I am adding an attached garage to my house. I"m going to be putting in a 100 Amp subpanel i beg your pardon is about 60 feet away and also run with the basement joists.

What gauge wire execute you recommend because that either aluminum and also copper? Also, execute you introduce one or the other?


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When identify feeder conductor size, you"ll desire to take into consideration the "lowest temperature rating of any connected termination, conductor, or device" as per National electric Code (NEC) write-up 110.14(C).

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While the cable/wire may be rated in ~ 90°C, you"ll likely discover that the terminals space rated in ~ 75°C, or not labeled at all. 110.14(C)(1)(a) tells us, that due to the fact that we"re working v 100 amperes or less. We need to use the 60°C shaft of Table 310.15(B)(16) to recognize the conductor size, uneven the equipment is provided and labeled for a higher temperature.

National electrical Code 2014

ARTICLE 110 needs for electrical Installations

110.14(C)(1) devices Provisions. The determination of discontinuation provisions of devices shall be based on 110.14(C)(1)(a) or (C)(1)(b). Uneven the devices is detailed and significant otherwise, conductor ampacities supplied in determining equipment termination provisions candlestick be based upon Table 310.15(B)(16) (formerly 310.16) as accordingly modified through 310.15(B)(6).

(a) discontinuation provisions of tools for circuits rated 100 amperes or less, or marked for 14 AWG with 1 AWG conductors, shall be used only for among the following:

(1) Conductors rated 60°C (140°F).

(2) Conductors with higher temperature ratings, detailed the ampacity of such conductors is determined based on the 60°C (140°F) ampacity that the conductor size used.

(3) Conductors with greater temperature ratings if the devices is provided and figured out for use with such conductors.

(4) because that motors significant with design letters B, C, or D, conductors having an insulation rating of 75°C (167°F) or greater shall be allowed to it is in used, provided the ampacity of together conductors does no exceed the 75°C (167°F) ampacity.

Since the cable will certainly run native a breaker in the main business panel, to either a breaker or lugs in a subpanel. We have to take into consideration the temperature rating of...

The conductorsThe terminals in the main panel whereby the conductors will certainly connect.The terminals in the below panel whereby the conductors will connect.

We"ll then use the shortest value, or 60°C if any type of of the above are no labeled. When we recognize the size of the overcurrent devices, and the lowest temperature rating, we have the right to use Table 310.15(B)(16) to recognize the conductor size and also material we"ll need.

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This will provide us the current carrying conductor size compelled for our feeder.

But wait...

If you"re functioning in a one-, two-, or multi-family dwelling unit, is short article 310.15(B)(7) applicable?

National electrical Code 2014

ARTICLE 310 Conductors for basic Wiring

310.15 Ampacities because that Conductors Rated 0–2000 Volts.

(B) Tables. Ampacities for conductors rated 0 to 2000 volts shall be as stated in the Allowable Ampacity Table 310.15(B)(16) through 310.15(B)(19), and Ampacity Table 310.15(B)(20) and Table 310.15(B)(21) as modified through (B)(1) through (B)(7).The temperature correction and also adjustment components shall be permitted to be used to the ampacity because that the temperature rating that the conductor, detailed the corrected and adjusted ampacity does no exceed the ampacity because that the temperature rating the the termination in accordance with the provisions that 110.14(C).

(7) 120/240-Volt, 3-Wire, Single-Phase dwelling Services and Feeders.

(a) for individual dwelling devices of one-family, two-family, and also multifamily dwellings, conductors, as provided in Table 310.15(B)(7), candlestick be allowed as 120/240-volt, single-phase service-entrance conductors and service lateral conductors.

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NO.

Notice the password says

"shall be permitted as 120/240-volt, single-phase service-entrance conductors and also service lateral conductors".

After reading the definition of this terms, it"s clear that this walk not use to the wire between the key panel and a subpanel.

Service-Entrance Conductors, Overhead System. The organization conductors in between the terminals of the company equipment and a allude usually exterior the building, clean of building walls, whereby joined through tap or splice to the organization drop or overhead service conductors.

Service-Entrance Conductors, underground System. The organization conductors in between the terminals the the business equipment and also the allude of connection to the organization lateral or underground business conductors.

Service Lateral. The underground conductors in between the utility distribution system and the organization point.

tl;dr

Conductors and all terminals rated in ~ or above 75°C.

Use 3 AWG copper or 1 AWG aluminium because that the existing carrying conductors.

Conductors rated at or above 75°C, terminals rated at 60°C or unlabeled.

Use 1 AWG copper or 1/0 AWG aluminium for the existing carrying conductors.

Conductors and also terminals rated at 60°C.

Use 1 AWG copper or 1/0 AWG aluminium for the existing carrying conductors.

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Conductors rated at 60°C, terminals rated greater than 60°C

Use 1 AWG copper or 1/0 AWG aluminium because that the present carrying conductors.