THHN Wire Summary - by K1VR - September 1997 Fred, I would suggest you do post an inquiry to the appropriate reflector(s) regarding the worthiness of THHN. Considerations include: electrical properties (velocity factor, high voltage RF breakdown characteristics of insulation) and mechanical properties (stretch, breakage, etc.). \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ At 10:18 AM 9/9/97 EDT, K1VR wrote: W1FV and I are working on a gain array for 160 using sloping wires. The time has come to select the wire. For cost and ease of use, I am thinking about using #12 THHN stranded. This is a readily available (any Home Depot or Home Quarters) wire which is covered with a jacket which is oil and abrasion resistant. The biggest problem, I suspect, is that in an antenna application it will stretch. John (W1FV) wants to know: * Electrical properties (velocity factor, high voltage RF breakdown characteristics of insulation), and * Mechanical properties (stretch, breakage, etc.). Anybody have this information for #12 THHN stranded? Is there a wires web page? Will publish results. -- Fred K1VR \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ From: Brian Beezley Fred, I can't help with the technical details you seek but I can provide some anecdotal information for the solid- conductor #14 THHN I got at Home Depot. The wire works fine as a 40m inverted V. One end happened to rub against a tree branch and the 600-volt 60 Hz insulation was not effective in preventing arcing at 500 watts output (the insulation carbonized and burned through but the copper remained intact). One thing that's attractive about the wire is that it's available in green (a dull, sea green sort of color) or light blue. These two colors greatly reduce wire visibility aloft. Brian Beezley, K6STI k6sti@n2.net \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ From: Pete Soper I had an 80m dipole up that was made out of #14 THHN. At various times it was under significant tension. I never noticed a shift in its resonant point. I made a 20m lazy-H out of #10 THHN. I think I could have folded over the Oak trees it was strung between and there would have still been zero stretch. This said, THHN is obviously made out of soft drawn copper and so with enough tension there will be stretching. The other positive and negative of THHN is the nylon over PVC insulation. This lowers the velocity factor and introduces a fudge factor of a few percent into your designs. I've found this to be a major source of grief for complex antennas designed with modelers because the modelers can't account with the VF. It would seem to be a simple thing, just knock X% off the lengths, but the reality is vexing. On the positive side the insulation can provide some benefits. Being able to have current maximums in contact with trees can be handy (wouldn't expect the insulation to handle voltage maximum points though). The antenna might be quieter too I guess. Pete KS4XG \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ From: bschwerdlin@hlb.com (Bob Schwerdlin) I have used #14 & #12 wire in the past, only to have the wires break after about 1 or 2 years. The antennas were 2 band "fan" dipoles for 40 & 80M. Most of the time it was one of the 80M legs that broke. It usually happened in the late spring, after the cruddy Chicago WX and very windy spring time. Well, I went to #10 THHN a few years ago and haven't had any problems since. I do notice that my resonant frequency did go down a little bit, only I can't be sure of how much. ... Bob, WG9L, V31RC, FP/WB9VLV \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ From: aa8u@modempool.com (Bruce Lallathin) I've used this stuff for years with good success. My five element delta loop array for 80M is made of #14. Be aware that some automotive type wire that has an oil resistant pvc covering may actually have a thin plastic outer layer which will age when exposed to uv radiation over time and will flake off. It seems to allow moisture to seep between the layers too which might cause resonant freq to go down a bit. My 80M 4-sq is also made of the same wire and it works very well. This March a major ice storm tore up most of the antenna farm here. The loops and the 4-sq were damaged by ice breaking the nylon ropes that held the elements. Jeff, N8CC did some experimentation with various wire types and found the pvc covered wire was approx 2-3% shorter than bare copper of similar gauge. I think I got that right. I suggest you e-mail him for the info . My experience on the low bands tells me that all the cut and try to get the resonance points due to the proximity of the ground far outweighs any minor velocity factor in the wire due to insulation type. -- Bruce \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ From: Kevin Drost Yes, THHN stretches. Also, THHN is plastic PVC covered by clear plastic. The plastic insulation doesn't stand up well to sunlight. The clear plastic coating cracks and falls off after two or three years. Otherwise, the wire is fairly rugged. THHN is used extensively in machine tool industrial wiring, and construction wiring inside conduit. I think you could probably get a better price in 1000' rolls from a electrical supply house or wire wholesaler - there are a couple BIG ones in Boston. (Celtic Wire & Cable?) (Northern Wire?) THHN is verrrrrry common, theres lotsa stock, and the price is low. But it does stretch, and the insulation falls off. At least that is my experience at K8LX .... I would think copperweld is more durable and possibly cheaper? 'cuz its mixed with iron and not solid copper, like THHN. Kevin, WA8ZDT \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ From: "Robert Shapiro" I tried doing a Yahoo search and found a few companies that offered THHN wire along with some specs, but in my limited search, none of the specs you desire. Southwire seems to be the most prominent company. Maybe if you contact them directly, they may be able to assist you. 73, Rob Rob Shapiro - ND3A, nd3a@worldnet.att.net \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ From: "Robert L. Carroll" I don't know the characteristics of this wire other than I have to cut it a lot shorter than copperweld. I have been using it successfully, however. Any info you pick up appreciated. \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ From: David Robbins on thhn, i don't think it is uv resistant. i put some up to run 12v car fog lights for night tower work and it has been shedding part of its insulation recently. for antenna elements here i am using 10ga solid pvc insulated copperweld, this was recommended by k2tr. it is heavy, its hard to work with, but you won't break it and the insulation is meant for long term outdoor use (the stuff is actually rural telephone wire). David Robbins K1TTT (ex KY1H) k1ttt@berkshire.net or robbins@berkshire.net http://www.berkshire.net/~robbins/k1ttt.html \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ From: Randy Thompson I use #12 THHN for all my wire antennas. The stuff is great! It is coated, so seems to last longer and stay in better shape than just copper wire. It is flexible and easy to work with. Seems to handle loads and the wind movement very well (although it will break at the points where there is lots of flexing under load). I can't say that stretch has been any problem at all. Velocity factor? This is wire -- you cut to length and then trim! ..... Randy, K5ZD \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ From: "Scott Lehman N9AG" > * Stretch Yep, it'll stretch. THHN has a hybrid insulation, designed to give high dielectric withstand with a thin wall. In most cases it can be replaced with general MTW wire which has just a thicker PVC insulation. The overcoat is Nylon, which does nasty things when it gets wet. Once nylon is wet, it stays wet. It doesn't affect its 60 Hz properties too much, but it isn't pretty at RF (mostly at VHF and above). > * Electrical properties > * Mechanical properties Most THHN and MTW are rated to 600 VAC. The conductor is copper, laid 6 around 1 stranding in the smaller sizes of interest. The tensile strength is basically that of the dead soft annealed copper. I'd never use it as a dipole or anything that has to support any weight. I have used it for Inverted Vees and we're using MTW as an Inverted-L on 160M at N8NR's place. It is supported by a rope at the 90' high point and has about 30 feet horizontal. It's been up since January and its resonance has moved from 1825 to 1780 KHz, hi. My guess of velocity of propagation for either type is 60-65%. The NEC (National Electric Code) has a lot of specs on this type of wire, conductor size, stranding, insulation thickness, etc. Don't have a copy at home, but I can get more info if you need it. Scott N9AG/J68AS \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ From: "Rick Andren" As an employee of Underwriters Laboratories Inc. our requirements for dielectric breakdown are the working voltage times two, pluse 1000. This being the case, we test THHN wire for (600v*2)+1000=2200 volts at 60 Hz. As you increase the frequency, the dielectric will have a tendency to breakdown at a lower voltage, and at RF, I think the insulation is just about transparent. I have pulled in excess of 500 lbs. on 14 gauge, without much stretching. I will ask around work for more information on this, or just put some on a machine and find out the tensile strength. I can't help you with the velocity factor of 12 gauge. The THHN designation is strictly the insulation type. It has nothing to do with the conductor itself. Rick Andren n9thc@foxvalley.net andrenr@ul.com \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ From: Garry & Yelena I will give you a pragmatic and relatively non-technical response--that stuff was not intended to be under tension, is quite soft, and will break. When my inverted L broke, it cost a small fortune to get the tree climbers up to retrieve the end--obliterating any savings. Wire is the last thing to scrimp on, unless it will NOT be under tension. -- Garry Shapiro, NI6T \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ From: Bill Bosler I've been making wire antennas out of THHN wire for years. Mostly #12 and some #10. We have it around the shop in 1000' spools. Also, every time I go to the scrap yard I look for spools of it. You can buy it real cheap. Never had any problems with stretching and it weathers real well. I have a 160 inverted L that's been up for years and several 40 meter antennas. I use it for radials, field day antennas and any sort of temporary antenna I want to throw up in the air. Bill Bosler - WF3M \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ From: Brian McGinness I had THHN on my 160m 2-el inv-L array, and after a couple years it started to deteriorate. I think the UV got it. I would suggest the stuff they call "#13 poly copperweld" that RF products sells. It is very very very tough. My issue with THHN is not it's electrical characteristics, but it's eventual deterioration. The poly stuff is much tougher. Brian N3OC \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ From: "Healy, Rus" I use #14 THHN extensively. (I probably have 2000 or 3000 feet of the stuff strung around the place). I worried about stretch, but have never experienced enough to make a noticeable difference. Probably my best example is an 80- meter dipole at 65 feet, strung between two big trees, with an RG-8 feed line. The antenna is supported at the center and the ends, and it's pretty much horizontal. When the wind really gets ripping (we had 75-mi/h winds three times last winter), the antenna gets s-t-r-e-t-c-h-e-d big time! It actually broke once--about 10 feet from the feed point. But until then I saw no difference in its resonance over time and stretching. As for the dielectric strength, I wouldn't worry about that. The only time it's a factor is when the wire is touching something--and that's not a desirable situation! If it's of any value, most of this wire has a breakdown rating of 600 V RMS (presumably at 60 Hz). The velocity factor is a big question mark. I believe it's between 95 and 97%. The trouble is, you have to make two antennas--one of #12 THHN and one of #12 copper, resonate them both at the same frequency in the same position, and measure the physical difference to tell for sure. I'm not motivated to do this at low HF frequencies! Maybe at 10 meters . . .some day. Dunno about a Web page, but I'd be interested in the URL if you find one. -- Rus, NJ2L \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\ Fred Hopengarten K1VR 617/259-0088 Six Willarch Road Lincoln, MA 01773-5105 permanent e-mail address: fhopengarten@mba1972.hbs.edu