You can obtain the Zs by calculation **Zs=Ze+(R1+R2)**, or by measurement using an Earth Fault Loop Impedance Meter.

How do you measure ZS on a ring circuit? To find the zs of a ring circuit you need to cross connect at the origin of the ring, ie, connect the incoming phase to the outgoing cpc and vice-versa, then measure between phase & cpc at all of the sockets, the one with the highest reading gives the r1+r2 figure, just add this to your ze figure and you`re there!Sep 6, 2007

What is maximum permitted Zs?

Zs is **maximum earth fault loop impedance to operate the fuse element of the disconnection device (overload and short circuit) in the required disconnection time**. On TN systems the values in tables 41.2 and 41.3 will be relevant. In TT systems the earth fault loop is satisfied by the condition in 41.5.

What is the correct calculation for calculating Zs?

Therefore, where reliable measured values are available for the external earth loop impedance (Ze) and for the loop resistance of the line and protective conductors (R₁ + R₂) of the circuit, it is permissible to derive the loop impedance of a circuit by using the following formula: **Zs = Ze + (R₁ + R₂)**.

How do you measure Zs at DB?

Zs is your total impedence of the circuit including your sub main. There is only one Ze which is at the origin of the supply. The board fed by the sub main will have a Zs value at the board which will roughly equal Ze = R1 +R2. **You measure the Zs at the incomming terminals of the sub board**.

How is Zs calculated?

Therefore, where reliable measured values are available for the external earth loop impedance (Ze) and for the loop resistance of the line and protective conductors (R₁ + R₂) of the circuit, it is permissible to derive the loop impedance of a circuit by using the following formula: **Zs = Ze + (R₁ + R₂)**.

What is the maximum ZS permitted by BS 7671?

Note: Values of Zs for disconnection times other than **0.4 s or 5 s** shown may be required by BS 7671. For example, 0.2 s may be required for a 230 V final circuit not exceeding 32 A in a TT system (Table 41.1 refers).

How do you find Zs of a circuit?

Therefore, where reliable measured values are available for the external earth loop impedance (Ze) and for the loop resistance of the line and protective conductors (R₁ + R₂) of the circuit, it is permissible to derive the loop impedance of a circuit by using the following formula: **Zs = Ze + (R₁ + R₂)**.

What is the 80% ZS rule?

The 80% rule of thumb is **only intended to be applied to a test result taken from an impedance test**. You have to ensure that the tested value does not exceed 80% of the tabulated value.

What if Zs is too high?

If a Zs value is high, then you need to **establish whether it is due to circuit conditions, supply conditions, or a fault**. You can then descide the appropriate course of action. Just installing an RCD or RCBO may not be the solution in a deteriorating installation.

**Related Questions
**

### How do you calculate Ze electrical?

**Zs = Ze + (R₁ + R₂)**.

### How do you calculate actual Zs?

**Zs = Ze + (R₁ + R₂)**.

### How do you calculate maximum Zs?

Max Zs Calculation Formula

So for a Type B 32 Amp MCB to BS EN 60898 the calculation would be: **5×32(In) = 160 Amps (la)** **218.5(Uo) / 160 (la) = 1.36525 (rounded to 1.37)** Maximum Zs Value.

### Can you test Zs at the board?

Zs is your total impedence of the circuit including your sub main. There is only one Ze which is at the origin of the supply. The board fed by the sub main will have a Zs value at the board which will roughly equal Ze = R1 +R2. **You measure the Zs at the incomming terminals of the sub board**.

### How do you find the real Zs?

You can obtain the Zs by calculation **Zs=Ze+(R1+R2)**, or by measurement using an Earth Fault Loop Impedance Meter.

### What does a high Ze reading mean?

High ZE readings essentially refer to **earthing arrangements in the property**. High readings could be due to a wiring fault on the earth cable.

### How do you calculate Ze from PFC?

You'd do **I = V/R**, which is the same as PFC = V/Ze. I know R is resistance and Z is impedence, but that is the formlae and it's the calculation a tester makes when taking a PFC reading.Aug 1, 2007

### What is the rule of thumb for ZS value?

The Rule of Thumb **leans on the side of safety by making allowances for the possibility of a smaller csa protective conductor**. For example: A circuit has a max Zs value of 1.37Ω. The measured value of R1 + R2 is 0.92Ω and the Ze is 0.14Ω.

### How do you calculate max Zs in ACB?

Answer: The Zs value of an ACB is actually dependant on the short circuit current setting (I3), rather than the over current setting (I1). **It is calculated based on the I3 setting multiplied by the nominal current of the breaker** – in this case 800A. For an I3 value of 10 times, the Zs value would be 0.024 ohms.

### How do you find actual Zs?

**Zs = Ze + (R₁ + R₂)**.

### What do you do if Zs is too high?

If a Zs value is high, then you need to **establish whether it is due to circuit conditions, supply conditions, or a fault**. You can then descide the appropriate course of action. Just installing an RCD or RCBO may not be the solution in a deteriorating installation.

### What is an acceptable Ze reading?

The value of external earth loop impedance (Ze) measured or otherwise determined in accordance with Regulation 313.1 may differ from the applicable typical maximum value declared by the electricity distributor, which is usually: **0.8 Ω for TN-S system**. **0.35 Ω for a TN-C-S system**.

### What happens if Zs is too high?

If a Zs value is high, then **you need to establish whether it is due to circuit conditions, supply conditions, or a fault**. You can then descide the appropriate course of action. Just installing an RCD or RCBO may not be the solution in a deteriorating installation. It would appear that PME is psychic.

### How do you calculate prospective short circuit current?

So the transformer is 500 kVA, we convert to VA by multiplying by 1000 and then divide by the square root of three x the nominal voltage, 3 phase of 400 V. Now, to calculate the Short Circuit Current, **multiply the rated full load current by 100 and then divide by the actual percentage impedance of the transformer**.

### How do you find Zs on a database?

Zs is your total impedence of the circuit including your sub main. There is only one Ze which is at the origin of the supply. The board fed by the sub main will have a Zs value at the board which will roughly equal **Ze = R1 +R2**. You measure the Zs at the incomming terminals of the sub board.