What is zs in electrical terms

It is the measured resistance of the supply transformer winding, the supply phase conductor, and the erath return path of the supply.

The measurement is made with an Earth Fault Loop Impedance tester with the Main Switch in the OFF open position and with the means of earthing disconnected from the installation to avoid parallel paths. This is a live test so extra care is advised! Step 1. Step 2. Test on the incoming side of the installation. Connect one test lead to the Line terminal, the second test lead to the Neutral terminal and the third usually green test lead to the incoming Earth conductor.

Step 3. Press the TEST button. The measurement should be a low reading ohm value. Locate the furthest point on the circuit to be tested such as the furthest socket Step 2. When checking that the value of Zs is sufficiently low to achieve disconnection within the required maximum time, account must be taken of characteristics of the protective device used for automatic disconnection. RA is the sum of the resistances of the earth electrode to Earth and the protective conductor connecting it to the exposed conductive-part.

For RCDs not covered by Table However, for an installation that is in service, there may be serious consequences for the user of the premises if, for example, computer data is lost or a home life support system switched off as a result of an inadvertent interruption of supply during the test, such as might be caused by the unintended operation of an RCD.

Inadvertent disconnection of a circuit, group of circuits, distribution board or even a whole installation could occur if an RCD operates when an earth fault loop impedance test is carried out. As a result, a number of methods have been developed to minimise the likelihood of an RCD operating during such a test. One such method, calculation, is described below.

Further, as the loop test is being performed on the supply side of any RCD protecting the circuit in question, it should not, in most cases, cause the RCD to operate when the measurement of Ze or Zdb is taken.

This method is explained in more detail below. Measurement of Ze Regulation Measurement of Ze necessarily involves the working on or near live parts. However, this needs to be done only once during initial verification of the installation and once during each subsequent periodic inspection.

Regulation It is recommended that the test be carried out with a supply having a no-load voltage between 4V and 24 V, d.

Read more. Luminaires and lighting installations This article looks at the selection and erection of luminaires and some of the requirements of Information is key When carrying out new installation works and alterations to an existing commercial premises,