Earthing Measurement and Residual Current Device Checks

How do earthing and residual current devices protect employees?

A common route to electric shock is an employee touching a metal enclosure that is not normally live, such as a machine housing or a panel door. When the insulation of a cable inside fails, this enclosure becomes live. Two protections work together against this situation:

• Earthing: Connects the metal enclosure to earth via a low-resistance path. When there is a fault to the enclosure, current flows along this path, the touch voltage on the enclosure is limited, and the current needed for a protective device such as a fuse or circuit breaker to trip is generated.
• Residual current device (RCD): Compares the current going into the circuit with the current coming back. When the difference, i.e. the current leaking somewhere, reaches the device's rated value, it cuts the circuit. Devices with a rated residual current of 30 mA are used for life protection because they cut the current passing through the human body before it reaches a dangerous duration.

The two protections do not replace each other. On a machine whose earth connection is broken, a fault may go unnoticed until someone touches the enclosure; on a panel where the RCD has been bypassed, earthing alone may not cut the circuit on small leakages. For the general rules of working with electricity, see our article on the five safety rules in electrical work.

What does legislation require?

The subject is governed jointly by three regulations:

• Annex 1 of the Regulation on Health and Safety Measures in Workplace Buildings and Annexes: The electrical installation is set up to protect employees against direct or indirect contact; its maintenance, repair and inspection are ensured, TS HD 60364-4-43 is taken into account in tests and records are kept. Residual current devices complying with the principle of selectivity are installed in the workplace's main and sub-distribution panels. The Construction Work Regulation also requires suitable RCDs in the main and sub-panels on construction sites.
• Annex III, Table 3 of the Regulation on Health and Safety Conditions for the Use of Work Equipment: Electrical installations and earthing installations are inspected at least once a year unless standards specify an interval. The inspection is carried out according to the Regulation on Earthing in Electrical Installations, the Regulation on Heavy Current Electrical Installations, the Regulation on Internal Electrical Installations and the TS HD 60364 series of standards. The installation design is required during the inspection; for an installation without a design, the employer must have one prepared.
• The Regulation on Earthing in Electrical Installations: Sets out measurement methods, permissible touch voltages and inspection intervals.

Those authorised to carry out the inspection are electrical and electrical-electronic engineers, technical teachers who graduated from electrical education departments, and electrical technicians and higher technicians. For installations of 1 kV and below, electronic engineers are also authorised. The person must be registered in EKİPNET, the Ministry's register of authorised inspectors, and the contract must be set up on ISG-KATİP, the Ministry's online OHS registration system, at least 1 day before the inspection.

When is earthing measured?

Annex P of the Earthing Regulation gives recommended intervals for inspections and measurements during operation. Read together with the one-year maximum interval in the Regulation on Work Equipment, the picture is as follows:

Regardless of these intervals, do not wait to measure in the following situations:

• When a new building section, line or high-power machine is added,
• When a main or sub-panel is replaced or rearranged,
• After an event that could damage the earthing installation, such as flooding, fire or excavation work,
• After an electrical accident or frequently recurring RCD trips.

The Earthing Regulation also requires checks by measurement or calculation after major changes affecting the basic rules of earthing.

What should a good earthing report contain?

The measurement and inspection section of the Earthing Regulation lists the work to be done in order: continuity of protective conductors and equipotential bonding connections, insulation resistance of the installation, soil resistivity, earthing resistance, and checking whether the supply is disconnected by automatic disconnection. Measuring instruments must be calibrated. Look for the following in the report you receive:

• A list of the panels and points measured, with the measured value and permissible limit for each point,
• The measurement method used and the serial numbers and calibration details of the instruments,
• Measurements of the tripping current and tripping time of the residual current devices,
• The location and description of non-conformities,
• The name, profession, EKİPNET registration number and signature of the inspector, and the ISG-KATİP contract number,
• A clear conclusion on whether the installation may be used.

Residual current device testing: what is done on site?

At the annual inspection, the device's tripping current and time are measured with a tester. In the time in between, the way to check that the device's mechanism has not seized is the T (test) button on the device. Pressing the button creates an artificial leakage inside the device, and the device should trip.

1. Before the test, warn users of circuits connected to the device; bring loads sensitive to interruption, such as computers, control systems or refrigeration, to a safe state.
2. Press the T button; the device should trip immediately.
3. Reset the device and check that the circuit works normally.
4. Record the result with the date, panel and device number.
5. If the device does not trip, do not use the circuit and report it to an authorised electrician.

Take the test interval from the manufacturer's user manual; if the manual gives no clear interval, we recommend a monthly test and record. Remember that the test button only tests the mechanism: it does not show that the device trips at the correct current and fast enough. The annual measurement shows that.

Selectivity is also important. When the same type of device is used in the main panel and a sub-panel, a leakage in a sub-circuit can also trip the main device and leave the whole facility in the dark. The Earthing Regulation states that time-delayed (type S) devices can be connected in series with general-type devices to ensure selectivity. If devices keep tripping, the solution is not to disable the device but to find the source of the leakage.

Common non-conformities

• The residual current device being bypassed, or none being fitted in sub-panels,
• The protective conductor to a machine enclosure being removed or never connected,
• Broken protective conductors in extension leads and portable hand tools,
• Missing earth connections on panel doors,
• No installation design, or one that does not reflect the current situation,
• Only a single earthing value written in the measurement report, with no panel-by-panel measurements,
• Non-conformities identified in the report not being remedied by the following year.

The 2026 basic administrative fine for failing to have the required inspections and measurements carried out is 33,326 TL. Enter the electrical installation inspection into the OHS calendar; for the full Annex III table, see our article on periodic inspection intervals for work equipment, and for the contract steps, ISG-KATİP contract approval. For planning inspections, see our periodic inspection service, and for risks in facilities with a lot of electrical equipment, our metal and machinery page.

Frequently Asked Questions

When is earthing measured?

Electrical and earthing installations are inspected at least once a year unless standards set a shorter interval. The Earthing Regulation recommends that earthing resistances in industrial facilities be measured once a year; for movable equipment this period is 6 months. After major changes, panel renewals or events such as flooding, measurements are made without waiting for the interval.

Who can carry out earthing measurements?

Electrical engineers, electrical-electronic engineers, technical teachers who graduated from electrical education departments, and electrical technicians and higher technicians registered in EKİPNET. For installations of 1 kV and below, electronic engineers are also authorised. The contract is set up on ISG-KATİP at least one day before the inspection.

How often should a residual current device be tested?

The interval for on-site tests with the test button is set by the manufacturer; if there is no clear interval, we recommend a monthly test and record. The device's tripping current and time are measured with an instrument at the annual periodic inspection.

What should we do if the device keeps tripping?

Do not bypass the device or replace it with one of a higher rating. Constant tripping shows that there is a real leakage, damp, a damaged cable or a selectivity problem in the circuit. Find the source by having an authorised electrician take measurements.