I need to run a 100amp/220 service 180' from a main 200amp service. Can I use 2 runs #2awg copper and 2 runs #6 copper (4 runs total ) for this service?

Let's see if I got this correct, To have a working amperage of 100 Amps and 120/240V over a distance of 180', copper, you will need:

(Guessing at underground and into a 60C device), 3 - #3/0 AWG Conductors (2 hots and 1 Neutral) and a #4 AWG EGC.

Since this is to a sub-panel, you will need a four conductor feeder.

Also, the conductor size might change if you connect to a 75C device.

At the sub-panel you will need to isolate the Neutral feed from the cabinet and the Equipment Grounding bus. You will also need to use a #6 EGC to connect to a ground rod at the sub-panel.

A sub-feed does not use the full amperage to figure voltage drop. Most times we size this by experience since the actual demand load is close to an impossible number to find.

Without knowing the load, I will say that 180' is pretty far, so I would up size the feeder by at least one size.

You could use 60A as the load and be fine. It would be extremely rare that a 100A sub-feed in a residential application would ever see more than 60a @ 240v.

Stan,

Given that there are no " Fully Rated" breakers available for residential use, and that we should plan a load up to 80% of the fully rated load (In this case 80 A max.)

Is that why you come up with only one jump in conductor sizing?

#2 would suffice for a single load, such as a 240 volt pump. But for the service AT LEAST 2/0 is indicated. 3/0 is certainly a good idea.

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Originally Posted by donf

Given that there are no " Fully Rated" breakers available for residential use,

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I am not sure what you mean by a "fully rated breaker". Every breaker is rated to it's capacity.

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Originally Posted by donf

and that we should plan a load up to 80% of the fully rated load (In this case 80 A max.)

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We could plan for 80%. The load calc is the only way to know for sure what the demand load is.
A sub-feed or service can carry 80% of the load continuously. It can carry 100% non-continuously.

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Originally Posted by Missouri Bound

#2 would suffice for a single load, such as a 240 volt pump. But for the service AT LEAST 2/0 is indicated. 3/0 is certainly a good idea.

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This is not a service, it is a sub-feed.

This particular sub-feed can carry 60A @ 240v continuously on #2AL. If you take into account a 5% drop then it can carry even more.

1/0AL is more than adequate compensation for distance here.

Hmm. My mistake. When the original poster said "service".. I took it literally.