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#98200 - 05/12/06 10:03 AM Service Conductors
shortcircuit Offline
Member
Registered: 06/27/04
Posts: 608
Loc: massachusetts
Hi guys...I'm in a debate about the size of a service lateral and the main disconnects that feed a single family dwelling.

This is how I see it...
Calculated load: 260 amps
Service lateral conductors: 2-500MCM AL and 1-350MCM AL in a 3" pvc conduit from pole to 320 amp residential meter socket.(table 310.15(B)(6) allows 500MCM at 350amps)

Then from the 320 meter I'll run 2-2" PVC conduits with 2-4/0 AL and 1-2/0 AL in each to 2-200amp main breaker panels ajacent to each other in the dwelling basement.

The other side says:
Since 500 MCM AL is only rated for 350 amps then I can NOT use 2-200amp main breaker panels...because that would require 400 amp rated service lateral conductors.

They say the panels can only be rated at 150amp each.

I said the service lateral conductors need only be rated for the load to be served.

I said I could put 6-100amp main panels in the house if I wanted and it would be code compliant.

Any comments??

thanx,

shortcircuit
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#98201 - 05/12/06 11:16 AM Re: Service Conductors
George Little Offline
Member
Registered: 01/18/04
Posts: 1488
Loc: Michigan USA
You'd be right and you could look at 230.90(A)Ex.3 as a code reference ('02 NEC)
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George Little
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#98202 - 05/12/06 11:36 AM Re: Service Conductors
Roger Offline
Member
Registered: 05/18/02
Posts: 1716
Loc: N.C.
Shortcircuit, I agree with George that you are right.

Using the "other sides" logic would mean that once you install (1) 50 amp breaker say for a range and (3) 30 amp breakers, say for water heater, dryer, and well pump, you would only be allowed to install (3) 20 amp breakers in a 200 amp panel before you'd need to up size the feeder or service.

This would mean that the required branch circuits for the Small Appliances, Bathroom, Laundry, AFC"s for Bedrooms and General lighting loads would put most 100,125,150, and 200 amp services out of any installation.

Roger
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#98203 - 05/12/06 02:25 PM Re: Service Conductors
shortcircuit Offline
Member
Registered: 06/27/04
Posts: 608
Loc: massachusetts
Thanx George and Roger...

OK, here is another question:

Am I allowed to use 4/0 AL (XHHW/USE) to each of the 2 200amp mains according to 310.15(B)(6)?

Seems to be a gray area disputed often. But in reality, with the load diversity of dwellings, I don't think it would ever be a problem...

But also, XHHW AL is good for 180amps and the next size up breaker is 200amp...right?

shortcircuit
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#98204 - 05/12/06 03:11 PM Re: Service Conductors
George Little Offline
Member
Registered: 01/18/04
Posts: 1488
Loc: Michigan USA
ShortCircuit- You're right again. IMHO I have heard arguements that would have you going to 250 kcmil Since we are talking a non-continious load I don't think is see an issue.
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George Little
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#98205 - 05/12/06 04:59 PM Re: Service Conductors
shortcircuit Offline
Member
Registered: 06/27/04
Posts: 608
Loc: massachusetts
Thanx for the feedback George Little. Ummm...hope all is well with you and the rest of you guys.

Around here houses are NOT sellin and construction is slowin way down. Copper is way up...$62 for 250ft of 14-2RX and a wopping $104 for a coil of 12-2RX. This is crazy...it will become a grave situation soon if something doesn't change

shortcircuit
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#98206 - 05/12/06 05:41 PM Re: Service Conductors
Redsy Offline
Member
Registered: 03/28/01
Posts: 2056
Loc: Bucks County PA
Does this link help?
http://electrical-contractor.net/ubb/Forum2/HTML/002542.html

Similar issues, lower numbers.

[This message has been edited by Redsy (edited 05-13-2006).]
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#98207 - 05/15/06 02:06 PM Re: Service Conductors
JG Offline
Member
Registered: 03/24/04
Posts: 16
You are exceeding the rating of meter with two 200 amp mains: possibly this is what your inspector is saying
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#98208 - 05/15/06 05:57 PM Re: Service Conductors
shortcircuit Offline
Member
Registered: 06/27/04
Posts: 608
Loc: massachusetts
JG...the computed load calculation is 260amps which is well under the 320 meter sockets rating.
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