Long Underground Cable Run for Residential Service

[pjcoors]

Hi everyone, I've been reading the tons of helpful information on this site. I am evaluating the feasibility for a 1000 ft run of buried cable for a 200A residential service. I've been able to estimate the trenching and conduit costs, but am having a hard time estimating the required wire size and cost. The POCO has been less than helpful and is only interested in running overhead service. What is your opinion on conductor size and using AL v. CU? All your help is much appreciated.

Thanks
PJ

 

[iceworm]

The POCO wants to put the transformer 1000' from the house? yuck

Disclaimer: My work is all industrial. I don't do residential - except mine as a DIY

Couple of questions:
Where is the service disconnect/meter? Is is out at the road - 1000' feet from the house?
Who is paying the bill on the wire? POCO or customer?
Who would be paying the bill to put in the poles?
The reason is the customer does not want to look at the overhead, they want buried?

The job is all about cost/benifit analysis.

As for wire size, consider design for maybe 3% drop at 200A. That should minimize the light blinks.

You would be looking at 240 x .03 = 7.2 volts. Total R = 7.2/200 = .036 ohms. For 2000' of wire, that is .036/2 = .018 ohms/1000.

Parallel 350CU
Tripple 350AL​

Let the VD go up to 5% - that's 12 V drop, total R = .060 ohms. For 2000", that's .030 ohms/1000

parallel 4/0 (maybe 250s) CU
parallel 350AL
tripple 4/0AL​

Consider a pole out at the edge of the property line with the meter and disconnect. Put a 50kva, 240/480 xfm at the pole. (25kva maybe - depending on the loading). Now you are looking at a 3% drop on 480V = 14.4V, current is 100A, total R = 14.4/100 = .14 ohms. Which gives .07 ohms/1000

parallel 2/0 - but you only need two legs, don't need a neutral​

For 5% drop, that's 24V/100A/2 = .12 ohms/1000

single 3/0AL​

Put another xfm at the house with a disconnect and panel.

Just have to compare the cost of the cable to the cost of the transformers.

If I were doing it (only for me, of course), I'd look for 240/600V xfm and run smaller wire yet.

Unless, I could get the POCO to give me the service at 480V. Other than they get stuck It shouldn't matter much to them. Now you have costs for a 480V disconnect/meter, small cable, and one transformer to compare against lots of fat cables.

Just some ideas.

ice

 

[hurk27]

Using copper
for 3% drop I come up with 750kcmil
For 5% drop I get 500kcmil,
Using aluminum
for 3% I get 1250kcmil
for 5% I get 750kcmil

The 5% might also have a little light dimming when AC kicks in if the 200 amp service is loaded over 150 amps, but if you have all gas heating and appliances I wouldn't expect over 100 amp of load depending on how big this house is, what is the calculated load on the service?

Will the POCO place a transformer up by the house? will they run underground primary?, most will want a right of way for a primary or even poles for that matter, also if they run secondaries I will bet they wont even come close to keeping the voltage drop down, you will be lucky to even get 350kcmil aluminum as they have a different way of thinking.

Even going the transformer route 45kva transformers are not going to be cheap either, if they can get the POCO to run the primaries it might be cost effective if they take the cost off the bill over time, here they will charge you the full amount but you don't pay an electric bill until you have used enough electricity that equals the amount of the up front charge of the transformer and primary feed, but they may request a right of way because they have to have access to their equipment.

With the cost of wire the POCO way might be the cheapest route in most cases, but you need to get all the info together as well as prices and present it to the owner.

 

[broadgage]

1,000 feet at utilisation voltage is far from ideal, doable if you/your customer throw enough money at it, but far from optimum.

It would be preferable to have the utility bring MV service nearer the home, underground if prefered. Or possibly obtain 480 volt service as suggested above.

Even 3% drop is a bit much, remembering that 3% is the recomended limit on voltage drop from service to point of use. In this case 3% drop is proposed up to the house, with more lost within the premises wiring.

At significand load, the voltage drop represents real losses in money.
If transformers are used, then the custormer is paying forever for the iron losses, and also for the copper losses whilst loaded.

 

[GoldDigger]

For this distance, look seriously at using Al or Cu-clad Al for cost reduction, even though you may need to pigtail with Cu to fit lug terminations at panels, etc because of the large size wire needed.
If properly handled there is no reason not to use Al.

Tapatalk!

 

[dfmischler]

I should think the local POCO would prefer underground installation as long as the customer is willing to pay for it. No worrying about trees, or storm damage...

I built a house in '98. The local POCO suggested dropping a transformer 50 feet from the foundation, with an underground feed. I paid an excavator to dig a single trench wide enough to hold the POCO's cable (13.8 KV? Not sure anymore), plastic natural gas pipe, and phone wire, with the required separations between services. Gas pipe and electric line were buried in sand before backfill. The POCO insisted that their cable and transformer be near the driveway for maintenance access even though that was not the shortest path from the nearest pole. They said they charged me based on the shortest distance and ate the difference. IIRC they charged about $3000 for installation; I paid separately for excavation, sanding and backfill. Very happy with the results.

 

[bob]

ice at 240 volts.

ice at 240 volts.

I would not consider taking service at 240 volts. I would request 480 volts or 600 volts from the utility. Install a transformer
close to your house. The conductors would be much smaller and flicker would not be a factor. Conductor requirements at 600 volts would
be 80 amps or #3 cu. However you would need 1/0 cu for VD.