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-   -   325m run of underground power to get 240v at the other end? (http://www.diychatroom.com/f18/325m-run-underground-power-get-240v-other-end-150429/)

 Farmer steve 07-16-2012 05:49 AM

325m run of underground power to get 240v at the other end?

I want to get power out to a fence line on my property, and want to know what I need to get 240 volts at the end of a 325m underground run,
Can some wise electrician tell me what I need to use in cable.
I do have the capability of putting a 480volt transformer that I have at the start of the line, if that would help!

 AllanJ 07-16-2012 06:39 AM

You would need fatter wires and/or a pair of transformers to step up the voltage at the supply end and step the voltage back down at the far end.

How much power (in terms of how many amperes or watts) will be needed?

(325m is a little over a thousand feet or a little over 2000' round trip.)

The number of volts lost due to voltage drop depends on the number of amperes and the size/material of the wire and is independent of the supply voltage. So stepping up to 480 volts will improve the situation compared with leaving it at 240 volts not counting the cost of the transformers.

One example: You would need #4 copper wire to get 20 amps at 240 volts out there with no transformer. Boosting the voltage to 480 (and back down at the far end) would give you slightly less than 20 amps at 240 volts (call it 18 amps) using #8 (correction, #10) wire.

But systems are always designed to have more than 95% of the supply voltage out at the far end for the desired number of amperes. You do not do things like boost it to 480 volts at the supply end expecting to have 240 volts remaining at the outer end. Such a scheme would have the voltage varying all over the map as the number of amperes drawn changed.

 andrew79 07-16-2012 07:46 AM

It's amperage dependant but If your taking a full 15a out you'd need 1/0

 Yoyizit 07-16-2012 12:47 PM

If you only need power occasionally there are other options. You running an electric fence?

 dmxtothemax 07-16-2012 07:22 PM

What are you running ?
Is it really important to have at least 240 v,
Most loads will work quite happily at reduced supply !

How much power (in amps or watts) do you need at the end of the run ?

 andrew79 07-16-2012 09:10 PM

Quote:
 Originally Posted by dmxtothemax What are you running ? Is it really important to have at least 240 v, Most loads will work quite happily at reduced supply ! How much power (in amps or watts) do you need at the end of the run ?
Huh? Since when is undervoltage good

 kontoose 07-16-2012 10:19 PM

240volts at end of 325m underground run.

...Also, it makes a difference what conduit your are installing underground - PVC or RSC (Rigid Steel Conduit)...or are you going "UF"? Because at this distance, "Inductive" and "Capacitive", eddy current and hysteresis losses need to be taken into account.:jester:

 kontoose 07-16-2012 10:19 PM

Quote:
 Originally Posted by kontoose (Post 967608) ...Also, it makes a difference what conduit your are installing underground - PVC or RSC (Rigid Steel Conduit)...or are you going "UF"? Because at this distance, "Inductive" and "Capacitive", eddy current and hysteresis losses need to be taken into account.:jester:
Doh...!:whistling2:

 andrew79 07-16-2012 10:37 PM

Why would he have to worry about that. The wires insulated and I highly doubt he needs to worry about any residual magnetism or any increase in frequency.

I'm going to do a facepalm after this one but can you use rigid in the states underground or is that just more bull.

 kontoose 07-16-2012 11:03 PM

Seriously.

Quote:
 Originally Posted by andrew79 (Post 967626) Why would he have to worry about that. The wires insulated and I highly doubt he needs to worry about any residual magnetism or any increase in frequency. I'm going to do a facepalm after this one but can you use rigid in the states underground or is that just more bull.
Absolutely. Rigid conduit is, more than often, used underground in the states, and by the way, on this length of a run, all the losses that I mentioned earlier - do - come into play...especially if there is a large current draw; which you mentioned earlier. (Take a look at the most precise voltage drop formula in the "Ugly's" book (not sure if you can get this little jewel up where you're at, but...)?
You bring up good points on this one here.:yes:

 Farmer steve 07-17-2012 02:42 AM

Thanks everyone big help from all!
To answer some or most of the questions,
1. I just need 10amps at the end
2. It will only run an electric fence Energizer (mains power unir only)
3. its run in PVC underground
4. The energizer will run at 220volts min
5. I have 240 to 480 and a 480 to 240 step up and down transformers (antisipated that one)
so I really just need to know what cable to use as I don,t understand the formulers with all the resistance and ohms stuff!!!

 mpoulton 07-17-2012 03:31 AM

Quote:
 Originally Posted by Farmer steve (Post 967718) Thanks everyone big help from all! To answer some or most of the questions, 1. I just need 10amps at the end 2. It will only run an electric fence Energizer (mains power unir only) 3. its run in PVC underground 4. The energizer will run at 220volts min 5. I have 240 to 480 and a 480 to 240 step up and down transformers (antisipated that one) so I really just need to know what cable to use as I don,t understand the formulers with all the resistance and ohms stuff!!!
10A at 240V is quite a lot of power. A fence charger will need only a small fraction of an amp. At this distance, though, it's simply impractical to run wire for such a small load. Solar is definitely the way to go.

 Farmer steve 07-17-2012 04:04 AM

Tried Solar not efficent for the km I have to run plus The energizer in not Solar equiped

 dmxtothemax 07-17-2012 05:15 AM

Quote:
 Originally Posted by andrew79 (Post 967558) Huh? Since when is undervoltage good
Did I say under voltage was good ?
All I said was some loss is not significant in all cases.

IE a 120v lamp will still produce useable light at say 115v.

 AllanJ 07-17-2012 06:16 AM

Ten amps at 240 volts, using the two transformers for 480 volts over practically all of the run, you can use 12 gauge wire.

Some loads will work happily at reduced voltage, but not most. Some (some resistance heaters, incandescent lights) will perform acceptably although in a somewhat more energy inefficient manner not counting the amount of energy dissipated in the wiring and with less total output.

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