Weather Durable Wiring

[simonB2013]

Hello,

So my next project is a simple pir system to guard my garden/driveway.
The design and construction couldn't be simpler for the most part, but being outdoors all year round in the UK - well that is a new challenge for me.

I have so far, researched various approaches to coating boards/components with coatings, and I'm happy with plans so far.

However, where I am still in the dark, is what connecting wire and terminals to use.
The arduino itself will be indoors, no problem.
But both power lines (5-9v tbc) and signal lines (3.3v) will have to venture outdoors, service 6-12 pir sensors along a perimeter of maybe 12-20 meters.

Being in the UK,temperatures from -26 to +38 (max/min according to Wikipedia) in the shade.
.. so I am thinking basic machine/hookup wire might not last too long.

As far as connections go, where my main wiring loop is spurred for individual PIR sensors, is another dilemma.
I could glue/resin coat connections, making them at least semi-permenant.
Yet I do recall some garden light kit from my childhood.. each light had a connection with 'snake teeth' that bit into the main cable so that you could position/reposition then at will.
I've seen similar on components shops, manly for ribbon cable... but I'm sure these are not weatherproof!
Any suggestions ??


Many Thanks

[johnwasser]

Since you have "6-12" PIR sensors do you need a separate conductor for each?

What is the current draw from each PIR sensor?

How far is the protected perimeter from the indoor location of the Arduino?

Do you want to run the cable through the air (Aerial Outdoor Cable) or underground (Direct Burial Outdoor Cable)? You can get either kind of Cat5 UTP (four pair) cable in 1000' reels for roughly $100.

[simonB2013]

Good Q's !

Conductor arrangement is not finalised as I am trying to make it modular.
In reality, there maybe a 12meter loop with 4 sensors; and 2 spurs with 1-2 sensors each, 1 of 4 meter, the other of 2 meter.
I'll work in parallel where possible.

Current: for each sensor I am expecting .120ma with peak .200ma (no data sheet - working of other user's comments until I can measure for myself)

Arduino location will not significantly add to the distances mentioned above, 0.5m maxmum.

Cable will be routed along a mixture of terrain  : along walls, behind strips of wood; and buried if possible.




From your cable suggestion, I guess I ought to add the complexity of wiring in parallel.
If I have 4 PIRs on a loop, I'll need 4 signal wires + 2 power lines.
Had I been doing this indoors, I'd probably have used 2 power lines on a ring/spur, and 1 ribbon per PIR to send back the signal.
Leaving things open for expansion, I could go with 2 power + 6 signal.

On the other hand, I'm sure this has been done before ... so open to advise.

[dc42]

You have a few weather and environmental-related issues to guard against:

1. Ingress of water where the cable is terminated. To prevent this, use waterproof glands where the cable enters the PIR detectors and any junction boxes you have. Feed the cables into the underside of the detectors/junction boxes and/or use drip loops to prevent water running down the cable and into the glands.

2. Degredation of the cable sheath because of UV light. Use a suitable outdoor cable, or run the cable in conduit.

3. Rodents attacking the cable (some rodents need to chew on things to prevent their teeth getting too long, and they love wires). Use conduit or steel-armoured cable.

[simonB2013]

thanks dc42,

in addition to those points, will sub-zero temperatures, or the contraction/expansion between temperatures degrade sheathing ?
I was also wondering about condensation on the wires within sheath...

[dc42]

in addition to those points, will sub-zero temperatures, or the contraction/expansion between temperatures degrade sheathing ?

I'm not an expert in this field, but I don't think so provided you don't stretch the wire too tight. However, you could get mechanical erosion of the sheath due to differential movement of surfaces the cable is attached to.

I was also wondering about condensation on the wires within sheath...

Shouldn't be a problem, because the wires are separately insulated, and there should be very little moisture inside the sheath. OTOH you do need to take precautions against condensation in the detectors and junction boxes.

[Henry_Best]

Good Q's !

Conductor arrangement is not finalised as I am trying to make it modular.
In reality, there maybe a 12meter loop with 4 sensors; and 2 spurs with 1-2 sensors each, 1 of 4 meter, the other of 2 meter.
I'll work in parallel where possible.

Current: for each sensor I am expecting .120ma with peak .200ma (no data sheet - working of other user's comments until I can measure for myself)

Arduino location will not significantly add to the distances mentioned above, 0.5m maxmum.

Cable will be routed along a mixture of terrain  : along walls, behind strips of wood; and buried if possible.

I've used some neoprene covered speaker cable (twin with shielding) outdoors. It's carrying 14V AC at about 1A.  Much of it (about 5 Mtrs) is buried inside a length of garden hose (to prevent someone putting a spade through it!). The rest is cable-clipped to wood and brick. The inside of the junction box was given a good spray of WD40 before the lid was screwed down. It's been in over a year with no problems.

[lafontas]

I live in a climate that gets even colder than your part of the world (if you can imagine that.)

If you're able to bury a cable then you might consider some sort of PVC conduit to place your wiring inside. To save money I usually by a roll of inexpensive PVC tubing and run ordinary Cat 5 Ethernet cable through it. While you're picking up the PVC tubing at your local home improvement store have a look in the electrical section at their PVC junction boxes and other fittings. You'll find all kinds of components to keep your cable and sensors dry and operating for years to come.

Don't forget to bury your conduit below the frost line, your local building department can tell you what depth that is and it's always a good idea to consider getting a line locate from your local utilities so you don't interfere with other underground services.  I have low voltage cables running hundreds of meters to farm outbuildings using the method I've described and they have given reliable service for over 20 years.

[eforman]

If using "direct burial speaker wire" for low voltage (e.g. 12V 5A) applications, there seems to be two kinds out there - a cheaper thinner version and a fatter version with an extra layer of protection. Here's an example of a cheap thin version - http://amzn.com/B008VRQ2QA, and here's an example of an expensive fatter version with an extra layer of protection - http://www.htd.com/4-conductor-direct-burial-speaker-cable. The manufacturers say they are "not approved" for non-audio applications, but wire is wire right? They are both rated for direct burial. Is there an appreciable difference over many years, considering frost, rocks, rodent chewing?