1000' undergrund

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MBLES

Senior Member
i need to get 200amp/240 service from the utility easement 1000' away. the land owner dont want utility poles on land. i fgure i can run parallel with 480 with XFMR. thats one problem,the other is once i get it to XFMR now i gotta terminate these large wires inside...This is a crazy request but if that what the customer wants....... Any Ideas?
 

kwired

Electron manager
Location
NE Nebraska
If it were my property, I'd try to get POCO to bring primary voltage and their transformer closer to the load, they do make medium voltage underground cable. But if owner wants to pay for larger conductors I will certainly be happy to bill them for it.

Either way they have some underground lines, and a transformer or other gear that has to go somewhere.

MV cable does cost some and uses some methods not so conventional to under 600 volt wiring methods, but the amount of copper (or aluminum) needed for each voltage level is still a huge enough factor in the overall cost.

POCO may charge customer for this, may even want contractor to so some of the work - like install raceways that they can use to pull their lines through.

If you add an extra pair of transformers just for voltage drop reasons you can spend a lot of $$ on those alone depending on what capacity they need to be. If full 200 amp/240 volt capacity is necessary you are looking at a pair of 50kVA transformers, and still likely will consider some upsized conductors beause of the distance. Bring a 7200 volt line up that property, the smallest cable the POCO uses is probably still much larger then needed for voltage drop reasons - when the 240 volts is fully loaded to 200 amps the 7200 primary is only running at about 6.66 amps. I don't think they make cable like they use in 14 AWG but it probably would be all that is needed ampacity wise - you likely get about 6 or 4 AWG minimum.
 

luckylerado

Senior Member
I agree. Either have the utility get a whole lot closer or look into a higher voltage transformer and wiring method. Back of the napkin calc says 300mcm copper at 480V to keep it at 2% VD. That would be incredibly difficult and expensive. If that is the way it goes, maybe the utility can provide a 480V drop. Might save you on 1 transformer.

Terminating should not be a problem with proper lug kits.

I would get the utility to send out an engineer or planner to discuss options.
 

kwired

Electron manager
Location
NE Nebraska
I agree. Either have the utility get a whole lot closer or look into a higher voltage transformer and wiring method. Back of the napkin calc says 300mcm copper at 480V to keep it at 2% VD. That would be incredibly difficult and expensive. If that is the way it goes, maybe the utility can provide a 480V drop. Might save you on 1 transformer.

Terminating should not be a problem with proper lug kits.

I would get the utility to send out an engineer or planner to discuss options.

I didn't do any VD calculation of my own, but OP only said 200 amp 240 volt service.

Actual connected load will make a difference on actual voltage drop, but guessing your calculation was for 200 amps of load @ 240 volts, this also doesn't account of transients happen when starting motors or air conditioning equipment - getting the source closer still can make a big difference in this area as you likely didn't consider how much current would flow for a short period when starting these loads.

Op may have a 200 main disconnect (or equivalent) after stepping up then down, but may only have a calculated load something less then 200. A lot of 200 amp dwelling services seldom see 200 amps of load and is very brief in duration if they do.
 

kingpb

Senior Member
Location
SE USA as far as you can go
Occupation
Engineer, Registered
Your gonna need something like 2 x 75KCMIL per phase at 240V, 1000' to keep it under 3%.

In a distribution area, its unlikely your gonna get 480V from the utility, even then it still requires two transformers (MV to 480, and 480 to 240V) I would look at staying with MV cable for your 1000' run. The smallest I think is going to be a #6AWG. You could possible use direct bury cable and avoid the conduit as well. VD is not an issue anymore.

Proper advice has already been given; i.e. contact local utility service engineer. You have to get them involved at some point anyway, and better to do it early on. They will be more than happy to tell you exactly what you need to do.
 

iwire

Moderator
Staff member
Location
Massachusetts
Assuming the customer has to pay for the work on their property I would be very surprised if using medium voltage would cost less than just getting a 480 or maybe 600 volt volt service from the utility and placing a 480-240/120 at the home.
 

iwire

Moderator
Staff member
Location
Massachusetts
this is why we need wireless power distribution.


:thumbsup:

wardenclyffe_tower1.jpg
 

kwired

Electron manager
Location
NE Nebraska
Assuming the customer has to pay for the work on their property I would be very surprised if using medium voltage would cost less than just getting a 480 or maybe 600 volt volt service from the utility and placing a 480-240/120 at the home.
All depends on the POCO and what they are willing to do. Most will allow the underground primary, but customer may be paying total cost of everything needed, others maybe only charge you a price that depends on expected return on their investment, the more power you will use the better price you will get. I don't know prices of MV equipment, but at today's copper prices one concentric 6 AWG cable rated for at least 7200 volts is probably a little less cost then two pairs of 750 kcmil plus a pair of grounded conductors.
 

iwire

Moderator
Staff member
Location
Massachusetts
All depends on the POCO and what they are willing to do.

Ahh, didn't I cover that with "Assuming the customer has to pay the work on their property"?:huh:

I think it goes without saying that if the power company will run the service up to the house at any voltage for free it will cost the customer less. :D
 

kwired

Electron manager
Location
NE Nebraska
Ahh, didn't I cover that with "Assuming the customer has to pay the work on their property"?:huh:

I think it goes without saying that if the power company will run the service up to the house at any voltage for free it will cost the customer less. :D
Well we do run into different policies with different POCO's and the trends of those companies does vary from region to region as well.

POCO's in my area may do all the work to get primary to this place, but may do it for less then I can do it for. Others possibly will charge more then I can (but typically not in my area, as they are all publicly owned utilities and that is just the way they are.) Then there are some that tell owner what size raceway to bury and they will do the rest - usually still with a range on their price that depends on other factors - #1 being how fast will they recover their investment from energy sales.
 

Fulthrotl

~Autocorrect is My Worst Enema.~
i need to get 200amp/240 service from the utility easement 1000' away. the land owner dont want utility poles on land. i fgure i can run parallel with 480 with XFMR. thats one problem,the other is once i get it to XFMR now i gotta terminate these large wires inside...This is a crazy request but if that what the customer wants....... Any Ideas?

assuming you have 240 single phase at utility demarcation point, you could use a pair of single phase xfmr's
at 480 volts to bump it up and back down. 100 amps at 480 for 1,000' comes to 2.19% loss on 350 mcm AL,
so if you were to run direct burial cable in aluminum, you are looking at $1.65 / ft or about $3,500.
you'll also need a ground. #6 aluminum is what is needed for a 100 amp circuit, but the long length may
reuqire upsizing that. time to ask an engineer on this one. i've seen engineers specify a ground larger than
the feeders.

so you are in prolly about $6k, not counting labor and trenching, and profit. if you are running conduit, i'd
not go smaller than 3" for that length of run... and i'd blow air thru it pretty often, and make sure to keep
crud out of the pipe. all you need is a 1k run you can't blow string thru.... :rant:
 

JDB3

Senior Member
A contractor that I know wired a golf course. The largest cable that he used was #10 copper. He used step "up" & step "down" transformers. He had figured it all sort of ways, & this was the most economical.
 

growler

Senior Member
Location
Atlanta,GA
I would get the utility to send out an engineer or planner to discuss options.

Around here the power companys would want you to consult with their engineer even before you start a project like this. That way everyone is one the same page and they agree to whatever plan you come up with before things get started.
 

kwired

Electron manager
Location
NE Nebraska
assuming you have 240 single phase at utility demarcation point, you could use a pair of single phase xfmr's
at 480 volts to bump it up and back down. 100 amps at 480 for 1,000' comes to 2.19% loss on 350 mcm AL,
so if you were to run direct burial cable in aluminum, you are looking at $1.65 / ft or about $3,500.
you'll also need a ground. #6 aluminum is what is needed for a 100 amp circuit, but the long length may
reuqire upsizing that. time to ask an engineer on this one. i've seen engineers specify a ground larger than
the feeders.

so you are in prolly about $6k, not counting labor and trenching, and profit. if you are running conduit, i'd
not go smaller than 3" for that length of run... and i'd blow air thru it pretty often, and make sure to keep
crud out of the pipe. all you need is a 1k run you can't blow string thru.... :rant:
250.122(B) requires the EGC to be proportionally increased in size if the ungrounded conductors are increased from the minimum size that provides sufficient ampacity, so we are looking at needing to increase the EGC by the same proportion that we increased the ungrounded - from a minimum needed 1AWG to a 350kcmil. I come up with needing at least a 2/0 AWG aluminum EGC for that application.

A contractor that I know wired a golf course. The largest cable that he used was #10 copper. He used step "up" & step "down" transformers. He had figured it all sort of ways, & this was the most economical.
total VA of load, number of phases along with how much you step up the voltage are major determining factors in what size conductor is needed. Length of runs factors in as well, but am assuming you are going to have some significant distances on a golf course. Golf courses I have been around in this area simply don't have much for power away from the clubhouse area - or if they do they may have POCO supply a separate service in the area where they do have other structures with power.

If your friend was using 600 volts as the high voltage - he was limited to 18kVA single phase, or 31.176kVA three phase before even considering voltage drop impact. Those are some pretty significant load values for on a golf course - other then possibly for irrigation pumps/wells, so it still comes down to how much load and how much impact does distance have on voltage.
 

texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
Here is an option that makes very efficient use of material.
 

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kwired

Electron manager
Location
NE Nebraska
Here is an option that makes very efficient use of material.
Care to submit the source of that drawing. I am not yet going to totally shoot it down, but I have been back and forth between few code sections trying to verify whether it is a code compliant install or not, but am still leaning towards you needing a separate equipment grounding conductor between the first SDS and the second structure.

One thing that makes this a little unusual and the reason it is more complicated then usual is the secondary is only two wire secondary. No secondary overcurrent protection is needed, the primary side overcurrent device is allowed to be the feeder or even a branch circuit overcurrent protection device in this situation.

But your grounded conductor in this case is not just a bonding jumper it is also a circuit conductor and carries same current as the ungrounded conductor therefore it's minimum size is not according to 250.102(C) but rather to general current carrying conductor sizing rules in 310 - it will have same minimum size as the ungrounded conductor because it is carrying the same current.

I could see 250.32(B) exceptions allowing this - but only where already existing and was once allowed to be done that way.

I don't see the conductor between buildings/structures as being a supply side bonding jumper if it is also carrying the normal operating current of the circuit either.

I'm all for more input on this for or against doing it like shown in that drawing. I don't give it a final approval or rejection at this point, but am currently leaning toward rejection.
 

Iron_Ben

Senior Member
Location
Lancaster, PA
i need to get 200amp/240 service from the utility easement 1000' away. the land owner dont want utility poles on land. i fgure i can run parallel with 480 with XFMR. thats one problem,the other is once i get it to XFMR now i gotta terminate these large wires inside...This is a crazy request but if that what the customer wants....... Any Ideas?

Bringing the HV POCO primary to the house is obviously the way to go if $$ is no object. But of course it is an object and the biggest one, so why not start with getting their price? Underground is implied here since the owner doesn't want poles, but get prices for both OH and UG just to see. Yes it will probably be in the five figure range, but there's an allowance based on the size of the house, so get their proposals first. I know from experience that a fair amount of judgment (and guesswork) goes into the POCO decision models. You might have one guy look at it on Monday and figure $20,000, while another guy comes out on a Wednesday and prices it at $12,000. Just sayin'.

I think the step-up-and-then-step-down idea is more trouble than it's worth. If we're talking about an 1100' run and we step up to 480, that's the same as a 550' run at 240 from an IR drop perspective. And 550' is too long for a service. Yes it can be made to "work" with big wire, but it's just a poor idea. And that 550' is not including the resistance of the two transformers. Not a huge number, but it's not zero either and there are two of them, adding to the circuit resistance.

Get the power company out to the site. You need their price to make your best decision and who knows, it may be less than you think.
 

iwire

Moderator
Staff member
Location
Massachusetts
Yes it can be made to "work" with big wire, but it's just a poor idea.

Iron, I think that perspective is based on your position, experience, the tools, labor procedures and relaxed requirements opposed to the NEC etc. available to a power company designer.

On the other hand those of us who do not work with over 600 volts find big wire a fine option many times.

I still maintain that for 1,000 feet the cost to the customer would be higher to run medium voltage to the home unless the power company is willing to pay for or provide much of the work.
 
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