Size of service entrance conductor for residential building.
- Thread starter dala
- Start date
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- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
It would help to know the calculated load, not just the service size.
kwired
Electron manager
- Location
- NE Nebraska
And/or number and setting of overcurrent protective devices.
Two one hundred amp mains could be called a 200 amp service. But if total load calculation is only 80 amps - you still really only need an 80 amp conductor. Except if it is a one family dwelling then between 230.42(B) and 230.79(C) you will still need at least a 100 amp conductor even if the total load were only 10 amps.
Shouldn't one assume the maximum load be 200 amps being that the only thing/protection device between the point of utility service attachment and the customer owned distribution panel is a 200 amp breaker? If conductor ampacity is being sized based on the current load there won't be room for expansion. Currently there is a 200 amp main breaker in the breaker panel.
- Occupation
- Licensed Electrician
No. A load calc should be done. After that I would do the code minimum without hesitation or remorse. NEC load calcs are grossly oversized.
- Occupation
- Licensed Electrician
Then I would use 2/0/CU or 4/0 AL and be done unless there is some extra, above average stuff going on in the house.
electricalist
Senior Member
- Location
- dallas tx
I think the answer your going to get is if there's no actual load calculations for the ser the you can put as much money in the ground as you want that's over 100 amps but for the install to work and be for the price required there needs to be a load calculation then it's requirements.
Others who know literally will explain I'm sure.
Others who know literally will explain I'm sure.
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
I would use 2/0 or 3/0 copper depending on the load but do you really want to use copper? I would run conduit and use aluminum and smile. The load is the big issue. If you expect a 200 amp load on the house then a 300 kcm aluminum is necessary and a 3/0 copper would work. If the load is 150 amps or less you could get by with 4/0 aluminum.
Most homes don't come anywhere near 150 amp load so I think 2/0 copper or 4/0 aluminum is fine
The house is a residential home but it's on a large piece of property. There are other buildings (2 barns, and a camper) that need to be fed from the main panel and there are some large pieces of equipment that get used for some farming. I like copper because it's stronger and more reliable and i never use aluminum. I always hear the utility linemen complain when they come across aluminum service feeds but then again, i live on an island surrounded by salt water - highly corrosive. The homeowner wants the highest quality product and knows copper is expensive. He's also going to dig the trench and bury the wire. My job will be to make the connections. I think i'm going to go with 3/0 copper unless anyone can convince me it's way overkill!
- Occupation
- Licensed Electrician
3/0 CU is fine but I would use conduit.
electricalist
Senior Member
- Location
- dallas tx
That's interesting to know about all vs cu . I used to look at the poco wires and ours and think we have got to be creating a self inflicted copper demand.
It just didn't make sense the poco can figure out how to power Disney land with al but my house is a death trap because it's wired in al.
Look at me now.....GO AL
kwired
Electron manager
- Location
- NE Nebraska
If there is only one single service disconnect/overcurrent device then you must supply it with a 200 amp conductor,otherwise like I was mentioning before if you have multiple service disconnecting means a common supply conductor to them only needs sized for the total load calculation, which is why I said you could have a 80 amp conductor for an 80 amp load even though you have 2-100 amp mains. That one is kind of rare, but say you have a three family dwelling with three 100 amp mains. You need a 100 amp conductor from each meter to each main but the common feed to all three meters could possibly only be 125 amp conductor if that is all the load calc for all three dwellings is.
Also keep in mind that 310.15(B)(7) allows you to reduce the conductor to 83% (this in 2014 NEC) of the overcurrent device for a conductor that is the service or feeder to a single dwelling unit. Since you are feeding more then just a dwelling unit with this conductor though it may be questionable if you can use (B)(7).
If you are concerned of voltage drop because of a long run - that is a different issue, NEC only requires a minimum 200 amp conductor to a 200 amp service disconnect but you could have much larger then that if combination of load/length causes an undesirable voltage drop.
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