Extreme distance voltage drops

[tortuga]

I would go with solar if it is possible. Did you say what the load is?

If solar wont work can you use Chaper 9 Table 8 note2 to calculate a multiplier for K to use the actual soil temp at 2 Ft or whatever your depth is?
My guess is you would have 18° C or a k= 10.5 for copper or 17.2 for aluminum.

If your load is around 1000VA for eaxmple
#4 AL USE/XHHW-2 Aluminum @6500 FT with a K =17.2 would be around 468V

For medium sized loads like 7-12kw you could use a 1000V nominal system and PV wire:
http://hvac.southwire.com/wp-conten...OVOLTAIC-WIRE-1000-VOLT-TYPE-RPVU-–-BLACK.pdf
I am looking into that for water pumping on a large farm now.

 

[oldsparky52]

Is there not a set of drawings to work from? What did the drawings call for?

 

[electrofelon]

Another case of the OP disappearing without comment, update, or feedback

 

[LarryFine]

Another case of the OP disappearing without comment, update, or feedback ☹

"Mr. Monk and the Missing OP"

 

[mbrooke]

Yes very important. Not panel size, not breaker size, not article 220 load, preferably not even nameplate load - ACTUAL load.

I am guessing the actual load for something like this is quite small, but being a roadway project, there are probably many people willing to waste lots of money.

I wouldn't be worried about voltage drop. I'd be worried about someone getting killed or injured from a breaker that does not trip. Breaker size is the governing factor here.

 

[ptonsparky]

I wouldn't be worried about voltage drop. I'd be worried about someone getting killed or injured from a breaker that does not trip. Breaker size is the governing factor here.

If you are worried about a breaker tripping you need to worry about VD.

 

[mbrooke]

If you are worried about a breaker tripping you need to worry about VD.

True- but they aren't always one in the same. It possible for a 1 amp device to still function while a dead short at the far end does not clear.

 

[electrofelon]

For medium sized loads like 7-12kw you could use a 1000V nominal system and PV wire:
http://hvac.southwire.com/wp-content/uploads/2017/03/PV-PHOTOVOLTAIC-WIRE-1000-VOLT-TYPE-RPVU-–-BLACK.pdf
I am looking into that for water pumping on a large farm now.

I know you are familiar with my 2.4kv system I mentioned here because you replied: https://forums.mikeholt.com/threads/my-solar-system.148865/ but for others reading this: PV wire goes up to 2KV, which is of course better for wire size/VD issues, but the issue with going above 1kv is then the installation would have to fall under 300.50(A)(3) which requires RGC/IMC or PVC encased in concrete which may very well make it a deal breaker. The NEC is not very friendly to unshielded cables.

 

[ramsy]

Another case of the OP disappearing without comment, update, or feedback ☹

Engineer mistakes costing architect too much greif. That guy was canned

 

[tortuga]

Whats the best practice for ensuring the OCPD works for a long run like that? Since the OP is gone for now lets say the load is 1kw @ 6500 FT

 

[ptonsparky]

True- but they aren't always one in the same. It possible for a 1 amp device to still function while a dead short at the far end does not clear.

Lived it.

 

[mbrooke]

Lived it.

Not everyone does. The thing that gets my panties in a bunch is the CMPs know it, and instead of making a simple rule limiting how far a any particular wire gauge can travel they're slowly mandating various GFCIs and "special circuit protectors" which is great for manufacters but not how you would go about fixing a loop hole in the code.

 

[ptonsparky]

Whats the best practice for ensuring the OCPD works for a long run like that? Since the OP is gone for now lets say the load is 1kw @ 6500 FT

Current limiting and/or fast acting fuses. For 1KW @480 you talking less than 3 amps. Dead short means no arc to worry about.

 

[ramsy]

My point

Whats the best practice for ensuring the OCPD works for a long run like that? Since the OP is gone for now lets say the load is 1kw @ 6500 FT

For Short Circuit Analysis of 1kw / 277vac / 1.732, my point-to-point SCA shows ~41 Amps, which trips 20A breaker on #8, 6500 ft away, 2.9%vd.

Setting power factor to 85% matches "C" table results, published by IEEE Std. 241-1990, IEEE Recommended Practice for Commercial Power Systems.

Overload protection should be integrated within fused utilization equipment.

 

[ptonsparky]

Why do you use 277?

 

[tortuga]

My point

For Short Circuit Analysis of 1kw / 277vac / 1.732, my point-to-point SCA shows ~41 Amps, which trips 15A breaker on #8, 6500 ft away, 2.9%vd.

Setting power factor to 85% matches "C" table results, published by IEEE Std. 241-1990, IEEE Recommended Practice for Commercial Power Systems.

Overload protection should be integrated within fused utilization equipment.

Interesting thanks! 277 is L to G fault probably worst case?

 

[ptonsparky]

Interesting thanks! 277 is L to G fault probably worst case?

Was the the question Short Circuit and not Ground Fault?

 

[ramsy]

Why do you use 277?

Op was using 480. Not sure about L-N worse case SCA with Y xfmr.
L-N maybe worse case SCA for short runs of center tap 120/240v

 

[ramsy]

Tried it on an iPhone app, selected 480vac L-L, 75 kva xfmr 1%Z, 6500ft of #8, got SCA of 66 Amps.
EATON Bussman series FC2 fault current calculator

 

[tortuga]

Op was using 480. Not sure about L-N worse case SCA with Y xfmr.
L-N maybe worse case SCA for short runs of center tap 120/240v

What are you using for a k value? and what do you get for #4 AL?