Voltage Drop for 750 feet advice needed

[fordmantpw]

I will preface my response by saying that my degree is in electrical engineering, though I don't practice (I'm a computer programmer instead). I remember many of the concepts from school 15+ years ago.

I will start off by saying that I don't think what you are wanting to do is going to be practical for you. I would be best handled by the electric company, as you need to deal with higher voltages. I am not doubting your skills, BTW, just thinking practically.

Essentially, the reason you have voltage and power drop in the line is due to the resistance in the line.
Power = Voltage * Current
Power Loss = Resistance * Current^2

You have to transmit the same amount of power, so if you double your voltage, you halve your current. Halving your current quarters your power loss. If you step the voltage up to 2200, your power loss is 1% of what it is at 220V. This is the reason electric companies run transmission lines of 100,000 volts +.

Now, to run it 750 feet, you are going to have a substantial drop in voltage, not to mention a lot of money spent just in the power loss of resistance of that line. Increasing the size of the wire decreases your resistance, therefore reducing your power loss and resultant voltage drop, but then the cost skyrockets. You could buy your own transformers and step your voltage yourself, but you really need an engineer to design and lay all of that out to do it correctly. You are better off just having the electric company do it. Electricity isn't something to play with, especially if you don't know what you are doing.

My recommendation would be to have the electric company put in a pad-mounted transformer close to where your building will be, running the supply to that transformer underground (this keeps the wires out of the trees and it looks much cleaner). They will put a meter right next to it, and you can run power to your building from that meter. Then, you could also come off of that meter and go to your deer blind (that's a fancy deer blind! ) where you could put a panel to run power on to your gazebo from there.

This is going to be the most efficient way to do it. Plus, all the power losses will be covered by the electric company and you won't be paying just to heat up the wires.

Best of luck in your planning. Whatever you do, I'm sure it will come out great, and I can't wait to follow it as with the lake build!

 

[farmer2009]

Eddie in your first post you said you have 1200 amp service. Are you sure? Man that is a bunch. If you are already feeding 600 off you may want to make sure. You don't want to melt the meter like I did last week on 320 amps.
Now as far as running power that far I am thinking I would let the power company handle it.

 

[EddieWalker]

Old picture, but this is my meter and 1,200 amp breaker box

Eddie

 

[bob722]

That kind of distance, 750 feet, the norm is a 25 kva transformer from the high line. Here in Canada our high line is 14,400 AC volt then a transformer to drop to house current. Don't try to skimp on this one, it will cost more and your quality will be lower. The length of your low voltage drop will require double ott tec cable and you don't want to buy that. Cheaper with a transformer and the correct way to go. Another alternative is a 25 to 100k watt Onan generator which runs on natural gas or propane. That can be costly too.

 

[farmer2009]

All I can say is WOW! How did you get that? Here we have to prove a need for 400+.

 

[mikim]

Eddie-- what about putting in a new meter, but in the name of your event company? Instead of "eddie W" -- use "Weddings R us" or whatever. It would then go on your books as an overhead expense for "the company". Might save some $$ at the end of the year that way.

 

[CobyRupert]

Eddie in your first post you said you have 1200 amp service. Are you sure? Man that is a bunch. If you are already feeding 600 off you may want to make sure. You don't want to melt the meter like I did last week on 320 amps.
Now as far as running power that far I am thinking I would let the power company handle it.

[As a side note: Something seems out of whack. In the picture there's 2 risers with weatherheads, presumably for the service drop from the pole. You would need 2 sets of 1000MCM conductors to equal 1200amps.-Not going to happen. I suppose it's possible they used 4 sets of 300MCM, with 2 sets going to each conduit?]

More importantly, did they give you a "single phase" 120/240V or a 3 phase 120/208V service? At 1200 amps, it's would be much more likely they gave you a "three phase" 120/208V service. This makes a huge difference when calculating how much power you're sending down the line.

Just because you have a 200amp breaker, doesn't mean you'll have 200 amps of load and the resultant voltage drop. You really need to determine how much power will be required by the A/C and other loads. Even with a 200 amp breaker, by code you wouldn't size it to be loaded (continuously) at over 80% (160 amps).

Some scenarios for 750', trying to limit voltage drop to <3%:
Scenario I: Assuming a single phase 120/240 service, with a 60 amps of load, this equals 14.4kVA or a little over what a 10hp 240V single phase motor would draw): ( in layman's terms, think of 1 kva as the same thing as 1kilowatt (1 kW).)

a) 2 sets of #2/0 awg, aluminum (270 amp capacity on a 200A breaker!) = 3% (of 240V) voltage drop.
b) 2 sets of #1 awg copper (220 amps worth) = 2.9% (of 240V) voltage drop.
c) 1 set of #3/0 awg copper (200 amps) = 2.9% (of 240V) voltage drop.
d) 1 set of #300 MCM aluminum (230 amps worth) = 2.6% (of 240V) voltage drop.

Scenario II: 3 phase 120/208V power.
The voltage drop (% wise) is the same as scenario I, because you have the same current, but because you have 3 phases of power being transmitted, 60 amps equates to 21.5kVA, or about what a 20 hp, 208V, 3 phase motor would draw. ( i.e feeder would support a much bigger A/C. What size is yours?).

Here's an example of what happens if you try to size it for full capacity of the 200A panel or circuit breaker (you're chasing your tail when you only need to chase the actual load!)
Scenario III (single phase 120/240 service, again with 160 amps (38.4kVA) of load:
a) 1 set of 750 MCM (!!!) aluminum (385 amps worth on a 200A breaker!!) = 2.8% voltage drop
b) 1 set of 500 MCM (!!!) copper (380 amps worth!!!) = 2.6% voltage drop.
c) 2 sets of 4/0 awg copper (460 amps worth !!!) = 3% voltage drop.
d) 2 sets of #350 MCM (!!!) aluminum (500 amps worth!!!) = 3% voltage drop.


[...and for all the teckies who want to check my calcs : They are based on the 75 deg C ratings of cables (and terminations!). Results are better if based on the 90 deg C rating (and you can prove all terminations are also similarly 90 deg C rated!) ]

 

[grsthegreat]

eddie,

does your area allow multiple (parallel) runs to supply power. Here, i can run, say, parallel runs of 250 MCM runs (2 hots, a downsized neutral and a #4 ground) in a 2-1/2" or 3" conduit and that would satisfy the voltage drop requirements.

this is much easier to run than 500 MCM wires. and alot cheaper.

 

[grsthegreat]

i put in lots of 800 and 1,000 amp services on residential houses. Its getting more and more the norm on large places.

were hydroelectric up here, and at $0.06/KWH its cheap power.

Personally, i ran the voltage drop calcs for your situation, and you could get by with 400 MCM with a 5.6% voltage drop. thats allowed here in pacific northwest..not sure about texas. Heat affects wire , and were colder up here.

 

[EddieWalker]

eddie,

does your area allow multiple (parallel) runs to supply power. Here, i can run, say, parallel runs of 250 MCM runs (2 hots, a downsized neutral and a #4 ground) in a 2-1/2" or 3" conduit and that would satisfy the voltage drop requirements.

this is much easier to run than 500 MCM wires. and alot cheaper.

View attachment 392814

I'm not familiar with this and will look into it. Would you connect both hot wires to the same 200 amp breaker or would one go to one breaker and the other to another 200 amp breaker?

Thank you,
Eddie