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Fixed Wireless Equipment

Be Careful With Cables

Members of the ISP-Wireless list share tips on running cables up your towers.

[November 6, 2006]

On the ISP-Wireless list in October, JV asked:

A few questions for the list:

(1) I just arranged a deal for my second POP on a 135' grain leg. Brand new, nice work platform at the top, good ladder, etc. I was trying to decide the best way to run conduit to the top for Ethernet. I'm leaning toward 1" PVC, but wondered if maybe metal conduit would be better for RF shielding reasons (or any other reason)? Seems like the PVC would be easier to work with, and 60 percent the cost of metal. (This site is out in the country, probably 3 miles from anything other than farmland, woods and scattered houses)

(2) I've never pulled cable through conduit before. I was going to start with four cables I think. Then when I need more, pull 6-8 that time. I was comparing the size of four Cat5 cables to the 1" PVC and that wasn't even taking up 20 percent of the inside. Sound reasonable, or will I have problems pulling the second batch of cables? Oh, the conduit would be basically a straight shot up, but with two 90 degree bends at the base

(3) Anybody had experience (good or bad) with the Home Depot Indoor/ Outdoor Cat 5e cable? The box I bought was General Cable brand, "Command Linx", UL type CMR/CMX 24ga, part # 2137116H. I think it was $86 for a 500' box. It says "for outdoor exposure for short distances".

If anyone cares to make suggestions on setting up on one of these grain legs, I'd love to hear details.

[RS replied] "You do not want to pull in enough cables to the point of making the last one tight. You need to allow 20 percent free space in the conduit. If cables are tightly packed, it can cause problems, i.e. the last one pulled in could be tight and this could cause stretching, which alters the conductivity of the cable. . . also, cables running close to each other over long distances interfere with each other. As to plastic verses metal, I would go for metal and ground it (if cost is not a problem) because it helps to reduce RF interference.

[KC agreed] "I agree with the comments [above]. The structured cabling standards call for no more than 40 percent fill. Be sure to use cable lubricant as well."

[TI added] "Also, leave a pull string inside and put pull boxes at each end of the straight conduit section."

[RS agreed] "Good point on the draw cord. Also, if there are bends, try to make them as shallow as possible. If the bends are tight, you can burn existing cable whilst pulling additional cables later (I've been there)."

[JS added] "I have to run all my cabling (POE and Heliax) in EMT for my SCADA customer. I use one inch for POE and 2 inches for Heliax—lots of room and easy to run. I use weather heads, watertight couplings, and Andrew hot-dipped galvanized clamps to attach to towers. All the counduit runs to a NEMA cabinet. On the elbow before it enters the cabinet, I drill a small weep hole to let condensation drip out. We use some rubber boots to seal connector inside of NEMA box. It looks like the boot material used by Andrew but you can mold it. The electricians have it and they buy it at some distributor. The best thing to have is a quality flexible fish to use run pull strings—always leave a pull string or two for future use."

[CP suggested] "1) use exterior shielded cable to avoid cross talk between cables.

2) Be sure to ground the shield wires at least at one end.

3) Don't forget lightning protection for all cables."

[MS advised] "Here are a couple of tricks from my old electrician days. Have someone at the top with a roll of twine. Hook a cloth streamer to it. At the bottom hook up a shop vac. Suck the streamer down to the ground. It'll be really easy. These days I use that marking twine they use at construction sites. The ones to lay out concrete pours etc. It's very small but realllly strong. Wear gloves and it's not too hard to pull it. Or use it to pull a bigger rope in. Also, use a screw driver or some such device to hold the roll of string, it'll burn the hell out of your fingers if you try to hold it that way. If you get a good streamer/vac combo the string will travel really fast. Back when I was a linesman we'd use a jack hammer air compressor and build a parachute for the 4" conduit that we used. We could do a run of 500' in just a few seconds. The sting would fly off the roll scary fast!"

[MS added] "Make sure you keep your gear where it won't get filled with the explosive dust! Have the grain company people help you put it all in. They know the rules and what's safest."

JS warned:

I used that Home Depot cable once and had to replace it within a few months—the cover gets brittle and breaks.

[RA replied] "Home depot sells either 4 or 5 kinds of cable around here, depending on if they are selling the cat6 as well. Their grey cable has the problem JS describes. I have been using the beige cable for two years and it has yet to get brittle unless it's below -10. But it doesn't have UV protection so does age in the sun. For conduit use this shouldn't be a problem. We use outdoor rated cat 5 if it's going outside in the sun now, and still use the indoor/outdoor for all protected runs."

[CP added] "Getting a few boxes and making one pull (downward) also smart. Once it gets going, it should pull itself down to the ground due to its own weight (also be sure to tie off the top or you'll lose the ends).

[JS agreed] "We were running some Cat 5e cable down an access well next to elevator about five floors and someone forgot to tie the cable (okay it was me) . . . and the cable flew past us, and it hurts!"

—End