What type aluminum wire should I use to run 150 feet direct bruial for 100 amp sub pa

Assuming 40 amps of 120 volt load, #2 Al with USE insulation would result in 2.94% voltage drop.

Should be sufficient as long as there are not any large 120 V motors >3HP.

A popular 4 wire cable direct burial cable is #2-4 AL URD.

Are you aware of the codes for installing DB cable?

sub panel will mainly feed a 60 amp hot tub...just want to have extra circuits available down the road.....(URD)underground rsidential distribution wire i have never used before...is urd the type?...or there other types that have proven good to use? .always used copper-- xlpe wire.......wanted to know what is the better type aluminum direct burial wire to use...heard about aluminum breaking down sometimes when direct buried..(Newer wire should bebetter now)..code for direct bruial wire...as far as i know...have to be two feet under ground.....i always put a caution ribbon a foot or so above the wire when backfilling...i understand the rest...float the neutral...add grounding rod at new sub panel.....oxide inheibitor on connections...mainly wanted to know best type of aluminum wire to use...and size to use...was gonna use #2 copper ( 3--#2 xlpes and 1--# 6 grounding wire)..but the price is to high....

Underground Residential Distribution cable is widely used by utilities and electricians to feed underground service entrances.

URD cable can be USE, RHH, RHW, or XLPE insulation.

XLPE is one of the new types of insulation, and I believe to be the most resistant to damage. Very popular for Medium Voltage, greater than 600 volts.

Cross-linked polyethylene - Wikipedia, the free encyclopedia

http://cmewire.com/catalog/power/sec...-Al-01-AMP.pdf

Quadruplex Aluminum Cable Type URD - Aluminum URD Cable - Aluminum Building Wire

To install DB cable:

For residential can be 18 inch deep, deeper is better.
If soil is rocky, use 6 inches of sand below and above cable.
Warning Tape 12 inches below grade, this Code is required for
service entrance laterals, wise practice to do for any underground cable.
Not required, but recommended for residential if cable is under pavement, use conduit to sleeve the cable to help with replacing cable later.

A 120/240 volt feeder shall be 4 wire, one is the equipment ground. The neutral bar in the new panel shall be "floated", which means insulated and not bonded to equipment ground.

The panel will need a separate equipment ground bar bolted to the panel using machine thread screws and the grounding electrode conductor from the ground rod, minimum # 6 copper rod and all branch circuit green or bare wires shall only connect to the equipment ground bar.

The neutral bar shall only be for white neutral conductors.

Some states require more than one ground rod. Check local codes.

The new panel shall have a Main Circuit Breaker. There is a "six switch rule" I will not get into details.

Some aluminum wire does not require anti-oxidant inhibitor compound, but better to use on all aluminum wire terminations to be sure.

Be sure to note the torque ratings of any mechanical connections and torque connections to proper values. This requires a torque wrench or screwdriver. This is for aluminum and copper wire bolted connections.

Of course, wherever the URD cable rises out of the ground to enter electrical equipment, it shall be sleeved in conduit. URD cable is stiff and will require a large conduit, #2-4 may need min of 2.5 in. 2" may be sufficient if conduit sleeve length is short.

4 wire URD cable can be considered as 1 conductor and not fill a conduit more than 53% of the internal cross sectional area.

That's all I can think of at the moment.

Have fun digging.