I would like to install a sub-panel in the basement, in our utility room. I am planning to install a 70A dual pole fuse in the main panel to feed the sub-panel. My main is 200A service, with single phase, residential, single family home. My load calculations is under 100A for the main. My new sub-panel box is rated at 150A with CU bus bar. I would be running 25 feet feed from the main to the sub-panel (via the 70A 240v dual pole fuse).

Our local electrical supply store sells CU romax NM-B cables with all sorts of sizes. They sell size #6/3 with Ground, #4/3 with Ground, #2/3 with Ground to name a few.

They also sell CU #3/3 with ground which is XHHW, SER, 90 oC.

I like these cables over individual cables. Since individual cables must be run through a conduit. These cables allow me to omit the conduit, and then I can simply drill through the joist for neater and easier installation.

Question1 - the basement and utility room (contains heating system, water heater, oil tank, etc) in the basement is considered as a dry location ?

Question2 - is romas NM-B size #4/3 W/G (or I prefer size #2/3 W/G for future expansion) be OK to connect the main to the sub-panel ? I know these sizes are overkill for now, but I would like future expansion without having to change the wire later. I am willing to
pay the extra cost for the 25 feet total length I need.

Question3 - By using the NM-B (say size #2/3 W/G), would I need to worry about cable heat? I recall, seeing 90 oC rating on the store's #3/3 W/G XHHW SER wire. I noticed that their NM-B #2/3 cable didn't mention anything about temperature ratings.

Question4 - Why the #3/3 XHHW SER cable had the temp listed on the cable, and the NM-B #2/3 cable doesn't have temp listed?

Question5 - What does temperature really mean? Is it the melting point of the wire insulation, if the wire gets overloaded, or is it the temperature of the surrounding, where the cable is installed? 90 oC = 194 oF.

Thanks
-been

1) Yes, your basement is considered a DRY location.

2) I would use the 4/3 and a 90 or 100 amp sub-feed breaker. I do not buy the "future expansion" mentality. Do it that way now. Using larger wire (or a smaller breaker) makes no sense in most cases.

3, 4, 5) You do not need to worry about heat or the heat rating of the cable. As long as you don't run the cable against a furnace flue for instance, which is common sense, you are fine.