Service Conductor Size

["Jacob Robinson"]

I don't know a lot about service wiring (I've put in some ceiling fans and recepticals, but that's about it) and I was wanting to get a rough estimate on how much it will cost me for the wire to my pole barn.

I am putting in a new 200amp service and running it about 175' (from road to meter)

The local Power Co. said If I bury it I will have to purchase the cable, but if I can run it over-head they will buy it and put it in.

Basically what I am asking is what size wire will I need, So I can call a supply house and get a rough Idea on how much it is gonna cost for the cable.

[Chris Friesen]

You should talk to the utility and see what they require/recommend. You'll likely need to pull a permit anyways, and that normally gives you access to ask questions of the inspector.

[David G Baker]

The length of your run could change the size, when I put in my 200 amp service I used 00 size copper. My run was only about 20 feet from the weather head to the main box. The price of the wire fluctuates from day to day. It is a bit cheaper now than it was a year ago when I did some kitchen remodel work. If you are going underground, I don't know the price of the wire. You can save a bunch if you go aluminum but it will increase the size wire by a size or two.
Suggestion, if you have a meter put in at your pole barn you will have to pay an extra monthly fee but if you can up grade your house main panel and run from your house to your pole barn you will save quite a bit of $ over time.
A supply house will give you the wire size you need determined on the information you give them.

[Von Bickley]

Jacob,

Around here, the local inspectors recognize 2 AWG copper or 4 AWG aluminum for a 200 amp service.

[Tom Veatch]

Jacob,

Around here, the local inspectors recognize 2 AWG copper or 4 AWG aluminum for a 200 amp service.

Don't you mean 2/0 and 4/0?

2 AWG Copper USE is only good for about 115 amps and 4 AWG Aluminum USE is only good for about 65 amps.

The OP should be OK with distance/voltage drop for those sizes (2/0 copper or 4/0 aluminum) as they result in about 2.8-2.9% voltage drop over 175 feet with single phase 240v/200 amps.

[Daniel Thompson]

For the shop I'm having built here in Colorado, I have a 450 foot run from the utility box out by the road to my building. I have 200A service for the shop. I would have to look at the left over cable to get the exact designation but it is aluminum for direct burial. Each of the 3 conductors is multistrand and about 1 inch in diameter. It was about $7 a foot. Thankfully, code didn't require copper. I would hate to imagine what it would have cost.

[Von Bickley]

Don't you mean 2/0 and 4/0?

2 AWG Copper USE is only good for about 115 amps and 4 AWG Aluminum USE is only good for about 65 amps.

The OP should be OK with distance/voltage drop for those sizes (2/0 copper or 4/0 aluminum) as they result in about 2.8-2.9% voltage drop over 175 feet with single phase 240v/200 amps.

Around here, the big stuff is 2 AWG copper & 4 AWG aluminum.

The smaller stuff is #2, #4, #6 & #8......

[Chuck Thoits]

In these parts the power company, building inspector, and the supply house will all tell you the same thing. Ask your electrician.I have three subs two 200 amp and one 100 amp all running off 2awg copper and all right around 175 feet. The 60 amp one is around 70 feet and I think is on a 10 maybe an 8 wire.

[Tom Veatch]

Around here, the big stuff is 2 AWG copper & 4 AWG aluminum.

The smaller stuff is #2, #4, #6 & #8......

Must be a regional thing. I know if I walked into a supply house around here and asked for 4 AWG aluminum wire, what I'd get would be totally unacceptable for 200 amp service entrance.

Check out this (or similar) table. The numbers in the column "AWG or KCMIL" below "4/0" are wire sizes in KCMIL (thousand circular mils). Those above "1/0" are wire sizes in AWG. The "1/0" through "4/0" is a code for AWG sizes would be otherwise be "0" through "-3". Those are the wire size designations that I thought, up until now, were standard and universal - at least in those areas that use the NEC.

[Tom Veatch]

...I have a 450 foot run from the utility box out by the road to my building. I have 200A service for the shop. ... Each of the 3 conductors is multistrand and about 1 inch in diameter. ...

Almost certainly sized for voltage drop instead of ampacity.

If you're correct on the wire diameter it's probably 1000 kcmil (1,000,000 circular mils) stranded aluminum cable in which each conductor is a little over 1" diameter, has a little less than 2% voltage drop for 240v/200a over 450 feet, an ampacity of 445 amps in cable or direct burial or 750 amps for single conductors in free air, and is far larger than necessary if only ampacity is considered.

[Ken Massingale]

Don't you mean 2/0 and 4/0?

2 AWG Copper USE is only good for about 115 amps and 4 AWG Aluminum USE is only good for about 65 amps.

The OP should be OK with distance/voltage drop for those sizes (2/0 copper or 4/0 aluminum) as they result in about 2.8-2.9% voltage drop over 175 feet with single phase 240v/200 amps.

Yep, I 'think' so. I've just completed a new shop with 200 amp service. The power company and county said 4/0 Al. With copper prices what they are I didn't even check on the size or price.

[Chris Padilla]

Around here, the big stuff is 2 AWG copper & 4 AWG aluminum.

The smaller stuff is #2, #4, #6 & #8......

Von,

I think there must be some confusion.

AWG is American Wire Gauge and is a logrithimic based-scale which is why larger numbers mean smaller wires. Sometimes instead of AWG, we say "gauge" : 6 gauge, 12 gauge, or #6, #12, etc.

When they got to 0 AWG and wanted to go larger, they ran out of numbers and so started using mulitple zeroes to represent larger and larger wires.

Those are often referred to as "ought", "double ought", "triple ought", and so on or sometimes as "2 ought" or "3 ought" or 2/0, 3/0, 4/0....

Ought is pronounced like "awt" and in mathematics, simply is another word for zero.

I think you are confusing "awg" and "ought".... Easy mistake and as we all get older, our hearing isn't what it used to be!

[Roger Frazee]

If I may shed a tad bit of light on this subject....

Utilities use totally different rules for conductor sizing.....when they are overhead and in 'free air'. These companies follow the NESC sizing rules in these situations not the NEC as homeowners and residential electricians, contractors etc... Which include over head services to the service mast of the dwelling or detached structure. In general conductors installed by the utilities in overhead 'free air' applications will be much smaller than the service entrance conductors covered under the NEC. As a bit of information most overheads are three wire 'messenger' cables to dwellings and that wire that is bare and looks like 'wire rope' is your neutral.

From the mast to the meter and to the service disconnect are sized to NEC requirements using table 310.15(B)(6). Any service entrance conductor or feeder conductor that carries the entire load of the house uses this table. All other applications use table 310.16 of the NEC....for just about everything load side of any distribution panel containing branch circuit breakers.
So those who are wondering the service equipment is the first means of disconnect (OCPD) that the service entrance lands on. So if the service entrance conductors land on a single disconnect before going on to a distribution panel in the house that disconnect is the service equipment and the panel in the house will be main lug and considered a sub panel fed by 4 wires (4th is the equipment ground) from the remote service rated disconnect. This is so neutral and ground can be separated at the mlo panel. If the dwelling panel is a main breaker panel then it is the first means of disconnect for the dwelling and is considered the service equipment assuming there is no service disconnect ahead of it. A main breaker panel will be fed 3 wires since the dwelling disconnect is located in the panel and neutral and ground will be bonded there. The neutral and ground are bonded at the 'service equipment' only.... so you see the importance of understanding what is the service equipment.
This is important because all conductors in either situation will be sized to 310.15(B)(6) until they land at the distribution panel not necessarily the service disconnect. After that there won't be any conductors that carry the entire dwelling/building load and you will use the 310.16 table.

In the case of conductors in conduit buried as a 'service' lateral to the dwelling. These conductors are not 'free air' and are subject to much more heat loss restraints. In most cases to single family dwellings these conductors will be required to be sized to NEC table 310.15(B)(6) whether the responsibilty of the home owner or utility... which requires 2/0 copper or 4/0 aluminum for 200 amps... and of course will be up-sized from that if voltage drop due to long distances enters the equation. In most cases underground service laterals to dwellings fall under NEC rules whether conductors in conduit or direct burial.. Inside city limits in most sub-division developments underground service laterals are pretty much always required to be in conduit....no direct burial. The utility will direct bury within their easements as they run the distribution conductors to the pad mounts (transformers) but the lateral (transformer to home) will be in conduit.

So to summarize once conductors enter a conduit to a dwelling that is the 'service' lateral NEC rules apply. Any overhead service conductors once they reach the "point of attachment" at the mast fall under NESC utility rules. From there on they are service entrance conductors and fall under NEC rules.
Sizing of service and service entrance conductors is applicable to whose responsibilty they fall under NESC or NEC rules.

In rural areas service laterals are allowed direct burial in many cases but these are almost always the responsibility of the homeowner and would also require sizing from NEC tables.

And as usual with electrical installations there are always exceptions.....



Hope this helps.

[Roger Frazee]

Von said

Around here, the local inspectors recognize 2 AWG copper or 4 AWG aluminum for a 200 amp service.

With respect this just isn't true, local inspectors follow NEC table 310.15(B)(6) for dwelling services. I believe as Chris pointed out that you mean 2/0 and 4/0.


#2 awg copper is good for 125 amps for service entrance

#4 aluminum is not allowed for 100 amp or above services it is only allowed to serve as a 55 or 65 amp conductor depending on whether it is cable or a individual wire in conduit.

[Von Bickley]

I will try this again. If I go to an electrical supply house around here and I ask for 4/0 aluminum, I will pronounce it 4 AWG. If I want 2/0 copper, I will pronounce it 2 AWG copper.

This is the way we have always pronounced it and I was a certified electrician for over 30 years......