Here’s a listing of the standard aluminum service entrance wire sizes for residential 3-wire single-phase service. Wire sizes are AWG (American Wire Gauge), and adjustments may be necessary due to temperature rating or length of wire run. An often-used rule-of-thumb is to jump up one wire size for each 100 feet of a long run.

SERVICE SIZE     WIRE SIZE    

100 amp                    #2               

125 amp                    #1/0            

150 amp                    #2/0            

200 amp                    #4/0            

225 amp                    #250 

    The neutral wire is often one or two sizes smaller than the two hots. The correct sizing of the neutral depends on doing a calculation of the “unbalanced load,” which is an estimate of the amount of 120-volt current usage. 

    Wire size may be marked on the side of the cable, followed by the letters “AWG,” like in the photo below. But not all cables are clearly marked and sometimes the lettering strip is just not visible. Electricians and experienced inspectors can tell at a glance if the service cable size is correct most of the time. 

    Aluminum wire sizes are usually one notch larger than copper for the same service rating. Also, the grey or black gooey stuff you will see around the aluminum wire lug connections is a required anti-oxidant paste.

    The aluminum wire used for service cables and wiring for larger-amperage circuits in a home is multi-strand and a different metal composition that the solid aluminum wiring used during the early 1970s, that was later banned as a fire hazard. 

    For the sizing of copper service entrance cables, see our blog post What are typical copper service entrance wire/cable sizes for the electrical service to a house?

    These sizes for service conductors also apply to feeder conductors. Go to our articles What is a service conductor? and What is a feeder conductor? for the difference between the two.

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Here’s links to a collection of our other blog posts about ELECTRICAL WIRING:

• What is a service conductor?

• Can service condutors be installed in the same raceway/conduit with feeder or branch circuit conductors?

• What is the maximum spacing requirement for securing NM-cable (nonmetallic-sheathed cable)?

• Is it alright to just put wire nuts on the end of unused or abandoned NM-cable or wiring?

• What causes copper wires to turn green or black in an electric panel?  

• Does a wire nut connection need to be wrapped with electrical tape?

• What is the minimum clearance of overhead electric service drop wires above a house roof?

• What are the requirements for NM-cables entering an electric panel box?

• What is the color code for NM cable (Romex®) sheathing?

• Why is undersize electric wiring in a house dangerous? 

• What are the most common electrical defects found in a home inspection? 

• What is the life expectancy of electrical wiring in a house? 

• What is an "open junction box"? 

• How dangerous is old electrical wiring? 

• What is a ground wire? 

• I heard that aluminum wiring is bad. How do you check for aluminum wiring?  

    Visit our ELECTRICAL page for other related blog posts on this subject, or go to the INDEX for a complete listing of all our articles.