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View Full Version : Electric power line size QUESTION........?



Sourdough
10-05-2011, 08:38 PM
The meter head and service panel will be approx. 275 feet to 300 feet from the cabin. They will deliver 200 AMP service to the meter head, using 2 ought wire .555 each in diameter.

I have to buy the 275 feet of cable, I have to dig the trench & install my burried line/cable.

Question: What is the smallest size aluminum cable that I should consider buying to have minimal loss of power 275/300 feet away at the cabin.......?

Second Question what would the diameter of the metalic part be, which has to fit into the buss.......?

Thank You,

Winter
10-05-2011, 08:59 PM
I don't know the answer but, ouch, that's gonna cost ya.

Rick
10-05-2011, 09:33 PM
I really think you need to pose this question to your utility company. I'm sure they will inspect the wiring prior to hook up and if it doesn't meet their specs they won't hook you up. You may go out and purchase the minimum size wire only to find out that the utility company or local codes (if you have any) requires something larger.

Sourdough
10-05-2011, 09:46 PM
Rick, They only care about upto the meter head. Think about it like this, it is just like if the meter was on your house, they don't what you do after the meter head. They were here for three hours yesterday.

OK, is there a chart of cable diameter, I can't go bigger than 3/8 dia.

natertot
10-05-2011, 11:51 PM
2 ought 2 ought 4 ought stranded is what I would go with. I would also talk to an electrician or inspector. Even if they don't care, they can still give sound advice.

Rick
10-05-2011, 11:59 PM
SD - I don't think that's true. It might be there but if they come out and you had extension cords ran they wouldn't hook you up. Their responsibility ends at the meter head just like it does here but their liability does not. The won't hook up anything that's not code. At least they won't around here. And that's true of a lot of places. I would still run it past them. If they say they don't care then at least you'll know your clear as far as they are concerned.

Where's our linemen at? Jump in here.

crashdive123
10-06-2011, 07:02 AM
Sourdough - a friend of mine is a Master Electrician. I'll give him a call today and ask. I would also ask the electric company as suggested. They may not care what happens on your side of the meter but they certainly have the knowledge to point you in the right direction.

crashdive123
10-07-2011, 07:31 AM
I gave him a call yesterday - he was working (home inspector) and not near any reference but said 2 ought should be the right one. He wasn't sure of the voltage drop, but I found this calculator that might be helpful. http://www.csgnetwork.com/voltagedropcalc.html

Still - I would recommend checking with your power company folks just to verify the info.

SARKY
10-07-2011, 11:31 AM
I don't know the answer, but what I remember from my highschool electrical class, the larger the outside diameter the less resistance.

aflineman
10-07-2011, 01:13 PM
2/0 sounds right, but I don't have my stuff here at the house for voltage drop calcs. (I don't do it enough to have it at the top of my head). You can get 3/0 to fit, but since they are feeding you with 2/0, you really won't gain anything.

natertot
10-07-2011, 02:26 PM
I don't know the answer, but what I remember from my highschool electrical class, the larger the outside diameter the less resistance.

True, to a point, I believe. If I remember correctly, electricity doesn't travel through wire, but on the surface of the wire. So saying that a larger diameter is less resistance is true because of more surface area. However, a smaller diameter stranded wire may have less resistance than a larger diameter solid wire because of the amount of surface area present. I maybe wrong on that, but that is my understanding.

kyratshooter
10-07-2011, 04:54 PM
Natertot, all the large guage primary wire is multi-strand after you get past 10 ga.

This is going to cost you out the wazoo SD!

Around here they are stealing wire right off the poles, stripping a mile at a time.

Rick
10-07-2011, 05:09 PM
DC voltage travels throughout the cross-section of wire. AC travels mostly on the outside. That's a direct result of the magnetic fields. Since AC alternates the magnetic field it stays near the surface because the inductance is higher at the center of the wire than on the outer surface. Since electricity takes the path of least resistance it travels along the outer surface where there is less inductance.

natertot
10-07-2011, 05:09 PM
Natertot, all the large guage primary wire is multi-strand after you get past 10 ga.

Ah, I did not know that. 10Ga is the biggest I've worked with in the building arena. I have dealt with some larger stuff in the automotive realm that was always stranded, but it was also performance stuff. Have you ever priced out 6ga gold wire? It'll make you develop a nack for words you never even heard before!

tipacanoe
10-07-2011, 07:32 PM
SD, here is a link that dealt with the same question as yours. As large as your cabin is, why do you need 200 amps? I know when you get the power you will be leaving the lights on just because you can, but unless you are going with electric heat I can't see why you would need more than 100 amps. http://www.diychatroom.com/f18/what-size-wire-use-running-underground-91945/

whitis
10-07-2011, 10:31 PM
The skin depth at 60hz is about 8.5mm. The wire size where resistance increases by 10% due to skin effect is 1inch diameter and less for smaller sizes. Resistance decreases in proportion to the square of the wire diameter until skin effect becomes an issue. Stranded wire doesn't really help much with skin effect unless the strands are individually insulated from each other.

2/0 is marginal at that distance. That will give a voltage drop at 200A/300ft of about 5.5V even with copper wire (aluminum is worse). Code recomendation is no more than 5% (or about 5.85V) drop including branch circuits (no more than 3% in either branch or feeder). You will also be wasting 5% of your power heating the air. 2/0 is rated at 145 to 195A depending on allowed insulation temp, though maybe higher in open air (the end that ties into the house might be enclosed). Aluminum requires twice the cross sectional area (41% larger diameter or about 3 wire gauges) vs copper. Skin effect is greater at the larger wire size. Based on voltage drop 4/0 would be the minimum size for copper and somewhere around 8/0 for aluminum.

Sourdough
10-10-2011, 01:15 PM
Thanks, it appears that 4/0 aluminum is the largest that I can afford.

I have a NEW question. The power Company say's that they only use 2/0 aluminum.

What I don't understand is how they could deliver (if they wanted to) 110/220V 200Amps 275 feet away using 2/0 but I will have a loss of voltage with 4/0 so what pushes the voltage down the line......?

frdgrss
10-10-2011, 06:10 PM
You will need four wire 4/0 URD wire. this will give you 200 amps at your caben

frdgrss
10-10-2011, 06:15 PM
The power Co. Can use 2/0 becouse thay areb in open air you will be putting your 4/0 in a trench

Sourdough
10-10-2011, 07:35 PM
The power Co. Can use 2/0 becouse thay areb in open air you will be putting your 4/0 in a trench

No. They told me that if they run underground service they use 2/0 three strand. Now I may have misunderstood. It would not be the first time. As it stands now I plan to run 4/0 4/0 2/0 I have found a fairly good deal on aluminum cable.

Camp10
10-10-2011, 07:58 PM
The power company only has to have the amperage potential to the meter trim. I dont know your distances but their chart must allow 2/0 to do that. We (CMP, the power company I work for) do not use 2/0 for any distance. We go from #2 to 4/0 with nothing in between. I would recommend the 4/0 also to avoid voltage drop over the distance. I would also try to sweet talk them into using it on their end of you can. It might be worth moving your service pedestol 40 feet farther from their pole to make it so they have to step up the size to 4/0... Run that by them first. The other option, and the way a lineman thinks is to rise from your service pole and go overhead with 1/0 triplex to your cabin. The best part about that is how confused the meter readers look when they try to find the meter to read it and it isnt at the end of the wire!

Rick
10-10-2011, 08:14 PM
Camp10 = Why kind of amperage do you run on the triplex to the meter on residential? I know some homes around here are going with 400 amp because of home theaters, etc. and I was just wondering what the transformer was sending downstream.

Camp10
10-10-2011, 08:27 PM
Camp10 = Why kind of amperage do you run on the triplex to the meter on residential? I know some homes around here are going with 400 amp because of home theaters, etc. and I was just wondering what the transformer was sending downstream.
It all depends on the size of the transformer. Here, the 10KVA is still our bread and butter but it is only good for 190 amps (going from memory) per leg. We wouls use a 50 KVA and 336 triplex for a 400 amp service. But a 25KVA and 1/0 would probably handle the load fine.

Sourdough
10-10-2011, 11:02 PM
Does power always arrive as 220V and the owner splits it out to 110V ????

natertot
10-10-2011, 11:27 PM
Does power always arrive as 220V and the owner splits it out to 110V ????

It is your circuit breaker that makes 220 available. You'll have a double pole breaker in which you run two 110V wires to an outlet.

crashdive123
10-11-2011, 06:24 AM
Since the power company is running power to the meter, could the meter be put closer to the cabin? Or is there a distance limit they will run the cables?

Sourdough
10-11-2011, 06:59 AM
Since the power company is running power to the meter, could the meter be put closer to the cabin? Or is there a distance limit they will run the cables?

They could, for $12.50 per foot X 275 feet= $3,437.50

Camp10
10-11-2011, 05:18 PM
Does power always arrive as 220V and the owner splits it out to 110V ????

It is actually 240V. 120 per hot let in reference to neutral. Your main breaker has a hot leg in each side, you can split your 120 with the bus work under the breaker or use a 240V breaker and use both legs.

Sourdough
10-11-2011, 05:54 PM
Thanks........

Sourdough
10-11-2011, 05:56 PM
They are having a meeting today to decide my fate.

Rick
10-11-2011, 07:11 PM
Aw, don't sweat it. We've had several of those around here and you come out okay. You'll do fine on this one.

Sourdough
10-11-2011, 07:51 PM
Aw, don't sweat it. We've had several of those around here and you come out okay. You'll do fine on this one.

I'll just bet that is true.

Rick
10-11-2011, 08:06 PM
Oh, sure. It's all highly technical and full of science type stuff. But suffice it to say that whether you come up heads or tails is always a 50/50 shot. We're nothin' if not fair, right? Oops, gotta go flip a coin on Pal.