Use of formula is always a cumbersome exercise.
In pactical 1.5A/sqmm for al,cable & 2.5A/sq.mm is
considered in practical way. means a 50sqmm Al cable will
carry at least 75A and same size copper cable will carry
125A.

1.0 To 1.5A/sqmm for al,cable & 2.0 TO 2.5 A/sq.mm is
considered in practical way. means a 50sqmm Al cable will
carry at least 75A and same size copper cable will carry
125A.

Thumb rule
For Al Conductor Cable Multiply Sq mm size by 1.5.
&
For Cu cable Multiply sq mm size by 4.
e.g.
70 sq mm Al Cable can take 70×1.5=105 A
&
16 sq mm Cu cable can take 16×4=64 A

Check the CCC by any supplier's brochure.
Derate the CCC on the following parameters
Maximum Ambient temp.
Cable buried UG / on air
Clearance between adjuscent cables.
185 mm2 4 c Alu XLPE cable's ccc = 200 Amps in the Gulf.

As we know that Resistance of conductor is calculated by

R= row*l/a
where row=specific resistance of the conductor i.e
aluminium and copper(depends of material)
l=length of the conductor
a=area of cross-section of the conductor.

And as we know that the conductivity of the aluminium
conductor is <=1 (depends upon the distance of the cable
laid avg.0.8-1) and conductivity of copper is <=1.5
(depends on cable laid. avg. 1.2-1.5).

for ex.take cable length of 180 sq.mm Al. cable

if we want to know the current carryng capacity is
180*o.9=168 A approx.

why the Different manufacture's
rating of Gas genset are different?
i.e : cummins genset rating is in
KVA .( 625kv). While GE- Jenbacher
make genset have rating in Kw. (625
kw)