Would like to replace my 200-amp service panel with a Square-D 100-amp box, and wonder if installing the 100-amp stranded aluminum wire from my 200-amp service pole breaker to the new panel will be okay. 100-amp cable (80 feet) will be encased and buried. Other than a lightning strike or an idiot with a backhoe, I can think of nothing that would cause the 200-amp service to attempt to deliver more than 100 amps to my building.
History: Flaky lights, dimming and flickering in my 'barn.' Decided to investigate. 200-amp Federal Pacific panel in 1200-sq foot concrete block building converted to barn by previous homeowner. Went looking for lower amp breakers because the builder had wired all his socket/light circuits to 30-amp FedPacific breakers with 12/2 wire. NO junction boxes used - bared wire connections made with electrical tape/solder on all circuits, all laid on wall top plates and ceiling joists. Found one 'junction' with SIX 12/2 wires attached, just bared, taped together, and left open in the rafters! Failed to find lower-amp FedP breakers, but I did find out that FedPacific assisted America in setting fire to many mobile homes before they went out of business. Confirmed that the unit may have come from a mobile home by finding several runs of 12/2 ALUMINUM in the building! I have stripped circuits and re-run 12/2 copper only, with 220v 10-guage copper to the single 220v unit (small air compressor on a 20amp circuit.) Installed junction boxes instead of using the 'bare-wire' technique. As the building is now a barn/shop, no stove, water heater, etc. - just lights, sockets, compressor, a 1500w wall heater and a 110-volt window air conditioner in a small 'office' room I kept intact..
Anyone see a problem with drawing 100 amps.from a 200amp service?

OK, what is the cable/wire feeding the panel now?
If the wire is OK why replace it, and why down grade. IMO that makes no sense.

Services don't deliver amperage, loads pull amperage. It's not like the amperage is bottled up in the service cable looking to get out. It's just available to use.
Amperage is only a measure of current flow.

Typically 100A is fine to a residential shop for most uses, especially if you'll be working alone most of the time, but if you have the capability to go 200A I say definitely go for it. You'll never be upset that you have too much capacity or breaker space.

200 Amps is the Max rated capacity of the main breaker. It has no effect on the box running 50 amps. Look for an interchange breaker to get 20 amps. If you Google Federal
Pacific breaker interchange you should find some. Siemans breakers interchange well to Mabel panels. They may not be UL approved but are compatible.

Stanfortyman;
Cable is 6/2 (yep, that's 6/2 run between the pole and panel 200amp breakers.) If I pull over 30 amps, I figure my grass'll catch fire. 100amp cable will be an upgrade. Prev owner was a self-styled 'electrical expert' in the neighborhood. Since I moved in, there have been several houses burn down. Electrical fires - go figure. My question is simply whether it is safe to power the 100amp cable/service panel breaker off the power pole breaker 200amp. Effectively, I believe this makes the power pole breaker useless, but my panel would break at 100+ amps anyway. Question is whether it is a problem to run 100amp cable off the 200amp service pole. I do work alone, and will rarely use over 30amps total. The 20-place Square-D is more than I need - I'll have 8 positions open when I'm done.

If you are going to run new wire to a new 100 amp panel in your building then you should be able to change the 200amp breaker at the pole service to a 100 amp breaker. The breaker at the pole is considered to be the main disconnect so the service to the building would be 100amp max.