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Service entrance cable sizing

Old 07-09-2013, 08:48 AM
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Default Service entrance cable sizing

Putting in a 200 amp service. Cannot find my NEC book for sizing. Internet research says 2/0 in copper for residential and 4/0 for aluminum. I just want to confirm with an electrician on the board. 30 feet from panel to weather head
Old 07-09-2013, 09:34 AM
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It's an interesting subject. Although there will be guidelines in NEC, I had a friend who upgraded from 100 to 200 Amp Service. He didn't change the service entrance conductors. Apparently didn't need to. Since the conductors are in free air, any extra warmth generated by the increased current flow was well within the specs for what conductors were already in place. In your case, since you are going with new construction I'd def make it more rather than less.
Old 07-09-2013, 10:09 AM
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Table 310.15(B)(7) requires minimum 2/0 copper or 4/0 aluminum for a 200A residential service. If it was a commercial application, you would need to use 3/0.
Old 07-09-2013, 10:14 AM
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Originally Posted by aln View Post
It's an interesting subject. Although there will be guidelines in NEC, I had a friend who upgraded from 100 to 200 Amp Service. He didn't change the service entrance conductors. Apparently didn't need to. Since the conductors are in free air, any extra warmth generated by the increased current flow was well within the specs for what conductors were already in place. In your case, since you are going with new construction I'd def make it more rather than less.
Going from 100A to 200A is a big jump. At the end of the run, the wires need to enter a conduit at the end of a weatherhead before entering the meter can. NEC 310.17 has alternate ratings for conductors in free air, but for a 200A service you need 1/0 copper (assuming 75C insulation). Under the residential rules, they could have used #4 copper for a 100A service. Not sure where he got that advice.
Old 07-09-2013, 10:33 AM
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Whatever size is required by code in your area you should ckeck to see if your neutral needs to be the same size as your hot feeds (going with the smaller size will save you money).....your ground should be a smaller size than your hot feeds as well.
Old 07-09-2013, 10:38 AM
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Thanks for the confirmation

I believe I need the same size neutral and know that the ground is sized smaller but will confirm with the building inspector.
Old 07-09-2013, 10:43 AM
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Originally Posted by Garett View Post
Whatever size is required by code in your area you should ckeck to see if your neutral needs to be the same size as your hot feeds (going with the smaller size will save you money).....your ground should be a smaller size than your hot feeds as well.
Call the building department and ask if they allow reduction of neutral below current carrying conductor size - some don't allow it. There are no tables or rules, you need to calculate the unbalanced neutral loads first.

On the ground size, if the service entrance conductors are 2/0 or 3/0, you need to use a #4 or larger (Table 250.66).
Old 07-09-2013, 10:46 AM
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seems like extra warmth is costing you money on the electric bill?
Old 07-09-2013, 10:46 AM
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Originally Posted by louiefl View Post
Call the building department and ask if they allow reduction of neutral below current carrying conductor size - some don't allow it. There are no tables or rules, you need to calculate the unbalanced neutral loads first.

On the ground size, if the service entrance conductors are 2/0 or 3/0, you need to use a #4 or larger (Table 250.66).
True & true.
Old 07-09-2013, 11:34 AM
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Originally Posted by louiefl View Post
Going from 100A to 200A is a big jump. At the end of the run, the wires need to enter a conduit at the end of a weatherhead before entering the meter can. NEC 310.17 has alternate ratings for conductors in free air, but for a 200A service you need 1/0 copper (assuming 75C insulation). Under the residential rules, they could have used #4 copper for a 100A service. Not sure where he got that advice.
In his circumstance he just needed room for a few more breakers so he put in a 200A panel mostly for the real estate. Practically everything in his house going full tilt would not come close to 200A nor do most residential applications. I think he made up the part about not needing bigger service conductors to tell you the truth but amateur electricians are a touchy lot, so I don't press him on it. He also put a 2 pole fused disconnect on the line with 200A fuses which you don't see much on residential applications either. Maybe this was his way of feeling better about not upgrading the conductors. Again, although this is a waste of money and does nothing to protect the service conductors, I don't press him on this either.
Old 07-09-2013, 12:00 PM
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Originally Posted by aln View Post
In his circumstance he just needed room for a few more breakers so he put in a 200A panel mostly for the real estate. Practically everything in his house going full tilt would not come close to 200A nor do most residential applications. I think he made up the part about not needing bigger service conductors to tell you the truth but amateur electricians are a touchy lot, so I don't press him on it. He also put a 2 pole fused disconnect on the line with 200A fuses which you don't see much on residential applications either. Maybe this was his way of feeling better about not upgrading the conductors. Again, although this is a waste of money and does nothing to protect the service conductors, I don't press him on this either.
Wow...

Obviously he did not realize that redundant means of over current protection will not help much with undersized conductors.
Old 07-09-2013, 12:42 PM
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The breaker should be the weakest link in any circuit. You can put in a meter can rated for 200A, a panelboard rated for 200A, but if the wire is not rated for 200A, your breaker should not be 200A. If it was my home (and didn't want to replace the wire), I would check the wire size and then replace the fused disconnect with one appropriately sized. The panel should be clearly marked so that the next owner of the house doesn't assume he has 200A service. Kind of half assed, but safer.

From Single Phase Dwelling Service Table (assuming copper): #4 = 100A, #2 = 125A, #1 = 150A. If he has #4 copper, then he should replace the 200A fused disconnect with a 100A device. If this keeps tripping, it is a sign that he is drawing more than 100A.
Old 07-09-2013, 03:24 PM
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Upgraded my 100 amp service to 200 amps a few years ago. Conductors 000, neutral 000, #4 ground, 10' long 3/4" with proper clamp ground rod. Sizing was spelled out in pamphlet from the power company.

The ground rod requirements might be different in other locals.
Old 07-09-2013, 03:52 PM
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Originally Posted by edwardh1 View Post
seems like extra warmth is costing you money on the electric bill?
Not when it is upstream of the meter.

When you get all your stuff up to snuff for 200 amp service, hopefully the power company will actually hook you up to 200A service.

Some power companies will only provide what they think you will need, not what you want.
I know this via personal experience.
Old 07-10-2013, 05:26 PM
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C'mon, has anyone really tripped a 200 amp main breaker?
Old 07-10-2013, 05:38 PM
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Originally Posted by billinstuart View Post
C'mon, has anyone really tripped a 200 amp main breaker?

Yes, I see it a few times a year at work.
I'm the Lineman Sup. where I work.
Old 07-10-2013, 10:45 PM
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The real fear is not a connected load of more than 200A tripping the breaker, it is protection from a short that could get those big conductors hot in a hurry.

I have 125 A service in my mostly gas home and can't pull any more than 3000W, if I tried. That's around 12.5 A, or one tenth the main breaker size. For 200A service mainly you want the bigger panel for more branch circuits that you run out of in a smaller panel.
Old 07-11-2013, 02:45 AM
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Originally Posted by billinstuart View Post
C'mon, has anyone really tripped a 200 amp main breaker?
I've seen a 1,200A main tripped to a 277/480V distribution center for a grocery store.
Old 07-11-2013, 03:49 AM
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I have to laugh at all of you who think you know what your talking about, do not comment on electrical work if you dont have the proper knowledge, hire an electrician. Heat....Free air.... what the hell are you talking about? Are we wiring primaries on a 13.8kv transformer? hugha.... Good luck to the guys who "do it yourself" ......burn baby burn.....
Old 07-11-2013, 03:54 AM
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480/277 is gfi protected thats why the main tripped dude.

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