Wire Size

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Old 09-30-02, 05:30 PM
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Conductor Size

I posted a question a while back regarding sizing a service panel. Now I was hoping I could get your input on sizing the conductor.

From the 400A meter base to first 200A Panel is about 12'.

From the 400A meter base to second 200A Panel is about 45'

From the second 200A Panel to 125A Sub in Basement is about 65'.

What is the properly sized conductor for Al and Cu?

Thanks,

abkent
 

Last edited by abkent; 10-01-02 at 12:07 PM.
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Old 09-30-02, 07:24 PM
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Where is the main disconnect(s), at the meter or in the 200A panels? Is there breakers or fuses between the meter and 200A panels? What size fuses/breakers if any?
 
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Old 09-30-02, 09:10 PM
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You will need disconnects outside after the meter before you can run wire this far inside the dwelling to the panels.

conductors........If you use type SE for the 200 amp runs,it would be 3/0 copper or 250mcm alum.

125 amp.........type SE #1 copper or 2/0alum
 
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Old 10-01-02, 08:30 AM
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Disconnects

200A disconnects are at the meter base.

The first 200A panel is located on the opposite side of an 11' wall. Physical location is less than 2' from the meter base/disconnects. Does this panel need a panel mounted disconnect?

The second 200A panel has a 200A disconnect mounted in the panel in addition to the one at the meter base.

The 125A sub panel has a 125A overcurrent in the second 200A panel listed above. Does this panel need a panel mounted disconnect?

Is 1/0 Al for the 125A and 4/0 Al for the 200A ok? Other than size of conductor what are the pro/con's of Al vs Cu?

Thanks,

abkent
 
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Old 10-01-02, 07:23 PM
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abkent,
You stated that there are disconnects at the meter. Are these just disconencts or to they have overcurrent protection (like fuses or circuit breaker type)? Since these 200A feeder conductors are between the main disconnects and the panelboard, I would agree to use Table 310.15(B)(6) so, 200a is 2/0 cu or 4/0 al. The 125A sub panel feeder does not originate at the main disconnect, so you will have to use Table 310.16 so, #1 copper or 2/0alum.

The two main benifits of cu over al is less voltage drop, and less re-tourquing. Don't get me wrong, the re-tourquing doesn't happen more often for al than cu, but it should. Be sure your terminations are rated for the material you decide to use.
 
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Old 10-01-02, 08:22 PM
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Old 10-01-02, 08:58 PM
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I think you'll find a majority of the aliminum problems as described on the previous web site are related to branch circuit wiring. Generally service conductors don't go through the major temperature changes (load changes) to be as bad as branch wiring (completely on/off).
 
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Old 10-02-02, 07:40 AM
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The service disconnects at the meter are circuit breakers. (Square D Q2L2200H)

If you had your choice which would you go with Cu or Al?

abkent
 
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Old 10-02-02, 08:50 AM
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Sizing feeders to dwelling units.

Originally posted by abkent
"The service disconnects at the meter are circuit breakers. (Square D Q2L2200H)

If you had your choice which would you go with Cu or Al?

abkent"

I would use the aluminum for the cost savings. For feeder and service entry conductors there is nothing wrong with aluminum when it is properly installed. Just do not neglect to wire brush the conductors and immediately apply anti oxidize compound.

The answer to your wire sizing question depends on whether one or two of the two hundred ampere panels is installed in the home. If only one of the panels is installed in the home and the other is installed in an outbuilding such as a detached garage, barn, or shop then the feeder can be sized based on table 310.15 (b) (6). The conductor size for that panel would then be 2/0 Cu or 4/0 Al. If both panels are located in the same house then neither feeder is "the main power feeder to a dwelling unit." Only one feeder to each dwelling unit can be sized as a dwelling unit feeder. If two feeders serve the same dwelling unit then the feeders would have to be sized using Table 310.16. This would give you a conductor size of 3/0 Cu or 250 MCM Al for each of the two feeders that serve the single dwelling unit. The reason for restricting the reduction in size to a single feeder is that the division of the load between two or more feeders serving the same dwelling unit eliminates the diversity of the load that permits the reduction in the first place. Either of the feeders could end up overloaded because of differences in the demand of the load applied to them.
--
Tom
 
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Old 10-02-02, 08:59 AM
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If given the choice, I always go with copper. Although short, the conductors you are installing are after the meter, thus you pay for any conductor losses. In the long run, the copper pays back. Although a "sales" site, look at the site below:
http://buildingwire.copper.org/
 
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Old 10-02-02, 10:25 AM
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Both panels would be considered in the same dwelling. One is in the garage serving the garage/shop area and outside. The other is located in the utility room of the main floor with a feed to a subpanel located in the basement.

The panel located on the main floor of the house obviuosly carries considerably more load, and in my mind would be considered the main service feed for the dwelling, but it makes sense that you would not want the main conductor sized smaller than the secondary conductor feeding the garage. The definition from hornetd seems clear enough. That leaves me with:

From Table 310-16
3/0 Cu or 250 MCM Al feeding the 200A panels and
#1 Cu or 2/0 Al feeding the 125A subpanel


Thanks for your help,

abkent
 
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