[ltwayne]

I have a distance of about 250 feet that I want to put electricity to a building from my existing meter pole. I would like to know what size wire to put in the ground.

Use: a few small cabins (12'x16', 12'x12', and another 12'x12'). The cabins will have a window unit A/C, a small refrigerator, and possibly run an air compressor or some power tools once in a while.

The service is about 250 feet away from the pole. I plan on burying the cable. I also have to run through a small creek (not usually wet). 100amp meter pole (already there).

What do you recommend?

[tkrussell]

You can use aluminum wire rated for direct burial, called URD (Underground Residential Distribution) cable.

This comes in 3 and 4 wire, if the main breaker is at the meter, then use 4 wire, if the main breaker is at the cabin, then only 3 wire is needed.

Assuming a 50 amp load, #1/0 Al will get you a 3.2 % voltage drop. If you can afford it, esp if you plan to add more load later, then I really recommend using #4/0 Al URD cable. This will allow 100 amps of load at 3.6% Vd.

[ltwayne]

Please forgive my ignorance, but I would also like to understand more about what you are suggesting...
I have heard of direct burial cable, but I am not sure if the cost of 250 feet will be really significant or not. I priced THHN and for number to the electric company quoted $1.28 per foot. I also priced Direct Burial (3 number 2's with a ground) it was about $5.93 per foot. Does that sound about average? Number 4 was $.81 and $4.15 respectively.
Is there a difference in "Number 4" and "#4/0"? (again, please forgive my ignorance... that is why I am here at the site for advice)

[tkrussell]

All your prices seem reasonable, I am assuming the #2 THHN is copper, and that the direct burial is aluminum.


Forget THHN, that is for dry locations only, not allowed in wet locations, which would be a conduit underground.

Most THHN is also rated THWN which can be used in underground conduit. THHN/THWN must always be in a conduit, never direct buried.

The smaller the number the larger the wire, #12, #10, #8, #6, #4, #3, #2, #1, #1/0, #2/0, #3/0, #4/0. The "0" stops there, and starts with the actual circular mils called MCM. Ok enough on wire sizes.

If you use #2 copper, there will be a 3.2% Vd with a 40 amp 120 volt load.

If you use #2 aluminum, there will be a 4.5% Vd with a 40 amp 120 volt load.

I should explain that the maximum recommended voltage drop is 3% for a feeder, and 2% for a branch circuit to the last outlet.

With the AC and motors you mention, really need to keep the Vd as close to or below 3% as much as practical.

[ltwayne]

I have talked to several people here locally (friends, not electricians). They are mostly telling me to stay away from aluminum (because of corrosion and heat). The cost is about 75% less for aluminum. Should I stay away? What are your thoughts?

[KISS]

FYI #4/0 is the same as 0000. Just like purity numbers of 5N5 is 99.9995% pure, but that another area all together. It's just shorthand.

[Stratmando]

Kiss, sounds like 5N5 is purer than Tripple Nine Fine?

[KISS]

See, I'm not making it up.

Virtual Travelog | 5 Nines and other Nonsense - Interaction of Quality Attributes in System Design

Type as a Google search "5N5 purity"

[Mr_am]

Hi, Aluminum is less reliable (cheaper).. copper is the best.