How IDR works

IDR, DR, and DDR

IDR stands for Residual Differential Switch, DR stands for Residual Differential, which demonstrates that DR is another way of naming IDR. DDR stands for Residual Differential Circuit Breaker. The IDR differs from the DDR in that it does not work as a circuit breaker, which is the case with DDR. IDR acts only in cases of leakage current, not short circuits. The DDR works as a circuit breaker and also in cases of leakage current.

IDR is the device that accuses the leakage of current and disarms the circuit, either due to a bad installation, cable wear or even a person getting a shock. The use of IDR does not dispense with the use of the circuit breaker, as it does not perform the function of the circuit breakers.

IDR function

The Residual Differential Switch has the function of automatically disconnecting the circuit if there is a leakage current that exceeds 30 mA, that is, if a leakage current greater than 30 mA occurs, the IDR automatically recognizes and shuts down the circuit. IDR has this feature for protection against electric shock. This value of 30 mA is precisely chosen for the protection of human beings, as this is the maximum intensity that a human being can withstand. Some IDRs can also present this value with variations, not exactly 30 mA, as they are specific for protection of machines or equipment, and this 30mA is exclusive for the protection of human beings against electric shock.

Operation of the IDR

The IDR is simple to operate. Internally it has a Toroidal Core where the cables to be monitored are wound. Phase and neutral cables are connected to the input poles of the IDR (depending on the model used). Between these cables, there is a potential difference (voltage or voltage) and it is from there that electrical energy flows. If 10 A enters through the phase cable and they leave via the neutral cable, the IDR remains armed, but if this does not happen, the IDR understands that there is a current leak, from there the internal devices of the IDR calculate this leakage value if it is greater than 30 mA the IDR disarms the circuit. The neutral serves to make the reading, to understand if it is being lost at any moment and for some reason the current value that entered the phase cable.

In practice, imagine that someone has leaned against some point in the circuit and is subjected to electric shock. At this moment, part of the electric current is transferred to your body, instead of making the appropriate “path”, in this the IDR misses this part of the current and depending on the value (30 mA) it disarms this circuit in a matter of seconds, also interrupting the shock that this person is suffering.

See the illustrated and commented explanation in the video below:

This contact with electrical energy can be direct, in the case of an exposed conductor or direct contact with the energized conductor, or indirect, which is when there are failures in the installation. These failures can be due to wear on the conductors or poorly done work, such as splicing, for example.

Constructive characteristics

The IDR has what we call poles, through which the cables to be monitored are connected. The number of poles in the IDR may vary according to the model, which can be tetrapolar, bipolar, etc.

Residual Differential Switch.

Something peculiar to the IDR is the existence of a test button, it simulates a current leak to test whether the trip is going to be carried out, it is a way of checking and also preventing accidents because in the test the trip was not carried out in a situation real this would not happen either. In the IDR there is also an on and off button, with green signaling for off and red signaling for on.

Some information is displayed on the surface of the IDR, such as:

  • In = working current, quantified in amps in amps;
  • Trip current, quantified in amperes;
  • Working voltage, quantified in volts;

IDR in NBR-5410 standard

The NBR-5410 stipulates the minimum conditions necessary for the adequate and safe operation of low voltage installations. The NBR-5410 in item 5.1.2.2 talks about the mandatory use of IDRs in:

  • In circuits that serve as a point of use located in places that contain a shower or bathtub;
  • In circuits that supply sockets located in areas outside the building;
  • In circuits that supply sockets in internal areas that may supply equipment in external areas;
  • In circuits that serve as points of use located in kitchens, pantries, laundries, service areas, garage and other internal rooms that are wet or subject to washing;

The standard does not specify the requirement of this device by point, by circuit or by a group of a circuit. But the use of only one IDR is not recommended for all residential electrical installations.