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Fencepost
Re: Small Subpanel Replacement

Old thread, so I'm probably way too late to the party.

MyMilan wrote:

I'm going to run some new wire to the subpanel when I install it. There is not much of a load in the garage. The lighting consists of 5 LED lights (at 9 watts each) and two 15 amp receptacles. The attic has 3 LED lights @ 8 watts each. That is it. Running 8/3 should be more than enough correct?

For the load you describe, 10/3 as a 30A/240V service would be plenty adequate. But if you ever want to run heavier power tools (like an air compressor) you might want to go with a little heavier service (8/3 as 40A/240V). An air compressor starting up when you're running some other power tool could cause the circuit breaker feeding the garage to trip.

You might never need the extra capacity, but having it could be a selling point when you're ready to move on. And if you ever imagine using an industrial-sized welder, you'll probably want at least 60A service.

If it's more than a couple hundred cable-feet (one-way distance) from the main panel in the house, you might want to upsize your wire to prevent voltage drop. If the no-load voltage is 123V, putting 30A of load at the end of a 200-foot run of 10/3 will drag the voltage down to 111V.

Calculate voltage drop here: http://www.calculator.net/voltage-drop-calculator.html

John freeman
Re: Small Subpanel Replacement

For your lighting load as described 14/2 on a 15 amp breaker will be enough.

For your entire panel 10/3 on a 30 amp breaker will be enough. If you add more receptacle circuits or believe you might expand in the future then you might consider 8/3 on a 40 amp breaker. If cost is not important then 8/3 might be the way to go.

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