ns am adding an enclosed garage to mine house. I"m going come be putting in a 100 Amp subpanel i m sorry is about 60 feet away and also run v the basement joists.

What gauge wire do you recommend for either aluminum and copper? Also, execute you recommend one or the other?



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

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

National electric Code 2014

ARTICLE 110 needs for electric 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). Unless the devices is detailed and significant otherwise, conductor ampacities provided in determining tools termination provisions chandelier be based on Table 310.15(B)(16) (formerly 310.16) as appropriately modified by 310.15(B)(6).

(a) termination provisions of devices for circuits rated 100 amperes or less, or significant for 14 AWG with 1 AWG conductors, candlestick be offered only for one of the following:

(1) Conductors rated 60°C (140°F).

(2) Conductors with greater temperature ratings, noted the ampacity of such conductors is determined based upon the 60°C (140°F) ampacity the the conductor size used.

(3) Conductors with greater temperature ratings if the equipment is noted and determined for use v such conductors.

(4) for motors marked with architecture letters B, C, or D, conductors having actually an insulation rating the 75°C (167°F) or higher shall be permitted to it is in used, detailed the ampacity of together conductors does not exceed the 75°C (167°F) ampacity.

Since the cable will run native a breaker in the main service panel, to either a breaker or lugs in a subpanel. We have actually to consider the temperature rating of...

The conductorsThe terminals in the main panel wherein the conductors will connect.The terminals in the below panel where the conductors will connect.

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


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

But wait...

If you"re working in a one-, two-, or multi-family apartment unit, is post 310.15(B)(7) applicable?

National electric Code 2014

ARTICLE 310 Conductors for general Wiring

310.15 Ampacities because that Conductors Rated 0–2000 Volts.

(B) Tables. Ampacities for conductors rated 0 come 2000 volts shall it is in as mentioned in the Allowable Ampacity Table 310.15(B)(16) v 310.15(B)(19), and also Ampacity Table 310.15(B)(20) and also Table 310.15(B)(21) together modified by (B)(1) through (B)(7).The temperature correction and also adjustment components shall be allowed to be applied to the ampacity for the temperature rating that the conductor, noted the repair and readjusted ampacity does not exceed the ampacity because that the temperature rating that the discontinuation in accordance through the provisions of 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 multifamily dwellings, conductors, as listed in Table 310.15(B)(7), shall be permitted as 120/240-volt, single-phase service-entrance conductors and also service lateral conductors.



Notice the password says

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

After analysis the an interpretation of this terms, it"s clear the this does not apply to the wire between the key panel and a subpanel.

Service-Entrance Conductors, Overhead System. The company conductors between the terminals that the business equipment and also a allude usually external the building, clean of building walls, whereby joined by tap or splice come the service drop or overhead organization conductors.

Service-Entrance Conductors, secret System. The business conductors between the terminals the the service equipment and the suggest of link to the business lateral or underground service conductors.

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


Conductors and also all terminals rated at or above 75°C.

Use 3 AWG copper or 1 AWG aluminium for the present carrying conductors.

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

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

Conductors and terminals rated at 60°C.

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

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Conductors rated in ~ 60°C, terminals rated higher than 60°C

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