R1+R2 Zs Calculator

Zs is the value of Earth Loop Impedance of an electrical circuit measured in Ohms.

Circuit protective devices such as MCB’s and fuses have a maximum permissible Zs value known as Max Zs.

The maximum permissible Zs values for Fuses and MCB’s vary depending on the device type and rating.

MCCB and ACB maximum Zs values also vary between different manufacturers.

To lookup or calculate the maximum permitted Zs value for circuit protective devices take a look at our Max Zs Values App.

MCB = Miniature Circuit Breaker.

MCCB = Molded Case Circuit Breaker.

ACB = Air Circuit Breaker.

To calculate Zs:

• Input an R1+R2 value.
• Input a Ze value.
• Tap Calculate.

To calculate a ring circuit R1+R2 value we need to measure the r1 and r2 end to end values of the ring final circuit.

r1 = Ring Circuit, Line Conductor.

r2 = Ring Circuit, Circuit Protective Conductor.

This R1+R2 calculator can calculate the R1+R2 value from the known measured Zs and Ze values.

We also have a r1 r2 to R1+R2 converter calculator included with our Electrical Tools and Reference app for calculating R1+R2 from r1 r2.

The preferred method is to directly measure r1+r2, however many people confuse r1+r2 with R1+R2. Where we have mentioned r1+r2 in red we are actually referencing R1+R2.

r1 and r2 refer to ring final circuit end to end values of the line and cpc conductors separately.

For example, r1 = the resistance of the ring circuit line conductor at each end, i.e. the two ends of cables connected together at the same MCB.

• r1 = Ring circuit line conductor resistance.
• r2 = Ring circuit cpc conductor resistance.

The little r1 and r2 values can be converted to R1+R2 using the figure of four calculation, this calculation is included with our Electrical Tools and Reference App

R1+R2 refer to the final circuit resistance of the line conductor and circuit protective conductor (cpc or eath) together.

• R1 = Circuit line conductor resistance
• R2 = Circuit cpc conductor resistance
• R1+R2 = the above added together

R1+R2  is the value of resistance in an electrical circuit which is measured on Ohms.

R1 = Line Conductor.

R2 = Circuit Protective Conductor (cpc).

R1+R2 = The total value of R1 and R2.

R1, R2 should not be mistaken for r1, r2 .

r1 = Ring Circuit, Line Conductor End to End Value.

r2 = Ring Circuit, Circuit Protective Conductor (cpc) End to End Value.

To calculate R1+R2:

• Input a Zs value
• Input a Ze value
• Tap Calculate.

To convert r1 r2 to R1 R2 you may use our Electrical Tools and Reference App which includes a ring circuit r1 r2 to R1 R2 converter.

r1 r2 is sometimes referred to as little r1 r2.

R1 R2 is sometimes referred to as big R1 R2.

No, Ze should never be calculated, to obtain a Ze value the most accurate way is by direct measurement.

How to obtain a Ze value:

1. By direct measurement
2. By inquiry

By direct measurement is the preferred method for obtaining a Ze value.

When measuring external loop impedance Ze the correct procedure must be followed in-order to actually record a true Ze value.