ns am adding an attached garage to mine house. I"m going come be placing in a 100 Amp subpanel which is about 60 feet away and also run with the basement joists.

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



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

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While the cable/wire may be rated at 90°C, you"ll likely uncover that the terminals room rated at 75°C, or not labeled in ~ 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 tower of Table 310.15(B)(16) to determine the conductor size, uneven the tools is noted and labeled because that a greater temperature.

National electric Code 2014

ARTICLE 110 requirements for electric Installations

110.14(C)(1) devices Provisions. The determination of discontinuation provisions of equipment shall be based on 110.14(C)(1)(a) or (C)(1)(b). Uneven the equipment is noted and marked otherwise, conductor ampacities supplied in determining devices termination provisions chandelier be based on Table 310.15(B)(16) (formerly 310.16) as as necessary modified by 310.15(B)(6).

(a) termination provisions of tools for circuits rated 100 amperes or less, or significant for 14 AWG v 1 AWG conductors, chandelier be used only for among the following:

(1) Conductors rated 60°C (140°F).

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

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

(4) for motors significant with style letters B, C, or D, conductors having actually an insulation rating the 75°C (167°F) or higher shall be allowed to it is in used, listed the ampacity of together conductors does no exceed the 75°C (167°F) ampacity.

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

The conductorsThe terminals in the key panel wherein the conductors will certainly connect.The terminals in the sub panel wherein the conductors will connect.

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


This will give us the present carrying conductor size forced for ours feeder.

But wait...

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

National electric Code 2014

ARTICLE 310 Conductors for basic Wiring

310.15 Ampacities because that Conductors Rated 0–2000 Volts.

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

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

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



Notice the codes says

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

After analysis the definition of these terms, it"s clear the this does not use to the wire in between the main panel and a subpanel.

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

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

Service Lateral. The secret conductors between the utility circulation system and also the service 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 for the existing carrying conductors.

Conductors and terminals rated in ~ 60°C.

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

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

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