How do you calculate total resistance in parallel?

Answer 1

In words: The total conductance is the sum of the individual conductances. Since conductance is the reciprocal of resistance:

1/R = 1/R1 + 1/R2 + 1/R3...

where R is the combined (or equivalent) resistance, and R1, etc. are the individual resistances. In other words, you first take the reciprocal of the resistances, add everything up, then (to get the actual combined resistance), you take the reciprocal again.

Sample calculation: resistances are 2 and 3 Ohms.

1/R = 1/2 + 1/3

1/R = 3/6 + 2/6

1/R = 5/6

R = 6/5 or 1.2

Answer 2

Add the admittance, or inverse of the resistance.

Example 1: two 100 ohm resistors in parallel: 1/100 + 1/100 = 2/100 siemens, or 100/2 = 50 ohms.

Example 2: one 50 ohm, two 25, three 15 ohm resistors in parallel: 1/50 + 2/25 + 3/15 = 45/150 siemens, or 3.33 ohms.

Answer 3

Since I don't have the tools here to type math, I'll state it in plain english. The reciprocal of Total Resistance is equal to the sum of the reciprocals of the resistance of each leg.

Stated another way... 1/R(t) = 1/R(1) + 1/R(2) + 1/R(3)......

Guess I did have the tools to type this formula after all.

If the parallel legs are all equal resistance, it's easier... then R(t) = R/N where R = the resistance of each individual leg and N = the number of legs.
1/ Rt =1/ r1+1/r2+1/r3 +...1/Rn

Answer 4

If R1 and R2 are connected in parallel then its effective resistance R1*R2 /(R1+R2)

Suppose R1, R2 and R3 are connected in parallel, then the effective value will be

R1*R2*R3 /(R1R2+R2R3+R3R1)

Answer 5

if the total resistance r_total and the resistance of the parallel elements is r_1, r_2 etc

Then the total resistance is 1/r_total = 1/r_1 + 1/r_2 ....

If the parallel elements have capacitance or inductance, the resistances above can be replaced by impedances z_1, z_2 ....

Answer 6

1/R= 1/R+1/R+1/R.... The first R is total resistance and the other R's are the resistances of the individual resistors