What is difference between Ze and Zs?

Zs is the total impedance of the complete circuit and it is made up of: The impedance of the supply cables and transformer windings, Ze. The resistance of our circuit line conductor, R1. The resistance of our circuit cpc, R2.

What does Zs and Ze stand for?

– Zs is the earth fault loop impedance (Ω) – Ze is the measured value of external impedance (Ω), and. – (R1 + R2) is the measured value of resistance (Ω) for the line conductor and protective conductor, at the most distant point or accessory from the distribution board or consumer unit.

What is a Ze reading?

`Ze` is a measurement of the external earth fault impedance of the installation. It is the measured resistance of the supply transformer winding, the supply phase conductor, and the erath return path of the supply. `Ze` can be obtained by enquiry to the electricity supplier or by direct measurement at the supply.

What is ze value?

Ze is the measured value of external earth fault loop impedance in ohms. (R1 + R2) furthest is the value in (R1 + R2) in ohms measured at the electrically most distant point or accessory from the distribution board (or consumer unit).

Is Zs at DB the same as Ze?

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. This is sometimes also called Zdb. At the end of the final circuits fed from this board will be a Zs for each circuit.

TESTING Ze Zs UNDERSTAND THE DIFFERENCE BETWEEN Ze AND Zs AND HOW TO TEST CORRECTLY

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 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.

What is Zs in electrical installation?

Zs represent earth fault loop impedance and consists of Ze and (R1+R2). R1 is the phase and R2 is the CPC. These are measurements of the fault current from the supply transformer to the building. It covers the entire electrical cycle.

What is actual Zs?

Zs is the total impedance of the complete circuit and it is made up of: The impedance of the supply cables and transformer windings, Ze. The resistance of our circuit line conductor, R1. The resistance of our circuit cpc, 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 does ZS test prove?

A Zs test is not to prove an earth connection exists, although it would do so, but to prove that the CPD would operate within the time required by BS7671. Smpling should be of circuits, not equipment of a circuit that is being tested.

Are Ze and ZDB the same?

Comlec Screwfix Select. Where a DB is fed from the installation origin then the Ze and Zdb are essentially the same. If a switch fuse was added and the DB located elsewhere then the Zdb would be slightly different.

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!

What is the tripping time for a 30mA RCD?

What is the maximum allowable tripping time? A common misconception is that RCDs must trip in 30 ms. In fact, an RCD when tested at its rated sensitivity must trip in 300 ms. When tested at five times, ie, 150 mA for a 30 mA device, it should trip in 40 ms.

When should a 100mA RCD be used?

To suggest that a 100mA RCD, be used in the event of problems with a 30mA unit is irresponsible; it may protect the kiln but it does not protect the user.

What RCD is used for fault protection?

An RCD is a sensitive safety device that switches off electricity automatically if there is a fault. An RCD is designed to protect against the risks of electrocution and fire caused by earth faults.

Is ZS a live test?

The presenter does live Zs testing at sockets with a plug top lead switching on the socket switch before taking the test. So this in the words of the Regulation would be "reasonable".

What is a good earth loop reading?

It is generally accepted that, where the measured earth fault loop impedance of a circuit is not greater than 80% of the relevant limit specified in BS 7671, the impedance can be expected to be sufficiently low under earth fault conditions to meet the relevant limit specified in BS 7671, and for the protective device ...