electrical line size

[cisco]

I've 2 questions for our resident electricians and contractors, as follows:
1. A contractor is putting up a garage/apartment (2 story) on my country property this Fall, something I'm really looking forward to having. Right now, I've 60 amp service for a well pump and incidental stuff. I'm going to ask the power company (who put in a transformer at the end of the line they ran to my property) for 200 amp service to the current power pole. That power pole and well (and transformer) are about 150 feet from where the garage/apartment will be. What size electrical line should I use between the power pole and where the dwelling will be? I'm going to run a 3/4 PVC water line in the same trench, and only want to do this once.
2. I also need to run power and water lines 900 feet to the front of my property, where such will be used on a dock for a boat lift and wash down. I will need a solid 15 amps (to run the lift motors). I have previously trenched and laid power/water lines to the other side of my property, about 1000 feet, for watering and to power an entrance gate. I used 12 gauge wire, and get about ? 10-12 amps at the 1000 foot mark (not quite enough to use a 15 amp rated compressor I had hoped to use in spraying the fenceline, but more than enough to trickle charge a gate opener, supply lights & operate a radial arm saw). I had planned on 10 gauge to the dock, but will such be adequate for 15 amps at 900 feet?
Oh yeah, I trench first with a subsoiler to break up roots, dislodge rocks and the like, then open a wider trench with a potato plow (middle buster) - only need 12" depth on the coast of South Carolina (heck, it rarely freezes, and then just barely and for a short period of time).

 

[Slamfire]

I think I'd want number 4 wire to the garage/apt, and something bigger to the boat house, I guess 2 would do. The thing is drawing 15 amps to run a motor is possible with smaller wire but starting the motor takes 2 to 3 times the current. With smaller wire you might not get the motor started.

 

[bgott]

Run a 240 volt branch circuit to the dock. According to the voltage drop calculator I used, to get 15 amps out of 120 volts at 900' you are going to need to use 1/0 cable. 15 amps at 240 volts will take #3 cable. If you are going to do it, you might as well do it right and get some underground service entrance cable and run 50 amps at 240 volts down there. Here is the URL to the voltage drop calculator I used, they also have a few other useful calculators on this webpage.

http://www.elec-toolbox.com

 

[johnbilt]

Hi

Sounds like a great project. I will try to give you a few guidelines.

1) Be sure to follow all grounding and safety guidelines so that any electrical faults (shorts) will be protected by the circuit breaker.

2) The minimum electrical line size is dictated by the circuit breaker rating. Copper (Cu) or Aluminum (Al) wire shall be used. The aluminum is generally cheaper, but requires a larger wire due to the increased resistance.

It sounds like you have one electrical service that you are distributing to your various locations. I am assuming that the current 60A service for your well is sufficient and that you have a 60A panel or switch for this right now.

You will need to purchase a 200A panel with a main disconnect and a buss for adding extra branch circuits or feeder panels. The 200A service requires a #6 copper ground wire bonded to two 8 ft copper ground rods driven into the earth.

The existing well circuit can be reconnected to a 60A breaker on the new panel.

I would recommend that you install a 125A feeder to a subpanel at your Garage/Apt. This is a standard size and would allow the flexibility for the branch circuits you will need.
The 125A service will require a minimum of 1/0 Aluminum or #2 Copper. Electrical supply will carry 3 wire cable for direct burial.

I would run the feeder for your dock from the closest source, Either the 125A subpanel or the 200A main panel. You may consider running another 125A service with a subpanel to the dock as well. It will give you a big enough wire to account for voltage drop over the long distance, and you can run appropriate branch circuits from the dock subpanel for everything you need. Branch circuits would be #12 for a 20A circuit. Be sure to use GFCI outlets at all locations.

Electrical code requires a minimum burial depth. I believe this is 24 inches, but would have to check code.

Please remember, small amounts of knowledge can be dangerous. This is only a snippet of information. I would strongly recommend that you consult a licensed electrician to approve a layout. There are many sections of NEC code that apply to your installation. If you are subject to inspection, you must meet all of the requirements. If not, I am sure that you want a safe system with no shock or fire hazards !! /forums/images/graemlins/confused.gif

Be careful and have fun...

John /forums/images/graemlins/smile.gif

 

[StanInCalif]

There is an excellent book entitled "Wiring Simplified" by Richter and Schwan. It is inexpensive and very informative. It includes charts showing voltage drop and ampacity of wire and covers domestic and farm wiring. Available at most lumberyards and home centers.

 

[Phred]

Cisco,

The others have given you some good advice.

Wire size is all about voltage drop.

I have a 1hp ( 240V ) well pump that needs at least 10 gauge.
Asuming a reasonable power factor its probably pulling a little more than 1 Kwatt, which would only be about 5 amps.
Way over kill if you look at a standard wire table.
The problem is its a deep well.

Also do your self a favour and run conduit, and a larger size than you neeed.
I pulled the initial wire as 10 gauge to the well head and then needed an additional load ~ 1year latter.
Connected the end of a spool of 8 gauge to one end of the existing 10 gauge line and pulled it back through.
Sure was easier and cheaper than digging it back up.

I recommend PVC pipe and watch the 90s. General rule is no more than 3. The 90s add a lot of friction.
Also the pulling lube helps.

Fred