Buried Pet Fence Wire

[TheDogTrainer]

OK,
So I'm not an electrician and don't know jack about NEC codes, but I'm trying to learn.
I'm a dog trainer and I've also been installing hidden pet fences for last couple years. I'm using PE-rated wire, specifically HWMPE, which I've been told by people smarter than me is the best for this application. So far so good, no issues. However, lately I've had several calls to repair broken systems (not any of the ones I've done) and it looks like most installers are using THHN/THWN wire, which I know is approved for wet-weather, outdoor conditions but evidently not approved for "direct-burial"? Is this correct, and if so can anyone give me some more specific info about how to determine what is and isn't approved for "direct-burial"? And WTF does "raceway" mean? Evidently THHN/THWN is OK for burial if in conduit or "raceway"?
I'm just trying to do right by my customers and provide best quality service and product possible. I spent 2 hrs this morning trying to figure out why a customer with THHN/THWN wire wasn't getting signal- used a good quality Breakfinder but found no breaks at all. They had they're system installed 11 years ago, from my research that's a pretty good lifespan for the wire.

Any advice or suggestions?
Thanks!

 

[Dennis Alwon]

IMO, the nec doesn't have any say in electric fences and I have not known any electricians who installs them. I would read the manufacturers specs on installation. I would bet that thwn would work just fine in this situation.

 

[augie47]

I've installed a few systems and found the HWMPE to have a tougher insulation than THWN.
Here's a cut sheet:
[h=5]Application:[/h] For use to protect against electrolytic and galvanic corrosion in pipelines, storage tanks, steel pilings, well casings, and other buried or water-submerged metallic surfaces. The high molecular weight polyeth-ylene (HMWPE) used in cathodic protection cable provides outstanding dielectric strength with excellent resistance against moisture, abrasion, and corrosive chemicals.

 

[kwired]

IMO, the nec doesn't have any say in electric fences and I have not known any electricians who installs them. I would read the manufacturers specs on installation. I would bet that thwn would work just fine in this situation.

Dennis this is not an "electric fence" but rather a buried transmitting wire for a wireless system that uses a shock collar worn on the dog to warn them they are too close to the border.

I think the covering on the recommended wire is likely thicker and more durable than what you would find on THHN/THWN. These wires are also buried pretty shallow where they will be subjected to more damage by both people and critters.

 

[GoldDigger]

Dennis this is not an "electric fence" but rather a buried transmitting wire for a wireless system that uses a shock collar worn on the dog to warn them they are too close to the border.

I think the covering on the recommended wire is likely thicker and more durable than what you would find on THHN/THWN. These wires are also buried pretty shallow where they will be subjected to more damage by both people and critters.

Good points.
Also, FWIW, the radio frequency signal in the wire will be attenuated along the length as it leaks out via capacitive losses to the soil (bad) as well as by radiating (good). It is possible that using a wire with thicker insulation (lower capacitance) would allow a longer run of wire with the same transmitter power and sensitivity.
Also the question of stranded versus solid can have an effect on the skin-effect resistance of the wire at those frequencies.

TheDogTrainer: A raceway is just any closed pipe or housing which is made to contain and protect the wire. There are only certain types of construction which are recognized by UL and allowed by NEC. Anything else is just a protective sheath rather than a raceway, and may protect from physical damage but not satisfy other NEC requirements.

It is possible that in the case where you found no breaks in the wire at the failed installation there was instead a short circuit (or very low resistance at the fence frequency) which was shorting out the signal. One way to check that you would be to follow the wire with a signal strength meter or else to disconnect the wire completely and use a high voltage insulation tester (megger) to determine whether an actual break in the insulation is the problem.

In a pinch, instead of a signal strength meter you could just use a collar receiver wired to deliver a visible or audible output instead of a shock, and go all the way from the transmitter along the wire to the other end. Or you could just wear the collar.

 

[kwired]

Good points.
Also, FWIW, the radio frequency signal in the wire will be attenuated along the length as it leaks out via capacitive losses to the soil (bad) as well as by radiating (good). It is possible that using a wire with thicker insulation (lower capacitance) would allow a longer run of wire with the same transmitter power and sensitivity.
Also the question of stranded versus solid can have an effect on the skin-effect resistance of the wire at those frequencies.

TheDogTrainer: A raceway is just any closed pipe or housing which is made to contain and protect the wire. There are only certain types of construction which are recognized by UL and allowed by NEC. Anything else is just a protective sheath rather than a raceway, and may protect from physical damage but not satisfy other NEC requirements.

It is possible that in the case where you found no breaks in the wire at the failed installation there was instead a short circuit (or very low resistance at the fence frequency) which was shorting out the signal. One way to check that you would be to follow the wire with a signal strength meter or else to disconnect the wire completely and use a high voltage insulation tester (megger) to determine whether an actual break in the insulation is the problem.

In a pinch, instead of a signal strength meter you could just use a collar receiver wired to deliver a visible or audible output instead of a shock, and go all the way from the transmitter along the wire to the other end. Or you could just wear the collar.

I kind of thought there may be some difference in transmission performance, but don't really know enough about this area to comment on it.

 

[mgookin]

Or use a microphone & dB meter with the colar on a cat!

 

[Dennis Alwon]

Dennis this is not an "electric fence"

Yes I know and I have no idea why I wrote electric fence .

 

[renosteinke]

Hidden fences, electric fences ... I'm surprised I seem to be the only one who has had any dealings with these! To return to the OP's questions:

1) A wire suitable for direct burial will be marked as such. Soil often contains materials that quickly destroy wire insulation.

2) A 'raceway' is, in simple terms, a pipe; something that will keep the wires from directly touching the soil.

3) Sometimes the guys who write the instructions know what they're talking about. Unfortunately, far too often "Bubba" will happily put together some kludge, say 'look- it works!', and cite this as proof of how clever he is.

 

[Hv&Lv]

You have any friends that work for the phone company or POCO? I use a sheath fault locator to find breaks or more likely a spot where the insulation is rubbed off and the wire is earth faulted but not broken.

 

[RichB]

TheDog Trainer--You may also want to look into a product by a company called Pro-Trace (or equivelent)--They have a wire that is used in underground locating--it can carry a signal for just about forever, is rated for direct burial, and fairly inexpensive (IIRC about 68 cents per foot)

 

[jim dungar]

FWIW
The TFFN/MTW/AWM (18AWG), I installed around my house has been in the ground for +14years. The only failures I have had have been from 'garden tools'. At my cabin, the manufacturer's insulation has failed in at least 2 spots.