Long distance run

[lgmagone]

I am trying to design an electrical system a client that would like to have a driveway gate at the edge of his propety. The client's property is large and the gate will be located approximately 1000' away from the house. The local electric company has said it would be expensive to install a second meter because an additional transformer would be necessary plus the additional cost of metering.

What is the easiest way to run power from the house to the driveway? I calculated (at 3% voltage drop) that a 3/0 conductor would have to be run to provide 20 amps at 120V at the gate location. This would be a very expensive wire!

I could run 208V to the driveway gate as a subpanel and then drop 120V from the subpanel. This would allow me to use 1/0 wire for a 3% voltage drop, still expensive.

Are there any other solutions that may cost less? I don't have a lot of familarity with running power over long distances. I'm thinking I specify two transformers and increase the voltage at the house and drop it back down at the gate, but again, this may get expensive depending on the cost of transformers.

Thanks,

L. Greg Magone, EIT

 

[charlie b]

Do you really think the load will be 20 amps? You don't have to calculate voltage drop on the basis of the rating of the circuit. I just did a quick check, and if the load is 5 amps I think a #4 wire would suffice.

Welcome to the forum.

 

[dbuckley]

Yep, two transformers, 480V in between. The one in the house would best have a 240V primary rather than a 120V. Do the math and compare costs.

The cost of copper is so high these days (and rising) that what would once have been a simple run of heavy cable is now an expensive proposition.

 

[winnie]

In addition to calculating for the actual load, keep in mind that 3% is a suggestion, not a requirement. The _requirement_ is set by the load itself; what sort of supply voltage range can it tolerate. Many loads are quite comfortable with a 10% or more voltage drop.

-Jon

 

[kingpb]

Use a 2KVA 240 - 120V transformer at the gate, utilize the taps to help offset voltage drop, and allow the VD to be 8% and adjust with 5% taps to get you to the 3% desired level. Doing this should allow you to use #6 AWG conductors and get 16A at the other end at 120V.

Another issue will be how many intermediate pull boxes will you need to keep the pulling tension to an acceptable level.

 

[LawnGuyLandSparky]

Keep in mind that after the electric automatic gate, comes the intercom, the automatic annunciator, the security camera, lighting, and then holiday lighting...

 

[LarryFine]

The client's property is large and the gate will be located approximately 1000' away from the house. The local electric company has said it would be expensive to install a second meter because an additional transformer would be necessary plus the additional cost of metering.

With a yard like that, "expensive" is a relative term. If he wants what he wants, it requires what it requires, and it costs what it costs.

If the other options are also "expensive", then get a real price on the POCO installation.

What is the easiest way to run power from the house to the driveway? I calculated (at 3% voltage drop) that a 3/0 conductor would have to be run to provide 20 amps at 120V at the gate location. This would be a very expensive wire!

I'd look into using something like URD or USE, or SEU, or whatever it is. As for expensive, see above.

I could run 208V to the driveway gate as a subpanel and then drop 120V from the subpanel.

That won't change anything. You'd still be drawing from one line conductor and the neutral, unless everything out there is rated for the higher voltage.

By the way, it would be 240 unless the house has 3-phase power. I've seen it before.

I'm thinking I specify two transformers and increase the voltage at the house and drop it back down at the gate, but again, this may get expensive depending on the cost of transformers.

Again, see above. You have to compare all of the options, but make informed decisions. Determine the real load, choose the materials wisely, and make accurate price comparisons.

An adequately sized cable may be the best choice, maybe a pair of transformers. Don't forget the transformers need to have a place to live, and you have to make proper terminations.

Don't forget to include labor in your comparisons: trenching and burying 1000' of cable, connecting the transformers, etc. The POCO idea is starting to look better.

 

[LarryFine]

Use a 2KVA 240 - 120V transformer at the gate, utilize the taps to help offset voltage drop, and allow the VD to be 8% and adjust with 5% taps to get you to the 3% desired level. Doing this should allow you to use #6 AWG conductors and get 16A at the other end at 120V.

Don't forget that, for a given power delivery, whenever you use taps, buck-boosts, etc., to compensate for a low voltage, the line current ahead of the compensation is higher than what the load requires.

That is also what is behind Mr. Buckley's recommendation to use the higher-voltage primary at the source end.

For that matter, it's also why the 480v transmission and the transformers is a viable option in the first place.

 

[hardworkingstiff]

One other option is to feed the remote location with a 240-volt (or 208-volt if that is what you have) circuit and install a 240(208)/120-volt transformer. You won't have a step-up transformer, won't have to pull a neutral. The voltage drop would be less and easier (than pulling 3/0) to manage with taps on the transformer. If you mananger VD with taps though, be careful you don't have too high a voltage with minimal loading.

 

[LarryFine]

One other option is to feed the remote location with a 240-volt (or 208-volt if that is what you have) circuit and install a 240(208)/120-volt transformer. You won't have a step-up transformer, won't have to pull a neutral. The voltage drop would be less and easier (than pulling 3/0) to manage with taps on the transformer. If you mananger VD with taps though, be careful you don't have too high a voltage with minimal loading.

That was King's idea in post #5.

 

[kingpb]

Don't forget that, for a given power delivery, whenever you use taps, buck-boosts, etc., to compensate for a low voltage, the line current ahead of the compensation is higher than what the load requires.

That is also what is behind Mr. Buckley's recommendation to use the higher-voltage primary at the source end.

For that matter, it's also why the 480v transmission and the transformers is a viable option in the first place.

Yes, the current on the 240V side would go up slightly, but since the line side maximum current on a 2KVA transformer is 8.33, there is no danger of over loading a 2P 20A breaker. Second, your overlooking the fact that the current will also go down on the load side of the transformer, for the same secondary load. The outcome is a net positive, which will reduce the amount of copper going 1000'.

 

[stickelec]

Use a DC gate controller. Might drop your AC load to 1 or 2 amps.

It would even work in a power outage.

 

[petersonra]

I vote for the transformer idea. Soup it up to 600V at the one end, and back down to 120/240 at the other end. Only need to run 2 wires that way.

Since the cost of the labor and wire is going to far exceed anything else, I'd be inclined to maybe install a small panelboard out near the gate in case they decide to add a light or other electrical users.

Might want to toss an UG cat5 cable or two in the trench as well, in case they want to put a phone, or security camera out at the gate.

If cheap is the answer, there are solar powered gate systems. They have batteries that charge during the day. Opening and closing the gate does not take a lot of energy, and is not normally done very often.

 

[danickstr]

do they make a 600v warning tape?

and I like the trans idea too, but wouldn't it need a ground bar?

 

[LarryFine]

Yes, the current on the 240V side would go up slightly, but since the line side maximum current on a 2KVA transformer is 8.33, there is no danger of over loading a 2P 20A breaker. Second, your overlooking the fact that the current will also go down on the load side of the transformer, for the same secondary load. The outcome is a net positive, which will reduce the amount of copper going 1000'.

Overloading the breaker was not my point. And, no, the current won't "go down" on the secondary. Compared to the primary, yes it will be less, but the load current will be a function of the secondary voltage and the load impedance, as always.

In reference to your first post, you proposed running straight service voltage for the distance, and placing a 240/120v transformer at the end of the run, near the load. That makes the 1000' run the primary circuit, not the secondary.

Therefore, any voltage-drop compensation's effect would be to add current, and thus add voltage drop, to the long run. That's not the end of the world, but it should be taken into account while calculating the best compromise in wire-size selection.

Using 240v instead of 120v is absolutely a good idea, of course, but the "outcome" of using voltage-tap compensation would be slightly more current along the long run, not less, and won't allow "less copper" for the 1000' run. Using 240v will.

 

[Cow]

Solar powered gate?

 

[hardworkingstiff]

That was King's idea in post #5.

Ah, so it was (not sure how I misread that post).

 

[wireman71]

And who cares how much it costs.. A person with a 1000' freaking driveway can afford the wire. Do your calcs and tell them the cost. They take it or they don't.

 

[LarryFine]

And who cares how much it costs.. A person with a 1000' freaking driveway can afford the wire. Do your calcs and tell them the cost. They take it or they don't.

Absoloopy!

 

[sparkydon]

In my area, DC and solar gates are used mostly and are extremely reliable. Iv'e worked with a gate company, wired quite a few up and their a joy to do. A local sheet metal guy makes these nice SS battery boxes, and the install looks clean. Wish I had pics.

You only need a 15A circuit for a battery trickle charger, and I doubt it ever draws more than 2-3A at a time...

If you did power the gate with AC, how would it work in a power outage?