Would like to run an electric circuit from 200 amp main panel to a new 100 amp sub-panel in the attic.

Need 220volts @ 30 amps for hw heater, and would like to provide electrical capacity for eventual finishing of attic as bedroom and office.

The circuit run is about 25' from main panel. Was planning on using #4 copper.

Can I use a 60 amp breaker in the main panel? Should I consider anything else?

Yes, you can use a 60 amp breaker to supply the 100 amp panel in the attic, using the #4 conductors.

The feeder will need 3- #4 for the two hots and one neutral, and min 1 -# 10 fr the equipment ground.

The neutral bar will need to be insulated and isolated from any equipmet grounds.

The #10 will need to connect to a separate equipment ground bar bolted directly to the metal panel box with machine screws, and only be for bare or green equipment grounding conductors.

60 amp is a bit light, at least 26 amps will be used for the heater. Is 60 amps enough for the total future load?

I caution you about putting a bedroom in an attic. Building and fire codes require two egress (exits) in the event of a fire. You will learn this when you apply for building permits.

Smoke detectors will be needed, no matter if a bedroom exists or not.


Best I can think of what you need to consider.

Is access now through a code legal stairway? If not you may find it tricky to add one without killing a lot of space on the floor below. I've been there.
A 60 amp panel will give you 14,400 watts of use. A hot water heater is usually 4,500 watts. If you use electric heat, then two 8 foot heaters, one for each room, total 4,000 watts, leaving you with nearly 6,000 watts for everything else. This is a lot, a whole lot.