Running power 4000 feet

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mbrooke

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Currently 20kva of power needs to be run to an outbuilding about 4000 feet away. To keep wiring practical the voltage will be stepped up at the main building, run via underground conduit, and then stepped back down. My question is it is possible to use 1000 volts between the two buildings instead of 600 volts and if so how would one go about doing it? I want to keep VD no more then 3% across this run.
 

curt swartz

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I don't think 1000 volts is even a standard rating for equipment. Even if it is once your get past 600 volts you are into to medium voltage equipment and cables. Equipment, wire and labor become much higher. If you are going to use medium voltage equipment you might as well go with 4160. For such a small load I doubt it would be worth using anything over 600 volts.

Is this single phase or 3 phase? At 600 volts your load is about 33 amps for single phase or 19 amps for 3 phase.
 

mbrooke

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I don't think 1000 volts is even a standard rating for equipment. Even if it is once your get past 600 volts you are into to medium voltage equipment and cables. Equipment, wire and labor become much higher. If you are going to use medium voltage equipment you might as well go with 4160. For such a small load I doubt it would be worth using anything over 600 volts.

Is this single phase or 3 phase? At 600 volts your load is about 33 amps for single phase or 19 amps for 3 phase.


For now the plan is single phase. I saw somewhere in the NEC that 600 volts was raised to 1000 volts, what does this apply to in reality?
 

big john

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I know solar systems are really pushing the limits of low-voltage installs and there is definitely more 1kV stuff out there now. I don't believe it would be cheaper, but you might as well look into what they sell for disconnects and wiring in the 1-2kV range.

Otherwise, I would have also said go with a 2400V system a and couple little dry-types, but that would definitely be MV and you'd need shielded cable, term kits, and a different set of rules.
 

mbrooke

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I know solar systems are really pushing the limits of low-voltage installs and there is definitely more 1kV stuff out there now. I don't believe it would be cheaper, but you might as well look into what they sell for disconnects and wiring in the 1-2kV range.

Otherwise, I would have also said go with a 2400V system a and couple little dry-types, but that would definitely be MV and you'd need shielded cable, term kits, and a different set of rules.

Thats what I might do.

Question. If the NEC lets you do a corner grounded 600 volt system, why not a center tapped 300-0-300 volt system?
 

GoldDigger

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Thats what I might do.

Question. If the NEC lets you do a corner grounded 600 volt system, why not a center tapped 300-0-300 volt system?
I don't see any reason why not. NEC lists standard system voltages, but I do not see any prohibition for using non-standard voltages where appropriate.
Just do not expect it to be supplied as a POCO service.
For this use as a customer feeder voltage, why not? You just may need custom transformers to do it.
 

Tony S

Senior Member
I was under the impression that <1000V AC or <1500V DC was LV for both the NEC and BS7671. International standards etc.

Much hangs on the voltage grade of cable to be used and the skill of the cable jointer. I don’t even want to think of a 4000Ft drum of cable so joints are inevitable.
 

big john

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Location
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Why not a center tapped 300-0-300 volt system?
Because you're probably gonna pay a premium for that transformer. I suppose in a pinch you could gang two 240:600 trannys and feed them at 120V. But all that seems overly complicated, I'd corner-ground and be done with it.
 

iwire

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I was under the impression that <1000V AC or <1500V DC was LV for both the NEC and BS7671. International standards etc.

Much hangs on the voltage grade of cable to be used and the skill of the cable jointer. I don’t even want to think of a 4000Ft drum of cable so joints are inevitable.

In general the vast majority of our equipment is rated 600 volts or less. Most electricians and electrical contractors here only work on systems of 600 volts or less.

To go above 600 volts here adds a lot of cost to the job. Of course it still may make sense.
 

mbrooke

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Because you're probably gonna pay a premium for that transformer. I suppose in a pinch you could gang two 240:600 trannys and feed them at 120V. But all that seems overly complicated, I'd corner-ground and be done with it.



This is more hypothetical, but if equipment can handle 600 volts line to ground (corner grounded), why not 1000 volts line to line here the line to ground is only 500 volts?
 

mbrooke

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In general the vast majority of our equipment is rated 600 volts or less. Most electricians and electrical contractors here only work on systems of 600 volts or less.

To go above 600 volts here adds a lot of cost to the job. Of course it still may make sense.

But when you do find 1000 volt equipment, isn't it similar to 600 volt termination? Not saying it is or isnt, but just curious.
 

iwire

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But when you do find 1000 volt equipment, isn't it similar to 600 volt termination? Not saying it is or isnt, but just curious.

I really do not know the answer to that. I have very little experiance or knowledge of equipment over 600 volts.

When the company I work for has work above 600 volts they sub contract the terminations.
 

mbrooke

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I really do not know the answer to that. I have very little experiance or knowledge of equipment over 600 volts.

When the company I work for has work above 600 volts they sub contract the terminations.

That would make sense in way since anything over 600 volts goes into the medium voltage range. But, I saw somewhere in the NEC where 600 volts was changed to 1000 volts recently, what does this change?

Edit: I found this, hence my confusion:


http://www.ieci.org/newsroom-and-insights/600-volts-to-1000-volts
 

Tony S

Senior Member
In general the vast majority of our equipment is rated 600 volts or less. Most electricians and electrical contractors here only work on systems of 600 volts or less.

To go above 600 volts here adds a lot of cost to the job. Of course it still may make sense.

So like everything it boils down to cost. Not knowing what your PoCo’s would charge but knowing what our DNO’s charge (an eye watering amount.)
I was quoted £70K ($107K) for a 200m MV UG feed in 2013. With groundwork’s, buildings and our equipment there wasn’t much change out of £150K.

The limiting factor as I see it is affordable cable of a suitable grade. Cable CSA and voltage becomes a juggling act.
Higher voltage = lower cable CSA but finding that mid point is going to be the interesting part.

The cost of transformers is going to fade in to insignificance compared to the rest of the job.
 

mbrooke

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I was under the impression that <1000V AC or <1500V DC was LV for both the NEC and BS7671. International standards etc.

Much hangs on the voltage grade of cable to be used and the skill of the cable jointer. I don’t even want to think of a 4000Ft drum of cable so joints are inevitable.

Curious, how would the IEC take approach to this? Am I correct to assume SWA cable would be used and 1000 volt switches are readily available? And no stress cones provided the Line to earth voltage is 500 volts and under?
 

Fulthrotl

~Autocorrect is My Worst Enema.~
Currently 20kva of power needs to be run to an outbuilding about 4000 feet away. To keep wiring practical the voltage will be stepped up at the main building, run via underground conduit, and then stepped back down. My question is it is possible to use 1000 volts between the two buildings instead of 600 volts and if so how would one go about doing it? I want to keep VD no more then 3% across this run.

'k, but there is an issue with some jurisdictions that are holding feeders to 2% now.
california is, as part of their glowing title 24 kool aid. have a sip, it's only a little bitter.

3% is a reasonable drop, assuming electrons still flow where reason exists.

bump it from 240 3ph to 575 3ph. someone will wind you a transformer, for enough money.
if it was me, i'd do three phase 208 volt wye ~ 575 delta on both ends. your 20kva will work
better for your voltage drop.

20kw will come out to 35 amps single phase @ 575 volts
35 amps on 300 MCM will come out to 2.86% voltage drop

20kw will come out to 19 amps three phase @575 volts
19 amps on 3/0 will come out to 2.89% voltage drop.

12,000' of 300 aluminum will run about $20,000
16,000' of 3/0 aluminum will run abour $14,600

2 1/2" pvc will be about $5,400
3" pvc will be about $6,600

so, single phase is $26,600
three phase is $20,000

i'm betting the 3 phase transformers will be more affordable as well.
a single phase 575 xfmr is probably not even available anywhere.
 

mbrooke

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Thank you! Those numbers are a life saver! :happyyes::)

Then I will go with 3 phase.

Im however tempted to pick a 208 delta 600Y transformer just so I can have a mid point ground.


If I did choose 1000 volts, I would need cable other then typical THHN/THWN?
 

Tony S

Senior Member
Curious, how would the IEC take approach to this? Am I correct to assume SWA cable would be used and 1000 volt switches are readily available? And no stress cones provided the Line to earth voltage is 500 volts and under?



IEC agree with <1000V AC <1500V DC as LV. They’d better do, they set the values.

I can’t say about your cable ratings without looking them up. Our BS2764 SWA is rated 600/1000V (600V to earth, 1000V Ph to Ph). I’ve tested them to many times that.

As I said earlier the cable jointing is going to have to be done by a skilled person. As always joints are the weak point. (My knees included.)

Stress relief doesn’t come in to play with <1000V just common sense. Not putting sharp bends in the joint or termination conductors.
For MV it depends on the cable construction, screened need stress relief, unscreened extra insulation in the cable crutch, (this is sounding perverse now!)

I can work on up to 33KV cables, that is where stress relief really is needed. Now that I’m retired there’s no chance. Horrible muddy holes, rain, snow, etc. The jointers mate bailing the hole out with the pan I was planning to cook our breakfast in. To hell with that game!

Only once did I get a cable jointing job I really enjoyed. Four 11KV through joints at the side of a pasture, glorious summer days, beautiful Derbyshire dales scenery. The local farmer was bringing us eggs, home cured bacon, home made sausage and black pudding along with a Derbyshire specialty, oat cakes.
Strange how that job ran on for days longer than it should have done.
 
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