In S.D., re-routing 7.2kV overhead distribution underground to a 6 residence transformer, although only 2 or 3 homes will ever be served by it. Terrain from 40' pole is 100' along a road edge, 45' steep drop from road down to creek, 35' creek then 200' lawn and gravel driveway. Approx. 380' underground (plus pole and transformer connection lengths) with two turns - one at creek/lawn and one at hilltop/road. Drilling under creek is not an option since attempts elsewhere have not went well (e.g. broken bits). A longer run involving a steel pipe mounted to a steel bridge railing is permitted, but is too expensive. So, wondering what best (reliability/longevity/maintenance, material/labor install cost) alternative is in view of code. Is 4' open trench with direct bury all the way the "best" or only option? Are PVC and/or steel pipe runs "better"? Even if conduit is sealed and water blown out seems likely water will creep in over time. A key question is can steel pipe be used under the creek and/or on the steep hillside to bury less than 4' (less labor, but higher material cost) or does code prohibit this? If anyone has preferred brand/model of direct bury or other underground 7.2kV distribution cables please advise on that too? Thanks for any advice.
I'm a fan of raceway installation over direct burial personally. Yes, any raceway located outside...will have water infiltration and condensation, therefore it is considered a wet location and requires conductors with suitable insulation.
My areas in NJ, the residential BUD (buried underground distribution) is all utility installed and maintained. The majority of their installs is DB primary & secondary. On rare occasion they have a contractor install conduit for them, mostly PVC
Comm jobs here (Pad mount xfr) the POCO requires 4" sch 80 PVC for the primary feed (13.2KV), contractor installed, pole to pad; POCO supplys & installs primary (HV) cabling & terminates. All of the private sites with HV service & distribution utilize raceways, not DB. PVC is the majority, concrete encasement is not unusual.
Someone else may have resi HV dist experience & thoughts
Have you checked with the local AHJs for any input?
Thanks John. It's about the same division of work here without special circumstances. Another alternative is to move the transformer across the creek. Problem is two homes are served. If anyone knows, the big question about code was whether the standard 4' depth can be reduced with the use of steel pipe for the creek and steep hillside crossings.
#201630 - 06/14/1102:29 AMRe: Underground residential distribution (7.2kV)
Unfortunately it has to cross the creek to service two homes South of the creek. All other homes are along a road North of the creek. Would be a cakewalk but for the 35' creek and 45' steep hillside. Would help if steel pipe and markers could be used in lieu of 4' burial depth.
#201636 - 06/14/1101:49 PMRe: Underground residential distribution (7.2kV)
Yes, I'm waiting on the power company bid for their part of it, but wanted to know what others already know about what rules allow. POCO says it knows all the rules and almost always does it's business without input by county or municipal gov't. I, like POCO, hold local gov't in low regard because they are generally incompetent.
#201668 - 06/15/1106:16 PMRe: Underground residential distribution (7.2kV)
" I, like POCO, hold local gov't in low regard because they are generally incompetent."
I have to take the above to task! I happen to be a state licensed electrical inspector, and work for a municipality. I also have great relationships with POCO inspectors and engineers in my Twp and other areas that I worked in as an EC.
Over the years, I learned that relationships with inspectors, POCO inspectors, engineers and architects were a very valuable asset.
Yes, our POCOs here know the 'rules', and yes, they for the most part are exempt from the NEC that I enforce on their installations that they are allowed to do under state laws.
The purpose of this forum is for electrical trade professionals to share knowledge, assist each other, and act in a professional manner.
Last edited by HotLine1; 06/15/1106:22 PM. Reason: added 'relationship' sentence.
There's nothing unprofessional about being truthful. Not all people are equally competent. In the area where I live and work, there is not a contractor I know that says good things about local officials. Every time they have alleged a violation with me the've been proven wrong very quickly. But here it's not limited to gov't officials/employees. It's the same competence problem with many professionals like doctors, accountants, attorneys, etc. SD is simply not a state with much home grown talent. I don't think you'd praise every single doctor any more than you'd praise every single gov't official/employee. If you did, you'd be awfully biased.
Last edited by fusion; 06/15/1106:54 PM.
#201672 - 06/15/1107:43 PMRe: Underground residential distribution (7.2kV)