Wire size for 200 amp service? - Homesteading Today

 Homesteading Today Wire size for 200 amp service?
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#1
03/17/08, 11:59 PM
 Join Date: Jun 2004 Location: OK Posts: 192
Wire size for 200 amp service?

I am needing to run wire from a meter pole 260' to the service panel. It is a 200 amp service. This is going to be burried most likely in conduit and none of it will be indoors and will probably be THHN aluminum. I am not sure what size wire to use. I was told that according to electrical code, a 200 amp service can't be loaded beyond 80%. My question is, when calculating wire size do I use 160 amps (80%) or 200 amps? Or what wire size should I use?

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Last edited by SouthernThunder; 03/18/08 at 12:04 AM.
#2
03/18/08, 12:36 AM
 Join Date: Oct 2007 Location: Hawaii Posts: 2,075

A sheer guess would be around double aught and the stuff ain't cheap!

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#3
03/18/08, 12:58 AM
 Join Date: Jan 2004 Location: MN Posts: 6,668

I'm just a simple dirt farmer.

I use this voltage drop calculator to play 'what if' stuff. I'm told it is a little bit harsh, you can get by with less. I donno, electric motors will be happy if you don't get by with too much less. I think they use 3% drop, assuming you will get more drop in the wires in the building, making a total of 5% allowable drop. Some folks want to do the whole 5% drop in the feed wires......

http://www.elec-toolbox.com/calculators/voltdrop.htm

Maybe you can find different one that gives you a better answer.

Says 350 mcm which is about the size of your thumb. That is what the pros used to make 200 amp runs like that on my place a few years ago.

Looks like double aught would only carry 100 amp or less at this distance? Need more than that for such a long distance, for sure.

I think you need to use the full capacity when calculating wires, but at the end box you should only assume 80% is there.

But again, I'm just a simple farmer, get better advice than mine.

--->Paul

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#4
03/18/08, 01:35 AM
 Join Date: Jan 2005 Location: SE Idaho Posts: 507

Can you say BIG.

Use the 200 amps. Nothing stops you from using all 200 amps from the service.

80% is for single branch circuit loads. Some NEC calculations use a 125% margin and these, if worked backwards, will yield 80% (125 times .8= 100)

But for this you should worry about voltage drop at 200 amps.

600 kcmil would be about a 3% drop worst case and is oversized (all current on one side of the line) With 200 amps on each side of the line a 300 kcmil would have about a 3% drop.

4/0 would have a 5.2v drop (on a 125v side) but still be within the 5% total allowed for feeder and branch. How long is the 240 line on the other side of your meter? If it's long you should be more conservative on the wire size.

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#5
03/18/08, 09:18 AM
 Udderly Happy! Join Date: Jan 2006 Location: Oklahoma Posts: 2,752

I agree with idahodave. While I'm not on the engineering side of things, I'm a lineman at an electrical coop and usually see at least 350kcmil and have seen it parralleled for a similiar service (depending on the distance on the load side of the service panel).

While code is prescribed for "worst case" scenario, it's prescribed for a reason. I've shown up at a lot of folks houses and heard complaints of burned up appliances only to figure out that their service wire is too small on load side of the panel. I know that the wire is pricy, but I'd reccomend going with whatever the code book specifies.

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#6
03/18/08, 09:29 AM
 Join Date: Dec 2003 Location: White Mountains, Arizona Posts: 2,306

I also agree with idahodave. My power company determined the minimum wire size for my 250' run. Even then my lights dimmed when the central air conditioner (5 ton unit) came on and I had a power surge limiter installed. Now everything works fine.

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#7
03/18/08, 03:29 PM
 Join Date: Jun 2004 Location: OK Posts: 192

Ok thanks for the replies folks. Basically I need to go with 350 aluminum or equivalent. Next question... I have a 1000' of 3 conductor #2 copper. Could I take all 3 conductors and run them in parallel for each hot leg and get by that way? That is to say 3 runs of #2 copper to one hot, 3 runs to the other hot, and 3 to the neutral?

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#8
03/18/08, 05:50 PM
 Join Date: Jan 2004 Location: MN Posts: 6,668

I think your electrical inspector would have a heart attack.......

Aside from that, it looks like, on the voltage drop calculator, a #2 wire will carry 40 amps 260 feet.

So...... doing it that way, you would end up with 120 amp max, not the 200 amps you want? If my math is right?

--->Paul

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#9
03/18/08, 05:58 PM
 Registered Users Join Date: Mar 2008 Location: North Central Arkansas Posts: 16

The National Electrical Code does not allow paralleling of conductors smaller than 1/0.
Jugum

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#10
03/18/08, 06:00 PM
 Join Date: Jan 2005 Location: SE Idaho Posts: 507

NEC says parallel wires can be used for 1/0 and bigger, so not according to NEC....also three #3 AWG will have a resistance slightly greater than 4/0 aluminum and would drop 4.3v on the 125v side at 200 amps.

Edit...oops read #3 too many times. 3 runs of #2AWG would be about 3.2 volts drop on the 125 v side

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Last edited by idahodave; 03/18/08 at 06:07 PM. Reason: did #3 gauge wire not #2
#11
03/18/08, 11:28 PM
 Join Date: Jun 2004 Location: OK Posts: 192

Thanks again guys, Im gonna pick yer brains one more time here...

There is no code to speak of in my area but I have always built everything to code or better. I understand that there is a good reason for every rule in the NEC(usually something to do with keeping you from getting shocked or burned to death) That being said, in my non-electrician mind I can't realy understand why this would be a hazard. Even considering the slight increase in ohms I still come up with about a 3% voltage drop which I think is within code.

What I came up with was, for a copper wire to carry 240V @ 200A over 270' I would need a diameter of 193500 mil. #2 has a diameter of 6636mil and 3 of 'em is 199080mil which gives me the right diameter and a total voltage drop of 3%....

Guess my last question is just one of curiousity. Why are parallel conductors less than 1/0 not allowed by the NEC. What exactly is the safety/reliabilty issue here? Thanks!

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#12
03/19/08, 12:09 AM
 Join Date: Feb 2008 Posts: 4,231

Just what will this service cable be running to?

To calculate service drop you will have to know the load amps of your house or what ever it is your running the 200 amp service too. Just because you have a 100, 150,175,200, 400 amp service doesn't mean that's how much your load is. So this is kind of tricky.

When a electrical contractor wires your house they are suppose to do a load calculation of your home to determine the size of service for your home. If the load calculation comes up to 179 amps and you have a 200 amp service, then the 179 amps is what you would use in you voltage drop calculation.

Voltage drop calculation would be [(2 X Resistance of one circular mil foot of conductor) X Lenth of Wire X amps(load)] divided by Circular mil of conductor used.
2 X Resistance X Lenth X load amps divided by cm of wire.

Assuming you want to run this 200 amp service to a new house your building is there anyway you could get the electrical company to place the meter pole closer. Most generally a 4/0 URD cable is run from the meter pole to the 200 amp panel box. But if your house has a small calculating load you may not need to worry about voltage drop even at 260 feet. A lot of houses have a overkill on the service amps. They may be hooked up to a 200 amp service and their demand load may only be 90 amps. However this gives them room to build work shops and such and have enough service amps to carry the extra load.

Do you know what the load amps will be of whatever your are needing the 200 service to?

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#13
03/19/08, 12:14 AM
 Join Date: Jan 2005 Location: SE Idaho Posts: 507

I can only guess...

Helps with standardized construction for electricians and others that do maintenance and modifications.

Lessens the chance of an overload should one conductor fail, break or have a poor connection.

It's cheaper to run one wire rather than two.

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#14
03/19/08, 12:22 AM
 Join Date: Jan 2004 Location: MN Posts: 6,668

I don't understand why a person would want to run multiple wires - one fat one has much less problems.

In a really big wire, can be difficult to bend & run so multiple smaller is more manuverable.

Otherwise, on small wires, it is so easy to get one cut or broken & not realize it - other 2 are carrying full load & can't.

One fat wire should be cheaper than running 3 thin ones.

You seem to want to make this harder than it will be?

--->Paul

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#15
03/19/08, 02:36 AM
 Born city, love country Join Date: Mar 2006 Location: Houston, Texas Posts: 219
Quote:
 Originally Posted by SouthernThunder What I came up with was, for a copper wire to carry 240V @ 200A over 270' I would need a diameter of 193500 mil. #2 has a diameter of 6636mil and 3 of 'em is 199080mil which gives me the right diameter and a total voltage drop of 3%....
I had the same problems with a 400' run at 200A and found out that it would cost me about \$16,000 to install under ground. I am changing my mind on the building site since I was hoping to build my 40'x60' shop for less than \$25,000.

Your math above seems good but unless I am totaly off base, I think it is flawed in that wire is provided to you in measurements of diameter but it is the total wire volume that is able to carry the load. If my failing memory serves me correctly, the area of a circle is Pi times the radius squared. So to compare, you would have to calculate the area of the three wires and add them together and compare this to the area of a single larger wire.

Based on your numbers you provided, three of your smaller wires would have an area of 3.1416 times half the diameter squared times three wires would be 103758791 square mils and the larger single wire would be 29407143150 square mils which is 283 times more surface area of the single larger wire compared to three smaller ones. I am certainly no electrician but the math seems correct.
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#16
03/19/08, 10:13 PM
 Join Date: Jan 2004 Location: MN Posts: 6,668
Quote:
 Originally Posted by chuckhole I had the same problems with a 400' run at 200A and found out that it would cost me about \$16,000 to install under ground.
Really? I had my farm site rewired 2.5 years ago, 200 amp service, all underground, 11 buildings to hook up with 60 amps to each building; 200 amp runs to all but the last building in the line, 3 runs of 80 feet, 300 feet, & 360 feet. New panel in the house. All for \$11,000. Was underground aluminumn wire. I beleive a lot was the 350 size, or at best one size less.

Don't think aluminum went up that much?

--->Paul
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#17
03/19/08, 10:48 PM
 Master Of My Domain Join Date: Sep 2005 Location: Pennsylvania Posts: 7,209

isn't most current conducted by the outer portion of a conductor and resistence related to the inner portion...or core? so perhaps one should calculate the surface area of 3 vs. 1 conductor and see what that reveals. i am just curious.

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#18
03/20/08, 11:22 AM
 Join Date: Jan 2005 Location: SE Idaho Posts: 507

Skin current is a concern at radio frequencies (RF) not 60Hz power line. If the load had a high power factor, the impedance (Z) of the feeder would be considered (caused by the inductance of the wire) but it is usually so low as not to be a factor.

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#19
03/20/08, 01:42 PM
 Master Of My Domain Join Date: Sep 2005 Location: Pennsylvania Posts: 7,209

thanks!

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#20
03/20/08, 04:25 PM
 Join Date: Sep 2006 Location: NE Kansas Posts: 499

I'm no electician by any means but I have pulled enough wires to see that pulling nine wires through your conduit could be a real p.i.t.a. Lets say you have one of the conductors short to gound, your going to be redioing it anyway, so why not just use the correct size wire and use smaller conduit? my2 cents

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#21
03/20/08, 09:38 PM
 Join Date: Oct 2003 Location: Carthage, Texas Posts: 11,977

Are you pulling off of an already used meter box? One that's already supplying a house or barn or whatnot? Do you have a 'co-op' or a corporate type electric company? Or is it a standalone meter box?

I'd call my electric provider and ask if they couldn't extend the wires right to where you need it. I know mine would add another meter right where I need it, within a quarter mile, for free. My big barn is 300' from my current home. I've already asked if they'd drop a line to the barn, and they said it'd be free. I'd have to pay from the meter box to the barn... the 7.50\$/month fee would be a heckuva lot cheaper than stringing three wires underground. I bought 120' of 8-3 for a job two years ago... it's double that now, in cost. Buying 000 or 0000 wire would probably cost near a grand... plus a days labor getting the hole trenched, and putting that much wire in conduit is NOT FUN... BTDT.

All the electric company can say is NO! If they say yes and extend the wires (our co-op will even go underground nowadays... saves them very expensive poles, and yearly maintenance clearing r.o.w.'s) you'll be golden!

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#22
03/21/08, 03:01 AM
 Join Date: Nov 2004 Posts: 3,510

Yeah my Co-op does that sort of thing for free. Like texican's mine likes to run everything underground now too. When I put in service they ran it underground and said they much preferred to do it that way even though it is a little more work at the time. Less problems and maintenance from trees, ice storms, winds, lightning etc.

I'd give my electric company a call and see if they won't put the power right where you need it.

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#23
03/21/08, 04:10 AM
 Join Date: Aug 2006 Location: South central Virgina Posts: 2,137
Quote:
 Originally Posted by SouthernThunder I am needing to run wire from a meter pole 260' to the service panel. It is a 200 amp service. This is going to be burried most likely in conduit and none of it will be indoors and will probably be THHN aluminum. I am not sure what size wire to use. I was told that according to electrical code, a 200 amp service can't be loaded beyond 80%. My question is, when calculating wire size do I use 160 amps (80%) or 200 amps? Or what wire size should I use?
You need to check with your service provider. In Va. I had to mount the breaker box, (of course), and they gave me the meter box to mount.
We have to have the ditch dug 36" minumum, and have a 2 1/2" plactic conduit come from the meter to I think it was 12" below grade (I am not 100% sure of that, it's been a while and after falling I can't some things are foggy) into the ditch.
I had to run 4/0 cable from the breaker box, (also in conduit) to the meter box. And the meter box has got to be eye level.

After that they were responsible to run the line from the pole to the meter box and make that hook up. They brought their own wire and as I said provided the meter can also but you have to go pick it up.

Check with the provider and you will probably find you don't have to pay for the wire at all, itcept from meter to breaker box.
Dennis
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#24
03/21/08, 09:19 AM
 Join Date: Dec 2005 Posts: 97

Around here neither the big electric provider nor the electric coop do anything for free.....I needed service extend 2000 feet to my building site and their cost was 3x what I ran the line myself for. Of course I had to run a much bigger line because they wouldn't give me high voltage out of the transformer, just 240. It was still a lot cheaper to do it myself....I may regret it in the long run but rolled the dice....

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#25
03/21/08, 09:24 AM
 Join Date: Jun 2004 Location: OK Posts: 192

Thanks for the replies again folks.

First of all, yes, I could do this a lot cheaper if I let the power company set a few poles on my property BUT I am not because I do not want to give them an easment on my property. (If you gotta ask why, then you probably wouldn't understand)

Second, I think some of you might not have caught that I was going to use 3conductor #2. This is 3 wires bundled together in XHHW so its not like I would be pulling any more wires than if I was pulling individual strands for each lug.

Also this is direct burial so as there realy aint a whole lot of pulling going on anyway.

The reason I want to be difficult and do this the hard way is because I already have a 1000' spool of 3/2. This saves me a considerable amount of money (roughly \$2500) and still keep my property free of utility easments.

It would seem that my only concern is that if one conductor fails then I would overload the other two.

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#26
03/21/08, 12:01 PM
 Join Date: Oct 2003 Location: Carthage, Texas Posts: 11,977
Quote:
 Originally Posted by SouthernThunder First of all, yes, I could do this a lot cheaper if I let the power company set a few poles on my property BUT I am not because I do not want to give them an easment on my property. (If you gotta ask why, then you probably wouldn't understand)
I'm pretty open minded about easements, there positives and negatives... I went 13 years without grid electricity, because of easement problems. It would've taken ~100K for electric wires to be strung to my home. Plus, paying three other landowners for easements across their properties. None of them would agree to put up a shack or barn on their places, to lessen, or negate the need for paying the electric company (to string wires...). They give you around 2k feet free... so if there was a barn every 2k feet, my electrics would've been basically free. So, I couldn't/didn't get on the grid.

When the grid did get down close to my place, a major concern for me was was the evil relatives who own land next door going to be able to hook up to the grid, and put their trailer trash outlaw vermin children next to me. Luckily, for me, the vermin vandalized a multimillion dollar dam, the owner caught them, and was cursed on his own property.... Needless to say, said owner want's nothing to do with them. So, I had to promise (and sign a waiver) that I'd not let the vermin hook up to my electric line. I talked with the co-op's engineer, and we mapped out an easement that would disallow any connections off of the lines. I lost maybe twenty or thirty old post oak trees. The lines cross near my orchard, and though my buck pasture... so there's nothing the line hurts.

Are you worried about line crews coming in to check wires? Other people connecting to your lines?

The line crews know I have an orchard... when they visit, they come to the house and ask if they can cut down overhanging trees... they only cut dead trees, or have permission to cut the leaning ones. There's no possibility of anyone connecting to my lines.

You may have been bitten by an easement in the past... who hasn't? But there are good and bad easements... If I "want" a service, and an easement is required, and there's no way it can hurt me, I give it. If I was afeared of the electric company, I wouldn't have a meter box on my place...(assume they have an easement, up to the point of the meter pole) I'd go solar, wind, or hydro.
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#27
03/21/08, 01:13 PM
 Join Date: Aug 2006 Location: South central Virgina Posts: 2,137
Quote:
 Originally Posted by SouthernThunder I am needing to run wire from a meter pole 260' to the service panel. It is a 200 amp service. This is going to be burried most likely in conduit and none of it will be indoors and will probably be THHN aluminum. I am not sure what size wire to use. I was told that according to electrical code, a 200 amp service can't be loaded beyond 80%. My question is, when calculating wire size do I use 160 amps (80%) or 200 amps? Or what wire size should I use?
I am confused now. I missed the "meter" part of the "meter pole".
Here with no more that 260 feet to run, hey do as I said in the earlier post. The transformers they use have several sets of lugs to hook up to and the engineers figure out the distance and they hook the wires to the correct set so when it get to the meter box there is a full 120 volts there per leg. They correct for any line loss at the transformer.
If it is underground they have no easement for it. Only if they need to set poles.

Now if you had to run several thousand feet the last I heard around here was about \$750 per pole but that was several years ago so I don't know what it is now.

The electrical codes are a national thing but individual localities make up their own riles about setting the post and burying the cables, what they charge etc.

And I thought \$750 per pole was a rip off, LOL. Live and learn. Maybe Virginia isn't as bad a buch as I thought they were.
Dennis
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