The basic lessons are, use the right materials for the environment, protect your facilities, and right-size your conduit system for today and the foreseeable future.
Your infrastructure is often down and dirty, buried beneath the surface, and those things you don't see such as conduits and pull boxes are out of sight. But it's still important to know what you have there: It's a no-brainer that you need to use the right materials for the right kind of job. Using inside wire for outside plant is never a good idea; to use outside wire or cable for outside use is good, but sometimes it's just not good enough. Hopefully, this series of images with related explanations will illustrate the point:
Image 1 above is a 2-inch black flexible duct used in the 1960s, in this instance between two buildings with a 50-pair PVC cable between them. Flex duct is cheap and offers no protection against backhoe operators, shovels, ground settlement and water. Over the years, wire pairs have gone bad between the two buildings, disrupting services and not just because the flex duct was damaged--since water almost always finds its way into underground conduits and flex duct, you still must use the proper material--and PVC cable used as an outside cable plant material isn't acceptable.
Image 2 above is a 4-inch conduit with a sweep coming out of the building, and the sweep is improperly elevated. The height of the sweep brings it too close to the surface. The inspector won't pass it, since it's not buried below the frost line. Frost lines are moving targets from county-to-county and state-to-state. The reason the sweep isn't below grade is that after we disconnected services running the sub-ducting (orange flexible duct), we couldn't back-pull the cables and sub-ducting to the new communications pull box to eliminate the sweep with the improper depth and turns.
After laborers hand-dug back towards the turn they discovered a white clump of quickrete around the 4-inch conduit. Next, as they continued to dig, they uncovered a 4-foot section of a banded oversized conduit connecting a previously damaged 4-inch conduit. (See Images 3 and 4 below). This 4-foot section had to be uncovered and then cut away using hand tools and portable saws:
Once this was completed, the four orange flex ducts with cables inside them were back-pulled to the new pull box. The entire sweep, turn and 30 extra feet of conduit were removed. (See Image 5 below).
Image 6 above shows a utility worker with safety vest (half-cropped-off at the left) using a Ditch Witch tool to locate buried cables and power lines, and two workers busy breaking the old 4-inch conduit, and the track hoe about to dig a new ditch straight from the pull box to the corner of the building, eliminating the old sweep, conduit and unnecessary turn with about 30 feet of extra length.
These projects don't always happen in the way you think--The utility worker marks first and then the next day work begins. Let me add that the markings are actually beyond the pull box to yet another building and another conduit project. Still, it can be challenging to coordinate both marking buried lines and working against the weather when digging is required.
Image 7 above shows a new trench directly from the corner of the building, and Image 8 above shows the other end of the trench to the pull box. Once the old conduit and sweep were removed, new conduit was connected to the pull box. The four flexible conduits (sub-ducting) were re-installed, and the cables removed from service were reconnected inside an old Telco wire can. The new conduit and sweep are now buried at the appropriate depth, and rigid schedule-80 conduit connects the building to the pull box.
Image 9 above shows the new rigid schedule-80 conduits also coming from the facility vault that houses all the utility entrances from the street underground. One of the three gray conduits is for Comcast and other providers, and the other two are for Verizon, with the second of these being for redundancy as required by Verizon.
By scale, this job site is very small compared to large enterprise or data centers. The lessons are the same, as are the mistakes often made in repairing old infrastructure or adding new.
The basic lessons are, use the right materials for the environment, protect your facilities, and invest in the rigid conduit (PVC Schedule-80 is often used) and right-size your conduit system for today and the foreseeable future. Use sweeping gradual bends, especially since fiber will be used more often by the carriers; then provide sub-ducting with pre-installed pull strings (from the factory)--your installers will appreciate this. But be sure to admonish your installers to add pull-strings behind them.
You may notice some backfill (gravel) in some of the photos, and this is also used to stabilize the ground and minimize settling, which can lead to broken or even separated conduits where there's a collar. For those with a sharp eye, maybe you noticed a "wire" of sorts on Image 7 that is against the building left wall near the corner. This wire grounds the original OSP (outside plant). This copper wire must be shortened and reattached, and preferably with a new ground rod. While the old OSP is remaining, it will be abandoned once fiber from the street and private fiber drops are installed between the remaining buildings. Still, remember that circuit protection is as only as good as your grounding.
Details, details, details....