Direct Bury 4-20 ma

[ptonsparky]

Customer needs a 4-20 ma loop for a flow meter. Distance of about 1/4 mile. He can readily get 1000' and 500' spools and wants to know if splicing is a good idea. Direct bury. Two wire shielded with drain. My initial thought is No. For application of chemicals to crops via two separate wells feeding one pivot. Any good way to splice such cable underground?

 

[iwire]

I would look into wireless systems

http://www.oleumtech.com/

 

[Open Neutral]

Any good way to splice such cable underground?

3M, I think, makes encapsulation forms and ?2-part? resin. Splice [I'd solder], clamp form around, pour in resin.

Give some thought as to the voltage drop and available open circuit voltage. At 20ma, it won't be much drop.

 

[jim dungar]

4-20mA is just like any other electrical circuit, voltage drop is normally the primary factor in determining circuit length.

Factors affecting voltage drop:
Capacity of source, most 4-20mA circuits are driven by a 30VDC max source
Is loop self/device powered or does it have an external supply?

In reality it is easy to see 1/4 mile circuit lengths, even completely inside of a building.

 

[gar]

110330-1429 EST

Open Neutral's suggestion makes sense.

A quick calculation. Loop length is 3000 ft. If we assume 15 V drop can be allocated to the cable, then at 20 MA this would be a maximum loop resistance of 15/.02 = 750 ohms. The copper wire size closest to this is #33 at 207 ohms/1000 ft. Thus, any size larger is OK and the choice would be between mechanical strength and cost. I would guess at #20 or #22 as a mechanically good range. Note: #26 is 40 ohms/1000 ft.

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[iwire]

I think some are forgetting that digging 1/4 mile of trench is expensive. And repairing direct buried cables if damaged is also expensive.

To each their own.

 

[jim dungar]

I think some are forgetting that digging 1/4 mile of trench is expensive. And repairing direct buried cables if damaged is also expensive.

To each their own.

The OP mentions this is an open pivot irrigation system. It will most likely require a trench for the power and fluids, so why not one more item underground?

 

[ptonsparky]

He has a trench and power cable going in tomorrow. (Why call until you need it?). His concern was splicing the underground 4-20 ma cable. My concern was the splice, direct bury, and laying directly next to a Cablecon with the 480v pivot power.

Radio is sounding better all the time.

 

[Cow]

He has a trench and power cable going in tomorrow. (Why call until you need it?). His concern was splicing the underground 4-20 ma cable. My concern was the splice, direct bury, and laying directly next to a Cablecon with the 480v pivot power.

Radio is sounding better all the time.

I think it's definitely worth looking into. Around here, it's not uncommon for the farmers to dig into the 480v when they're servicing the water lines. I wouldn't want to deal with having to splice damaged signal cable too...

We do some work for a large crop farm. They told me they have the largest private wireless network in the US, if I remember right. Everything is wireless. They start pumps, pivots, you name it, using radios and computers. If they can make something like this work, I'd think you'd have a pretty good shot at coming up with something for what you need.

 

[ptonsparky]

I would look into wireless systems

http://www.oleumtech.com/

Good link. Thanks. We'll see where it leads.

 

[Open Neutral]

I think it's {wireless} definitely worth looking into.

I heart real wires. Find some 24Ga PE-39 or PE-89 comm cable, and put it in place. You can protect the splices until you find the encapsulation kits; leave enough slack.

Icky PIC telecom cable last decades, typically until it fails from backhoe fade.

 

[ptonsparky]

I think it's definitely worth looking into. Around here, it's not uncommon for the farmers to dig into the 480v when they're servicing the water lines. I wouldn't want to deal with having to splice damaged signal cable too...

We do some work for a large crop farm. They told me they have the largest private wireless network in the US, if I remember right. Everything is wireless. They start pumps, pivots, you name it, using radios and computers. If they can make something like this work, I'd think you'd have a pretty good shot at coming up with something for what you need.

I have a couple other guys that could probably use it with remote grain drying systems.