BURIED ALTERNATIVE: CABLE IN CONDUIT
Underground distribution? Cable-in-conduit may increase protection and cut total costs.
- Published in Southwire's T&D Update newsletter in March 1998
- Reprint permission granted
If you're planning direct-buried power distribution, there's an alternative you may want to consider. Burying cables pre-installed in extruded plastic conduit.
"In installations, pre-installed cable-in-conduit may cut your total application casts and extend cable life over direct-burial installation," says Sid Ticker, Southwire senior applications engineer.
Use Your Favorite URD
What is cable-in-conduit? Start with your favorite underground residential distribution (URD) cable or conductors. Now extrude a high-density polyethylene (HPDE) conduit — up to four inches in diameter - around the conductors. Size the conduit for a good fill ratio. Wind the whole thing on a reel and ship it to the field. It's ready to bury and terminate.
Making the cable-in-conduit process work call for careful manufacturing control. Your cable s need protection from extrusion heat. A mechanical barrier provides that and also keeps them from sticking to the conduit. To make conduit lie flat and straight when it comes off the reel, cooling and annealing are precisely programmed.
Think About Installation Costs
Why pay the extra cost of the extruded conduit? It may save you significant amounts in total installed costs.
In direct burial, placing the cable properly — and protecting it from damage while you're doing it — eats up time and takes extra crew members. Cable-in-conduit can shrink your installation time by up to 50 percent. Typically it can be done by two workers with the right equipment. In many cases you can safely put cable-in-conduit in the ground with a plow.
Another cable-in-conduit saving is the cost of select backfill bedding, transporting it and distributing it in the trench. Don't forget the cost of downtime if it isn't delivered on schedule.
With the cable-in-conduit, the tough HDPE conduit gives excellent mechanical protection. The cost of select backfill may be eliminated completely. You also get real protection from dig-ins later. Dig-ins are one of the major causes of direct-buried cable damage.
Wet locations or unfavorable soil chemistry may contribute to water treeing in direct-buried cables. When you lay cable-in-conduit in continuous runs, the seamless extruded conduit makes a good water barrier, which helps to reduce treeing.
Cable upgrades may be less expensive also. Instead of re-opening the entire trench, closing it up again, and then doing restoration, you can pull the old cables out of the conduit and pull new ones in. The seamless HDPE conduit provides a good surface, to help keep pulling tensions low.
"If your planning a direct-burial installation, try running the numbers with cable-in-conduit," says Ticker. "You may be surprised at the possible savings." |
