex to me. But you did get me thinking about throwing a Raspberry Pi in there, have all the sensors communicate with the Pi, and have the Pi talking via Ethernet to a computer in the other building. It would be nice to have everything passing through Ethernet, and to have the Pi next to the sensors so that there are no long wire runs. I'll have to think about it more.

And for now I'll be brainstorming about putting a rigid conduit between the buildings. That sounds like a safe and smart way to avoid having problems in the future.

Thanks!!
 


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