Voltage drop measurement

In this method, the three prongs of the device are connected to the outlet or the test probe is connected to the main busbars of the panel and the voltage drop test is performed. It should be noted that before testing the circuit, the ZREF value should be tested and evaluated at the beginning of the distribution circuit.

The voltage drop is calculated based on the following equation:

Limitation of voltage drop values

 The permissible limits for line voltage drop for various uses are as per the table below.

 Scope of test application

RCDs are used to protect against fault currents and voltages.

In TT systems, relative leakage currents between the phase and earth wires can create dangerous contact voltages on accessible metal surfaces.

 This test is carried out for the following purposes:

Effectiveness and proper operation of the RCD

Specification of the tripping current and tripping time

Determining whether fault currents are present in the system? The sum of the current in the circuit and the applied test current causes the RCD switch to trip.

 Operation of Residual Current Devices (RCDs)

RCDs operate on the difference between the sum of the phase currents and the return current of the neutral conductor. If the calculated current is greater than the operating current of the installed RCD, the RCD operates and the mains voltage is interrupted. The differential current must Flow to ground. This current can be in the form of leakage current (through insulating or capacitive coupling) or in the form of fault current (defective insulation or short circuit between live parts and accessible metal parts).

Residual current device (RCD)

Types of RCDs

There are three types of RCDs based on the shape of the fault current. Table 1 shows the difference in response of RCD types to different shapes of residual current.

What can be seen is that:

Type AC protects only against AC leakage currents

Type A protects against AC and pulsed DC leakage currents.

Type B protects against all types of leakage currents including rectified DC currents.

The AC type RCD is the simplest type of RCD. Many electronic circuits can produce pulsed or smooth DC leakage currents, so installing a type A or B RCD in these circuits is inevitable.

 Based on the Trip out time or RCD function, two types of RCDs can be divided:

• Standard Type: with uninterrupted operating time

• Selective Type: with delayed operating time

• Selective RCD type has a delayed operating time of about 10 milliseconds. If an installation is protected by more than one RCD, they are usually installed on the input side of the electrical installation. Standard Type RCD Usually, a Selective type RCD is installed downstream. This type of installation and commissioning allows for selective protection and trip out in the part of the circuit where the fault current has occurred.

Measurement principles and limitations The following parameters should be evaluated in RCD testing:

• Contact voltage UC

• Earthing system resistance RE

• Non-Tripping test

• Operating time test (usually at 1 time ∆I or 5 times ∆I) in phase 00 or 1800

• Operating current test ∆I

RCD Test Principles

In this test, the test device is connected to the mains voltage between the phase and earth conductors and a selected test current ∆I is injected. The injected currents are as follows:

• 0.45*∆I for non-tripping testing

• 1.05*∆I and 5.25*∆I for measuring operating times

• Slope of rising current for testing the operating current (usually between 0.2 and 1.1 times ∆I)

• Voltage drop is also measured to measure the contact voltage and resistance of the earthing system.

Principles of RCD testing

No-tripping test, contact voltage and fault loop resistance

The results determined by the no-tripping test are as follows:

• Rloop: Fault loop resistance

• Uc: Contact voltage

• RCD (No-Triping): Determines correct operation

• Determines whether there is a leakage current in the installation.

 Contact voltage:

The contact voltage cannot exceed 50 V. The following conditions must be met at the value of ∆I.

Earthing system resistance: In TT system, the earthing system resistance REH is a large part of the fault loop impedance. The following equation must be satisfied and the contact voltage must not exceed 50 V when the RCD operates.

R_E

In this equation, UClimit is 50 volts, RE is the resistance of the earthing system, and ∆I is the rated operating current of the RCD.

The permissible resistance of the earthing system is based on the rated operating current of the RCD according to the following table:

A sample output from the test device is as follows:

Sample output of RCD tester in time test mode

RCD operation current test

In order to measure the tolerable leakage current threshold, the fault current is applied to the system incrementally and at the threshold current the leakage current switch operates and the data is recorded. If the values ​​in the table below are in accordance with the IEC standard60755 is provided, the RCD performance is confirmed.

The output sample of the RCD tester in this case is as follows:

An example of an incremental flow of actions is as follows:

Rising current shape for RCD current testing