Sub-Panel rewired

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A1cbr

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Got a de attach garage that has a ITE main lug panel box, that is about 300' away from the ITE main panel. This garage is on a 60Amp DP breaker in the main panel. I was planning on running #1Al but I am being told that all i need is a #2 Al. How is that possible? I was also taking in consideration of Voltage Drop,and ambient temperature. Oh the reason I am rewiring is that when it rains there is a direct short.
 
This thread had been temporarily closed. This action was taken because the nature of the question and the occupation shown in the Original Poster's profile raised a concern that this may have been an attempt by a Do It Yourself person to obtain "how-to" information.

In an exchange of Private Messages, the Original Poster has provided assurances that he is a licensed electrician, and works part time in that capacity. Therefore, I am reopening the thread. I offer an apology to the OP for the inconvenience and the delay.

The OP has revised his profile to show the dual occupation (full time job plus part time electrician).
 
A1cbr said:
I was planning on running #1Al but I am being told that all i need is a #2 Al. How is that possible?
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You can oversize the conductors to your hearts content.

I assume the detached garage is at a dwelling. If so, "all you need" is #4 Al. . .but the "all you need" is based on a Code minimum that is not necessarily intended to be practical.
 
al hildenbrand said:
You can oversize the conductors to your hearts content.

I assume the detached garage is at a dwelling. If so, "all you need" is #4 Al. . .but the "all you need" is based on a Code minimum that is not necessarily intended to be practical.
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However, #4 AL could be practical in this situation if run with direct-burial cable, because of the cooler ambient temperature and lower thermal resistance. At 30A/240V/.9PF loading, the voltage drop would be roughly 3%. And that would be 1.5% for balanced 120V loads.
 
It's kind of interesting to note that the calculator that Dennis links to above shows that a 240 volt, single phase load of 30 amps at a one-way distance of 300 feet suggests an aluminum conductor that is #2.
 
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al hildenbrand said:
It's kind of interesting to note that the calculator that Dennis links to above shows that a 240 volt, single phase load of 30 amps at a one-way distance of 300 feet suggests an aluminum conductor that is #2.
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That calculator has no compensation for ambient temperature or thermal conductivity. To get a rough idea how these parameters affect voltage drop, compare ampacities for the type and size of wire under consideration in Table 310.16 to Table B.310.8. The difference in ampacities is directly related to heat dissipation. Retained heat is the major factor contributing to voltage drop for higher current levels through the conductors. Reducing the temperature of the conductors at those levels also reduces voltage drop.

I guess I should mention that portions of the cable not buried must be kept at a minimum, as you can't just bury say a few feet and expect the balance of the run to perform the same as the buried portion :smile:
 
OP states is using a main lug need to have disconnecting means at structure when main disconnect is not with in sight and more than 15 feet from structure served
 
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