Long residential run, voltage drop and my options

Status
Not open for further replies.
E

e_things4you

Member
Location
Grass valley, California
I will be getting a 240v, 400 amp (320 amp continuos) drop from the power company, and would like to split it to two 200 amp services, one for a future house near the meter, and one for a house that is about 800ft away. I need to get the 240v, 200 amps to the house 800ft away, and would like some ideas on wire sizing, a single larger guage run per leg, or a few runs of smaller guage, should I go direct burial or PVC conduit, copper or aluminum, possibility of a voltage booster to reduce wire size and overall cost. Any ideas would be very helpful, this is my first residential hookup of this distance, and this project is on a tight budget, so I am looking for the best and most cost effective solution.
 
The earybird gets the worm...you sure got up early this morning.

Since you are a general contractor, I would say your best bet is to contact an electrical contractor in your area. They will have the best answer for you as they will know the local requirements that we here on this site cannot help you with.
 
Call your power company, 800 feet to keep 200 amps is quite a distance. Not saying it couldn't be done but the economics might prove different. I work for a POCO and we don't run 800' secondaries or services, we locate the transformer closer.
 
I do know my POCO (and I think local code) say that you can not run more than 80 amps to a second building. You must have a second meter. This is only for residential.
 
got_nailed said:
I do know my POCO (and I think local code) say that you can not run more than 80 amps to a second building. You must have a second meter. This is only for residential.
Click to expand...

If you're under the International series of Codes, the International Energy Conservation Code, IECC, requires that individual dwelling units be individually metered. I believe that is a requirement of other Codes as well.

Jim T
 
You will need to perform an article 220 load calculation to determine the actual load before you can determine the voltage drop and if it will be a problem. That said, 800 feet is a long way to run any sort of relatively low voltage power. There should be some way to get a second transformer for the second house. If not, be prepared to run some fairly large (and expensive) conductors. I would certainly advise installing them in PVC conduit so that they may be replaced easily if needed. It will add a little to the initial cost, but could be a great savings in the future.
 
I agree that a load calc should be done to find the real load vs the main cb size. That said, if I were to want 200amps at the end of 800 ft I would use 3 runs of 250kcmil/3conductor CIC (cable in conduit) Aluminum. This assume a 120/240 volt 1 phase system. It will drop the 240 volts about 7.5 or just over 3%. The CICs can be laid in one shot and is a much more robust product than DB cable. I think this is overkill but it will work. I would also drop a couple of 2" or 3" spares in the trench with hand holes every couple hundred ft for future 'who knows whats'.
 
Another thing to consider is voltage flicker when the air conditioner, heat pump, or other motor kicks on, how will that dip the voltage and dim the lights.
 
got_nailed said:
I do know my POCO (and I think local code) say that you can not run more than 80 amps to a second building. You must have a second meter. This is only for residential.
Click to expand...
jtester said:
If you're under the International series of Codes, the International Energy Conservation Code, IECC, requires that individual dwelling units be individually metered. I believe that is a requirement of other Codes as well.
Click to expand...
Interestingly, several localities around here will not allow a second electric service/meter on a residential property, for fear that someone might rent out a living space in areas not zoned for two families, unless special permissions are sought and given.

For example, one of our customers build a large garage and converted it into a building for their band to practice in, including light show equipment. It got its own 200a service, meter and all, with a separate lateral from the pad-mounted transformer.
 
Last edited:
jtester said:
Larry

My comment applies only to two dwelling units. Code wants each tenant or dweller or whatever to be able to know his/her energy consumption.
Click to expand...
I see, said the blind man, again. :cool:
 
WOW! Thanks for all the replies.

After reading this and meeting with my POCO (PG&E) on friday, I am going to try and locate the transformer equal distances, about 800ft from both dwellings on 20 acres, one 1000sq ft existing granny unit, and a future 4000+sq ft house to be built in a few years. I will downsize to two, 200amp panels, and have them set each one with a meter 200ft to either side of the transformer. From there I plan to parallel 2 #350kcmil for each leg, in pvc conduit, for the last 600ft to each of the dwellings. Do I also have to upsize the groud and neutral, or would a single run of 350 for each be enough?

Not that it makes a difference, but I will also be doing a 2000+ watt solar grid-tie system, I have been living on solar for four years, and will be installing this entire sell-back system myself, so if anyone has any ???'s, I may be able to help.
 
Long Service Runs

Long Service Runs

You may want to consider installing a single 400amp service at or near the property line, close to the utility pole and then boosting the voltage for distribution to the dwelling locations. I have done this several times in Nevada for pleople with larger parcels of land. As an example, if you have two or three locations to supply you can install an oil-filled padmt transformer rated to carry the total service load required for all locations at the service location. You then back-feed the transformer and kick the voltage up to 2400 volts. You install a conduit and run a single primary shielded cable from the supply transformer to another oil-filled padmt at the first location and then later you can loop feed this same primary line to the next location. At the first house the pad-mt steps the 2400V down to 120/240 single-phase and you have no voltage drop issues at all. You will want to contact an electrtical contractor who can do the load-break elbows and install the lighting arrestors etc. Remember if you run large cable to compensate for voltage drop you will generate an IsqR heat loss in the cable and that loss is energy comsumption. The advantage of the oil-filled xfmrs is they are the same small pad-mt units the utilities use and they are totally enclosed and locked so no one can get into them unless they know what they are doing.

Grant
 
Better think about who is going to fix/change out all this equipment when it fails and it will fail. You need the POCO to own as much as possible where you can just pick up the phone and call them anytime day or night and they will come.
 
grant said:
You may want to consider installing a single 400amp service at or near the property line, close to the utility pole and then boosting the voltage for distribution to the dwelling locations. I have done this several times in Nevada for pleople with larger parcels of land.

[...]

Grant
Click to expand...

I've seen discussions with people considering doing exactly this, but you are the first person I've encountered who has actually done such an installation.

My biggest concern has always been that the impedance of the transformers would result in significantly worse 'voltage drop' than the conductors would have caused at the lower voltage.

What sort of voltage variation between low and full load do you see on these installations? What methods did you use to compensate for transformer impedance?

Thanks
Jon
 
Long Service Run

Long Service Run

Jon, I first came across this, if memory serves me right in the late 1970 or early 80's. We had several mountain top repeater installations for MCI or what ever it was called at that time. The project called out for a 200amp 120/240 meter pedestal to be installed at the bottom of each mountain and MCI contracted to have dierect burial cable installed which required a splice every mile going up the mountain. Most of these installations had about 5 miles of cable. At the top of each mountain was the pre-fab MCI station where we installed a transformer stepping back down to the 120/240V 1ph3w. As far as I know they are still in operation today. I never did take any readings on this system. Since that time I have had several ranchers who do not want to give any easements to the utility so we would take service near the property line and install the same type of transformers used by the Rural Electric Coop's. With the higher voltage and transformer taps at the final destination we have not had any problems. I like the secure installation and basically its the same thing the utility would do with the exception of the back-feeding at the low voltage supply service. I like the reliability of the load-break elbows and the ability to provide lightning arrestors as well as having the installation of the cable underground, away from the weather. Also sine the transformers are loop-feed you have the ability to continue on to some other load, such as the barn that will surely get added if youu have much land. Last I checked the wholesale cost of on of the transformers was not quite a thousand dollars and we typically run a larger than required primary cable because the load-break elbows will only work down to a certain size. I don't have my info with me now, but you can get the transformers with voltages higher than 5kv. The problem I have with the low-voltage feeders being calculated for such long distances is. the owners always change their minds somewhere along the line and it usually ends up requiring additional power, never less.
 
Status
Not open for further replies.
Top